Make mock listen on random port if 0 is specified

transport/mock/mock.go

@@ -2,7 +2,11 @@ package mock
 
 import (
 	"errors"
+	"fmt"
+	"math/rand"
+	"strings"
 	"sync"
+	"time"
 
 	"github.com/micro/go-micro/transport"
 )
@@ -126,15 +130,25 @@ func (m *mockTransport) Listen(addr string, opts ...transport.ListenOption) (tra
 	m.Lock()
 	defer m.Unlock()
 
-	if _, ok := m.listeners[addr]; ok {
-		return nil, errors.New("already listening on " + addr)
-	}
-
 	var options transport.ListenOptions
 	for _, o := range opts {
 		o(&options)
 	}
 
+	parts := strings.Split(addr, ":")
+
+	// if zero port then randomly assign one
+	if len(parts) > 1 && parts[len(parts)-1] == "0" {
+		r := rand.New(rand.NewSource(time.Now().UnixNano()))
+		i := r.Intn(10000)
+		// set addr with port
+		addr = fmt.Sprintf("%s:%d", parts[:len(parts)-1], 10000+i)
+	}
+
+	if _, ok := m.listeners[addr]; ok {
+		return nil, errors.New("already listening on " + addr)
+	}
+
 	listener := &mockListener{
 		opts: options,
 		addr: addr,

transport/mock/mock_test.go

@@ -58,3 +58,32 @@ func TestTransport(t *testing.T) {
 	}
 
 }
+
+func TestListener(t *testing.T) {
+	tr := NewTransport()
+
+	// bind / listen on random port
+	l, err := tr.Listen(":0")
+	if err != nil {
+		t.Fatalf("Unexpected error listening %v", err)
+	}
+	defer l.Close()
+
+	// try again
+	l2, err := tr.Listen(":0")
+	if err != nil {
+		t.Fatalf("Unexpected error listening %v", err)
+	}
+	defer l2.Close()
+
+	// now make sure it still fails
+	l3, err := tr.Listen(":8080")
+	if err != nil {
+		t.Fatalf("Unexpected error listening %v", err)
+	}
+	defer l3.Close()
+
+	if _, err := tr.Listen(":8080"); err == nil {
+		t.Fatal("Expected error binding to :8080 got nil")
+	}
+}