py-libp2p/libp2p/pubsub/gossipsub.py

from ast import literal_eval
import asyncio
import logging
import random
from typing import Any, Dict, Iterable, List, Sequence, Set

from libp2p.peer.id import ID
from libp2p.pubsub import floodsub
from libp2p.typing import TProtocol
from libp2p.utils import encode_varint_prefixed

from .mcache import MessageCache
from .pb import rpc_pb2
from .pubsub import Pubsub
from .pubsub_router_interface import IPubsubRouter

PROTOCOL_ID = TProtocol("/meshsub/1.0.0")

logger = logging.getLogger("libp2p.pubsub.gossipsub")


class GossipSub(IPubsubRouter):

    protocols: List[TProtocol]
    pubsub: Pubsub

    degree: int
    degree_high: int
    degree_low: int

    time_to_live: int

    mesh: Dict[str, List[ID]]
    fanout: Dict[str, List[ID]]

    peers_to_protocol: Dict[ID, str]

    time_since_last_publish: Dict[str, int]

    peers_gossipsub: List[ID]
    peers_floodsub: List[ID]

    mcache: MessageCache

    heartbeat_interval: int

    def __init__(
        self,
        protocols: Sequence[TProtocol],
        degree: int,
        degree_low: int,
        degree_high: int,
        time_to_live: int,
        gossip_window: int = 3,
        gossip_history: int = 5,
        heartbeat_interval: int = 120,
    ) -> None:
        self.protocols = list(protocols)
        self.pubsub = None

        # Store target degree, upper degree bound, and lower degree bound
        self.degree = degree
        self.degree_low = degree_low
        self.degree_high = degree_high

        # Store time to live (for topics in fanout)
        self.time_to_live = time_to_live

        # Create topic --> list of peers mappings
        self.mesh = {}
        self.fanout = {}

        # Create peer --> protocol mapping
        self.peers_to_protocol = {}

        # Create topic --> time since last publish map
        self.time_since_last_publish = {}

        self.peers_gossipsub = []
        self.peers_floodsub = []

        # Create message cache
        self.mcache = MessageCache(gossip_window, gossip_history)

        # Create heartbeat timer
        self.heartbeat_interval = heartbeat_interval

    # Interface functions

    def get_protocols(self) -> List[TProtocol]:
        """
        :return: the list of protocols supported by the router
        """
        return self.protocols

    def attach(self, pubsub: Pubsub) -> None:
        """
        Attach is invoked by the PubSub constructor to attach the router to a
        freshly initialized PubSub instance.
        :param pubsub: pubsub instance to attach to
        """
        self.pubsub = pubsub

        logger.debug("attached to pusub")

        # Start heartbeat now that we have a pubsub instance
        # TODO: Start after delay
        asyncio.ensure_future(self.heartbeat())

    def add_peer(self, peer_id: ID, protocol_id: TProtocol) -> None:
        """
        Notifies the router that a new peer has been connected
        :param peer_id: id of peer to add
        :param protocol_id: router protocol the peer speaks, e.g., floodsub, gossipsub
        """
        logger.debug("adding peer %s with protocol %s", peer_id, protocol_id)

        if protocol_id == PROTOCOL_ID:
            self.peers_gossipsub.append(peer_id)
        elif protocol_id == floodsub.PROTOCOL_ID:
            self.peers_floodsub.append(peer_id)
        else:
            # We should never enter here. Becuase the `protocol_id` is registered by your pubsub
            #   instance in multistream-select, but it is not the protocol that gossipsub supports.
            #   In this case, probably we registered gossipsub to a wrong `protocol_id`
            #   in multistream-select, or wrong versions.
            # TODO: Better handling
            raise Exception(f"protocol is not supported: protocol_id={protocol_id}")
        self.peers_to_protocol[peer_id] = protocol_id

    def remove_peer(self, peer_id: ID) -> None:
        """
        Notifies the router that a peer has been disconnected
        :param peer_id: id of peer to remove
        """
        logger.debug("removing peer %s", peer_id)

        if peer_id in self.peers_gossipsub:
            self.peers_gossipsub.remove(peer_id)
        elif peer_id in self.peers_floodsub:
            self.peers_floodsub.remove(peer_id)

        if peer_id in self.peers_to_protocol:
            del self.peers_to_protocol[peer_id]

    async def handle_rpc(self, rpc: rpc_pb2.RPC, sender_peer_id: ID) -> None:
        """
        Invoked to process control messages in the RPC envelope.
        It is invoked after subscriptions and payload messages have been processed
        :param rpc: RPC message
        :param sender_peer_id: id of the peer who sent the message
        """
        control_message = rpc.control

