proxy: fix TestDial failures on wasm/js

Modified `TestDial` to emulate `internal/socks/dial_test.go` and leverage `nettest#NetLocalListener()` while also honoring the returned `net.Listener` address. It seems that the wasm/js runtime doesn't like dialing addresses with no host.

Fixes golang/go#32842

Change-Id: I1915f2ebac773f24a5b37ab7c09a52137abe758d
GitHub-Last-Rev: 8f2967fa7d37d1047e5e7d47f85436155be65a82
GitHub-Pull-Request: golang/net#45
Reviewed-on: https://go-review.googlesource.com/c/net/+/184178
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

proxy/dial_test.go

@@ -7,30 +7,26 @@ package proxy
 import (
 	"context"
 	"fmt"
-	"net"
 	"os"
 	"testing"
 	"time"
 
 	"golang.org/x/net/internal/sockstest"
+	"golang.org/x/net/nettest"
 )
 
 func TestDial(t *testing.T) {
 	ResetProxyEnv()
 	t.Run("DirectWithCancel", func(t *testing.T) {
 		defer ResetProxyEnv()
-		l, err := net.Listen("tcp", "127.0.0.1:0")
+		l, err := nettest.NewLocalListener("tcp")
 		if err != nil {
 			t.Fatal(err)
 		}
 		defer l.Close()
-		_, port, err := net.SplitHostPort(l.Addr().String())
-		if err != nil {
-			t.Fatal(err)
-		}
 		ctx, cancel := context.WithCancel(context.Background())
 		defer cancel()
-		c, err := Dial(ctx, l.Addr().Network(), net.JoinHostPort("", port))
+		c, err := Dial(ctx, l.Addr().Network(), l.Addr().String())
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -38,18 +34,14 @@ func TestDial(t *testing.T) {
 	})
 	t.Run("DirectWithTimeout", func(t *testing.T) {
 		defer ResetProxyEnv()
-		l, err := net.Listen("tcp", "127.0.0.1:0")
+		l, err := nettest.NewLocalListener("tcp")
 		if err != nil {
 			t.Fatal(err)
 		}
 		defer l.Close()
-		_, port, err := net.SplitHostPort(l.Addr().String())
-		if err != nil {
-			t.Fatal(err)
-		}
 		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 		defer cancel()
-		c, err := Dial(ctx, l.Addr().Network(), net.JoinHostPort("", port))
+		c, err := Dial(ctx, l.Addr().Network(), l.Addr().String())
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -57,19 +49,15 @@ func TestDial(t *testing.T) {
 	})
 	t.Run("DirectWithTimeoutExceeded", func(t *testing.T) {
 		defer ResetProxyEnv()
-		l, err := net.Listen("tcp", "127.0.0.1:0")
+		l, err := nettest.NewLocalListener("tcp")
 		if err != nil {
 			t.Fatal(err)
 		}
 		defer l.Close()
-		_, port, err := net.SplitHostPort(l.Addr().String())
-		if err != nil {
-			t.Fatal(err)
-		}
 		ctx, cancel := context.WithTimeout(context.Background(), time.Nanosecond)
 		time.Sleep(time.Millisecond)
 		defer cancel()
-		c, err := Dial(ctx, l.Addr().Network(), net.JoinHostPort("", port))
+		c, err := Dial(ctx, l.Addr().Network(), l.Addr().String())
 		if err == nil {
 			defer c.Close()
 			t.Fatal("failed to timeout")