net/http: make Redirect escape non-ASCII in Location header

Only ASCII is permitted there.

Fixes #4385

Change-Id: I63708b04a041cdada0fdfc1f2308fcb66889a27b
Reviewed-on: https://go-review.googlesource.com/31732
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/http/http.go

@@ -5,6 +5,7 @@
 package http
 
 import (
+	"strconv"
 	"strings"
 	"time"
 	"unicode/utf8"
@@ -56,3 +57,27 @@ func isASCII(s string) bool {
 	}
 	return true
 }
+
+func hexEscapeNonASCII(s string) string {
+	newLen := 0
+	for i := 0; i < len(s); i++ {
+		if s[i] >= utf8.RuneSelf {
+			newLen += 3
+		} else {
+			newLen++
+		}
+	}
+	if newLen == len(s) {
+		return s
+	}
+	b := make([]byte, 0, newLen)
+	for i := 0; i < len(s); i++ {
+		if s[i] >= utf8.RuneSelf {
+			b = append(b, '%')
+			b = strconv.AppendInt(b, int64(s[i]), 16)
+		} else {
+			b = append(b, s[i])
+		}
+	}
+	return string(b)
+}

src/net/http/serve_test.go

@@ -2050,23 +2050,6 @@ func TestTimeoutHandlerEmptyResponse(t *testing.T) {
 	}
 }
 
-// Verifies we don't path.Clean() on the wrong parts in redirects.
-func TestRedirectMunging(t *testing.T) {
-	req, _ := NewRequest("GET", "http://example.com/", nil)
-
-	resp := httptest.NewRecorder()
-	Redirect(resp, req, "/foo?next=http://bar.com/", 302)
-	if g, e := resp.Header().Get("Location"), "/foo?next=http://bar.com/"; g != e {
-		t.Errorf("Location header was %q; want %q", g, e)
-	}
-
-	resp = httptest.NewRecorder()
-	Redirect(resp, req, "http://localhost:8080/_ah/login?continue=http://localhost:8080/", 302)
-	if g, e := resp.Header().Get("Location"), "http://localhost:8080/_ah/login?continue=http://localhost:8080/"; g != e {
-		t.Errorf("Location header was %q; want %q", g, e)
-	}
-}
-
 func TestRedirectBadPath(t *testing.T) {
 	// This used to crash. It's not valid input (bad path), but it
 	// shouldn't crash.
@@ -2085,7 +2068,7 @@ func TestRedirectBadPath(t *testing.T) {
 }
 
 // Test different URL formats and schemes
-func TestRedirectURLFormat(t *testing.T) {
+func TestRedirect(t *testing.T) {
 	req, _ := NewRequest("GET", "http://example.com/qux/", nil)
 
 	var tests = []struct {
@@ -2108,6 +2091,14 @@ func TestRedirectURLFormat(t *testing.T) {
 		{"../quux/foobar.com/baz", "/quux/foobar.com/baz"},
 		// incorrect number of slashes
 		{"///foobar.com/baz", "/foobar.com/baz"},
+
+		// Verifies we don't path.Clean() on the wrong parts in redirects:
+		{"/foo?next=http://bar.com/", "/foo?next=http://bar.com/"},
+		{"http://localhost:8080/_ah/login?continue=http://localhost:8080/",
+			"http://localhost:8080/_ah/login?continue=http://localhost:8080/"},
+
+		{"/фубар", "/%d1%84%d1%83%d0%b1%d0%b0%d1%80"},
+		{"http://foo.com/фубар", "http://foo.com/%d1%84%d1%83%d0%b1%d0%b0%d1%80"},
 	}
 
 	for _, tt := range tests {

src/net/http/server.go

@@ -1890,7 +1890,7 @@ func Redirect(w ResponseWriter, r *Request, urlStr string, code int) {
 		}
 	}
 
-	w.Header().Set("Location", urlStr)
+	w.Header().Set("Location", hexEscapeNonASCII(urlStr))
 	w.WriteHeader(code)
 
 	// RFC 2616 recommends that a short note "SHOULD" be included in the