From a06009512e9951dd46cd64ada9e511741987245a Mon Sep 17 00:00:00 2001
From: Anton Skorokhod <anton@nsl.cz>
Date: Mon, 17 Aug 2015 10:31:27 +0200
Subject: [PATCH] Option to specify source ip for ping

---
 cmd/ping/ping.go | 11 ++++++++++-
 fastping.go      | 33 +++++++++++++++++++++++++++++----
 2 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/cmd/ping/ping.go b/cmd/ping/ping.go
index eddd695..456cd74 100644
--- a/cmd/ping/ping.go
+++ b/cmd/ping/ping.go
@@ -23,7 +23,7 @@ func main() {
 	flag.BoolVar(&useUDP, "udp", false, "use non-privileged datagram-oriented UDP as ICMP endpoints")
 	flag.BoolVar(&useUDP, "u", false, "use non-privileged datagram-oriented UDP as ICMP endpoints (shorthand)")
 	flag.Usage = func() {
-		fmt.Fprintf(os.Stderr, "Usage:\n  %s [options] hostname\n\nOptions:\n", os.Args[0])
+		fmt.Fprintf(os.Stderr, "Usage:\n  %s [options] hostname [source]\n\nOptions:\n", os.Args[0])
 		flag.PrintDefaults()
 	}
 	flag.Parse()
@@ -34,6 +34,11 @@ func main() {
 		os.Exit(1)
 	}
 
+	source := ""
+	if flag.NArg() > 1 {
+		source = flag.Arg(1)
+	}
+
 	p := fastping.NewPinger()
 	if useUDP {
 		p.Network("udp")
@@ -49,6 +54,10 @@ func main() {
 		os.Exit(1)
 	}
 
+	if source != "" {
+		p.Source(source)
+	}
+
 	results := make(map[string]*response)
 	results[ra.String()] = nil
 	p.AddIPAddr(ra)
diff --git a/fastping.go b/fastping.go
index 3bb23cb..b2bb348 100644
--- a/fastping.go
+++ b/fastping.go
@@ -130,6 +130,7 @@ type Pinger struct {
 	// key string is IPAddr.String()
 	addrs   map[string]*net.IPAddr
 	network string
+	source  string
 	hasIPv4 bool
 	hasIPv6 bool
 	ctx     *context
@@ -158,6 +159,7 @@ func NewPinger() *Pinger {
 		seq:     rand.Intn(0xffff),
 		addrs:   make(map[string]*net.IPAddr),
 		network: "ip",
+		source:  "",
 		hasIPv4: false,
 		hasIPv6: false,
 		Size:    TimeSliceLength,
@@ -185,6 +187,29 @@ func (p *Pinger) Network(network string) (string, error) {
 	return origNet, nil
 }
 
+// Source sets source IP for sending ICMP packets and returns the previous
+// setting. Empty value indicates to use system default one.
+func (p *Pinger) Source(source string) (string, error) {
+	origSource := p.source
+	if "" == source {
+		p.mu.Lock()
+		p.source = source
+		p.mu.Unlock()
+		return origSource, nil
+	}
+
+	addr := net.ParseIP(source)
+	if addr == nil {
+		return origSource, errors.New(source + " is not a valid textual representation of an IP address")
+	}
+
+	p.mu.Lock()
+	p.source = source
+	p.mu.Unlock()
+
+	return origSource, nil
+}
+
 // AddIP adds an IP address to Pinger. ipaddr arg should be a string like
 // "192.0.2.1".
 func (p *Pinger) AddIP(ipaddr string) error {
@@ -347,8 +372,8 @@ func (p *Pinger) Err() error {
 	return p.ctx.err
 }
 
-func (p *Pinger) listen(netProto string) *icmp.PacketConn {
-	conn, err := icmp.ListenPacket(netProto, "")
+func (p *Pinger) listen(netProto string, source string) *icmp.PacketConn {
+	conn, err := icmp.ListenPacket(netProto, source)
 	if err != nil {
 		p.mu.Lock()
 		p.ctx.err = err
@@ -364,14 +389,14 @@ func (p *Pinger) run(once bool) {
 	p.debugln("Run(): Start")
 	var conn, conn6 *icmp.PacketConn
 	if p.hasIPv4 {
-		if conn = p.listen(ipv4Proto[p.network]); conn == nil {
+		if conn = p.listen(ipv4Proto[p.network], p.source); conn == nil {
 			return
 		}
 		defer conn.Close()
 	}
 
 	if p.hasIPv6 {
-		if conn6 = p.listen(ipv6Proto[p.network]); conn6 == nil {
+		if conn6 = p.listen(ipv6Proto[p.network], p.source); conn6 == nil {
 			return
 		}
 		defer conn6.Close()