Welcome to python-ndn’s documentation!

Table Of Contents

python-ndn

A Named Data Networking client library with AsyncIO support in Python 3.

It supports Python >=3.10 and PyPy3.10 >=7.3.12.

Please see our documentation if you have any issues.

Installation

Install the latest release with pip:

$ pip install python-ndn

Install the latest development version:

$ pip install -U git+https://github.com/named-data/python-ndn.git

Instructions for developer

For development, poetry is recommended. You need poetry-dynamic-versioning plugin:

$ poetry self add "poetry-dynamic-versioning[plugin]"

And to install the development environment:

$ poetry install --all-extras

To setup a traditional python3 virtual environment with editable installation:

python3 -m venv venv
. venv/bin/activate
pip3 install -e ".[dev,docs]"

Run all tests:

poetry run make test

Run static analysis:

poetry run make lint

Generate the documentation:

poetry run make -C docs html
open docs/_build/html/index.html

VSCode users can also use the development container obtained from the .devcontainer folder.

`ndn.app` package

Introduction

The ndn.app package contains the class NDNApp , which connects an NDN application and an NFD node.

NDNApp provides the functionalities similar to application Face in ndn-cxx, which include:

Establish a connection to an NFD node.
Express Interests and handle the Data coming back.
Register and unregister a route with an Interest handling function.

This package does not support PIT token. To use PIT token, consider using ndn.appv2 package.

Keyword Arguments

Some functions which create a Interest or Data packet accept a kwargs, which can be used to support diversity in arguments provided to create a packet.

MetaInfo

These arguments are used to fill in the MetaInfo field of a Data packet.

meta_info (MetaInfo) - the MetaInfo field of Data. All other related parameters will be ignored.
content_type (int) - ContentType. ContentType.BLOB by default.
freshness_period (int) - FreshnessPeriod in milliseconds. None by default.
final_block_id (BinaryStr) - FinalBlockId. It should be an encoded Component. None by default.

InterestParameters

These arguments are used to fill in fields of an Interest packet.

interest_param (InterestParam) - a dataclass containing all parameters. All other related parameters will be ignored.
can_be_prefix (bool) - CanBePrefix. False by default.
must_be_fresh (bool) - MustBeFresh. False by default.
nonce (int) - Nonce. A random number will be generated by default. To omit Nonce, please explicitly pass None to this argument.
lifetime (int) - InterestLifetime in milliseconds. 4000 by default.

Warning

On Windows, a too small number may cause a memory failure of the NameTrie. Currently, >=10 is safe.
hop_limit (int) - HopLimit. None by default.
forwarding_hint (list[NonStrictName]) - see InterestParam.

Signature

These arguments are used to decide how the Interest or Data packet is signed and by which Signer. Supported arguments are different with each Keychain. Only those supported by the default Keychain are listed here. If there is a conflict, the earlier an argument is listed the higher priority it has.

Note

Only Interests with ApplicationParameters are signed. b'' can be used if that field is not needed by the application.

signer (Signer) - the Signer used to sign this packet. All other related parameters will be ignored. The Keychain will not be used.
no_signature (bool) - not signed. Not recommended.
digest_sha256 (bool) - using SHA-256 digest to protect integrity only. False by default.
cert (NonStrictName) - using the speficied Certificate to sign this packet. The Key name will be derived from the certificate name.
key - using the specified Key to sign this packet. Either a Key object or the NonStrictName of a Key is acceptable. KeyLocator will be set to the default Certificate name of this Key unless specified.
identity - using the default Key of the specified Identity to sign this packet. Either an Identity object or the NonStrictName of an Identity is acceptable. The default Identity will be used if all of the above arguments are omitted.
key_locator (NonStrictName) - using the specified KeyLocator Name regardless of which Key is used.

Reference

class ndn.app.NDNApp(face=None, keychain=None)

An NDN application.

Variables:

face – the Face used to connection to a NFD node.
keychain – the Keychain to store Identities and Keys, providing Signers.
int_validator – the default validator for Interest packets.
data_validator – the default validator for Data packets.

express_interest(name, app_param=None, validator=None, need_raw_packet=False, **kwargs)

Express an Interest packet.

The Interest packet is sent immediately and a coroutine used to get the result is returned. Awaiting on what is returned will block until the Data is received and return that Data. An exception is raised if unable to receive the Data.

Parameters:

name (NonStrictName) – the Name.
app_param (Optional[BinaryStr]) – the ApplicationParameters.
validator (Optional[Validator]) – the Validator used to verify the Data received.
need_raw_packet (bool) – if True, return the raw Data packet with TL.
kwargs – Keyword Arguments.

Returns:

A tuple of (Name, MetaInfo, Content) after await. If need_raw_packet is True, return a tuple (Name, MetaInfo, Content, RawPacket).

Return type:

Coroutine[Any, None, Tuple[FormalName, MetaInfo, Optional[BinaryStr]]]

The following exception is raised by express_interest:

Raises:: NetworkError – the face to NFD is down before sending this Interest.

The following exceptions are raised by the coroutine returned:

Raises:

InterestNack – an NetworkNack is received.
InterestTimeout – time out.
ValidationFailure – unable to validate the Data packet.
InterestCanceled – the face to NFD is shut down after sending this Interest.

async main_loop(after_start=None)

The main loop of NDNApp.

Parameters:: after_start (Awaitable) – the coroutine to start after connection to NFD is established.
Return type:: bool
Returns:: True if the connection is shutdown not by Ctrl+C. For example, manually or by the other side.

prepare_data(name, content=None, **kwargs)

Prepare a Data packet by generating, encoding and signing it.

Parameters:

name (NonStrictName) – the Name.
content (Optional[BinaryStr]) – the Content.
kwargs – Keyword Arguments.

Returns:

TLV encoded Data packet.

put_data(name, content=None, **kwargs)

Publish a Data packet.

Parameters:

name (NonStrictName) – the Name.
content (Optional[BinaryStr]) – the Content.
kwargs – Keyword Arguments.

Returns:

TLV encoded Data packet.

put_raw_packet(data)

Send a raw Data packet.

Parameters:: data (BinaryStr) – TLV encoded Data packet.
Raises:: NetworkError – the face to NFD is down.

async register(name, func, validator=None, need_raw_packet=False, need_sig_ptrs=False)

Register a route for a specific prefix dynamically.

Parameters:

name (NonStrictName) – the Name prefix for this route.
func (Optional[Callable[[FormalName, InterestParam, Optional[BinaryStr]], None]]) – the onInterest function for the specified route. If None, the NDNApp will only send the register command to forwarder, without setting any callback function.
validator (Optional[Validator]) – the Validator used to validate coming Interests.
need_raw_packet (bool) – if True, pass the raw Interest packet to the callback as a keyword argument raw_packet.
need_sig_ptrs (bool) – if True, pass the Signature pointers to the callback as a keyword argument sig_ptrs.

Return type:

bool

Returns:

True if the registration succeeded.

Raises:

ValueError – the prefix is already registered.
NetworkError – the face to NFD is down now.

route(name, validator=None, need_raw_packet=False, need_sig_ptrs=False)

A decorator used to register a permanent route for a specific prefix.

This function is non-blocking and can be called at any time. If it is called before connecting to NFD, NDNApp will remember this route and automatically register it every time when a connection is established. Failure in registering this route to NFD will be ignored.

The decorated function should accept 3 arguments: Name, Interest parameters and ApplicationParameters.

Parameters:

name (NonStrictName) – the Name prefix for this route.
validator (Optional[Validator]) – the Validator used to validate coming Interests. An Interest without ApplicationParameters and SignatureInfo will be considered valid without calling validator. Interests with malformed ParametersSha256DigestComponent will be dropped before going into the validator. Otherwise NDNApp will try to validate the Interest with the validator. Interests which fail to be validated will be dropped without raising any exception.
need_raw_packet (bool) – if True, pass the raw Interest packet to the callback as a keyword argument raw_packet.
need_sig_ptrs (bool) – if True, pass the Signature pointers to the callback as a keyword argument sig_ptrs.

Examples:

app = NDNApp()

@app.route('/example/rpc')
def on_interest(name: FormalName, param: InterestParam, app_param):
    pass

Note

The route function must be a normal function instead of an async one. This is on purpose, because an Interest is supposed to be replied ASAP, even it cannot finish the request in time. To provide some feedback, a better practice is replying with an Application NACK (or some equivalent Data packet saying the operation cannot be finished in time). If you want to use await in the handler, please use asyncio.create_task to create a new coroutine.

Note

Currently, python-ndn does not handle PIT Tokens.

run_forever(after_start=None)

A non-async wrapper of main_loop().

Parameters:

after_start (Awaitable) – the coroutine to start after connection to NFD is established.

Examples:

app = NDNApp()

if __name__ == '__main__':
    app.run_forever(after_start=main())

set_interest_filter(name, func, validator=None, need_raw_packet=False, need_sig_ptrs=False): Set the callback function for an Interest prefix without sending a register command to the forwarder.

Note

All callbacks registered by set_interest_filter are removed when disconnected from the the forwarder, and will not be added back after reconnection. This behaviour is the same as register. Therefore, it is strongly recommended to use route for static routes.

shutdown(): Manually shutdown the face to NFD.

async unregister(name)

Unregister a route for a specific prefix.

Parameters:: name (NonStrictName) – the Name prefix.
Return type:: bool

unset_interest_filter(name): Remove the callback function for an Interest prefix without sending an unregister command.

Note

unregister will only remove the callback if the callback’s name matches exactly the route’s name. This is because there may be one route whose name is the prefix of another. To avoid cancelling unexpected routes, neither unregister nor unset_interest_filter behaves in a cascading manner. Please remove callbacks manually.

`ndn.appv2` package

Introduction

The ndn.appv2 package contains NDNApp class. It offers the functionalities similar to an application face in other NDN libraries. Main features include:

Establish a connection to NDN forwarder.
Consumer: express Interests and receive the reply Data.
Producer: attach Interest handler function to a name prefix, to handle incoming Interests.
Producer: register and unregister prefixes in the forwarder.

This package is a rewrite from ndn.app package. Major differences from that package are:

Initial support for PIT token.
Send signed Interests for NFD management commands.

Reference

ndn.appv2.IntHandler

Interest handler function associated with a name prefix.

The function should use the provided reply callback to reply with Data, which can handle PIT token properly.

(name: FormalName, app_param: Optional[BinaryStr], reply: ReplyFunc, context: PktContext) -> None

Parameters:

name (FormalName) – Interest name.
app_param (Optional[BinaryStr]) – Interest ApplicationParameters value, or None if absent.
reply (ReplyFunc) – continuation function to respond with Data.
context (PktContext) – packet handler context.

Note

Interest handler function must be a normal function instead of an async one. This is on purpose, because an Interest is supposed to be replied ASAP, even it cannot finish the request in time. To provide some feedback, a better practice is replying with an Application NACK (or some equivalent Data packet saying the operation cannot be finished in time). If you want to use await in the handler, please use asyncio.create_task to create a new coroutine.

alias of Callable[[List[Union[bytes, bytearray, memoryview]], Optional[Union[bytes, bytearray, memoryview]], Callable[[Union[bytes, bytearray, memoryview]], bool], dict[str, any]], None]

class ndn.appv2.NDNApp(face=None, client_conf=None, registerer=None)

An NDN application.

attach_handler(name, handler, validator=None)

Attach an Interest handler at a name prefix. Incoming Interests under the specified name prefix will be dispatched to the handler.

This only sets the handler within NDNApp, but does not send prefix registration commands to the forwarder. To register the prefix in the forwarder, use register. The handler association is retained even if the forwarder is disconnected.

Parameters:

name (NonStrictName) – name prefix.
handler (IntHandler) – Interest handler function.
validator (Optional[Validator]) – validator for signed Interests. Non signed Interests, i.e. those without ApplicationParameters and SignatureInfo, are passed to the handler directly without calling the validator. Interests with malformed ParametersSha256DigestComponent are dropped silently. If a validator is not provided (set to None), signed Interests will be dropped. Otherwise, signed Interests are passed to the validator. Those failing the validation are dropped silently. Those passing the validation are passed to the handler function.

detach_handler(name)

Detach an Interest handler at a name prefix.

This only deletes the handler within NDNApp, but does not unregister the prefix in the forwarder. To unregister the prefix in the forwarder, use unregister.

Parameters:: name (NonStrictName) – name prefix. This must exactly match the name passed to attach_handler. If there are Interest handlers attached to longer prefixes, each handler must be removed explicitly.

express(name, validator, app_param=None, signer=None, **kwargs)

Express an Interest.

The Interest packet is sent immediately and a coroutine used to get the result is returned. Awaiting on the returned coroutine will block until the Data is received. It then returns the Data name, Data Content value, and PktContext. An exception is raised if NDNApp is unable to retrieve the Data.

Parameters:

name (NonStrictName) – Interest name.
validator (Validator) – validator for the retrieved Data packet.
app_param (Optional[BinaryStr]) – Interest ApplicationParameters value. If this is not None, a signed Interest is sent. NDNApp does not support sending parameterized Interests that are not signed.
signer (Optional[Signer]) – Signer for Interest signing. This is required if app_param is specified.
kwargs – arguments for InterestParam.

Returns:

A tuple of (Name, Content, PacketContext) after await.

Return type:

Coroutine[Any, None, Tuple[FormalName, Optional[BinaryStr], PktContext]]

The following exceptions may be raised by express:

Raises:

NetworkError – the face to NFD is down before sending this Interest.
ValueError – when the signer is missing but app_param presents.

The following exceptions may be raised by the returned coroutine:

Raises:

InterestNack – an NetworkNack is received.
InterestTimeout – time out.
ValidationFailure – unable to validate the Data packet.
InterestCanceled – the face to NFD is shut down after sending this Interest.

async main_loop(after_start=None)

The main loop of NDNApp.

