net/http, net/url: deal with URL.Opaque beginning with //

Update #4860

R=adg, rsc, campoy
CC=golang-dev
https://golang.org/cl/7369045

Author: bradfitz

src/pkg/net/http/requestwrite_test.go

@@ -353,6 +353,44 @@ var reqWriteTests = []reqWriteTest{
 			"Host: \r\n" +
 			"User-Agent: Go http package\r\n\r\n",
 	},
+
+	// Opaque test #1 from golang.org/issue/4860
+	{
+		Req: Request{
+			Method: "GET",
+			URL: &url.URL{
+				Scheme: "http",
+				Host:   "www.google.com",
+				Opaque: "/%2F/%2F/",
+			},
+			ProtoMajor: 1,
+			ProtoMinor: 1,
+			Header:     Header{},
+		},
+
+		WantWrite: "GET /%2F/%2F/ HTTP/1.1\r\n" +
+			"Host: www.google.com\r\n" +
+			"User-Agent: Go http package\r\n\r\n",
+	},
+
+	// Opaque test #2 from golang.org/issue/4860
+	{
+		Req: Request{
+			Method: "GET",
+			URL: &url.URL{
+				Scheme: "http",
+				Host:   "x.google.com",
+				Opaque: "//y.google.com/%2F/%2F/",
+			},
+			ProtoMajor: 1,
+			ProtoMinor: 1,
+			Header:     Header{},
+		},
+
+		WantWrite: "GET http://y.google.com/%2F/%2F/ HTTP/1.1\r\n" +
+			"Host: x.google.com\r\n" +
+			"User-Agent: Go http package\r\n\r\n",
+	},
 }
 
 func TestRequestWrite(t *testing.T) {

src/pkg/net/url/url.go

@@ -693,6 +693,10 @@ func (u *URL) RequestURI() string {
 		if result == "" {
 			result = "/"
 		}
+	} else {
+		if strings.HasPrefix(result, "//") {
+			result = u.Scheme + ":" + result
+		}
 	}
 	if u.RawQuery != "" {
 		result += "?" + u.RawQuery

src/pkg/net/url/url_test.go

@@ -798,6 +798,24 @@ var requritests = []RequestURITest{
 		},
 		"/a%20b",
 	},
+	// golang.org/issue/4860 variant 1
+	{
+		&URL{
+			Scheme: "http",
+			Host:   "example.com",
+			Opaque: "/%2F/%2F/",
+		},
+		"/%2F/%2F/",
+	},
+	// golang.org/issue/4860 variant 2
+	{
+		&URL{
+			Scheme: "http",
+			Host:   "example.com",
+			Opaque: "//other.example.com/%2F/%2F/",
+		},
+		"http://other.example.com/%2F/%2F/",
+	},
 	{
 		&URL{
 			Scheme:   "http",