protocols/identify: Allow at most one inbound identify push stream (#2694)

An identify push contains the whole identify information of a remote
peer. Upgrading multiple inbound identify push streams is useless.
Instead older streams are dropped in favor of newer streams.

protocols/identify/CHANGELOG.md

@@ -1,3 +1,7 @@
+# 0.36.1 - unreleased
+
+- Allow at most one inbound identify push stream.
+
 # 0.36.0
 
 - Update to `libp2p-core` `v0.33.0`.

protocols/identify/Cargo.toml

@@ -3,7 +3,7 @@ name = "libp2p-identify"
 edition = "2021"
 rust-version = "1.56.1"
 description = "Nodes identifcation protocol for libp2p"
-version = "0.36.0"
+version = "0.36.1"
 authors = ["Parity Technologies <admin@parity.io>"]
 license = "MIT"
 repository = "https://github.com/libp2p/rust-libp2p"
@@ -22,6 +22,7 @@ prost-codec = { version = "0.1", path = "../../misc/prost-codec" }
 prost = "0.10"
 smallvec = "1.6.1"
 thiserror = "1.0"
+void = "1.0"
 
 [dev-dependencies]
 async-std = "1.6.2"

protocols/identify/src/handler.rs

@@ -22,6 +22,7 @@ use crate::protocol::{
     IdentifyInfo, IdentifyProtocol, IdentifyPushProtocol, InboundPush, OutboundPush,
     ReplySubstream, UpgradeError,
 };
+use futures::future::BoxFuture;
 use futures::prelude::*;
 use futures_timer::Delay;
 use libp2p_core::either::{EitherError, EitherOutput};
@@ -30,6 +31,7 @@ use libp2p_swarm::{
     ConnectionHandler, ConnectionHandlerEvent, ConnectionHandlerUpgrErr, KeepAlive,
     NegotiatedSubstream, SubstreamProtocol,
 };
+use log::warn;
 use smallvec::SmallVec;
 use std::{io, pin::Pin, task::Context, task::Poll, time::Duration};
 
@@ -39,6 +41,7 @@ use std::{io, pin::Pin, task::Context, task::Poll, time::Duration};
 /// at least one identification request to be answered by the remote before
 /// permitting the underlying connection to be closed.
 pub struct IdentifyHandler {
+    inbound_identify_push: Option<BoxFuture<'static, Result<IdentifyInfo, UpgradeError>>>,
     /// Pending events to yield.
     events: SmallVec<
         [ConnectionHandlerEvent<
@@ -80,6 +83,7 @@ impl IdentifyHandler {
     /// Creates a new `IdentifyHandler`.
     pub fn new(initial_delay: Duration, interval: Duration) -> Self {
         IdentifyHandler {
+            inbound_identify_push: Default::default(),
             events: SmallVec::new(),
             trigger_next_identify: Delay::new(initial_delay),
             keep_alive: KeepAlive::Yes,
@@ -113,9 +117,14 @@ impl ConnectionHandler for IdentifyHandler {
             EitherOutput::First(substream) => self.events.push(ConnectionHandlerEvent::Custom(
                 IdentifyHandlerEvent::Identify(substream),
             )),
-            EitherOutput::Second(info) => self.events.push(ConnectionHandlerEvent::Custom(
-                IdentifyHandlerEvent::Identified(info),
-            )),
+            EitherOutput::Second(fut) => {
+                if self.inbound_identify_push.replace(fut).is_some() {
+                    warn!(
+                        "New inbound identify push stream while still upgrading previous one. \
+                        Replacing previous with new.",
+                    );
+                }
+            }
         }
     }
 
@@ -189,14 +198,30 @@ impl ConnectionHandler for IdentifyHandler {
 
         // Poll the future that fires when we need to identify the node again.
         match Future::poll(Pin::new(&mut self.trigger_next_identify), cx) {
-            Poll::Pending => Poll::Pending,
+            Poll::Pending => {}
             Poll::Ready(()) => {
                 self.trigger_next_identify.reset(self.interval);
                 let ev = ConnectionHandlerEvent::OutboundSubstreamRequest {
                     protocol: SubstreamProtocol::new(EitherUpgrade::A(IdentifyProtocol), ()),
                 };
-                Poll::Ready(ev)
+                return Poll::Ready(ev);
             }
         }
+
+        if let Some(Poll::Ready(res)) = self
+            .inbound_identify_push
+            .as_mut()
+            .map(|f| f.poll_unpin(cx))
+        {
+            self.inbound_identify_push.take();
+
+            if let Ok(info) = res {
+                return Poll::Ready(ConnectionHandlerEvent::Custom(
+                    IdentifyHandlerEvent::Identified(info),
+                ));
+            }
+        }
+
+        Poll::Pending
     }
 }

protocols/identify/src/protocol.rs

@@ -20,7 +20,7 @@
 
 use crate::structs_proto;
 use asynchronous_codec::{FramedRead, FramedWrite};
-use futures::prelude::*;
+use futures::{future::BoxFuture, prelude::*};
 use libp2p_core::{
     identity, multiaddr,
     upgrade::{InboundUpgrade, OutboundUpgrade, UpgradeInfo},
@@ -30,6 +30,7 @@ use log::trace;
 use std::convert::TryFrom;
 use std::{fmt, io, iter, pin::Pin};
 use thiserror::Error;
+use void::Void;
 
 const MAX_MESSAGE_SIZE_BYTES: usize = 4096;
 
@@ -143,12 +144,13 @@ impl<C> InboundUpgrade<C> for IdentifyPushProtocol<InboundPush>
 where
     C: AsyncRead + AsyncWrite + Unpin + Send + 'static,
 {
-    type Output = IdentifyInfo;
-    type Error = UpgradeError;
-    type Future = Pin<Box<dyn Future<Output = Result<Self::Output, Self::Error>> + Send>>;
+    type Output = BoxFuture<'static, Result<IdentifyInfo, UpgradeError>>;
+    type Error = Void;
+    type Future = future::Ready<Result<Self::Output, Self::Error>>;
 
     fn upgrade_inbound(self, socket: C, _: Self::Info) -> Self::Future {
-        recv(socket).boxed()
+        // Lazily upgrade stream, thus allowing upgrade to happen within identify's handler.
+        future::ok(recv(socket).boxed())
     }
 }