Parameters:: after_start (Awaitable) – the coroutine to start after connection to NFD is established.
Return type:: bool
Returns:: True if the connection is shutdown not by Ctrl+C. For example, manually or by the other side.

static make_data(name, content, signer, **kwargs)

Encode a data packet without requiring an NDNApp instance. This is simply a wrapper of encoding.make_data. I write this because most people seem not aware of the make_data function in the encoding package. The corresponding make_interest is less useful (one should not reuse nonce) and thus not wrapped. Sync protocol should use encoding.make_interest if necessary. Also, since having a default signer encourages bad habit, prepare_data is removed except for command Interests sent to NFD. Please call keychain.get_signer({}) to use the default certificate.

Parameters:

name (NonStrictName) – the Name.
content (Optional[BinaryStr]) – the Content.
signer (Optional[Signer]) – the Signer used to sign the packet.
kwargs – arguments for MetaInfo.

Returns:

TLV encoded Data packet.

async register(name)

Register a prefix in the forwarder.

This only sends the prefix registration command to the forwarder. In order to receive incoming Interests, you also need to use attach_handler to attach an Interest handler function.

Parameters:

name (NonStrictName) – name prefix.

Raises:

ValueError – the prefix is already registered.
NetworkError – the face to NFD is down now.

Return type:

bool

route(name, validator=None)

A decorator used to register a permanent route for a specific prefix. The decorated function should be an IntHandler.

This function is non-blocking and can be called at any time. It can be called before connecting to the forwarder. Every time a forwarder connection is established, NDNApp will automatically send prefix registration commands. Errors in prefix registration are ignored.

Parameters:

name (NonStrictName) – name prefix.
validator (Optional[Validator]) – validator for signed Interests. See attach_handler for details.

Examples:

app = NDNApp()

@app.route('/example/rpc')
def on_interest(name, app_param, reply, context):
    pass

run_forever(after_start=None)

A non-async wrapper of main_loop().

Parameters:

after_start (Awaitable) – the coroutine to start after connection to NFD is established.

Examples:

app = NDNApp()

if __name__ == '__main__':
    app.run_forever(after_start=main())

shutdown(): Manually shutdown the face to NFD.

async unregister(name)

Unregister a prefix in the forwarder.

Parameters:: name (NonStrictName) – name prefix.
Return type:: bool

class ndn.appv2.PendingIntEntry(future, deadline, can_be_prefix, must_be_fresh, validator, implicit_sha256=b'', task=None)

ndn.appv2.PktContext

The context for NDN Interest or Data handling.

alias of dict[str, any]

class ndn.appv2.PrefixTreeNode(callback=None, validator=None)

ndn.appv2.ReplyFunc

Continuation function for IntHandler to respond to an Interest.

(data: BinaryStr) -> bool

Parameters:: data (BinaryStr) – an encoded Data packet.
Returns:: True for success, False upon error.

alias of Callable[[Union[bytes, bytearray, memoryview]], bool]

ndn.appv2.Validator

Validator function that validates Interest or Data signature against trust policy.

(name: FormalName, sig: SignaturePtrs, context: PktContext) -> Coroutine[ValidResult]

Parameters:

name (FormalName) – Interest or Data name.
sig (SignaturePtrs) – packet signature pointers.
context (PktContext) – packet handler context.

alias of Callable[[List[Union[bytes, bytearray, memoryview]], SignaturePtrs, dict[str, any]], Coroutine[any, None, ValidResult]]

`ndn.encoding` package

Introduction

The ndn.encoding package contains classes and functions that help to encode and decode NDN Name, NameComponent, Data and Interest.

There are three parts of this package:

TLV elements: process TLV variables, Names and NameComponents.
TlvModel: design a general way to describe a TLV format. A TLV object can be described with a class derived from TlvModel, with members of type Field.
NDN Packet Fotmat v0.3: functions used to encode and parse Interest and Data packets in NDN Packet Format Spec 0.3.

`FormalName` and `NonStrictName`

To increase the flexibility, API in python-ndn accepts Name arguments in a wide range of formats, i.e. NonStrictName, but returns an unified form, FormalName.

A Component is a NameComponent encoded in TLV format.

component = b'\x08\x09component'

A FormalName is a list of encoded Components.

formal_name = [bytearray(b'\x08\x06formal'), b'\x08\x04name']

A NonStrictName is any of below:

A URI string.
```
casual_name_1 = "/non-strict/8=name"
```

A list or iterator of Components, in the form of either encoded TLV or URI string.

casual_name_2 = [bytearray(b'\x08\x0anon-strict'), 'name']
casual_name_3 = (f'{x}' for x in range(3))

An encoded Name of type bytes, bytearray or memoryview.

casual_name_4 = b'\x07\x12\x08\x0anon-strict\x08\x04name'

Customized TLV Models

See Customized TLV Models

Reference

TLV Variables

ndn.encoding.tlv_type.BinaryStr

A binary string is any of bytes, bytearray, memoryview.

alias of Union[bytes, bytearray, memoryview]

ndn.encoding.tlv_type.FormalName

A FormalName is a list of encoded Components.

alias of List[Union[bytes, bytearray, memoryview]]

ndn.encoding.tlv_type.NonStrictName

A NonStrictName is any of below:

A URI string.
A list or iterator of Components, in the form of either encoded TLV or URI string.
An encoded Name of type bytes, bytearray or memoryview.

Name and Component

`ndn.encoding.name.Component` module

Component module is a collection of functions processing NDN NameComponents. In python-ndn, a NameComponent is always encoded in TLV form, of type bytes, bytearray or memoryview.

The types of NameComonent follows Name Component Assignment policy. Type constants are following

Type	Description
TYPE_INVALID	Invalid name component type
TYPE_GENERIC	Implicit SHA-256 digest component
TYPE_IMPLICIT_SHA256	SHA-256 digest of Interest Parameters
TYPE_PARAMETERS_SHA256	Generic name component
TYPE_KEYWORD	Well-known keyword
TYPE_SEGMENT	Segment number
TYPE_BYTE_OFFSET	Byte offset
TYPE_VERSION	Version number
TYPE_TIMESTAMP	Unix timestamp in microseconds
TYPE_SEQUENCE_NUM	Sequence number

ndn.encoding.name.Component.CHARSET = {'%', '-', '.', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '=', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '_', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '~'}: The character set for NameComponent, which is unreserved characters + {‘=’, ‘%’}

ndn.encoding.name.Component.escape_str(val)

Escape a string to a legal URI string. Any characters not in the CHARSET will be converted into percent-hexadecimal encoding. '%' itself will not be escaped. For hex digits, lowercase is used.

Parameters:

val (str) – the string to escape.

Return type:

str

Returns:

the URI string.

Examples:

>>> from ndn.encoding.name import Component
>>> Component.escape_str('Kraus Bölter')
'Kraus%20B%C3%B6lter'

>>> Component.escape_str('all:%0a\tgcc -o a.out')
'all%3A%0a%09gcc%20-o%20a.out'

ndn.encoding.name.Component.from_byte_offset(offset)

Construct a Component from a byte offset.

Parameters:: offset (int) – the byte offset.
Return type:: bytearray
Returns:: the component.

ndn.encoding.name.Component.from_bytes(val, typ=8)

Construct a Component from bytes by adding a type and length.

Parameters:

val (Union[bytes, bytearray, memoryview]) – the value of the component.
typ (int) – the type of the component. TYPE_GENERIC by default.

Return type:

bytearray

Returns:

the component.

ndn.encoding.name.Component.from_hex(val, typ=8)

Construct a Component from hex string.

Parameters:

val (str) – a hexadecimal string.
typ (int) – the type of the component. TYPE_GENERIC by default.

Return type:

bytearray

Returns:

the component.

ndn.encoding.name.Component.from_number(val, typ)

Construct a Component from an integer.

Parameters:

val (int) – the integer.
typ (int) – the type of the component.

Return type:

bytearray

Returns:

the component.

ndn.encoding.name.Component.from_segment(segment)

Construct a Component from an segment number.

Parameters:: segment (int) – the segment number.
Return type:: bytearray
Returns:: the component.

ndn.encoding.name.Component.from_sequence_num(seq_num)

Construct a Component from a sequence number.

Parameters:: seq_num (int) – the sequence number.
Return type:: bytearray
Returns:: the component.

ndn.encoding.name.Component.from_str(val)

Construct a Component from URI string.

Parameters:

val (str) –

URI string. All characters should be from CHARSET, otherwise it would raise a ValueError.

Note

Additional periods are not allowed here. To create a zero-size Component, just pass an empty string '' in.

Return type:

bytearray

Returns:

the component.

Raises:

ValueError – the string is not a legal URI.

ndn.encoding.name.Component.from_timestamp(timestamp)

Construct a Component from a timestamp number.

Parameters:

timestamp (int) – the timestamp

Return type:

bytearray

Returns:

the component.

Examples:

>>> from ndn.encoding.name import Component
>>> from ndn.utils import timestamp
>>> Component.to_str(Component.from_timestamp(timestamp()))
'36=%00%00%01nH.%A7%90'

ndn.encoding.name.Component.from_version(version)

Construct a Component from a version number.

Parameters:: version (int) – the version number.
Return type:: bytearray
Returns:: the component.

ndn.encoding.name.Component.get_type(component)

Get the type from a Component.

Parameters:: component (Union[bytes, bytearray, memoryview]) – the component.
Return type:: int
Returns:: the type.

ndn.encoding.name.Component.get_value(component)

Get the value from a Component, in the form of memoryview.

Parameters:: component (Union[bytes, bytearray, memoryview]) – the component.
Return type:: memoryview
Returns:: the value.

ndn.encoding.name.Component.to_canonical_uri(component)

Convert a Component into a canonical URI string without naming conventions. Returns an empty string '' for a 0-size Component.

Parameters:: component (Union[bytes, bytearray, memoryview]) – the component.
Return type:: str
Returns:: a canonical URI string.

ndn.encoding.name.Component.to_number(component)

Take the number encoded in the component out.

Parameters:: component (Union[bytes, bytearray, memoryview]) – the component.
Return type:: int
Returns:: an integer, which is the value of the component.

ndn.encoding.name.Component.to_str(component)

Convert a Component into a URI string. Returns an empty string '' for a 0-size Component.

Parameters:: component (Union[bytes, bytearray, memoryview]) – the component.
Return type:: str
Returns:: a URI string.

`ndn.encoding.name.Name` module

Name module is a collection of functions processing NDN Names.

ndn.encoding.name.Name.TYPE_NAME = 7: The TLV type of NDN Name.

ndn.encoding.name.Name.from_bytes(buf)

Decode the Name from its TLV encoded form.

Parameters:: buf (Union[bytes, bytearray, memoryview]) – encoded Name.
Returns:: Decoded Name.
Return type:: FormalName
Raises:: ValueError – if the Type is not TYPE_NAME .

ndn.encoding.name.Name.from_str(val)

Construct a Name from a URI string.

Parameters:

val (str) –

URI string. Character out of ndn.encoding.name.Component.CHARSET will be escaped automatically. Leading and tailing '/' will be removed.

Note

Additional periods are not allowed here. To create a zero-size Component, use two slashes to surround it. Also, there should be no scheme identifier and authority component in the URI.

Return type:

List[bytearray]

Returns:

FormalName.

Examples:

>>> from ndn.encoding.name import Name
>>> Name.from_str("example/name")
[bytearray(b'\x08\x07example'), bytearray(b'\x08\x04name')]

>>> Name.from_str("/a//32=b/")
[bytearray(b'\x08\x01a'), bytearray(b'\x08\x00'), bytearray(b'\x20\x01b')]

>>> Name.from_str('/a/../b')
[bytearray(b'\x08\x01a'), bytearray(b'\x08\x02..'), bytearray(b'\x08\x01b')]

ndn.encoding.name.Name.is_prefix(lhs, rhs)

Test if a Name is a prefix of another Name.

Parameters:

lhs (NonStrictName) – prefix to be tested.
rhs (NonStrictName) – full name to test on.

Return type:

bool

Returns:

True if lhs is a prefix of rhs.

ndn.encoding.name.Name.normalize(name)

Convert a NonStrictName to a FormalName. If name is a binary string, decode it. If name is a str, encode it into FormalName. If name is a list, encode all str elements into Components.

Parameters:

name (NonStrictName) – the NonStrictName.

Returns:

the FormalName. It may be a swallow copy of name.

Return type:

FormalName

Raises:

TypeError – if the name or one of its element has a unrecognized type.

Examples:

>>> from ndn.encoding.name import Name
>>> Name.normalize(f'{i}' for i in range(3))
[bytearray(b'\x08\x010'), bytearray(b'\x08\x011'), bytearray(b'\x08\x012')]

>>> Name.normalize(['Алек', b'%\x01\x00'])
[bytearray(b'\x08\x08\xd0\x90\xd0\xbb\xd0\xb5\xd0\xba'), b'%\x01\x00']

ndn.encoding.name.Name.to_bytes(name)

Encode a Name via TLV encoding.

Parameters:: name (NonStrictName) – Name to encode.
Return type:: bytes
Returns:: Encoded Name.

ndn.encoding.name.Name.to_canonical_uri(name)

Convert an NDN Name to a canonical URI string without naming conventions.

Parameters:

name (NonStrictName) – the input NDN Name.

Return type:

str

Returns:

the canonical URI.

Examples:

>>> from ndn.encoding.name import Name
>>> Name.to_canonical_uri('Σπυρίδων')
'/%CE%A3%CF%80%CF%85%CF%81%CE%AF%CE%B4%CF%89%CE%BD'

ndn.encoding.name.Name.to_str(name)

Convert an NDN Name to a URI string.

Parameters:

name (NonStrictName) – the input NDN Name.

Return type:

str

Returns:

the URI.

