etcdhttp: trim StoreKeysPrefix from error in serveKeys

It returns error messaage like this now:
'{"errorCode":100,"message":"Key not found","cause":"/1/pants","index":10}'

The commit trims '/1' prefix from cause field if exists.

This is a hack to make it display well. It is correct because all error causes
that contain Path puts Path at the head of the string.

etcdserver/etcdhttp/http.go

@@ -124,6 +124,7 @@ func (h serverHandler) serveKeys(w http.ResponseWriter, r *http.Request) {
 
 	resp, err := h.server.Do(ctx, rr)
 	if err != nil {
+		err = trimErrorPrefix(err, etcdserver.StoreKeysPrefix)
 		writeError(w, err)
 		return
 	}
@@ -587,3 +588,10 @@ func trimNodeExternPrefix(n *store.NodeExtern, prefix string) *store.NodeExtern
 	}
 	return n
 }
+
+func trimErrorPrefix(err error, prefix string) error {
+	if e, ok := err.(*etcdErr.Error); ok {
+		e.Cause = strings.TrimPrefix(e.Cause, prefix)
+	}
+	return err
+}

etcdserver/etcdhttp/http_test.go

@@ -1100,6 +1100,7 @@ func TestBadServeKeys(t *testing.T) {
 		server etcdserver.Server
 
 		wcode int
+		wbody string
 	}{
 		{
 			// bad method
@@ -1109,6 +1110,7 @@ func TestBadServeKeys(t *testing.T) {
 			&resServer{},
 
 			http.StatusMethodNotAllowed,
+			"Method Not Allowed",
 		},
 		{
 			// bad method
@@ -1118,6 +1120,7 @@ func TestBadServeKeys(t *testing.T) {
 			&resServer{},
 
 			http.StatusMethodNotAllowed,
+			"Method Not Allowed",
 		},
 		{
 			// parseRequest error
@@ -1128,6 +1131,7 @@ func TestBadServeKeys(t *testing.T) {
 			&resServer{},
 
 			http.StatusBadRequest,
+			`{"errorCode":210,"message":"Invalid POST form","cause":"missing form body","index":0}`,
 		},
 		{
 			// etcdserver.Server error
@@ -1137,6 +1141,17 @@ func TestBadServeKeys(t *testing.T) {
 			},
 
 			http.StatusInternalServerError,
+			"Internal Server Error",
+		},
+		{
+			// etcdserver.Server etcd error
+			mustNewRequest(t, "foo"),
+			&errServer{
+				etcdErr.NewError(etcdErr.EcodeKeyNotFound, "/1/pant", 0),
+			},
+
+			http.StatusNotFound,
+			`{"errorCode":100,"message":"Key not found","cause":"/pant","index":0}`,
 		},
 		{
 			// non-event/watcher response from etcdserver.Server
@@ -1146,6 +1161,7 @@ func TestBadServeKeys(t *testing.T) {
 			},
 
 			http.StatusInternalServerError,
+			"Internal Server Error",
 		},
 	}
 	for i, tt := range testBadCases {
@@ -1158,6 +1174,9 @@ func TestBadServeKeys(t *testing.T) {
 		if rw.Code != tt.wcode {
 			t.Errorf("#%d: got code=%d, want %d", i, rw.Code, tt.wcode)
 		}
+		if g := strings.TrimSuffix(rw.Body.String(), "\n"); g != tt.wbody {
+			t.Errorf("#%d: body = %s, want %s", i, g, tt.wbody)
+		}
 	}
 }