Handle trying to write empty byte seq (#780)

libp2p/protocols/connectivity/relay/utils.nim

@@ -64,12 +64,14 @@ proc bridge*(connSrc: Connection, connDst: Connection) {.async.} =
       await futSrc or futDst
       if futSrc.finished():
         bufRead = await futSrc
+        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
+        if bufRead > 0:
           bytesSendFromDstToSrc += bufRead
           await connSrc.write(bufDstToSrc[0..<bufRead])
           zeroMem(addr(bufDstToSrc), bufDstToSrc.high + 1)

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())