Examples:

>>> from ndn.encoding.name import Name
>>> Name.to_str('Σπυρίδων')
'/%CE%A3%CF%80%CF%85%CF%81%CE%AF%CE%B4%CF%89%CE%BD'

TLV Model

exception ndn.encoding.tlv_model.DecodeError: Raised when there is a critical field (Type is odd) that is unrecognized, redundant or out-of-order.

exception ndn.encoding.tlv_model.IncludeBaseError: Raised when IncludeBase is used to include a non-base class.

class ndn.encoding.tlv_model.IncludeBase(base): Include all fields from a base class.

class ndn.encoding.tlv_model.Field(type_num, default=None)

Field of TlvModel. A field with value None will be omitted in encoding TLV. There is no required field in a TlvModel, i.e. any Field can be None.

Variables:

name (str) – The name of the field
type_num (int) – The Type number used in TLV encoding
default –
The default value used for parsing and encoding.
- If this field is absent during parsing, default is used to fill in this field.
- If this field is not explicitly assigned to None before encoding, default is used.

__get__(instance, owner)

Get the value of this field in a specific instance. Simply call get_value() if instance is not None.

Parameters:

instance – the instance that this field is being accessed through.
owner – the owner class of this field.

Returns:

the value of this field.

__set__(instance, value)

Set the value of this field.

Parameters:

instance – the instance whose field is being set.
value – the new value.

abstract encode_into(val, markers, wire, offset)

Encode this field into wire. Must be called after encoded_length().

Parameters:

val – value of this field
markers (dict) – encoding marker variables
wire (Union[bytearray, memoryview]) – buffer to encode
offset (int) – offset of this field in wire

Return type:

int

Returns:

encoded length with TL. It is expected to be the same as encoded_length() returns.

abstract encoded_length(val, markers)

Preprocess value and get encoded length of this field. The function may use markers[f'{self.name}##encoded_length'] to store the length with TL. Other marker variables starting with f'{self.name}##' may also be used. Generally, marker variables are only used to store temporary values and avoid duplicated calculation. One field should not access to another field’s marker by its name.

This function may also use other marker variables. However, in that case, this field must be unique in a TlvModel. Usage of marker variables should follow the name convention defined by specific TlvModel.

Parameters:

val – value of this field
markers (dict) – encoding marker variables

Return type:

int

Returns:

encoded length with TL. It is expected as the exact length when encoding this field. The only exception is SignatureValueField (invisible to application developer).

get_value(instance)

Get the value of this field in a specific instance. Most fields use instance.__dict__ to access the value.

Parameters:: instance – the instance that this field is being accessed through.
Returns:: the value of this field.

abstract parse_from(instance, markers, wire, offset, length, offset_btl)

Parse the value of this field from an encoded wire.

Parameters:

instance – the instance to parse into.
markers (dict) – encoding marker variables. Only used in special cases.
wire (Union[bytes, bytearray, memoryview]) – the TLV encoded wire.
offset (int) – the offset of this field’s Value in wire.
length (int) – the Length of this field’s Value.

offset_btl (int) –

the offset of this field’s TLV.

assert offset == (offset_btl
                + get_tl_num_size(self.type_num)
                + get_tl_num_size(length))

Returns:

the value.

skipping_process(markers, wire, offset)

Called when this field does not occur in wire and thus be skipped.

Parameters:

markers (dict) – encoding marker variables.
wire (Union[bytes, bytearray, memoryview]) – the TLV encoded wire.
offset (int) – the offset where this field should have been if it occurred.

class ndn.encoding.tlv_model.ProcedureArgument(default=None)

A marker variable used during encoding or parsing. It does not have a value. Instead, it provides a way to access a specific variable in markers.

__get__(instance, owner)

Returns:: itself.

__set__(instance, value): This is not allowed and will raise a TypeError if called.

get_arg(markers)

Get its value from markers

Parameters:: markers (dict) – the markers dict.
Returns:: its value.

set_arg(markers, val)

Set its value in markers.

Parameters:

markers (dict) – the markers dict.
val – the new value.

class ndn.encoding.tlv_model.OffsetMarker(default=None): A marker variable that records its position in TLV wire in terms of offset.

class ndn.encoding.tlv_model.UintField(type_num, default=None, fixed_len=None, val_base_type=<class 'int'>)

NonNegativeInteger field.

Type: int

Its Length is 1, 2, 4 or 8 when present.

Variables:

fixed_len (int) – the fixed value for Length if it’s not None. Only 1, 2, 4 and 8 are acceptable.
val_base_type – the base type of the value of the field. Can be int (default), an Enum or a Flag type.

class ndn.encoding.tlv_model.BoolField(type_num, default=None)

Boolean field.

Type: bool

Its Length is always 0. When present, its Value is True. When absent, its Value is None, which is equivalent to False.

Note

The default value is always None.

class ndn.encoding.tlv_model.NameField(default=None, type_number=7)

NDN Name field. Its Type is always Name.TYPE_NAME.

Type: NonStrictName

class ndn.encoding.tlv_model.BytesField(type_num, default=None, is_string=False)

Field for *OCTET.

Type: BinaryStr

Variables:: is_string – If the value is a UTF-8 string. False by default.

Note

Do not assign it with a str if is_string is False.

class ndn.encoding.tlv_model.ModelField(type_num, model_type, copy_in_fields=None, copy_out_fields=None, ignore_critical=False)

Field for nested TlvModel.

Type: TlvModel

Variables:

model_type (TlvModelMeta) – the type of its value.
ignore_critical (bool) – whether to ignore critical fields (whose Types are odd).

class ndn.encoding.tlv_model.RepeatedField(element_type)

Field for an array of a specific type. All elements will be directly encoded into TLV wire in order, sharing the same Type. The type_num of element_type is used.

Type: list

Variables:

element_type (Field) –

the type of elements in the list.

Warning

Please always create a new Field instance. Don’t use an existing one.

class ndn.encoding.tlv_model.TlvModelMeta(name, bases, attrs): Metaclass for TlvModel, used to collect fields.

class ndn.encoding.tlv_model.TlvModel

Used to describe a TLV format.

Variables:: _encoded_fields (List[Field]) – a list of Field in order.

__eq__(other)

Compare two TlvModels

Parameters:: other – the other TlvModel to compare with.
Returns:: whether all Fields are equal.

asdict(dict_factory=<class 'dict'>)

Return a dict to represent this TlvModel.

Parameters:: dict_factory – class of dict.
Returns:: the dict.

encode(wire=None, offset=0, markers=None)

Encode the TlvModel.

Parameters:

wire (Union[bytearray, memoryview]) – the buffer to contain the encoded wire. A new bytearray will be created if it’s None.
offset (int) – the starting offset.
markers (Optional[dict]) – encoding marker variables.

Return type:

Union[bytearray, memoryview]

Returns:

wire.

Raises:

ValueError – some field is assigned with improper value.
TypeError – some field is assigned with value of wrong type.
IndexError – wire does not have enough length.
struct.error – a negative number is assigned to any non-negative integer field.

encoded_length(markers=None)

Get the encoded Length of this TlvModel.

Parameters:: markers (Optional[dict]) – encoding marker variables.
Return type:: int
Returns:: the encoded Length.

classmethod parse(wire, markers=None, ignore_critical=False)

Parse a TlvModel from TLV encoded wire.

Parameters:

wire (Union[bytes, bytearray, memoryview]) – the TLV encoded wire.
markers (Optional[dict]) – encoding marker variables.
ignore_critical (bool) – whether to ignore unknown critical fields.

Returns:

parsed TlvModel.

Raises:

DecodeError – a critical field is unrecognized, redundant or out-of-order.
IndexError – the Length of a field exceeds the size of wire.

NDN Packet Format 0.3

class ndn.encoding.ndn_format_0_3.ContentType

Numbers used in ContentType.

Type	Description
BLOB	Payload identified by the data name
LINK	A list of delegation names
KEY	Public Key
NACK	Application-level NACK

class ndn.encoding.ndn_format_0_3.InterestParam(can_be_prefix=False, must_be_fresh=False, nonce=None, lifetime=4000, hop_limit=None, forwarding_hint=<factory>)

A dataclass collecting the parameters of an Interest, except ApplicationParameters.

Variables:

can_be_prefix (bool) – CanBePrefix. False by default.
must_be_fresh (bool) – MustBeFresh. False by default.
nonce (int) – Nonce. None by default.
lifetime (int) – InterestLifetime in milliseconds. 4000 by default.
hop_limit (int) – HopLimit. None by default.
forwarding_hint (List [ Tuple [ int , NonStrictName ]]) – ForwardingHint. The type should be list of Names. e.g.: ["/ndn/name1", ["ndn", "name2"]]

class ndn.encoding.ndn_format_0_3.KeyLocator

class ndn.encoding.ndn_format_0_3.Links

class ndn.encoding.ndn_format_0_3.MetaInfo(content_type=0, freshness_period=None, final_block_id=None)

class ndn.encoding.ndn_format_0_3.SignatureInfo

class ndn.encoding.ndn_format_0_3.SignaturePtrs(signature_info=None, signature_covered_part=<factory>, signature_value_buf=None, digest_covered_part=<factory>, digest_value_buf=None)

A set of pointers used to verify a packet.

Variables:

signature_info (SignatureInfo) – the SignatureInfo.
signature_covered_part (List [ memoryview ]) – a list of pointers, each of which points to a memory covered by signature.
signature_value_buf (memoryview) – a pointer to SignatureValue (TL excluded).
digest_covered_part (List [ memoryview ]) – a list of pointers, each of which points to a memory covered by ParametersSha256DigestComponent.
digest_value_buf (memoryview) – a pointer to ParametersSha256DigestComponent (TL excluded).

class ndn.encoding.ndn_format_0_3.SignatureType

Numbers used in SignatureType.

Type	Description
NOT_SIGNED	Not signed
DIGEST_SHA256	SHA-256 digest (only for integrity protection)
SHA256_WITH_RSA	RSA signature over a SHA-256 digest
SHA256_WITH_ECDSA	An ECDSA signature over a SHA-256 digest
HMAC_WITH_SHA256	SHA256 hash-based message authentication codes
NULL	An empty signature for testing and experimentation

class ndn.encoding.ndn_format_0_3.TypeNumber

TLV Type numbers used in NDN Packet Format 0.3.

Constant names are changed to PEP 8 style, i.e., all upper cases with underscores separating words.

ndn.encoding.ndn_format_0_3.make_data(name, meta_info, content=None, signer=None)

Make a Data packet.

Parameters:

name (NonStrictName) – the Name field.
meta_info (MetaInfo) – the MetaIndo field.
content (Optional [ BinaryStr ]) – the Content.
signer (Optional[Signer]) – a Signer to sign this Interest. None if it is unsigned.

Return type:

Union[bytearray, memoryview]

Returns:

TLV encoded Data packet.

ndn.encoding.ndn_format_0_3.make_interest(name, interest_param, app_param=None, signer=None, need_final_name=False)

Make an Interest packet.

Parameters:

name (NonStrictName) – the Name field.
interest_param (InterestParam) – basic parameters of the Interest.
app_param (Optional [ BinaryStr ]) – the ApplicationParameters field.
signer (Optional[Signer]) – a Signer to sign this Interest. None if it is unsigned.
need_final_name (bool) – if True, also return the final Name with ParametersSha256DigestComponent.

Returns:

TLV encoded Interest packet. If need_final_name, return a tuple of the packet and the final Name.

ndn.encoding.ndn_format_0_3.parse_data(wire, with_tl=True)

Parse a TLV encoded Data.

Parameters:

wire (BinaryStr) – the buffer.
with_tl (bool) – True if the packet has Type and Length. False if wire only has the Value part.

Returns:

a Tuple of Name, MetaInfo, Content and SignaturePtrs.

Return type:

Tuple [ FormalName , MetaInfo , Optional [ BinaryStr ], SignaturePtrs ]

ndn.encoding.ndn_format_0_3.parse_interest(wire, with_tl=True)

Parse a TLV encoded Interest.

Parameters:

wire (BinaryStr) – the buffer.
with_tl (bool) – True if the packet has Type and Length. False if wire only has the Value part.

Returns:

a Tuple of Name, InterestParameters, ApplicationParameters and SignaturePtrs.

Return type:

Tuple [ FormalName , InterestParam , Optional [ BinaryStr ], SignaturePtrs ]

`ndn.security` package

Introduction

The ndn.security package provides basic tools for security use.

Signer

A Signer is a class used to sign a packet during encoding.

class ndn.encoding.Signer

abstract get_signature_value_size()

Get the size of SignatureValue. If the size is variable, return the maximum possible value.

Return type:: int
Returns:: the size of SignatureValue.

abstract write_signature_info(signature_info)

Fill in the fields of SignatureInfo.

Parameters:: signature_info – a blank SignatureInfo object.

abstract write_signature_value(wire, contents)

Calculate the SignatureValue and write it into wire. The length of wire is exactly what get_signature_value_size() returns. Basically this function should return the same value except for ECDSA.

Parameters:

wire (Union[bytearray, memoryview]) – the buffer to contain SignatureValue.
contents (List[Union[bytearray, memoryview]]) – a list of memory blocks that needs to be covered.

Return type:

int

Returns:

the actual size of SignatureValue.

Validator

A Validator is a async function called to validate an Interest or Data packet. It takes 2 arguments: a FormalName and a SignaturePtrs, and returns whether the packet is validated.

Keychain

A Keychain is a class which contains Identities, Keys associated with Identities and associated Certificates.

class ndn.security.keychain.Keychain

The abstract Keychain class, derived from collections.abc.Mapping. It behaves like an immutable dict from FormalName to Identity. The implementation of Identity varies with concrete implementations. Generally, its methods should also accept NonStrictName as inputs. This includes operators such as in and [].

abstract get_signer(sign_args)

Get a signer from sign_args.

Parameters:: sign_args (dict[str, Any]) – the signing arguments provided by the application.
Returns:: a signer.
Return type:: Signer

KeychainDigest

class ndn.security.keychain.keychain_digest.KeychainDigest

A signer which has no Identity and always returns a SHA-256 digest signer.

get_signer(sign_args)

Get a signer from sign_args.

