akka/akka-core

UdpListener crashes when sending a message fails

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#19,771 opened on Feb 13, 2016

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 (5 comments) (0 reactions) (0 assignees)Scala (13,277 stars) (3,547 forks)batch import
1 - triagedhelp wantedt:dnst:io

Description

Currently akka.io.UdpListener seems to crash if one tries to send a packet to an unreachable target address (interesting: There is a mechanism to reply CommandFailed when NonFatal exceptions happen during a sent, but it only kicks in if the target address had to be resolved by Dns.resolve).

The following happens when I try to Udp.Send against an address that is unreachable from the address of the bound socket.

19:57:44.236 [DEBUG] [akka://IceAgentSpec/system/IO-UDP-FF/selectors/$a/0] akka.io.SelectionHandler - Network is unreachable
19:57:44.238 [DEBUG] [akka://IceAgentSpec/system/IO-UDP-FF/selectors/$a/0] akka.io.UdpListener - Closing DatagramChannel after being stopped

From a user perspective I'd rather expect to receive a Udp.CommandFailed message as a reply to my Udp.Send rather than a shutdown of the whole UdpListener.

There could be several reasons why a packet could not be sent:

  • SocketException("Network is unreachable") - this does currently crash the actor
  • SocketException("Invalid argument") - happens if we try to send to the target port 0, but probably could have other reasons. This does currently crash the actor
  • Target hostname could not be resolved - this case is currently ignored. The actor stays alive but the user does receive no CommandFailed or Ack.
  • Probably a lot more, maybe even something like SocketException("already closed") - I guess we would expect a listener shutdown in this case?

This is somewhat related to #13861 becase a fix of this issue would make a plain CommandFailed even harder to interpret from a user perspective.

Contributor guide

Tech stack
None
Domain
backend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Scala basicsAkka actorsUDP networking
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Investigate the `akka.io.UdpListener` and `akka.io.SelectionHandler` classes to understand how send failures are handled. The issue describes that non fatal exceptions during send only trigger CommandFailed if the address had to be resolved by Dns.resolve. Look at the code path where the send is performed and where the exception 'Network is unreachable' is caught. Consider modifying the error handling to send a CommandFailed to the sender instead of crashing the actor or closing the channel.
UdpListener crashes when sending a message fails · akka/akka-core#19771 | Good First Issue