        # Relay each rpc control message to the appropriate handler
        if control_message.ihave:
            for ihave in control_message.ihave:
                await self.handle_ihave(ihave, sender_peer_id)
        if control_message.iwant:
            for iwant in control_message.iwant:
                await self.handle_iwant(iwant, sender_peer_id)
        if control_message.graft:
            for graft in control_message.graft:
                await self.handle_graft(graft, sender_peer_id)
        if control_message.prune:
            for prune in control_message.prune:
                await self.handle_prune(prune, sender_peer_id)

    async def publish(self, msg_forwarder: ID, pubsub_msg: rpc_pb2.Message) -> None:
        """
        Invoked to forward a new message that has been validated.
        """
        self.mcache.put(pubsub_msg)

        peers_gen = self._get_peers_to_send(
            pubsub_msg.topicIDs,
            msg_forwarder=msg_forwarder,
            origin=ID(pubsub_msg.from_id),
        )
        rpc_msg = rpc_pb2.RPC(publish=[pubsub_msg])

        logger.debug("publishing message %s", pubsub_msg)

        for peer_id in peers_gen:
            stream = self.pubsub.peers[peer_id]
            # FIXME: We should add a `WriteMsg` similar to write delimited messages.
            #   Ref: https://github.com/libp2p/go-libp2p-pubsub/blob/master/comm.go#L107
            # TODO: Go use `sendRPC`, which possibly piggybacks gossip/control messages.
            await stream.write(encode_varint_prefixed(rpc_msg.SerializeToString()))

    def _get_peers_to_send(
        self, topic_ids: Iterable[str], msg_forwarder: ID, origin: ID
    ) -> Iterable[ID]:
        """
        Get the eligible peers to send the data to.
        :param msg_forwarder: the peer id of the peer who forwards the message to me.
        :param origin: peer id of the peer the message originate from.
        :return: a generator of the peer ids who we send data to.
        """
        send_to: Set[ID] = set()
        for topic in topic_ids:
            if topic not in self.pubsub.peer_topics:
                continue

            # floodsub peers
            for peer_id in self.pubsub.peer_topics[topic]:
                # FIXME: `gossipsub.peers_floodsub` can be changed to `gossipsub.peers` in go.
                #   This will improve the efficiency when searching for a peer's protocol id.
                if peer_id in self.peers_floodsub:
                    send_to.add(peer_id)

            # gossipsub peers
            in_topic_gossipsub_peers: List[ID] = None
            # TODO: Do we need to check `topic in self.pubsub.my_topics`?
            if topic in self.mesh:
                in_topic_gossipsub_peers = self.mesh[topic]
            else:
                # TODO(robzajac): Is topic DEFINITELY supposed to be in fanout if we are not
                #   subscribed?
                # I assume there could be short periods between heartbeats where topic may not
                # be but we should check that this path gets hit appropriately

                if (topic not in self.fanout) or (len(self.fanout[topic]) == 0):
                    # If no peers in fanout, choose some peers from gossipsub peers in topic.
                    self.fanout[topic] = self._get_in_topic_gossipsub_peers_from_minus(
                        topic, self.degree, []
                    )
                in_topic_gossipsub_peers = self.fanout[topic]
            for peer_id in in_topic_gossipsub_peers:
                send_to.add(peer_id)
        # Excludes `msg_forwarder` and `origin`
        yield from send_to.difference([msg_forwarder, origin])

    async def join(self, topic: str) -> None:
        # Note: the comments here are the near-exact algorithm description from the spec
        """
        Join notifies the router that we want to receive and
        forward messages in a topic. It is invoked after the
        subscription announcement
        :param topic: topic to join
        """
        logger.debug("joining topic %s", topic)

        if topic in self.mesh:
            return
        # Create mesh[topic] if it does not yet exist
        self.mesh[topic] = []

        topic_in_fanout: bool = topic in self.fanout
        fanout_peers: List[ID] = self.fanout[topic] if topic_in_fanout else []
        fanout_size = len(fanout_peers)
        if not topic_in_fanout or (topic_in_fanout and fanout_size < self.degree):
            # There are less than D peers (let this number be x)
            # in the fanout for a topic (or the topic is not in the fanout).
            # Selects the remaining number of peers (D-x) from peers.gossipsub[topic].
            if topic in self.pubsub.peer_topics:
                selected_peers = self._get_in_topic_gossipsub_peers_from_minus(
                    topic, self.degree - fanout_size, fanout_peers
                )
                # Combine fanout peers with selected peers
                fanout_peers += selected_peers