Parameters:: sign_args (Dict[str, Any]) – the signing arguments provided by the application.
Returns:: a signer.
Return type:: Signer

KeychainSqlite3

This is the default Keychain.

class ndn.security.keychain.keychain_sqlite3.Certificate(row_id, key, name, data, is_default)

A dataclass for a Certificate.

Variables:

id (int) – its id in the database.
key (FormalName) – the Name of the associated Key.
name (FormalName) – its Name.
data (bytes) – the content.
is_default (bool) – whether this is the default Identity.

property data: bytes | bytearray | memoryview

Get the binary data of the certificate, which is the wire form of the V2 certificate Data packet.

Returns:: Certificate binary data.

property key: List[bytes | bytearray | memoryview]

Get the Name of the Key

Returns:: Key Name.

property name: List[bytes | bytearray | memoryview]

Get the Name of the certificate

Returns:: Certificate Name.

class ndn.security.keychain.keychain_sqlite3.Identity(pib, row_id, name, is_default)

An Identity. It behaves like an immutable dict from FormalName to Key.

Variables:

row_id (int) – its id in the database.
name (FormalName) – its Name.
is_default (bool) – whether this is the default Identity.

default_key()

Get the default Key.

Return type:: Key
Returns:: the default Key.

del_key(name)

Delete a specific Key.

Parameters:: name (NonStrictName) – the Name of the Key to delete.

has_default_key()

Whether it has a default Key.

Return type:: bool
Returns:: True if there is one.

property name: List[bytes | bytearray | memoryview]

Get the Name of the identity

Returns:: Identity Name.

new_key(key_type)

Create a new key with default arguments.

Parameters:: key_type (str) – the type of the Key. Can be ec or rsa.
Return type:: Key
Returns:: the new Key.

set_default_key(name)

Set the default Key.

Parameters:: name (NonStrictName) – the Name of the new default Key.

class ndn.security.keychain.keychain_sqlite3.Key(pib, identity, row_id, name, key_bits, is_default)

A Key. It behaves like an immutable dict from FormalName to Certificate.

Variables:

row_id (int) – its id in the database.
identity (FormalName.) – the Name of the associated Identity.
name (FormalName) – its Name.
key_bits (bytes) – the key bits of the public key.
is_default (bool) – whether this is the default Identity.

default_cert()

Get the default Certificate.

Return type:: Certificate
Returns:: the default Certificate.

del_cert(name)

Delete a specific Certificare.

Parameters:: name (NonStrictName) – the Name of the Key to delete.

has_default_cert()

Whether it has a default Certificate.

Return type:: bool
Returns:: True if there is one.

property identity: List[bytes | bytearray | memoryview]

Get the Name of the Identity

Returns:: Identity Name.

property key_bits: bytes | bytearray | memoryview

Get the public key bits of the key.

Returns:: Public key bits.

property name: List[bytes | bytearray | memoryview]

Get the Name of the key

Returns:: Key Name.

set_default_cert(name)

Set the default Certificate.

Parameters:: name (NonStrictName) – the Name of the new default Certificate.

class ndn.security.keychain.keychain_sqlite3.KeychainSqlite3(path, tpm)

Store public infomation in a Sqlite3 database and private keys in a TPM.

Variables:

path (str) – the path to the database. The default path is ~/.ndn/pib.db.
tpm (Tpm) – an instance of TPM.
tpm_locator (str) – a URI string describing the location of TPM.

default_identity()

Get the default Identity.

Return type:: Identity
Returns:: the default Identity.

del_cert(name)

Delete a specific Certificate.

Parameters:: name (NonStrictName) – the Certificate Name.

del_identity(name)

Delete a specific Identity.

Parameters:: name (NonStrictName) – the Identity Name.

del_key(name)

Delete a specific Key.

Parameters:: name (NonStrictName) – the Key Name.

get_signer(sign_args)

Get a signer from sign_args.

Parameters:: sign_args (dict[str, Any]) – the signing arguments provided by the application.
Returns:: a signer.
Return type:: Signer

has_default_identity(): Whether there is a default Identity. :rtype: bool :return: True if there is one.

new_identity(name)

Create a new Identity without a default Key. This is used to control the Keychain in a fine-grained way.

Parameters:: name (NonStrictName) – the Name of the new Identity.
Return type:: Identity
Returns:: the Identity created.

new_key(id_name, key_type='ec', **kwargs)

Generate a new key for a specific Identity.

Parameters:

id_name (NonStrictName) – the Name of Identity.
key_type (str) –
the type of key. Can be one of the following:
- ec: ECDSA key.
- rsa: RSA key.
kwargs – keyword arguments.

Keyword Arguments:

key_size (int) - key size in bit.
key_id (Union[BinaryStr, str]) - a one-Component ID of the Key.
key_id_type (str) - the method to generate the ID if key_id is not specified. Can be random or sha256.

Return type:

Key

Returns:

the new Key.

set_default_identity(name)

Set the default Identity.

Parameters:: name (NonStrictName) – the Name of the new default Identity.

shutdown(): Close the connection.

touch_identity(id_name)

Get an Identity with specific name. Create a new one if it does not exist. The newly created one will automatically have a default ECC Key and self-signed Certificate.

Parameters:: id_name (NonStrictName) – the Name of Identity.
Return type:: Identity
Returns:: the specified Identity.

`ndn.schema` package

Warning

Name Tree Schema (NTSchema) is experimental and capricious. The current implementation is treated as a proof-of-concept demo.

Introduction

The ndn.schema package provides an implementation of Name Tree Schema, an application framework that organizes application functionalities by the applciation namespace. Modularized NDN libraries can be developed based on it, and application developers can use those libraries as building blocks.

The core concept of NTSchema is the namespace schema tree. The schema tree is a tree structure that contains all possible naming conventions of an application. Different from a tree of names, its edge may be a pattern variable instead of a specific name component. For example, the path /<Identity>/KEY/<KeyID> can be used to represents a naming convention of a key, where specific keys – like /Alice/KEY/%01 and /Bob/KEY/%c2 match with it.

Two main components of NTSchema are custom nodes and policies. In the schema tree, every node represents a namespace. After matching with a specific name, a node can be used to produce and consume data. For example, if we call matched_node = tree.match('/Alice/KEY/%01'), it will return a matching of node /<Identity>/KEY/<KeyID> with variable setting Identity='Alice', KeyID=\x01. Then we call matched_node.provide(key_data), it will generate the key with data key_data and make it available. When we call key_data = matched_node.need(), it will try to fetch the key. A custom node will have customized pipeline to handle provide and need function calls. Policies are annotations attached to nodes, that specifies user-defined policies that are security, storage, etc.

Examples

1 - File Sharing

Assume that Alice has several devices and wants to share some files among them. To simplify the case, we assume that all devices have Alice’s key, which can be used as the trust anchor. A file may be large, so segmentation is needed.

Design

First, let’s start with the namespace design. There are two kinds of object in the system, one is the key, the other is the file.

For the file, an option is RDR protocol. RDR protocol handles the version discovery and segmentation. There is no need to know the implementation details, since NTScheme allows we use an existing protocols as a black box. In short, RDR has:

A metadata packet that contains a version number of the content.
A series of data packets containing segmented data content.

For the key, we can use a single Data packet to contain the certificate.

Note

This example is only used for demo, which is different from the real-world scenario.

RDR is not necessary in this scenario, since there is only one version for each file.
In real world, Alice may want to have a trust anchor instead of sharing a single key.

The whole namespace design is shown as follows:

In the figure, /file/<FileName> is the file object and /<IDName>/KEY/<KeyID>/self/<CertID> represents the certificate. Here, <variable> is a pattern variable that matches exactly one name cpmponent. The real names may be /file/foo.txt and /Alice/KEY/%29/self/%F6. Also, note that /file/<FileName> is an object composed of multiple data packets, which are managed by RDRNode and not exposed to the programmer.

Then, let’s move to the policies part. We want to ensure the following requirements:

All data packets are stored in memory, so if another node requests this file, the current node can serve it. This applies to both the producer – which loads the file from the disk and create packets, and the consumer – which receives the file from another node.
Data packets of the file must be signed by Alice’s key. The certificate can be preloaded into memory when the program starts.

Let’s attach these two policies onto the namespace schema tree we have:

The MemoryCachePolicy indicates all data packets are stored in memory. And SignedBy requires data packets with prefix /file/<FileName> to be signed by key /<IDName>/KEY/<KeyID>. We can add restrictions, such as IDName == 'Alice', to limit the identity.

Coding

With NTSchema, we can translate our design into code directly:

# Make schema tree
root = Node()
root['/<IDName>/KEY/<KeyID>/self/<CertID>'] = Node()
root['/file/<FileName>'] = RDRNode()

# Set policies
id_name = Name.Component.get_value(app.keychain.default_identity().name[0])
cache = MemoryCache()
root.set_policy(policy.Cache, MemoryCachePolicy(cache))
root['/file/<FileName>'].set_policy(
    policy.DataValidator,
    SignedBy(root['/<IDName>/KEY/<KeyID>'],
             subject_to=lambda _, vars: vars['IDName'] == id_name))

The full source code can be found in examples/rdrnode.py.

Reference

Namespace Schema Tree

exception ndn.schema.schema_tree.LocalResourceNotExistError(name): Raised when trying to fetch a local resource that does not exist. Used only when LocalOnly is attached to the node.

class ndn.schema.schema_tree.MatchedNode(root, node, name, pos, env, policies)

MatchedNode represents a matched static tree node. That is, a node with all name patterns on the path from the root to it assigned to some value. For example, if the tree contains a node N on the path /a/<b>/<c>, and the user use the Name /a/x/y to match, then a matched node (N, {‘b’: ‘x’, ‘c’: ‘y’}) will be returned.

Variables:

root (Node) – the root of the static tree.
node (Node) – the matched node of the static tree.
name (FormalName) – the name used to match.
pos (int) – an integer indicating the length the name is matched. Generally, it equals the length of name.
env (Dict[str, Any]) – a dict containing the value all pattern variables matched on the path.
policies (Dict[Type[policy.Policy], policy.Policy]) – a dict collecting all policies that apply to this node. For each type of policy, the one attached on the nearst ancestor is collected here.

app()

The NDNApp the static tree is attached to.

Return type:: NDNApp
Returns:: the NDNApp.

async express(app_param=None, **kwargs)

Try to fetch the data, called by the node’s need function. It will search the local cache, and examines the local resource. If the corresponding Data cannot be found in the two places, it encrypts the app_param and expresses the Interest.

Note

This function only sends out an Interest packet when the Data is not cached locally.

Parameters:

app_param (Union[bytes, bytearray, memoryview, None]) – the ApplicationParameter of the Interest.
kwargs – other parameters of the Interest.

Returns:

whatever process_data returns. Generally this function is only called at the default node, so the return value is a tuple of the content and a dict containing metadata.

finer_match(new_name)

Do a finer match based on current match. new_name must include current name as its prefix. For example, if the current match name is /a/b and we want to get the matched node for /a/b/c, then we can call finer_match with /a/b/c.

Parameters:: new_name (List[Union[bytes, bytearray, memoryview]]) – the new name to be matched. Must include current name as its prefix.
Returns:: the new matched node.

need(**kwargs)

Consume an object corresponding to this node. Specific node type may have customized processing pipeline. For example, a SegmentedNode can do reassembly here. By default it sends an Interest packet to fetch a Data.

MatchedNode’s need simply calls the node’s need function.

Parameters:: kwargs – arguments from user input.
Returns:: the object needed, whose format is defined by specific node type. By default, it returns a tuple of the content and a dict of metadata.

async on_data(meta_info, content, raw_packet)

Called when a Data packet comes. It saves the Data packet into the cache, decrypts the content, and calls the node’s process_data function.

Parameters:

meta_info (MetaInfo) – the MetaInfo of the incoming Data packet.
content (Union[bytes, bytearray, memoryview, None]) – the content of the Data.
raw_packet (Union[bytes, bytearray, memoryview]) – the raw Data packet.

Returns:

whatever process_data returns.

async on_interest(param, app_param, raw_packet)

Called when an Interest packet comes. It looks up the cache and returns a Data packet if it exists. Otherwise, it decrypts ApplicationParameters and calls the node’s process_int function.

Parameters:

param (InterestParam) – the parameters of the incoming Interest.
app_param (Union[bytes, bytearray, memoryview, None]) – the ApplicationParameters of the Interest.
raw_packet (Union[bytes, bytearray, memoryview]) – the raw Interest packet.

provide(content, **kwargs)

Produce an object corresponding to this node, and make all generated Data packets available. Specific node type may have customized processing pipeline. For example, a SegmentedNode can do segmentation here. By default it makes a Data packet out of content and put it into the cache.

MatchedNode’s provide simply calls the node’s provide function.

Parameters:

content – the content of the object.
kwargs – other arguments from user input. Defined by specific node type.

async put_data(content=None, send_packet=False, **kwargs)

Generate the Data packet out of content. This function encrypts the content, encodes and signs the packet, saves it into the cache, and optionally sends it to the face. This function is called by the node’s provide function.

Parameters:

content (Union[bytes, bytearray, memoryview, None]) – the Data content.
send_packet (bool) – whether sends the Data packet to the face.
kwargs – other arguments generating the Data packet.

class ndn.schema.schema_tree.Node(parent=None)

Node represents a node in the static namespace tree.

Variables:

policies (Dict[Type[policy.Policy], policy.Policy]) – policies attached to this node
prefix (FormalName) – the prefix of the root node of the tree. Generally not set for other nodes.
~.app (Optional[NDNApp]) – the NDNApp this static tree is attached to. Only available at the root.

async attach(app, prefix)

Attach this node to a specified NDNApp, register all name prefixes. This node becomes the root node of the application static tree. prefix is the prefix of the tree, which will be prepended to all names under this tree. For example, if prefix='/a/blog', then the node with path /articles from this node will become /a/blog/articles.

