py-libp2p/libp2p/protocol_muxer/multiselect_client.py

from typing import Sequence

from libp2p.typing import TProtocol

from .exceptions import MultiselectClientError, MultiselectCommunicatorError
from .multiselect_client_interface import IMultiselectClient
from .multiselect_communicator_interface import IMultiselectCommunicator

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


class MultiselectClient(IMultiselectClient):
    """Client for communicating with receiver's multiselect module in order to
    select a protocol id to communicate over."""

    async def handshake(self, communicator: IMultiselectCommunicator) -> None:
        """
        Ensure that the client and multiselect are both using the same
        multiselect protocol.

        :param stream: stream to communicate with multiselect over
        :raise MultiselectClientError: raised when handshake failed
        """
        try:
            await communicator.write(MULTISELECT_PROTOCOL_ID)
        except MultiselectCommunicatorError as error:
            raise MultiselectClientError() from error

        try:
            handshake_contents = await communicator.read()
        except MultiselectCommunicatorError as error:
            raise MultiselectClientError() from error

        if not is_valid_handshake(handshake_contents):
            raise MultiselectClientError("multiselect protocol ID mismatch")

    async def select_one_of(
        self, protocols: Sequence[TProtocol], communicator: IMultiselectCommunicator
    ) -> TProtocol:
        """
        For each protocol, send message to multiselect selecting protocol and
        fail if multiselect does not return same protocol. Returns first
        protocol that multiselect agrees on (i.e. that multiselect selects)

        :param protocol: protocol to select
        :param stream: stream to communicate with multiselect over
        :return: selected protocol
        :raise MultiselectClientError: raised when protocol negotiation failed
        """
        await self.handshake(communicator)

        for protocol in protocols:
            try:
                selected_protocol = await self.try_select(communicator, protocol)
                return selected_protocol
            except MultiselectClientError:
                pass

        raise MultiselectClientError("protocols not supported")

    async def try_select(
        self, communicator: IMultiselectCommunicator, protocol: TProtocol
    ) -> TProtocol:
        """
        Try to select the given protocol or raise exception if fails.

        :param communicator: communicator to use to communicate with counterparty
        :param protocol: protocol to select
        :raise MultiselectClientError: raised when protocol negotiation failed
        :return: selected protocol
        """
        try:
            await communicator.write(protocol)
        except MultiselectCommunicatorError as error:
            raise MultiselectClientError() from error

        try:
            response = await communicator.read()
        except MultiselectCommunicatorError as error:
            raise MultiselectClientError() from error

        if response == protocol:
            return protocol
        if response == PROTOCOL_NOT_FOUND_MSG:
            raise MultiselectClientError("protocol not supported")
        raise MultiselectClientError(f"unrecognized response: {response}")


def is_valid_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
    """
    return handshake_contents == MULTISELECT_PROTOCOL_ID