        # Add fanout peers to mesh and notifies them with a GRAFT(topic) control message.
        for peer in fanout_peers:
            if peer not in self.mesh[topic]:
                self.mesh[topic].append(peer)
                await self.emit_graft(topic, peer)

        if topic_in_fanout:
            del self.fanout[topic]

    async def leave(self, topic: str) -> None:
        # Note: the comments here are the near-exact algorithm description from the spec
        """
        Leave notifies the router that we are no longer interested in a topic.
        It is invoked after the unsubscription announcement.
        :param topic: topic to leave
        """
        logger.debug("leaving topic %s", topic)

        if topic not in self.mesh:
            return
        # Notify the peers in mesh[topic] with a PRUNE(topic) message
        for peer in self.mesh[topic]:
            await self.emit_prune(topic, peer)

        # Forget mesh[topic]
        del self.mesh[topic]

    # Heartbeat
    async def heartbeat(self) -> None:
        """
        Call individual heartbeats.
        Note: the heartbeats are called with awaits because each heartbeat depends on the
        state changes in the preceding heartbeat
        """
        while True:

            await self.mesh_heartbeat()
            await self.fanout_heartbeat()
            await self.gossip_heartbeat()

            await asyncio.sleep(self.heartbeat_interval)

    async def mesh_heartbeat(self) -> None:
        # Note: the comments here are the exact pseudocode from the spec
        for topic in self.mesh:
            # Skip if no peers have subscribed to the topic
            if topic not in self.pubsub.peer_topics:
                continue

            num_mesh_peers_in_topic = len(self.mesh[topic])
            if num_mesh_peers_in_topic < self.degree_low:
                # Select D - |mesh[topic]| peers from peers.gossipsub[topic] - mesh[topic]
                selected_peers = self._get_in_topic_gossipsub_peers_from_minus(
                    topic, self.degree - num_mesh_peers_in_topic, self.mesh[topic]
                )

                fanout_peers_not_in_mesh: List[ID] = [
                    peer for peer in selected_peers if peer not in self.mesh[topic]
                ]
                for peer in fanout_peers_not_in_mesh:
                    # Add peer to mesh[topic]
                    self.mesh[topic].append(peer)

                    # Emit GRAFT(topic) control message to peer
                    await self.emit_graft(topic, peer)

            if num_mesh_peers_in_topic > self.degree_high:
                # Select |mesh[topic]| - D peers from mesh[topic]
                selected_peers = GossipSub.select_from_minus(
                    num_mesh_peers_in_topic - self.degree, self.mesh[topic], []
                )
                for peer in selected_peers:
                    # Remove peer from mesh[topic]
                    self.mesh[topic].remove(peer)

                    # Emit PRUNE(topic) control message to peer
                    await self.emit_prune(topic, peer)

    async def fanout_heartbeat(self) -> None:
        # Note: the comments here are the exact pseudocode from the spec
        for topic in self.fanout:
            # If time since last published > ttl
            # TODO: there's no way time_since_last_publish gets set anywhere yet
            if self.time_since_last_publish[topic] > self.time_to_live:
                # Remove topic from fanout
                del self.fanout[topic]
                del self.time_since_last_publish[topic]
            else:
                num_fanout_peers_in_topic = len(self.fanout[topic])

                # If |fanout[topic]| < D
                if num_fanout_peers_in_topic < self.degree:
                    # Select D - |fanout[topic]| peers from peers.gossipsub[topic] - fanout[topic]
                    selected_peers = self._get_in_topic_gossipsub_peers_from_minus(
                        topic,
                        self.degree - num_fanout_peers_in_topic,
                        self.fanout[topic],
                    )
                    # Add the peers to fanout[topic]
                    self.fanout[topic].extend(selected_peers)

    async def gossip_heartbeat(self) -> None:
        for topic in self.mesh:
            msg_ids = self.mcache.window(topic)
            if msg_ids:
                # TODO: Make more efficient, possibly using a generator?
                # Get all pubsub peers in a topic and only add them if they are gossipsub peers too
                if topic in self.pubsub.peer_topics:
                    # Select D peers from peers.gossipsub[topic]
                    peers_to_emit_ihave_to = self._get_in_topic_gossipsub_peers_from_minus(
                        topic, self.degree, []
                    )

                    for peer in peers_to_emit_ihave_to:
                        # TODO: this line is a monster, can hopefully be simplified
                        if (
                            topic not in self.mesh or (peer not in self.mesh[topic])
                        ) and (
                            topic not in self.fanout or (peer not in self.fanout[topic])
                        ):
                            msg_id_strs = [str(msg_id) for msg_id in msg_ids]
                            await self.emit_ihave(topic, msg_id_strs, peer)