Warning

The way to register prefixes is still under discussion. Currently, we register the nodes that we can reach without going through a pattern. Also, there is no detach function yet, and no means to change the static tree after it’s attached.

Parameters:

app (NDNApp) – the NDNApp to be attached to.
prefix (Union[Iterable[Union[bytes, bytearray, memoryview, str]], str, bytes, bytearray, memoryview]) – the prefix of the static tree.

Returns:

whether succeeded or not.

exist(key)

If it has a child with specified name component or nme pattern.

Parameters:: key – a name component (bytes) or a patten (tuple).
Returns:: whether the child node exists

get_policy(typ)

Get the policy of specified type that applies to this node. It can be attached to this node or a parent of this node.

Parameters:: typ (Type[Policy]) – a policy type
Returns:: the policy. None if there does not exist one.

match(name)

Start from this node, go the path that matches with the name, and return the node it reaches when it cannot go further.

Parameters:: name (Union[Iterable[Union[bytes, bytearray, memoryview, str]], str, bytes, bytearray, memoryview]) – an NDN name.
Returns:: a MatchedNode, which contains the destination node and variables matched.

async need(match, **kwargs)

Consume an object corresponding to this node. Specific node type can override this function to have customized processing pipeline. For example, a SegmentedNode can do reassembly here. By default it sends an Interest packet to fetch a Data.

Parameters:

match – the matched node object of this node.
kwargs – other arguments from user input.

Returns:

This is defined by the node type. By default it returns what process_data() returns. That is, a tuple of contect and metadata dict.

async on_register(root, app, prefix, cached)

Called when the root node root is attached to app, and the attach() wants to register prefixed under the subtree rooted at this node.

Parameters:

root – the root of the static tree.
app (NDNApp) – the NDNApp to be attached to.
prefix (List[Union[bytes, bytearray, memoryview]]) – the prefix of the static tree.
cached (bool) – If there is a cache policy that applies to this node.

Returns:

whether succeeded or not.

async process_data(match, meta_info, content, raw_packet)

Processing an incoming Data packet. Specific node type can override this function to have customized processing pipeline. By default it returns the content.

Parameters:

match – the matched node object of this node.
meta_info (MetaInfo) – the MetaInfo of the Data packet.
content (Union[bytes, bytearray, memoryview, None]) – the content of the Data packet.
raw_packet (Union[bytes, bytearray, memoryview]) – the raw Data packet.

Returns:

a tuple, whose first element is data content after processing, and second is a dict[str, Any] containing metadata.

async process_int(match, param, app_param, raw_packet)

Processing an incoming Interest packet. Specific node type can override this function to have customized processing pipeline.

Note

This function will not be called if the Interest packet is satisfied with a cached Data packet.

Parameters:

match – the matched node object of this node.
param (InterestParam) – the parameters of the Interest packet.
app_param (Union[bytes, bytearray, memoryview, None]) – the ApplicationParameters of the Interest packet.
raw_packet (Union[bytes, bytearray, memoryview]) – the raw Interest packet.

async provide(match, content, **kwargs)

Produce an object corresponding to this node, and make all generated Data packets available. Specific node type can override this function to have customized processing pipeline. For example, a SegmentedNode can do segmentation here. By default it makes a Data packet out of content and put it into the cache.

Parameters:

match – the matched node object of this node.
content – the content of the object.
kwargs – other arguments from user input.

set_policy(typ, value)

Attach a policy to this node.

Parameters:

typ (Type[Policy]) – the policy type.
value (Policy) – the policy to be attached to this node.

exception ndn.schema.schema_tree.NodeExistsError(pattern): Raised when trying to create a node which already exists.

Utils

ndn.schema.util.NamePattern

NamePattern is a list containing mixed name components and varaible patterns. A variable pattern is a capturing pattern that matches with exactly one name component. It is a tuple containing 3 variables:

The 1st element is reserved and always 0. This is a quick and dirty solution in this PoC implementation It will be used if we want to support multiple name components matching patterns.
The 2nd element is the TLV type of the name component to be matched.
The 3rd element is the name of the pattern variable.

alias of List[Union[bytes, bytearray, memoryview, Tuple[int, int, str]]]

ndn.schema.util.norm_pattern(name)

This function returns a normalized name pattern from a string, just like normalizing a name.

Parameters:: name (str) – the name pattern string.
Return type:: List[Union[bytes, bytearray, memoryview, Tuple[int, int, str]]]
Returns:: normalized name pattern.

Custom Nodes

class ndn.schema.simple_node.LocalResource(parent=None, data=None)

LocalResource is a custom node that preloads some data. When need() is called, it returns the loaded data directly. This node type does not interact with the network.

async need(match, **kwargs)

Consume an object corresponding to this node. Specific node type can override this function to have customized processing pipeline. For example, a SegmentedNode can do reassembly here. By default it sends an Interest packet to fetch a Data.

Parameters:

match – the matched node object of this node.
kwargs – other arguments from user input.

Returns:

This is defined by the node type. By default it returns what process_data() returns. That is, a tuple of contect and metadata dict.

async on_register(root, app, prefix, cached)

Called when the root node root is attached to app, and the attach() wants to register prefixed under the subtree rooted at this node.

Parameters:

root – the root of the static tree.
app – the NDNApp to be attached to.
prefix – the prefix of the static tree.
cached (bool) – If there is a cache policy that applies to this node.

Returns:

whether succeeded or not.

async provide(match, content, **kwargs)

Produce an object corresponding to this node, and make all generated Data packets available. Specific node type can override this function to have customized processing pipeline. For example, a SegmentedNode can do segmentation here. By default it makes a Data packet out of content and put it into the cache.

Parameters:

match – the matched node object of this node.
content – the content of the object.
kwargs – other arguments from user input.

class ndn.schema.simple_node.RDRNode(parent=None, **kwargs)

RDRNode represents a versioned and segmented object whose encoding follows the RDR protocol. Its provide function generates the metadata packet, and need function handles version discovery.

class MetaData(parent=None)

async need(match, **kwargs)

Consume an object corresponding to this node. Specific node type can override this function to have customized processing pipeline. For example, a SegmentedNode can do reassembly here. By default it sends an Interest packet to fetch a Data.

Parameters:

match – the matched node object of this node.
kwargs – other arguments from user input.

Returns:

This is defined by the node type. By default it returns what process_data() returns. That is, a tuple of contect and metadata dict.

async process_int(match, param, app_param, raw_packet)

Processing an incoming Interest packet. Specific node type can override this function to have customized processing pipeline.

Note

This function will not be called if the Interest packet is satisfied with a cached Data packet.

Parameters:

match – the matched node object of this node.
param – the parameters of the Interest packet.
app_param – the ApplicationParameters of the Interest packet.
raw_packet – the raw Interest packet.

class MetaDataValue

async need(match, **kwargs)

Consume an object corresponding to this node. Specific node type can override this function to have customized processing pipeline. For example, a SegmentedNode can do reassembly here. By default it sends an Interest packet to fetch a Data.

Parameters:

match – the matched node object of this node.
kwargs – other arguments from user input.

Returns:

This is defined by the node type. By default it returns what process_data() returns. That is, a tuple of contect and metadata dict.

async provide(match, content, **kwargs)

Produce an object corresponding to this node, and make all generated Data packets available. Specific node type can override this function to have customized processing pipeline. For example, a SegmentedNode can do segmentation here. By default it makes a Data packet out of content and put it into the cache.

Parameters:

match – the matched node object of this node.
content – the content of the object.
kwargs – other arguments from user input.

class ndn.schema.simple_node.SegmentedNode(parent=None, timeout=4000, retry_times=3, segment_size=4400)

SegmentedNode represents a segmented object. The segmented object is composed with multiple Data packets, whose name have a suffix “/seg=seg_no” attached to the object’s name. The provide function handles segmentation, and the need function handles reassembly.

Note

Currently, the fetching pipeline is a simple one-by-one pipeline. where only one Interest will be in-flight at one time.

async need(match, **kwargs)

Consume an object corresponding to this node. Specific node type can override this function to have customized processing pipeline. For example, a SegmentedNode can do reassembly here. By default it sends an Interest packet to fetch a Data.

Parameters:

match – the matched node object of this node.
kwargs – other arguments from user input.

Returns:

This is defined by the node type. By default it returns what process_data() returns. That is, a tuple of contect and metadata dict.

async process_int(match, param, app_param, raw_packet)

Processing an incoming Interest packet. Specific node type can override this function to have customized processing pipeline.

Note

This function will not be called if the Interest packet is satisfied with a cached Data packet.

Parameters:

match – the matched node object of this node.
param – the parameters of the Interest packet.
app_param – the ApplicationParameters of the Interest packet.
raw_packet – the raw Interest packet.

async provide(match, content, **kwargs)

Produce an object corresponding to this node, and make all generated Data packets available. Specific node type can override this function to have customized processing pipeline. For example, a SegmentedNode can do segmentation here. By default it makes a Data packet out of content and put it into the cache.

Parameters:

match – the matched node object of this node.
content – the content of the object.
kwargs – other arguments from user input.

Policies

Policy Types

class ndn.schema.policy.Cache: Cache policy determines how Data packets are stored.

class ndn.schema.policy.DataEncryption: DataEncryption policy is a type used to indicate the Data encryption policy. Used as the type argument of set_policy.

class ndn.schema.policy.DataSigning: DataSigning policy is a type used to indicate the Data signer. Used as the type argument of set_policy.

class ndn.schema.policy.DataValidator: DataValidator policy describes how to verify a Data packet.

class ndn.schema.policy.Encryption: Encryption policy encrypts and decrypts content. When a user uses encryption policy, he needs to specify whether its InterestEncryption or DataEncryption.

class ndn.schema.policy.InterestEncryption: InterestSigning policy is a type used to indicate the Interest encryption policy. Used as the type argument of set_policy.

class ndn.schema.policy.InterestSigning: InterestSigning policy is a type used to indicate the Interest signer. Used as the type argument of set_policy.

class ndn.schema.policy.InterestValidator: InterestValidator policy describes how to verify an Interest packet.

class ndn.schema.policy.LocalOnly: LocalOnly means the Data should be stored in the local storage. It prevents the node from sending Interest packets.

class ndn.schema.policy.Policy: Policy is an annotation attached to a node.

class ndn.schema.policy.Register: Register policy indicates the node should be registered as a prefix in the forwarder.

class ndn.schema.policy.Signing: Signing policy gives a signer used to sign a packet. When a user uses signing policy, he needs to specify whether its InterestSigning or DataSigning.

Trust Policies

class ndn.schema.simple_trust.SignedBy(key, subject_to=None)

SignedBy policy represents the trust schema, specifying the key used to signed the Interest or Data packet. It does the follows:

Match the key used to sign the packet in the static tree. The real key must match the node specified by key. Otherwise, the validation fails.
Call the checker subject_to with two matching variable dict. Fail if the checker returns False.
Call the need function of the matched key node to get the public key. Fail if the key cannot be fetched.
Verify the signature.

Note

Theoretically, SignedBy should also give the signer used to sign outgoing packets. However, this function is missing in current implementation.

For example,

# This checker checks the Author of Data is the same as the Author of the key.
def check_author(data_env, key_env):
    return data_env['Author'] == key_env['Author']

root = Node()
root['/author/<Author>/KEY/<KeyID>/self/<CertID>'] = Node()
root['/blog/<Author>/<Category>/<Date>'] = Node()
# The Data "/blog/<Author>/<Category>/<Date>" should be signed by
# the key "/author/<Author>/KEY/<KeyID>" with the same author.
root['/blog/<Author>/<Category>/<Date>'].set_policy(
    policy.DataValidator,
    SignedBy(root['/author/<Author>/KEY/<KeyID>'], subject_to=check_author))

Cache Policies

class ndn.schema.simple_cache.MemoryCache

MemoryCache is a simple cache class that supports searching and storing Data packets in the memory.

async save(name, packet)

Save a Data packet with name into the memory storage.

Parameters:

name (List[Union[bytes, bytearray, memoryview]]) – the Data name.
packet (Union[bytes, bytearray, memoryview]) – the raw Data packet.

async search(name, param)

Search for the data packet that satisfying an Interest packet with name specified.

Parameters:

name (List[Union[bytes, bytearray, memoryview]]) – the Interest name.
param (InterestParam) – the parameters of the Interest. Not used in current implementation.

Returns:

a raw Data packet or None.

class ndn.schema.simple_cache.MemoryCachePolicy(cache): MemoryCachePolicy stores Data packets in memory.

Light VerSec

Introduction

Light VerSec (LVS) is a domain-specific language used to describe trust schemas in NDN. It originates from VerSec, designed and implemented by Pollere, Inc. Based on pattern matching, the VerSec language allows to express signing relations between name patterns, and the VerSec library can use it to validate trust schema at compile-time, check if the signing key of a packet received is allowed to sign that packet, and infer proper key or certificate to use when producing data. LVS is a lightweight modification of VerSec that focuses on signing key validation.

Quick Example

The following example descrive a trust schema of a blog website:

from ndn.app_support.light_versec import compile_lvs, Checker

lvs_text = r'''
// Site prefix is "/a/blog"
#site: "a"/"blog"
// The trust anchor name is of pattern /a/blog/KEY/<key-id>/<issuer>/<cert-id>
#root: #site/#KEY
// Posts are signed by some author's key
#article: #site/"article"/category/year/month <= #author
// An author's key is signed by an admin's key
#author: #site/role/author/#KEY & { role: "author" } <= #admin
// An admin's key is signed by the root key
#admin: #site/"admin"/admin/#KEY <= #root

#KEY: "KEY"/_/_/_
'''
lvs_model = compile_lvs(lvs_text)

Once the LVS text schema is compiled into a binary model, one can use it to check matching relations:

checker = Checker(lvs_model, {})
# Xinyu's author key can sign an article
print(checker.check('/a/blog/article/math/2022/03',
                    '/a/blog/author/xinyu/KEY/1/admin/1'))  # => True
# Admin's key can sign Xinyu's author key
print(checker.check('/a/blog/author/xinyu/KEY/1/admin/1',
                    '/a/blog/admin/admin/KEY/1/root/1'))  # => True
# Root key cannot directly sign author's key
print(checker.check('/a/blog/author/xinyu/KEY/1/admin/1',
                    '/a/blog/KEY/1/self/1'))  # => False

Syntax and Semantics

Pattern

A component pattern or pattern for short is a named variable that captures one arbitrary name component. In LVS, a component pattern is represented by a C-style identifier. A name pattern is a sequence of name components and component patterns, which can be used to match an NDN name. In LVS, name component values are put into quotes. For example, /"ndn"/user/"KEY"/key_id is a name pattern which has two component values (ndn and KEY) and two patterns (user and key_id).

