net/http: Fix basic authentication with empty password

The encoded string must include the : separating the username
        and the password, even when the latter is empty. See
        http://www.ietf.org/rfc/rfc2617.txt for more information.

R=golang-dev, bradfitz, adg
CC=golang-dev
https://golang.org/cl/8475043

src/pkg/net/http/client.go

@@ -161,7 +161,18 @@ func send(req *Request, t RoundTripper) (resp *Response, err error) {
 	}
 
 	if u := req.URL.User; u != nil {
-		req.Header.Set("Authorization", "Basic "+base64.URLEncoding.EncodeToString([]byte(u.String())))
+		auth := u.String()
+		// UserInfo.String() only returns the colon when the
+		// password is set, so we must add it here.
+		//
+		// See 2 (end of page 4) http://www.ietf.org/rfc/rfc2617.txt
+		// "To receive authorization, the client sends the userid and password,
+		// separated by a single colon (":") character, within a base64
+		// encoded string in the credentials."
+		if _, hasPassword := u.Password(); !hasPassword {
+			auth += ":"
+		}
+		req.Header.Set("Authorization", "Basic "+base64.URLEncoding.EncodeToString([]byte(auth)))
 	}
 	resp, err = t.RoundTrip(req)
 	if err != nil {

src/pkg/net/http/client_test.go

@@ -10,6 +10,7 @@ import (
 	"bytes"
 	"crypto/tls"
 	"crypto/x509"
+	"encoding/base64"
 	"errors"
 	"fmt"
 	"io"
@@ -700,3 +701,37 @@ func TestClientHeadContentLength(t *testing.T) {
 		}
 	}
 }
+
+func TestEmptyPasswordAuth(t *testing.T) {
+	defer afterTest(t)
+	gopher := "gopher"
+	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+		auth := r.Header.Get("Authorization")
+		if strings.HasPrefix(auth, "Basic ") {
+			encoded := auth[6:]
+			decoded, err := base64.StdEncoding.DecodeString(encoded)
+			if err != nil {
+				t.Fatal(err)
+			}
+			expected := gopher + ":"
+			s := string(decoded)
+			if expected != s {
+				t.Errorf("Invalid Authorization header. Got %q, wanted %q", s, expected)
+			}
+		} else {
+			t.Errorf("Invalid auth %q", auth)
+		}
+	}))
+	defer ts.Close()
+	c := &Client{}
+	req, err := NewRequest("GET", ts.URL, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	req.URL.User = url.User(gopher)
+	resp, err := c.Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+}