client: Return the server's cluster ID as part of the Response

This allows the client to spot if the cluster ID changes, which
would indicate that the cluster has been rebuilt and watches may be
out of sync.

Helps work around #6652.

client/keys.go

@@ -272,6 +272,10 @@ type Response struct {
 	// Index holds the cluster-level index at the time the Response was generated.
 	// This index is not tied to the Node(s) contained in this Response.
 	Index uint64 `json:"-"`
+
+	// ClusterID holds the cluster-level ID reported by the server.  This
+	// should be different for different etcd clusters.
+	ClusterID string `json:"-"`
 }
 
 type Node struct {
@@ -665,6 +669,7 @@ func unmarshalSuccessfulKeysResponse(header http.Header, body []byte) (*Response
 			return nil, err
 		}
 	}
+	res.ClusterID = header.Get("X-Etcd-Cluster-ID")
 	return &res, nil
 }
 

client/keys_test.go

@@ -673,23 +673,24 @@ func TestUnmarshalSuccessfulResponse(t *testing.T) {
 	expiration.UnmarshalText([]byte("2015-04-07T04:40:23.044979686Z"))
 
 	tests := []struct {
-		hdr     string
-		body    string
-		wantRes *Response
-		wantErr bool
+		indexHdr     string
+		clusterIDHdr string
+		body         string
+		wantRes      *Response
+		wantErr      bool
 	}{
 		// Neither PrevNode or Node
 		{
-			hdr:     "1",
-			body:    `{"action":"delete"}`,
-			wantRes: &Response{Action: "delete", Index: 1},
-			wantErr: false,
+			indexHdr: "1",
+			body:     `{"action":"delete"}`,
+			wantRes:  &Response{Action: "delete", Index: 1},
+			wantErr:  false,
 		},
 
 		// PrevNode
 		{
-			hdr:  "15",
-			body: `{"action":"delete", "prevNode": {"key": "/foo", "value": "bar", "modifiedIndex": 12, "createdIndex": 10}}`,
+			indexHdr: "15",
+			body:     `{"action":"delete", "prevNode": {"key": "/foo", "value": "bar", "modifiedIndex": 12, "createdIndex": 10}}`,
 			wantRes: &Response{
 				Action: "delete",
 				Index:  15,
@@ -706,8 +707,8 @@ func TestUnmarshalSuccessfulResponse(t *testing.T) {
 
 		// Node
 		{
-			hdr:  "15",
-			body: `{"action":"get", "node": {"key": "/foo", "value": "bar", "modifiedIndex": 12, "createdIndex": 10, "ttl": 10, "expiration": "2015-04-07T04:40:23.044979686Z"}}`,
+			indexHdr: "15",
+			body:     `{"action":"get", "node": {"key": "/foo", "value": "bar", "modifiedIndex": 12, "createdIndex": 10, "ttl": 10, "expiration": "2015-04-07T04:40:23.044979686Z"}}`,
 			wantRes: &Response{
 				Action: "get",
 				Index:  15,
@@ -726,8 +727,9 @@ func TestUnmarshalSuccessfulResponse(t *testing.T) {
 
 		// Node Dir
 		{
-			hdr:  "15",
-			body: `{"action":"get", "node": {"key": "/foo", "dir": true, "modifiedIndex": 12, "createdIndex": 10}}`,
+			indexHdr:     "15",
+			clusterIDHdr: "abcdef",
+			body:         `{"action":"get", "node": {"key": "/foo", "dir": true, "modifiedIndex": 12, "createdIndex": 10}}`,
 			wantRes: &Response{
 				Action: "get",
 				Index:  15,
@@ -737,15 +739,16 @@ func TestUnmarshalSuccessfulResponse(t *testing.T) {
 					ModifiedIndex: 12,
 					CreatedIndex:  10,
 				},
-				PrevNode: nil,
+				PrevNode:  nil,
+				ClusterID: "abcdef",
 			},
 			wantErr: false,
 		},
 
 		// PrevNode and Node
 		{
-			hdr:  "15",
-			body: `{"action":"update", "prevNode": {"key": "/foo", "value": "baz", "modifiedIndex": 10, "createdIndex": 10}, "node": {"key": "/foo", "value": "bar", "modifiedIndex": 12, "createdIndex": 10}}`,
+			indexHdr: "15",
+			body:     `{"action":"update", "prevNode": {"key": "/foo", "value": "baz", "modifiedIndex": 10, "createdIndex": 10}, "node": {"key": "/foo", "value": "bar", "modifiedIndex": 12, "createdIndex": 10}}`,
 			wantRes: &Response{
 				Action: "update",
 				Index:  15,
@@ -767,24 +770,24 @@ func TestUnmarshalSuccessfulResponse(t *testing.T) {
 
 		// Garbage in body
 		{
-			hdr:     "",
-			body:    `garbage`,
-			wantRes: nil,
-			wantErr: true,
+			indexHdr: "",
+			body:     `garbage`,
+			wantRes:  nil,
+			wantErr:  true,
 		},
 
 		// non-integer index
 		{
-			hdr:     "poo",
-			body:    `{}`,
-			wantRes: nil,
-			wantErr: true,
+			indexHdr: "poo",
+			body:     `{}`,
+			wantRes:  nil,
+			wantErr:  true,
 		},
 	}
 
 	for i, tt := range tests {
 		h := make(http.Header)
-		h.Add("X-Etcd-Index", tt.hdr)
+		h.Add("X-Etcd-Index", tt.indexHdr)
 		res, err := unmarshalSuccessfulKeysResponse(h, []byte(tt.body))
 		if tt.wantErr != (err != nil) {
 			t.Errorf("#%d: wantErr=%t, err=%v", i, tt.wantErr, err)