fix goroutine leak if target host is not reachable

  * close `socket` when ping timeout is reached
  * this triggers the goroutine shutdown

fixes #4

arping.go

@@ -127,7 +127,7 @@ func PingOverIface(dstIP net.IP, iface net.Interface) (net.HardwareAddr, time.Du
 		duration time.Duration
 		err      error
 	}
-	pingResultChan := make(chan PingResult)
+	pingResultChan := make(chan PingResult, 1)
 
 	go func() {
 		// send arp request
@@ -162,6 +162,7 @@ func PingOverIface(dstIP net.IP, iface net.Interface) (net.HardwareAddr, time.Du
 	case pingResult := <-pingResultChan:
 		return pingResult.mac, pingResult.duration, pingResult.err
 	case <-time.After(timeout):
+		deinitialize()
 		return nil, 0, ErrTimeout
 	}
 }

arping_test.go

@@ -4,6 +4,8 @@ import (
 	"testing"
 	"net"
 	"strings"
+	"time"
+	"runtime"
 )
 
 
@@ -51,6 +53,38 @@ func TestGratuitousArpWithV6IP(t *testing.T) {
 	validateInvalidV4AddrErr(t, err)
 }
 
+func TestGoroutinesDoesNotLeak(t *testing.T) {
+	ip := net.ParseIP("127.0.0.1")
+	SetTimeout(time.Duration(10 * time.Millisecond))
+
+	spawnNumGoroutines := 5
+	for i := 0; i < spawnNumGoroutines; i++ {
+		_, _, err := Ping(ip)
+		if err != ErrTimeout {
+			t.Fatalf("timeout error expected, but not received - received err: %v", err)
+		}
+	}
+
+	ok := make(chan bool, 1)
+	go func(){
+		for {
+			if runtime.NumGoroutine() < spawnNumGoroutines {
+				ok <- true
+				return
+			}
+			time.Sleep(100 * time.Millisecond)
+		}
+	}()
+
+	select {
+	case <-ok:
+		// ok
+	case <-time.After(30 * time.Second):
+		t.Fatalf("timeout waiting for goroutine cleanup - num goroutines: %d",
+			runtime.NumGoroutine())
+	}
+}
+
 func validateInvalidV4AddrErr(t *testing.T, err error) {
 	if ! strings.Contains(err.Error(), "not a valid v4 Address") {
 		t.Errorf("unexpected error: %s", err)