net/http: fix inserting of implicit redirects in serve mux

In serve mux, if pattern contains a host name, pass only the path to
the redirect handler.

Add tests for serve mux redirections.

R=rsc
CC=bradfitz, gobot, golang-dev
https://golang.org/cl/6329045

src/pkg/net/http/serve_test.go

@@ -173,6 +173,9 @@ var vtests = []struct {
 	{"http://someHost.com/someDir/apage", "someHost.com/someDir"},
 	{"http://otherHost.com/someDir/apage", "someDir"},
 	{"http://otherHost.com/aDir/apage", "Default"},
+	// redirections for trees
+	{"http://localhost/someDir", "/someDir/"},
+	{"http://someHost.com/someDir", "/someDir/"},
 }
 
 func TestHostHandlers(t *testing.T) {
@@ -204,9 +207,19 @@ func TestHostHandlers(t *testing.T) {
 			t.Errorf("reading response: %v", err)
 			continue
 		}
-		s := r.Header.Get("Result")
-		if s != vt.expected {
-			t.Errorf("Get(%q) = %q, want %q", vt.url, s, vt.expected)
+		switch r.StatusCode {
+		case StatusOK:
+			s := r.Header.Get("Result")
+			if s != vt.expected {
+				t.Errorf("Get(%q) = %q, want %q", vt.url, s, vt.expected)
+			}
+		case StatusMovedPermanently:
+			s := r.Header.Get("Location")
+			if s != vt.expected {
+				t.Errorf("Get(%q) = %q, want %q", vt.url, s, vt.expected)
+			}
+		default:
+			t.Errorf("Get(%q) unhandled status code %d", vt.url, r.StatusCode)
 		}
 	}
 }

src/pkg/net/http/server.go

@@ -997,7 +997,15 @@ func (mux *ServeMux) Handle(pattern string, handler Handler) {
 	// It can be overridden by an explicit registration.
 	n := len(pattern)
 	if n > 0 && pattern[n-1] == '/' && !mux.m[pattern[0:n-1]].explicit {
-		mux.m[pattern[0:n-1]] = muxEntry{h: RedirectHandler(pattern, StatusMovedPermanently)}
+		// If pattern contains a host name, strip it and use remaining
+		// path for redirect.
+		path := pattern
+		if pattern[0] != '/' {
+			// In pattern, at least the last character is a '/', so
+			// strings.Index can't be -1.
+			path = pattern[strings.Index(pattern, "/"):]
+		}
+		mux.m[pattern[0:n-1]] = muxEntry{h: RedirectHandler(path, StatusMovedPermanently)}
 	}
 }