Handle trying to write empty byte seq (#780)

libp2p/protocols/connectivity/relay/utils.nim

@@ -64,15 +64,17 @@ proc bridge*(connSrc: Connection, connDst: Connection) {.async.} =
       await futSrc or futDst
       if futSrc.finished():
         bufRead = await futSrc
-        bytesSendFromSrcToDst.inc(bufRead)
-        await connDst.write(@bufSrcToDst[0..<bufRead])
-        zeroMem(addr(bufSrcToDst), bufSrcToDst.high + 1)
+        if bufRead > 0:
+          bytesSendFromSrcToDst.inc(bufRead)
+          await connDst.write(@bufSrcToDst[0..<bufRead])
+          zeroMem(addr(bufSrcToDst), bufSrcToDst.high + 1)
         futSrc = connSrc.readOnce(addr bufSrcToDst[0], bufSrcToDst.high + 1)
       if futDst.finished():
         bufRead = await futDst
-        bytesSendFromDstToSrc += bufRead
-        await connSrc.write(bufDstToSrc[0..<bufRead])
-        zeroMem(addr(bufDstToSrc), bufDstToSrc.high + 1)
+        if bufRead > 0:
+          bytesSendFromDstToSrc += bufRead
+          await connSrc.write(bufDstToSrc[0..<bufRead])
+          zeroMem(addr(bufDstToSrc), bufDstToSrc.high + 1)
         futDst = connDst.readOnce(addr bufDstToSrc[0], bufDstToSrc.high + 1)
   except CancelledError as exc:
     raise exc

libp2p/stream/chronosstream.nim

@@ -130,6 +130,9 @@ proc completeWrite(
 method write*(s: ChronosStream, msg: seq[byte]): Future[void] =
   # Avoid a copy of msg being kept in the closure created by `{.async.}` as this
   # drives up memory usage
+  if msg.len == 0:
+    trace "Empty byte seq, nothing to write"
+    return
   if s.closed:
     let fut = newFuture[void]("chronosstream.write.closed")
     fut.fail(newLPStreamClosedError())