When a name pattern matches a name, the name must have the same length as the name pattern, and every valued component must be exactly the same as components in the name at the same places. For example, the name pattern above matches with names /ndn/xinyu/KEY/1 and /ndn/admin/KEY/65c66a2a, but it does not match with /ndn/xinyu/key/1 or /ndn/xinyu/KEY/1/self/1.

In a matching, a component pattern can match only one arbitrary component, even the pattern occurs more than once. For example, name pattern /a/"b"/a/d can match with name /x/b/x/ddd but not name /x/b/y/ddd.

In LVS, you can embed a rule in a name pattern. For example, if #ndn is defined to be /"ndn" and #key is defined to be /"KEY"/key_id, then the above name pattern can be written as #ndn/user/#key for short.

Rule

A rule is a name pattern with component constraints and signing constraints. It has format:

#rule-name: name-pattern & component-constraints <= signing-constraints

A component constraint restricts how a pattern can match with a component. A signing constraint defines names of keys that can be used to sign packets matching with this rule. In the previous example, { role: "author" } is a component constraint, that limits the pattern named role can only match with component "author". #author: ... <= #admin is a signing constraint, which says an author’s key must be signed by an admin’s key.

Component constraints

A set of component constraints basically has a format as follows:

{pattern_1: constraint_1, pattern_2: constraint_2, ..., pattern_n: constraint_n}

A name must satisfy all constraints required in a constraint set to be matched with a name pattern.

LVS supports three different type of component constraints: component values, patterns, and user functions. A component value restricts the pattern variable to only match with a given component value, like { role: "author" }. If another pattern name is used as a constraint, the current pattern must have the same value as the given pattern. For example, the name pattern with constraint /a/"b"/c/d & {c: a} is equivalent to the aforementioned name pattern /a/"b"/a/d, as pattern c is required to equal a. A user function allows user to use some Python function to decide whether a value matches.

LVS allows a constraint to take multiple options, separated by |. For example, { role: "author"|"admin" } means role can match with either author or admin. Different options may have different types. Also, LVS allows multiple constraint sets to be given to a rule, separated by |. In that case, any constraint set holds will lead to a successful matching. For example, the following two rules:

#user1: #site/role/user/#KEY & { role: "author"|"admin" }
#user2: #site/role/user/#KEY & { role: "author" } | { role: "admin" }

mean the same thing: a key name of either an author or an admin user.

If a rule’s name pattern refers to other rules, the component constraints of those rules will be inherited. In the example above, #user1 and #user2 will inherit all component constraints of #site and #KEY. A rule may also add complementary constraints to the patterns inherited. For example, if #KEY has a component pattern named key-id, then #user1 can add a constraint like { key-id: "1" }.

Signing constraints

A signing constraint suggests a name pattern of a key that can be used to sign the packet matching with the rule. A rule can have multiple signing constraints, separated by |. Note that LVS does not allow giving name patterns or component constraints directly as a signing constraint.

A matched pattern is carried over through a signing chain. For example:

#post: #site/"post"/author/date <= #author | #admin
#author: #site/"author"/author/#KEY <= #admin
#admin: #site/"admin"/admin/#KEY <= #root

This means a post must be signed by an author with the same author in the name, or an arbitrary admin. For example, /site/post/xinyu/2022 can only be signed with /site/author/xinyu/KEY but not /site/author/zhiyi/KEY, because he is not the author of this post and the pattern author does not match with the same pattern in the post name. However, if Zhiyi has an admin key, he can use /site/admin/zhiyi/KEY to sign the post without any issue.

Warning

A component constraint can only refer to previous defined pattern, either from a previous component or from the rule signed by the current one. For example, /a/b/c & {b: c} will match nothing by itself, because c does not have a value when b is matched. Consider write /a/b/c & {c: b} instead. On the other hand, #r1: /a/b & {b: c} is valid if there is another rule #r2: /c/d <= #r1, when validating #r2’s signature, as c is matched in #r2’s name, and the matching is carried over to #r1’s matching. However, in this case, no key can sign #r1, so there must be another rule describing how the keys are further signed.

User Functions

User functions are named in the format of $function. They should be provided as a dictionary via Checker’s construction function by the application code using the trust schema. The name function of one user function should be the dictionary key and the corresponding function definition should be the dictionary value. A user function can take arguments of type component values and patterns. For example, $fn("component", pattern) is a valid function call. When used as a component constraint, the LVS library will always call the user function with two arguments: the first one is the value of the pattern constrained, and the second one is a list containing all arguments. The return value of one user function should be either True or False. For example, there is a user function called fn. It should be defined and provided as follows.

def fn(component, pattern):
    if condition:
        return True
    else:
        return False
user_fn={"fn": fn}
checker=Checker(lvs_model,user_fn)

In the trust schema, the user function can be called as

#rule: /a/b & { b: $fn("c", a) }

If we match it with name /x/y, the LVS library will call $fn with argument ("y", ["c", "x"]) when the matching process reaches b.

Temporary Identifiers

Identifiers starting with an underscore _ are temporary identifiers. For example, $_RULE and _PATTERN, and even $_ and _. As the name says, temporary identifiers are not memorized and thus cannot be referred to. Instead, it is safe to reuse temporary identifiers as many times and they won’t interfere each other. It is supposed to be used when one doesn’t want to give a name, doesn’t care the values, or used to avoid name collisions.

A temporary rule $_RULE can be defined as many times. But it is not allowed to be used in a name pattern like /$_RULE/"component".

A temporary pattern _pattern occuring in a name pattern does not need to match with a unique value. In the previous example, #KEY: "KEY"/_/_/_ can match with names like KEY/1/self/1, and there is no need for the last three components to be the same. A temporary pattern can be constrained, but it cannot occur on the right hand side of a component constraint of another pattern.

Formal Grammar

The formal grammar of LVS is defined as follows:

TAG_IDENT = CNAME;
RULE_IDENT = "#", CNAME;
FN_IDENT = "$", CNAME;
CNAME = ? C/C++ identifiers ?;
STR = ? C/C++ quoted string ?;

name = ["/"], component, {"/", component};
component = STR
          | TAG_IDENT
          | RULE_IDENT;

definition = RULE_IDENT, ":", def_expr;
def_expr = name, ["&", comp_constraints], ["<=", sign_constraints];
sign_constraints = RULE_IDENT, {"|", RULE_IDENT};
comp_constraints = cons_set, {"|", cons_set};
cons_set = "{", cons_term, {",", cons_term}, "}";
cons_term = TAG_IDENT, ":", cons_expr;
cons_expr = cons_option, {"|", cons_option};
cons_option = STR
            | TAG_IDENT
            | FN_IDENT, "(", fn_args, ")";
fn_args = (STR | TAG_IDENT), {",", (STR | TAG_IDENT)};

file_input = {definition};

See the source code for the grammar used by Lark parser.

Tutorial

Suppose that there is a blog platform that contains three roles: admin, author and reader. It follows these specifications: 1. The prefix of this platform is /ndn/blog. The trust anchor is /ndn/blog/KEY/<key-id>/<issuer>/<cert-id>. 2. There is a root certificate in this platform. 3. Admin has its certificate signed by root certificate. 4. The certificates of both author and reader are signed by admin’s certificate. 5. The IDs of both author and reader should be a 6-digit number. 6. Both author and admin can post the articles. 7. The name of a posted article should be /ndn/blog/ID/post/<year>/<id>. The “year” must be a 4-digit number.

Based on the above specifications, the trust schema can be written as:

// The platform prefix definition. The pair of quotes means that it can only be matched by the identical component.
#platform: "ndn"/"blog"
// The certificate name suffix definition. Each underscore can be matched by an arbitrary pattern except that contains slash.
#KEY="KEY"/_/_/_
// The root certificate definition, i.e., /ndn/blog/KEY/<key-id>/<issuer>/<cert-id>.
#root: #platform/#KEY
// Admin's certificate definition. The non-sharp patterns, role and adminID, are sent from the application. Each pattern can match an arbitrary components, but the matched components for the same pattern should be the same. The constraint shows that the component "_role" must be "admin". The underscore means that the matched components for the pattern "_role" may not be identical in the chain. The admin's certificate must be signed by the root certificate.
#admin: #platform/_role/adminID/#KEY & {_role: "admin"} <= #root
// author's certificate definition. The ID is verified by a user function. Both constraints must be met. It can only be signed by the admin's certificate.
#author: #platform/_role/ID/#KEY & {_role: "author", ID: $isValidID()} <= #admin
// author's and reader's certificate definition. The role can be either "reader" or "author". The ID is verified by a user function. Both constraints must be met. It can only be signed by the admin's certificate.
#user: #platform/_role/ID/#KEY & {_role: "reader"|"author", ID: $isValidID()} <= #admin
// article's trust schema. The component "year" is verified by a user function. The article can be signed by the admin's certificate or one author's certificate.
#article: #platform/ID/"post"/year/articleID & {year: $isValidYear()} <= #admin | #author

To build the checker of the above trust schema, we must define the user functions by using lambda expressions first.

# Build the dictionary
user_fn = {
    "$isValidID": lambda component, _pattern: len(Component.get_value(component)) == 6,
    "$isValidYear": lambda component, _pattern: len(Component.get_value(component)) == 4,
}

With the string of trust schema and the user function dictionary, we can compile the LVS model and initialize the checker.

from ndn.app_support.light_versec import compile_lvs, Checker

lvs_text = r'''
#platform: "ndn"/"blog"
#KEY="KEY"/_/_/_
#root: #platform/#KEY
#admin: #platform/_role/adminID/#KEY & {_role: "admin"} <= #root
#author: #platform/_role/ID/#KEY & {_role: "author", ID: $isValidID()} <= #admin
#user: #platform/_role/ID/#KEY & {_role: "reader"|"author", ID: $isValidID()} <= #admin
#article: #platform/ID/"post"/year/articleID & {year: $isValidYear()} <= #admin | #author
'''

# compile the LVS model
lvs_model = compile_lvs(lvs_text)
# initialize the checker
checker = Checker(lvs_model, user_fn)

With the function check, we can check whether one name is valid under one certificate name. Here are some testing examples.

# Admin's certificate can be signed by the root certificate
print(checker.check('/ndn/blog/admin/000001/KEY/1/root/1',
                    '/ndn/blog/KEY/1/self/1'))  # => True
# The component "key" does not match (should be upper-case)
print(checker.check('/ndn/blog/admin/000001/key/1/root/1',
                    '/ndn/blog/KEY/1/self/1'))  # => False
# One admin's certificate cannot be signed by another admin.
print(checker.check('/ndn/blog/admin/000002/KEY/1/root/1',
                    '/ndn/blog/admin/000001/KEY/1/root/1'))  # => False
# One author's certificate can be signed by an admin (with valid ID).
print(checker.check('/ndn/blog/author/100001/KEY/1/000001/1',
                    '/ndn/blog/admin/000001/KEY/1/root/1'))  # => True
# The author's ID is invalid.
print(checker.check('/ndn/blog/author/1000/KEY/1/000001/1',
                    '/ndn/blog/admin/000001/KEY/1/root/1'))  # => False
# One reader's certificate can be signed by an admin (with valid ID).
print(checker.check('/ndn/blog/reader/200001/KEY/1/000001/1',
                    '/ndn/blog/admin/000001/KEY/1/root/1'))  # => True
# One article can be signed by an author.
print(checker.check('/ndn/blog/100001/post/2022/1',
                    '/ndn/blog/author/100001/KEY/1/000001/1'))  # => True
# The author is wrong. The IDs in both article name and certificate name should be the same,
# as they use the same pattern "ID".
print(checker.check('/ndn/blog/100001/post/2022/1',
                    '/ndn/blog/author/100002/KEY/1/000001/1'))  # => False
# The year is invalid.
print(checker.check('/ndn/blog/100001/post/202/1',
                    '/ndn/blog/author/100001/KEY/1/000001/1'))  # => False
# The article cannot be signed by a reader.
print(checker.check('/ndn/blog/200001/post/2022/1',
                    '/ndn/blog/reader/200001/KEY/1/000001/1'))  # => False

References

`ndn.app_support.light_versec` package

ndn.app_support.light_versec.compile_lvs(lvs_text)

Compile a text Light VerSec file into a TLV encodable binary LVS model. The latter one can be used to create validators.

Parameters:

lvs_text (str) – Light VerSec text file

Return type:

LvsModel

Returns:

LVS model

Raises:

SemanticError – when the given text file has a semantic error
lark.UnexpectedInput – when the given text file has a syntax error

class ndn.app_support.light_versec.Checker(model, user_fns)

A checker uses a LVS model to match names and checks if a key name is allowed to sign a packet.

Variables:

model – the LVS model used.
user_fns – user functions

check(pkt_name, key_name)

Check whether a packet can be signed by a specified key.

Parameters:

pkt_name (NonStrictName) – packet name
key_name (NonStrictName) – key name

Return type:

bool

Returns:

whether the key can sign the packet

static load(binary_model, user_fns)

Load a Light VerSec model from bytes.

Parameters:

binary_model (BinaryStr) – the compiled LVS model in bytes
user_fns (dict[str, UserFn]) – user functions

match(name)

Iterate all matches of a given name.