        # TODO: Refactor and Dedup. This section is the roughly the same as the above.
        # Do the same for fanout, for all topics not already hit in mesh
        for topic in self.fanout:
            if topic not in self.mesh:
                msg_ids = self.mcache.window(topic)
                if msg_ids:
                    # TODO: Make more efficient, possibly using a generator?
                    # Get all pubsub peers in topic and only add if they are gossipsub peers also
                    if topic in self.pubsub.peer_topics:
                        # Select D peers from peers.gossipsub[topic]
                        peers_to_emit_ihave_to = self._get_in_topic_gossipsub_peers_from_minus(
                            topic, self.degree, []
                        )
                        for peer in peers_to_emit_ihave_to:
                            if (
                                peer not in self.mesh[topic]
                                and peer not in self.fanout[topic]
                            ):

                                msg_id_strs = [str(msg) for msg in msg_ids]
                                await self.emit_ihave(topic, msg_id_strs, peer)

        self.mcache.shift()

    @staticmethod
    def select_from_minus(
        num_to_select: int, pool: Sequence[Any], minus: Sequence[Any]
    ) -> List[Any]:
        """
        Select at most num_to_select subset of elements from the set (pool - minus) randomly.
        :param num_to_select: number of elements to randomly select
        :param pool: list of items to select from (excluding elements in minus)
        :param minus: elements to be excluded from selection pool
        :return: list of selected elements
        """
        # Create selection pool, which is selection_pool = pool - minus
        if minus:
            # Create a new selection pool by removing elements of minus
            selection_pool: List[Any] = [x for x in pool if x not in minus]
        else:
            # Don't create a new selection_pool if we are not subbing anything
            selection_pool = list(pool)

        # If num_to_select > size(selection_pool), then return selection_pool (which has the most
        # possible elements s.t. the number of elements is less than num_to_select)
        if num_to_select > len(selection_pool):
            return selection_pool

        # Random selection
        selection: List[Any] = random.sample(selection_pool, num_to_select)

        return selection

    def _get_in_topic_gossipsub_peers_from_minus(
        self, topic: str, num_to_select: int, minus: Sequence[ID]
    ) -> List[ID]:
        gossipsub_peers_in_topic = [
            peer_id
            for peer_id in self.pubsub.peer_topics[topic]
            if peer_id in self.peers_gossipsub
        ]
        return self.select_from_minus(
            num_to_select, gossipsub_peers_in_topic, list(minus)
        )

    # RPC handlers

    async def handle_ihave(
        self, ihave_msg: rpc_pb2.ControlIHave, sender_peer_id: ID
    ) -> None:
        """
        Checks the seen set and requests unknown messages with an IWANT message.
        """
        # Get list of all seen (seqnos, from) from the (seqno, from) tuples in seen_messages cache
        seen_seqnos_and_peers = [
            seqno_and_from for seqno_and_from in self.pubsub.seen_messages.keys()
        ]

        # Add all unknown message ids (ids that appear in ihave_msg but not in seen_seqnos) to list
        # of messages we want to request
        # FIXME: Update type of message ID
        msg_ids_wanted: List[Any] = [
            msg_id
            for msg_id in ihave_msg.messageIDs
            if literal_eval(msg_id) not in seen_seqnos_and_peers
        ]

        # Request messages with IWANT message
        if msg_ids_wanted:
            await self.emit_iwant(msg_ids_wanted, sender_peer_id)

    async def handle_iwant(
        self, iwant_msg: rpc_pb2.ControlIWant, sender_peer_id: ID
    ) -> None:
        """
        Forwards all request messages that are present in mcache to the requesting peer.
        """
        # FIXME: Update type of message ID
        # FIXME: Find a better way to parse the msg ids
        msg_ids: List[Any] = [literal_eval(msg) for msg in iwant_msg.messageIDs]
        msgs_to_forward: List[rpc_pb2.Message] = []
        for msg_id_iwant in msg_ids:
            # Check if the wanted message ID is present in mcache
            msg: rpc_pb2.Message = self.mcache.get(msg_id_iwant)

