net/url: better parsing of urls with @ symbol in authority

Fixes #3439

R=r, rsc, dsymonds, n13m3y3r
CC=golang-dev
https://golang.org/cl/6206090

src/pkg/net/url/url.go

@@ -401,11 +401,12 @@ Error:
 }
 
 func parseAuthority(authority string) (user *Userinfo, host string, err error) {
-	if strings.Index(authority, "@") < 0 {
+	i := strings.LastIndex(authority, "@")
+	if i < 0 {
 		host = authority
 		return
 	}
-	userinfo, host := split(authority, '@', true)
+	userinfo, host := authority[:i], authority[i+1:]
 	if strings.Index(userinfo, ":") < 0 {
 		if userinfo, err = unescape(userinfo, encodeUserPassword); err != nil {
 			return

src/pkg/net/url/url_test.go

@@ -188,6 +188,37 @@ var urltests = []URLTest{
 		},
 		"http://user:password@google.com",
 	},
+	// unescaped @ in username should not confuse host
+	{
+		"http://j@ne:password@google.com",
+		&URL{
+			Scheme: "http",
+			User:   UserPassword("j@ne", "password"),
+			Host:   "google.com",
+		},
+		"http://j%40ne:password@google.com",
+	},
+	// unescaped @ in password should not confuse host
+	{
+		"http://jane:p@ssword@google.com",
+		&URL{
+			Scheme: "http",
+			User:   UserPassword("jane", "p@ssword"),
+			Host:   "google.com",
+		},
+		"http://jane:p%40ssword@google.com",
+	},
+	{
+		"http://j@ne:password@google.com/p@th?q=@go",
+		&URL{
+			Scheme:   "http",
+			User:     UserPassword("j@ne", "password"),
+			Host:     "google.com",
+			Path:     "/p@th",
+			RawQuery: "q=@go",
+		},
+		"http://j%40ne:password@google.com/p@th?q=@go",
+	},
 	{
 		"http://www.google.com/?q=go+language#foo",
 		&URL{