Parameters:: name (NonStrictName) – input NDN name.
Return type:: Iterator[tuple[list[str], dict[str, Union[bytes, bytearray, memoryview]]]]
Returns:: iterate a pair (rule_names, context), where rule_names is a list containing corresponding rule names of current node, and context is a dict containing pattern->value mapping.

root_of_trust()

Return the root of signing chains

Return type:: set[str]
Returns:: a set containing rule names for all starting nodes of signing DAG.

save()

Save the model to bytes. User functions excluded.

Return type:: bytes

suggest(pkt_name, keychain)

Suggest a key from the keychain that is used to sign the specific data packet.

Parameters:

pkt_name (NonStrictName) – packet name
keychain (Keychain) – keychain

Return type:

List[Union[bytes, bytearray, memoryview]]

Returns:

the first key (in the order of storage) in the keychain that can sign the packet

validate_user_fns()

Check if all user functions required by the model is defined.

Return type:: bool

class ndn.app_support.light_versec.SemanticError: Raised when the LVS trust schema to compile has semantic errors.

class ndn.app_support.light_versec.LvsModelError: Raised when the input LVS model is malformed.

Implementation Details

This page introduces some implementation details and some discussion on design for maintainers to understand this work.

Compiler

The goal of compiling is to transform the input rules into a more “clean” graph structure, so the checker can do matching/verification by traveling along the graph, with backtracking if necessary. By doing so, with little sacrifice of flexibility, we make the checker simpler and more efficient.

To accomplish that goal, the LVS compiler is currently designed as follows:

Input/Output

LVS complier takes string format trust schema written in LVS.

Afterwards, LVS complier outs a name pattern tree using TLV Model. A name pattern tree has the following properties:

A name pattern tree has a single root. Every rule is a path originating from the root.
Every edge represents a component in name pattern.
There are two types of edges: edges with a component value; edges representing a pattern.
Every component constraint is put at the edge representing the pattern it constrains. For example, given /a/b & {b: "c"}, we will have a tree: / -> /a -> /a/b with one constraint b = "c" put at the edge /a->/a/b.
Each pattern edge can carry a set of constraints restricting the same pattern, with each constraints may have multiple options. To move along this edge, all constraints in the set must be satisfied by one of its options, i.e. CNF formula.
Signing constraints are put at the end node of a rule, in the form of a set referring to the rules that can be used to sign the current name pattern.
Patterns are stored using numerical IDs (natural numbers). An optional symbol table can be provided to store their names before compile.

The detailed format is defined in binary.py.

The LVS compiler does the following steps to generate the name pattern tree:

Parse the LVS schema into ASTs
Sort rule references.
Generate numerical ID for patterns.
Replicate rules with multiple constraint sets {...}|{...},
Generate the name pattern tree.
Replace rule names in signing constraints with node IDs.
Fill in the symbol table for name pattern.

Parsing

In python-ndn, LVS is parsed by Lark. The grammar is defined in grammar.py. Lark’s parser allows the user to define a function for every grammar rule, and calls it at the corresponding reduce step. These functions are defined in parser.py. Currently these functions only transform the input AST to some Python classes, so the LVS compiler can identify the types of terms easily, e.g., test whether a component in a name pattern is a component value or another rule. Parser does not do actual compiling work.

Sorting rules

LVS allow rules to refer to each other like #root: #site/#KEY. To effectively expand #root into a tree path, we have to expand #site and #KEY first. Therefore, the compiler uses topological sorting to sort rules, in the reverse order of references. Cyclic references are also detected at this step.

Generating pattern ID

At this step, the compiler goes through all rules and constraints to give every pattern a global unique numerical ID. IDs are starting from 1. A named pattern is given the same ID for every occurence. Every occurence of a temporary pattern is considered as a different pattern, so it is given a new ID every time. However, LVS allows the schema to give constraints to temporary patterns. In that case, the constraint will be replicated. For example, /_a/_a & {_a: $eq_type("v=0")} will become /1/2 & {1: $eq_type("v=0"), 2: $eq_type("v=0")}.

Since we don’t know the number of named pattern at the beginning, temporary patterns are numbered with minus number at this time. They will be turned into positive numbers when outputing the binary schema, because TLV supports non-negative integers better.

Replicating rules

After compilation, we only check component constraints at the point a pattern is matched. However, LVS allows one rule to have multiple constraint sets. For example, /a/b & {a: "a"} | {b: "b"}. This disjunctive relation cannot be verified when a is matched. Therefore, we replicate a rule with multiple constraint sets. The rule above will becode /a/b & {a: "a"} and /a/b & {b: "b"}. Also, references to other rules are resolved at this step. In the source code we call a rule after this step a chain.

Generating tree

This step simply merges all rule chains into a tree, and put all constraints at the edge of the first occurence of the constrained pattern. Note that singing constraints are still referring to rules by their names, as we have no idea about the ID of the end node of a rule chain.

Fixing signing constraints

Finally, we traverse the tree and replace all name-based signing constraints with node references.

A workflow demonstration with example trust schema is available at Compiler and Checker Demonstration.

Checker

A checker uses a LVS model to match names and checks if a key name is allowed to sign a packet. Additionally, the caller can supply with some user-defined functions to support customized trust schema checkings (e.g., $eq_type("v=0")).

To match a given name, the checker goes from the tree root, and recursively goes along edges that are allowed to pass. When the depth equals to the input name length, the matching succeeds and returns the end node as well as all matched patterns. The checker always tries value edges first, since there is at most one edge that can succeeds. After all value edges are tried, it tries pattern edges one by one. When all edges failed, e.g. at a leaf node, the matching backtracks to the parent node.

Signing key checking

To check whether name A can sign name B (i.e., check(pkt_name, key_name)), the checker matches the data name B first, and then tries to the key name A with the context of previous matching. If B can reach some node in the signing constraint list of A’s matching node, the checker returns true. False is returned when all possible matches are tried.

Signing key suggesting

To suggest a signing key name for packet name A (i.e., suggest(pkt_name, keychain)), the checker lists all certificats in the local keychain, and returns the first certificate name that can satisfy the signing restrictions. It assumes the corresponding certificate in the keychain is valid.

For example:

#KEY: "KEY"/_/_/_
#article: /"article"/_topic/_ & { _topic: "eco" | "spo" } <= #author
#author: /site/"author"/_/#KEY <= #admin
#admin: /site/"admin"/_/#KEY <= #anchor
#anchor: /site/#KEY & {site: "la" | "ny" }

This LVS schema allows both /la/author/1 and /ny/author/2 to sign packet under name /article/eco/day1. If both /la/author/1 and /ny/author/2 appears on the local keychain, signing suggestion would be the first certificate from the two identities that appear in the keychain storage (e.g., /la/author/1).

The suggest(pkt_name, keychain) itself does not further verify if /la/author/1’s certificate signer is legitimate and repeat the same process till the trust anchor. Instead, it trusts the keychain certificates in any case.

Schema Validation

The current things in a LVS trust schema are currently validated by the compiler or the checker:

No cyclic references in rule name patterns.
No cyclic references in signing relations.
The root of trust (i.e. the starting node of signing chains) matches with the name of trust anchor.
All user functions are provided.

Optimization

This section discusses possible optimizations that may be used. Note that not all the content in this section has been implemented.

Merging from the root (Done)

For simplicity of implementation, the current compiler treats all patterns as different edges. However, two nodes can be merged if the paths from the root to them have identical patterns and constraints. For example, given the schema:

#r1 = /"a"/b/c & {b: $fn1(), c: $fn2()}
#r2 = /"a"/b/c & {b: $fn1(), c: $fn3()}

The current result tree and optimized one are shown in the figure.

Merging from the leaves (Not Implmented)

If we waive the requirement of tree structure and accepts a DAG, then another way to simplify the result is to merge two nodes that have identical subtrees. This is the same as DFA minimization, so let me omit examples and figures.

Alternative Methods

This section lists related work known by the author. However, at current stage, there lack application scenatios and data to compare the pros and cons of them.

DFA / NTSchema

The differences between LVS tree and a NTSchema tree is like NFS vs DFA: a name can have multiple matches in a LVS tree, but at most one match in NTSchema.

In NTSchema, a pattern edge can only attach a component type, with out any further constraint. Every matching step moves along exact one edge, and never backtracks. After both the packet name and the key name are matched, NTSchema checks if the key name matching node is the node specified by signed-by policy attached at the packet node, and then checks other conditions. If the namespace is well-structured and the conditions are simple, NTSchema should be faster than LVS tree.

It is also possible to convert the LVS tree to a DFA while keeping the behavior to check conditions as we move. We can list a truth table for an step with multiple patterns & constraints, and use something similar to NFA->DFA algorithm to convert the LVS tree into a deterministic machine. However, since the number of nodes becomes larger, whether the performance will be better or not is unknown.

Conceptually, there is another big difference between LVS and NTSchema: NTSchema is designed to describe the application name space by cutting it into subspaces. Signing relation is just one property that a subspace has. However, LVS is rule-based, which means the structure of names in the system is already fixed, and the user uses this language to express specific rules to comply with the requirements of signing relations.

Decision-based systems

If we consider a name as “a list of values”, the problem can be transformed into a decision making problem: given variables $x_1,\ldots, x_n, y_1,\ldots, y_m$, we need to answer a yes-no question based on the truth value of some propositions like $x_i = v$, $x_i = y_j$, or $fn(x_i)$. There are multiple systems can do so. For example, Prolog allows user to describe logic. Decision tree, BDD/ZDD can be used to store the logic. We can even directly store the truth table if it is small. SAT/SMT can be used to validate the schema.

NDN-CXX Validator

NDN-CXX supports validator configuration file. It uses a special regular expression to capture names, which offers best flexibility of my knowledge. However, the implementation complexity is also very high.

Future Work

Access control (ABE)

LVS can be extended to describe attributes of packets easily. However, data – attribute binding (i.e. “which attribute the data have”) is only part of the access control system. We also need user – attribute binding (i.e. “who holds which attribute”) to do access control, and we believe this binding is out of the scope of this language. Actually, user – attribute binding is tightly related to certificate/key issuance, which is the scope of the trust authority.

Compiler and Checker Demonstration

This page gives a demonstration about how the compiler and the checker works, using the example trust schema. Please refer to Implementation Details for implementation details.

LVS schema input and parsing

We assume the following LVS schema:

#KEY: "KEY"/_/_/_
#site: "lvs-test"
#article: #site/"article"/author/post/_version & {_version: $eq_type("v=0")} <= #author
#author: #site/"author"/author/"KEY"/_/admin/_ <= #admin
#admin: #site/"admin"/admin/#KEY <= #root
#root: #site/#KEY

We ignore the parsing details since this is handled by Lark.

Sorting rules

The original schema has the following dependencies among the rules:

(1) #KEY: "KEY"/_/_/_
(2) #site: "lvs-test"
(3) #article: #site/"article"/author/post/_version & {_version: $eq_type("v=0")} <= #author
  --> (2) (4)
(4) #author: #site/"author"/author/"KEY"/_/admin/_ <= #admin
  --> (2) (5)
(5) #admin: #site/"admin"/admin/#KEY <= #root
  --> (1) (2) (6)
(6) #root: #site/#KEY
  --> (1) (2)

Topological sorting gives us:

(3) #article: #site/"article"/author/post/_version & {_version: $eq_type("v=0")} <= #author
  --> (2) (4)
(4) #author: #site/"author"/author/"KEY"/_/admin/_ <= #admin
  --> (2) (5)
(5) #admin: #site/"admin"/admin/#KEY <= #root
  --> (1) (2) (6)
(6) #root: #site/#KEY
  --> (1) (2)
(1) #KEY: "KEY"/_/_/_
(2) #site: "lvs-test"

Generating pattern ID

#site/”article”/1/2/-1 & {-1: $eq_type(“v=0”)} <= #author #author: #site/”author”/1/”KEY”/-2/3/-3 <= #admin #admin: #site/”admin”/3/#KEY <= #root #root: #site/#KEY #KEY: “KEY”/-4/-5/-6 #site: “lvs-test”

Replicating rules

In this schema, we don’t have have multiple constraint sets like /a/b & {a: "a"} | {b: "b"}. Therefore, no rule replication is needed.

Generating tree

Each node is a name prefix, and edge becoming the condition to

Fixing signing constraints

After constructing the tree, the compilier fill in the symbol table for non-temporary symbols:

author
post
admin

and model the name pattern tree into a TLV encodable model.

Checker

In order to check a name /lvs-test/article/alice/post1/v=2 can be signed by name /lvs-test/author/alice/KEY/%BDA%D6%DE%EA%09%3C%E0/admin/v=1647807153833, Checker first matches /lvs-test/article/alice/post1/v=2 against the name pattern tree, which gives the uppermost branch of the pattern tree.

Along the matching, checker fills the symbols with author = "alice" and post = "post1". The end of this branch indicates the node identifier (e.g., x) for this branch.

Then the checker matches the /lvs-test/author/alice/KEY/... against the name pattern tree, which gives the second branch from the top. When matching along this branch, checker uses “alice” for 1’s value. The end of this branch has the same node identifier x, thereby the checking succeeds.

Miscellaneous packages

`ndn.types` package

exception ndn.types.InterestCanceled

Raised when an Interest is cancelled due to the loss of connection to NFD.

Note

A very large packet may cause NFD shutting down the connection. More specifically,

The face is shutdown.
All pending Interests are cancelled with this exception.
App.run_forever() returns True.

exception ndn.types.InterestNack(reason)

Raised when receiving a NetworkNack.

Variables:: reason (int) – reason for Nack.

exception ndn.types.InterestTimeout: Raised when an Interest times out.

exception ndn.types.NetworkError: Raised when trying to send a packet before connecting to NFD.

ndn.types.Route

An OnInterest callback function for a route.

alias of Callable[[List[Union[bytes, bytearray, memoryview]], InterestParam, Optional[Union[bytes, bytearray, memoryview]]], None]

class ndn.types.ValidResult(value, names=None, *, module=None, qualname=None, type=None, start=1, boundary=None)

Validation result returned by a validator. Most of them are designed for the union checker, which chains multiple checkers in order. For NDNApp (v2), only PASS and ALLOW_BYPASS are considered as True.