            # Cache hit
            if msg:
                # Add message to list of messages to forward to requesting peers
                msgs_to_forward.append(msg)

        # Forward messages to requesting peer
        # Should this just be publishing? No
        # because then the message will forwarded to peers in the topics contained in the messages.
        # We should
        # 1) Package these messages into a single packet
        packet: rpc_pb2.RPC = rpc_pb2.RPC()

        packet.publish.extend(msgs_to_forward)

        # 2) Serialize that packet
        rpc_msg: bytes = packet.SerializeToString()

        # 3) Get the stream to this peer
        peer_stream = self.pubsub.peers[sender_peer_id]

        # 4) And write the packet to the stream
        await peer_stream.write(encode_varint_prefixed(rpc_msg))

    async def handle_graft(
        self, graft_msg: rpc_pb2.ControlGraft, sender_peer_id: ID
    ) -> None:
        topic: str = graft_msg.topicID

        # Add peer to mesh for topic
        if topic in self.mesh:
            if sender_peer_id not in self.mesh[topic]:
                self.mesh[topic].append(sender_peer_id)
        else:
            # Respond with PRUNE if not subscribed to the topic
            await self.emit_prune(topic, sender_peer_id)

    async def handle_prune(
        self, prune_msg: rpc_pb2.ControlPrune, sender_peer_id: ID
    ) -> None:
        topic: str = prune_msg.topicID

        # Remove peer from mesh for topic, if peer is in topic
        if topic in self.mesh and sender_peer_id in self.mesh[topic]:
            self.mesh[topic].remove(sender_peer_id)

    # RPC emitters

    async def emit_ihave(self, topic: str, msg_ids: Any, to_peer: ID) -> None:
        """
        Emit ihave message, sent to to_peer, for topic and msg_ids
        """

        ihave_msg: rpc_pb2.ControlIHave = rpc_pb2.ControlIHave()
        ihave_msg.messageIDs.extend(msg_ids)
        ihave_msg.topicID = topic

        control_msg: rpc_pb2.ControlMessage = rpc_pb2.ControlMessage()
        control_msg.ihave.extend([ihave_msg])

        await self.emit_control_message(control_msg, to_peer)

    async def emit_iwant(self, msg_ids: Any, to_peer: ID) -> None:
        """
        Emit iwant message, sent to to_peer, for msg_ids
        """

        iwant_msg: rpc_pb2.ControlIWant = rpc_pb2.ControlIWant()
        iwant_msg.messageIDs.extend(msg_ids)

        control_msg: rpc_pb2.ControlMessage = rpc_pb2.ControlMessage()
        control_msg.iwant.extend([iwant_msg])

        await self.emit_control_message(control_msg, to_peer)

    async def emit_graft(self, topic: str, to_peer: ID) -> None:
        """
        Emit graft message, sent to to_peer, for topic
        """

        graft_msg: rpc_pb2.ControlGraft = rpc_pb2.ControlGraft()
        graft_msg.topicID = topic

        control_msg: rpc_pb2.ControlMessage = rpc_pb2.ControlMessage()
        control_msg.graft.extend([graft_msg])

        await self.emit_control_message(control_msg, to_peer)

    async def emit_prune(self, topic: str, to_peer: ID) -> None:
        """
        Emit graft message, sent to to_peer, for topic
        """

        prune_msg: rpc_pb2.ControlPrune = rpc_pb2.ControlPrune()
        prune_msg.topicID = topic

        control_msg: rpc_pb2.ControlMessage = rpc_pb2.ControlMessage()
        control_msg.prune.extend([prune_msg])

        await self.emit_control_message(control_msg, to_peer)

    async def emit_control_message(
        self, control_msg: rpc_pb2.ControlMessage, to_peer: ID
    ) -> None:
        # Add control message to packet
        packet: rpc_pb2.RPC = rpc_pb2.RPC()
        packet.control.CopyFrom(control_msg)

        rpc_msg: bytes = packet.SerializeToString()

        # Get stream for peer from pubsub
        peer_stream = self.pubsub.peers[to_peer]

        # Write rpc to stream
        await peer_stream.write(encode_varint_prefixed(rpc_msg))