py-libp2p/libp2p/protocol_muxer/multiselect.py

from typing import Dict, Tuple

from libp2p.typing import StreamHandlerFn, TProtocol

from .exceptions import MultiselectCommunicatorError, MultiselectError
from .multiselect_communicator_interface import IMultiselectCommunicator
from .multiselect_muxer_interface import IMultiselectMuxer

MULTISELECT_PROTOCOL_ID = "/multistream/1.0.0"
PROTOCOL_NOT_FOUND_MSG = "na"


class Multiselect(IMultiselectMuxer):
    """
    Multiselect module that is responsible for responding to
    a multiselect client and deciding on
    a specific protocol and handler pair to use for communication
    """

    handlers: Dict[TProtocol, StreamHandlerFn]

    def __init__(self) -> None:
        self.handlers = {}

    def add_handler(self, protocol: TProtocol, handler: StreamHandlerFn) -> None:
        """
        Store the handler with the given protocol
        :param protocol: protocol name
        :param handler: handler function
        """
        self.handlers[protocol] = handler

    async def negotiate(
        self, communicator: IMultiselectCommunicator
    ) -> Tuple[TProtocol, StreamHandlerFn]:
        """
        Negotiate performs protocol selection
        :param stream: stream to negotiate on
        :return: selected protocol name, handler function
        :raise Exception: negotiation failed exception
        """

        # Perform handshake to ensure multiselect protocol IDs match
        await self.handshake(communicator)

        # Read and respond to commands until a valid protocol ID is sent
        while True:
            # Read message
            try:
                command = await communicator.read()
            except MultiselectCommunicatorError as error:
                raise MultiselectError(str(error))

            # Command is ls or a protocol
            if command == "ls":
                # TODO: handle ls command
                pass
            else:
                protocol = TProtocol(command)
                if protocol in self.handlers:
                    # Tell counterparty we have decided on a protocol
                    await communicator.write(protocol)

                    # Return the decided on protocol
                    return protocol, self.handlers[protocol]
                # Tell counterparty this protocol was not found
                await communicator.write(PROTOCOL_NOT_FOUND_MSG)

    async def handshake(self, communicator: IMultiselectCommunicator) -> None:
        """
        Perform handshake to agree on multiselect protocol
        :param communicator: communicator to use
        :raise Exception: error in handshake
        """

        # TODO: Use format used by go repo for messages

        # Send our MULTISELECT_PROTOCOL_ID to other party
        await communicator.write(MULTISELECT_PROTOCOL_ID)

        # Read in the protocol ID from other party
        try:
            handshake_contents = await communicator.read()
        except MultiselectCommunicatorError as error:
            raise MultiselectError(str(error))

        # Confirm that the protocols are the same
        if not validate_handshake(handshake_contents):
            raise MultiselectError(
                "multiselect protocol ID mismatch: "
                f"received handshake_contents={handshake_contents}"
            )

        # Handshake succeeded if this point is reached


def validate_handshake(handshake_contents: str) -> bool:
    """
    Determine if handshake is valid and should be confirmed
    :param handshake_contents: contents of handshake message
    :return: true if handshake is complete, false otherwise
    """

    # TODO: Modify this when format used by go repo for messages
    # is added
    return handshake_contents == MULTISELECT_PROTOCOL_ID