ALLOW_BYPASS = 2: The validator allows bypassing all following checkers. Succeed immediately.

FAIL = -2: Negative. The validation fails and the packet should be discarded. Abort.

PASS = 1: Affirmative. Passes the current check. Continue.

SILENCE = 0: The validator does not handle this type of packet and thus cannot decide. Continue.

TIMEOUT = -1: The validation process exceeds the Interest deadline. Abort.

exception ndn.types.ValidationFailure(name, meta_info, content, sig_ptrs, result=ValidResult.FAIL)

Raised when failing to validate a Data packet.

Variables:

name (FormalName) – the Name of Data.
meta_info (MetaInfo) – the MetaInfo.
content (Optional[BinaryStr]) – the Content of Data.
sig_ptrs (SignaturePtrs) – the signature pointers of Data
result (ValidResult) – the reason of failure.

ndn.types.Validator

A validator used to validate an Interest or Data packet.

alias of Callable[[List[Union[bytes, bytearray, memoryview]], SignaturePtrs], Coroutine[Any, None, bool]]

`ndn.utils` package

ndn.utils.gen_nonce()

Generate a random nonce.

Returns:: a random 32-bit unsigned integer.

ndn.utils.gen_nonce_64()

Generate a random 64-bit nonce.

Returns:: a random 64-bit unsigned integer.

ndn.utils.timestamp()

Generate a timestamp number.

Returns:: the time in milliseconds since the epoch as an integer

Examples

Here lists some examples of python-ndn.

Basic Applications

Connect to NFD

NDNApp connects to an NFD node and provides interface to express and process Interests. The following code initializes an NDNApp instance with default configuration.

from ndn.app import NDNApp
app = NDNApp()
app.run_forever()

If there is a main function for the application, use the after_start argument.

from ndn.app import NDNApp
app = NDNApp()

async def main():
    # Do something
    app.shutdown()  # Close the connection and shutdown

app.run_forever(after_start=main())

Consumer

A consumer can use express_interest to express an Interest. If a Data is received and validated, it returns the Name, MetaInfo and Content of Data. Otherwise, an exception is thrown.

from ndn.encoding import Name

async def main():
    try:
        data_name, meta_info, content = await app.express_interest(
            # Interest Name
            '/example/testApp/randomData',
            must_be_fresh=True,
            can_be_prefix=False,
            # Interest lifetime in ms
            lifetime=6000)
        # Print out Data Name, MetaInfo and its conetnt.
        print(f'Received Data Name: {Name.to_str(data_name)}')
        print(meta_info)
        print(bytes(content) if content else None)
    except InterestNack as e:
        # A NACK is received
        print(f'Nacked with reason={e.reason}')
    except InterestTimeout:
        # Interest times out
        print(f'Timeout')
    except InterestCanceled:
        # Connection to NFD is broken
        print(f'Canceled')
    except ValidationFailure:
        # Validation failure
        print(f'Data failed to validate')
    finally:
        app.shutdown()

Producer

A producer can call route to register a permanent route. Route registration can be done before application is started. NDNApp will automatically announce that route to the NFD node.

@app.route('/example/testApp')
def on_interest(name, interest_param, application_param):
    app.put_data(name, content=b'content', freshness_period=10000)

Customized TLV Models

Encoding

python-ndn provides a descriptive way to define a specific TLV format, called TLV model. Every object can be described by a class derived from TlvModel. Elements of a TLV object is expressed as an instance variable of Field. Fields are encoded in order.

from ndn.encoding import *

class Model(TlvModel):          # Model = [Name] [IntVal] [StrVal] [BoolVal]
    name = NameField()          # Name = NAME-TYPE TLV-LENGTH ...
    int_val = UintField(0x03)   # IntVal = INT-VAL-TYPE TLV-LENGTH nonNegativeInteger
    str_val = BytesField(0x02)  # StrVal = STR-VAL-TYPE TLV-LENGTH *OCTET
    bool_val = BoolField(0x01)  # BoolVal = BOOL-VAL-TYPE 0

model = Model()
model.name = '/name'
model.str_val = b'bit string'
assert model.encode() == b'\x07\x06\x08\x04name\x02\nbit string'

model = Model.parse(b'\x07\x06\x08\x04name\x02\nbit string')
assert model.str_val == b'bit string'

There is no required fields in a TLV model. Every Field is None by default, which means it will not be encoded.

Nested Model

python-ndn allows a TLV model to be a field (ModelField) of another TLV model, which enables a hierarchical structure. Also, a TLV model does not contain the outer Type and Length. This can be solved by encapsulating it into another TLV model.

class Inner(TlvModel):              # Inner = [Val1]
    val1 = UintField(0x01)          # Val1  = 1 TLV-LENGTH nonNegativeInteger

class Outer(TlvModel):              # Outer = [Val2]
    val2 = ModelField(0x02, Inner)  # Val2  = 2 TLV-LENGTH Inner

obj = Outer()
obj.val2 = Inner()
obj.val2.val1 = 255
assert obj.encode() == b'\x02\x03\x01\x01\xFF'

Repeated Model

RepeatedField is an array of a specific type of field. When encoding, elements are encoded in order.

class WordArray(TlvModel):                               # WordArray = *Words
    words = RepeatedField(UintField(0x01, fixed_len=2))  # Words = 1 2 2OCTET

array = WordArray()
array.words = [i for i in range(3)]
assert array.encode() == b'\x01\x02\x00\x00\x01\x02\x00\x01\x01\x02\x00\x02'

Derivation

To avoid duplication, a TlvModel can extend 1 or more other TlvModels. However, to indicate the locations of base classes in the TLV encoded wire, there must be an field for every base class to explicitly include its base class. These fields must have the value IncludeBase. TlvModel instances’ Include fields cannot be assigned, and will be ignored during encoding and parsing.

class Base(TlvModel):         # Base = [M2]
    m2 = UintField(0x02)

class Derived(Base):          # Derived = [M1] [M2] [M3]
    m1 = UintField(0x01)
    _base = IncludeBase(Base)
    m3 = UintField(0x03)

obj = Derived()
obj.m1, obj.m2, obj.m3 = range(1, 4)
assert obj.encode() == b'\x01\x01\x01\x02\x01\x02\x03\x01\x03'

Overriding

The derived class can override fields of its base classes. To override a field, declare a field with the same name after the including. Overriding fields will be encoded in their original places, irrelevant to the order of declaration.

class A1(TlvModel):          # A1 = [M1]
    m1 = UintField(0x01)

class A2(A1):                # A2 = [M1] [M2]
    _a1 = IncludeBase(A1)
    m2 = UintField(0x02)

class B1(TlvModel):          # B1 = [X] [A1] [Y]
    x = UintField(0x0a)
    a = ModelField(0x03, A1)
    y = UintField(0x0b)

class B2(B1):                # B2 = [X] [A2] [Y]
    IncludeBase(B1)
    a = ModelField(0x03, A2)

Parsing

A TlvModel can be parsed from a wire. All fields are parsed in order. Out of order or unknown fields are ignored if they are non-critical. An unknown critical field leads to DecodeError .

from ndn.encoding import *

class Model(TlvModel):          # Model = [Name] [IntVal] [StrVal] [BoolVal]
    name = NameField()          # Name = NAME-TYPE TLV-LENGTH ...
    int_val = UintField(0x03)   # IntVal = INT-VAL-TYPE TLV-LENGTH nonNegativeInteger
    str_val = BytesField(0x02)  # StrVal = STR-VAL-TYPE TLV-LENGTH *OCTET
    bool_val = BoolField(0x01)  # BoolVal = BOOL-VAL-TYPE 0

model = Model.parse(b'\x07\x06\x08\x04name\x02\nbit string')
assert Name.to_str(model.name) == '/name'
assert model.str_val == b'bit string'

Signature

Please contact the developer if you have to have a Signature field in your model.

Contribute and Support

Please submit any changes via GitHub pull requests.
If you use any existing code, please make sure it is compatible to Apache License Version 2.0
Ensure that your code complies to PEP8.
Ensure that your code works with Python 3.10 and PyPy3.10 7.3.12.
Please contact the author first if your changes are not back compatible or import new dependencies.
Write unit tests. There is no need to cover all code, but please cover as much as you can.
Add your name to AUTHORS.rst.

Future plans

Future releases will include:

Add more documentation
Add more tests
Security tools:
- Schematized trust (including its necessary components such as validator, certificate storage, etc.)
- Name-based Access Control
Application supports:
- Sync protocol
- DLedger

Authors

Xinyu Ma <https://zjkmxy.github.io>
Zhaoning Kong <https://jonnykong.com>
Eric Newberry <https://ericnewberry.com>
Junxiao Shi <https://yoursunny.com>
Tianyuan Yu <https://www.tianyuan-yu.com/>
Alwin Kahlert <https://github.com/akamos>
Dylan Hensley

Anonymous Contributors

GlassyYang

Changelog

0.4-1 (2023-08-21)

Update dependencies: drop cryptography.
Add ECIES support.

0.4 (2023-07-21)

Migrate from pipenv to poetry
Upgrade Python requirement to 3.10
Fix a race condition in NDNAppv2
Add support to State-Vector-Sync (SVS)

0.3-3 (2023-05-26)

Add NDNAppv2
Add NDN-DPDK Support
encoding: Add MapField

0.3-2 (2022-06-11)

Bug fix.
Add key suggestion to LVS checker.
Support implicit digest in Interest name for express_interest.
Add more interfaces for security.
Update ci.
Add Ed25519 algorithm.

0.3-1 (2022-03-20)

Add Light VerSec and cascade validator.
Add UDP support.
Support remote prefix registration.
NDNLPv2 protocol update.
NDN 0.3 protocol update (ForwardingHint).
Add Boost INFO parser.
Drop Python 3.8 support due to typing hint incompatability. CPython 3.8 should still work, but PyPy 3.8 is known to be incompatible.
Bug fixes.

0.3 (2021-11-21)

Add express_raw_interest function to NDNApp.
Add validator for known keys.
Add CodeQL scanning.
Add support to Windows CNG as a TPM backend.
Add binary tools pyndntools, pyndnsec and pynfdc.
Transition to Name Convention Rev03.
Add automatic type conversion for Enum, Flag and str.
Drop Python 3.7 support and add Python 3.10.

0.3a1-3 (2021-05-22)

Support Unix socket on Windows 10.
Fix semaphore running in a different event loop bug.

0.3a1-2 (2021-04-29)

Handle ConnectionResetError.
Drop Python 3.6 support.

0.3a1-1 (2021-01-31)

Transfer the repo to named-data/python-ndn.
Fix cocoapy to make it work on MacOS 11 Big Sur.
Add more supports to NDNLPv2 (CongestionMark).
Add dispatcher and set_interest_filter.

0.3a1 (2020-09-24)

Fix the bug that registering multiple prefices at the same time leads to 403 error.
Add Name Tree Schema.
Add .devcontainer for VSCode Remote Containers and GitHub Codespaces.

0.2b2-2 (2020-05-26)

Change the default sock file path from /var/run/nfd.sock to /run/nfd.sock on Linux.
Add FIB and CS management data structures
Add make_network_nack
Recognize NDN_CLIENT_* environment variables

0.2b2-1 (2020-03-23)

Fix RuntimeWarning for hanging coroutine when main_loop raises an exception.
Fix the issue when after_start throws an exception, the application gets stuck.
Set raw_packet of express_interest and on_interest to be the whole packet with TL fields.

0.2b2 (2020-02-18)

Switch to Apache License 2.0.
Add NDNApp.get_original_packet_value.
Improve NDNApp.route and NDNApp.express_interest to give access the original packet and signature pointers of packets.
Fix typos in the documentation.
Support more alternate URI format of Name Component (seg, off, v, t and seq)
Update Python version to 3.8 and add PyPy 7.2.0 in GitHub Action.
Fix Name.to_str so its output for [b'\x08\x00'] is correct.

0.2b1 (2019-11-20)

The initial release.

Welcome to python-ndn’s documentation!

Table Of Contents

python-ndn

Installation

Instructions for developer

ndn.app package

Introduction

Keyword Arguments

MetaInfo

InterestParameters

Signature

Reference

ndn.appv2 package

Introduction

Reference

ndn.encoding package

Introduction

FormalName and NonStrictName

Customized TLV Models

Reference

TLV Variables

Name and Component

ndn.encoding.name.Component module

ndn.encoding.name.Name module

TLV Model

NDN Packet Format 0.3

ndn.security package

Introduction

Signer

Validator

Keychain

KeychainDigest

KeychainSqlite3

ndn.schema package

Introduction

Examples

1 - File Sharing

Design

Coding

Reference

Namespace Schema Tree

Utils

Custom Nodes

Policies

Policy Types

Trust Policies

Cache Policies

Light VerSec

Introduction

Quick Example

Syntax and Semantics

Pattern

Rule

Component constraints

Signing constraints

User Functions

Temporary Identifiers

Formal Grammar

Tutorial

References

ndn.app_support.light_versec package

Implementation Details

Compiler

Input/Output

Parsing

Sorting rules

Generating pattern ID

Replicating rules

Generating tree

Fixing signing constraints

Checker

Signing key checking

Signing key suggesting

Schema Validation

Optimization

Merging from the root (Done)

Merging from the leaves (Not Implmented)

Alternative Methods

DFA / NTSchema

Decision-based systems

`ndn.app` package

`ndn.appv2` package

`ndn.encoding` package

`FormalName` and `NonStrictName`

`ndn.encoding.name.Component` module

`ndn.encoding.name.Name` module

`ndn.security` package

`ndn.schema` package

`ndn.app_support.light_versec` package

`ndn.types` package

`ndn.utils` package