124 lines
4.5 KiB
Python
124 lines
4.5 KiB
Python
from .multiselect_client_interface import IMultiselectClient
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from .multiselect_communicator import MultiselectCommunicator
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MULTISELECT_PROTOCOL_ID = "/multistream/1.0.0"
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PROTOCOL_NOT_FOUND_MSG = "na"
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class MultiselectClient(IMultiselectClient):
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"""
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Client for communicating with receiver's multiselect
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module in order to select a protocol id to communicate over
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"""
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def __init__(self):
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pass
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async def handshake(self, communicator):
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"""
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Ensure that the client and multiselect
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are both using the same multiselect protocol
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:param stream: stream to communicate with multiselect over
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:raise Exception: multiselect protocol ID mismatch
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"""
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# TODO: Use format used by go repo for messages
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# Send our MULTISELECT_PROTOCOL_ID to counterparty
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await communicator.write(MULTISELECT_PROTOCOL_ID)
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# Read in the protocol ID from other party
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handshake_contents = await communicator.read_stream_until_eof()
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# Confirm that the protocols are the same
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if not validate_handshake(handshake_contents):
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raise MultiselectClientError("multiselect protocol ID mismatch")
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# Handshake succeeded if this point is reached
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async def select_protocol_or_fail(self, protocol, stream):
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"""
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Send message to multiselect selecting protocol
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and fail if multiselect does not return same protocol
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:param protocol: protocol to select
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:param stream: stream to communicate with multiselect over
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:return: selected protocol
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"""
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# Create a communicator to handle all communication across the stream
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communicator = MultiselectCommunicator(stream)
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# Perform handshake to ensure multiselect protocol IDs match
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await self.handshake(communicator)
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# Try to select the given protocol
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selected_protocol = await self.try_select(communicator, protocol)
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return selected_protocol
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async def select_one_of(self, protocols, stream):
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"""
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For each protocol, send message to multiselect selecting protocol
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and fail if multiselect does not return same protocol. Returns first
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protocol that multiselect agrees on (i.e. that multiselect selects)
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:param protocol: protocol to select
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:param stream: stream to communicate with multiselect over
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:return: selected protocol
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"""
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# Create a communicator to handle all communication across the stream
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communicator = MultiselectCommunicator(stream)
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# Perform handshake to ensure multiselect protocol IDs match
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await self.handshake(communicator)
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# For each protocol, attempt to select that protocol
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# and return the first protocol selected
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for protocol in protocols:
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try:
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selected_protocol = await self.try_select(communicator, protocol)
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return selected_protocol
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except MultiselectClientError:
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pass
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# No protocols were found, so return no protocols supported error
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raise MultiselectClientError("protocols not supported")
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async def try_select(self, communicator, protocol):
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"""
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Try to select the given protocol or raise exception if fails
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:param communicator: communicator to use to communicate with counterparty
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:param protocol: protocol to select
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:raise Exception: error in protocol selection
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:return: selected protocol
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"""
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# Tell counterparty we want to use protocol
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await communicator.write(protocol)
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# Get what counterparty says in response
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response = await communicator.read_stream_until_eof()
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# Return protocol if response is equal to protocol or raise error
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if response == protocol:
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return protocol
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if response == PROTOCOL_NOT_FOUND_MSG:
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raise MultiselectClientError("protocol not supported")
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raise MultiselectClientError("unrecognized response: " + response)
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def validate_handshake(handshake_contents):
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"""
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Determine if handshake is valid and should be confirmed
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:param handshake_contents: contents of handshake message
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:return: true if handshake is complete, false otherwise
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"""
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# TODO: Modify this when format used by go repo for messages
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# is added
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return handshake_contents == MULTISELECT_PROTOCOL_ID
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class MultiselectClientError(ValueError):
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"""Raised when an error occurs in protocol selection process"""
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