How do I stop a Listening server in Go

Question

I've been trying to find a way to stop a listening server in Go gracefully. Because listen.Accept blocks it is necessary to close the listening socket to signal the end, but I can't tell that error apart from any other errors as the relevant error isn't exported.

Can I do better than this? See FIXME in the code below in serve()

package main

import (
    "io"
    "log"
    "net"
    "time"
)

// Echo server struct
type EchoServer struct {
    listen net.Listener
    done   chan bool
}

// Respond to incoming connection
//
// Write the address connected to then echo
func (es *EchoServer) respond(remote *net.TCPConn) {
    defer remote.Close()
    _, err := io.Copy(remote, remote)
    if err != nil {
        log.Printf("Error: %s", err)
    }
}

// Listen for incoming connections
func (es *EchoServer) serve() {
    for {
        conn, err := es.listen.Accept()
        // FIXME I'd like to detect "use of closed network connection" here
        // FIXME but it isn't exported from net
        if err != nil {
            log.Printf("Accept failed: %v", err)
            break
        }
        go es.respond(conn.(*net.TCPConn))
    }
    es.done <- true
}

// Stop the server by closing the listening listen
func (es *EchoServer) stop() {
    es.listen.Close()
    <-es.done
}

// Make a new echo server
func NewEchoServer(address string) *EchoServer {
    listen, err := net.Listen("tcp", address)
    if err != nil {
        log.Fatalf("Failed to open listening socket: %s", err)
    }
    es := &EchoServer{
        listen: listen,
        done:   make(chan bool),
    }
    go es.serve()
    return es
}

// Main
func main() {
    log.Println("Starting echo server")
    es := NewEchoServer("127.0.0.1:18081")
    // Run the server for 1 second
    time.Sleep(1 * time.Second)
    // Close the server
    log.Println("Stopping echo server")
    es.stop()
}

This prints

2012/11/16 12:53:35 Starting echo server
2012/11/16 12:53:36 Stopping echo server
2012/11/16 12:53:36 Accept failed: accept tcp 127.0.0.1:18081: use of closed network connection

I'd like to hide the Accept failed message, but obviously I don't want to mask other errors Accept can report. I could of course look in the error test for use of closed network connection but that would be really ugly. I could set a flag saying I'm about to close and ignore errors if that was set I suppose - Is there a better way?

Answer 1

I would handle this by using es.done to send a signal before it closes the connection. In addition to the following code you'd need to create es.done with make(chan bool, 1) so that we can put a single value in it without blocking.

// Listen for incoming connections
func (es *EchoServer) serve() {
  for {
    conn, err := es.listen.Accept()
    if err != nil {
      select {
      case <-es.done:
        // If we called stop() then there will be a value in es.done, so
        // we'll get here and we can exit without showing the error.
      default:
        log.Printf("Accept failed: %v", err)
      }
      return
    }
    go es.respond(conn.(*net.TCPConn))
  }
}

// Stop the server by closing the listening listen
func (es *EchoServer) stop() {
  es.done <- true   // We can advance past this because we gave it buffer of 1
  es.listen.Close() // Now it the Accept will have an error above
}