Simple utility package to send ICMP pings with Go

icmp_ping.go

// Copyright © 2016 Alex
//
// This program is free software: you can redistribute it and/or modify it under
// the terms of the GNU Affero General Public License as published by the Free
// Software Foundation, either version 3 of the License, or (at your option) any
// later version.
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
// FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
// details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.

package main

import (
        "fmt"
        "log"
        "net"
        "os"
        "time"

        "golang.org/x/net/icmp"
        "golang.org/x/net/ipv4"
)

func main() {
        addr := "google.com"
        dst, dur, err := Ping(addr)
        if err != nil {
                panic(err)
        }
        log.Printf("Ping %s (%s): %s\n", addr, dst, dur)
}

////////////////////////////////////////////////////////////////////////////////////////////////////

const (
        // Stolen from https://godoc.org/golang.org/x/net/internal/iana,
        // can't import "internal" packages
        ProtocolICMP = 1
        //ProtocolIPv6ICMP = 58
)

// Default to listen on all IPv4 interfaces
var ListenAddr = "0.0.0.0"

// Mostly based on https://github.com/golang/net/blob/master/icmp/ping_test.go
// All ye beware, there be dragons below...

func Ping(addr string) (*net.IPAddr, time.Duration, error) {
        // Start listening for icmp replies
        c, err := icmp.ListenPacket("ip4:icmp", ListenAddr)
        if err != nil {
                return nil, 0, err
        }
        defer c.Close()

        // Resolve any DNS (if used) and get the real IP of the target
        dst, err := net.ResolveIPAddr("ip4", addr)
        if err != nil {
                panic(err)
                return nil, 0, err
        }

        // Make a new ICMP message
        m := icmp.Message{
                Type: ipv4.ICMPTypeEcho, Code: 0,
                Body: &icmp.Echo{
                        ID: os.Getpid() & 0xffff, Seq: 1, //<< uint(seq), // TODO
                        Data: []byte(""),
                },
        }
        b, err := m.Marshal(nil)
        if err != nil {
                return dst, 0, err
        }

        // Send it
        start := time.Now()
        n, err := c.WriteTo(b, dst)
        if err != nil {
                return dst, 0, err
        } else if n != len(b) {
                return dst, 0, fmt.Errorf("got %v; want %v", n, len(b))
        }

        // Wait for a reply
        reply := make([]byte, 1500)
        err = c.SetReadDeadline(time.Now().Add(10 * time.Second))
        if err != nil {
                return dst, 0, err
        }
        n, peer, err := c.ReadFrom(reply)
        if err != nil {
                return dst, 0, err
        }
        duration := time.Since(start)

        // Pack it up boys, we're done here
        rm, err := icmp.ParseMessage(ProtocolICMP, reply[:n])
        if err != nil {
                return dst, 0, err
        }
        switch rm.Type {
        case ipv4.ICMPTypeEchoReply:
                return dst, duration, nil
        default:
                return dst, 0, fmt.Errorf("got %+v from %v; want echo reply", rm, peer)
        }
}

Question:
On Line 59

• You check that n equals the length of the binary, marshalled icmp.Message. Why do you do that? Are you worried in the edge case that the connection listener is broken; faulty NIC controller or RAM?

Still learning deeper parts of golang, I'll give the icmp package a read.

very helpful !!!

@tlhakhan sorry for such a late reply, probably missed a notification :(

This is old code by now, so of course any thoughts I had while writing it is now lost. Though I guess that check is for ICMP fragments, caused by poor connection or too large packet or yeah, some other fault on the host. A better way to handle it would be to retry sending it, instead of simply erroring out. But I think it was more for logging purposes.