Add support for GraphQL extensions

graphql.go

@@ -34,18 +34,36 @@ func NewClient(url string, httpClient *http.Client) *Client {
 // with a query derived from q, populating the response into it.
 // q should be a pointer to struct that corresponds to the GraphQL schema.
 func (c *Client) Query(ctx context.Context, q interface{}, variables map[string]interface{}) error {
-	return c.do(ctx, queryOperation, q, variables)
+	return c.do(ctx, queryOperation, q, variables, nil)
+}
+
+// QueryWithExtensions executes a single GraphQL query request,
+// with a query derived from q, populating the response into it.
+// q should be a pointer to struct that corresponds to the GraphQL schema.
+// Additionally, this will capture the extensions from the response.
+// extensions should be a pointer that corresponds to the extensions schema.
+func (c *Client) QueryWithExtensions(ctx context.Context, q interface{}, variables map[string]interface{}, extensions interface{}) error {
+	return c.do(ctx, queryOperation, q, variables, extensions)
 }
 
 // Mutate executes a single GraphQL mutation request,
 // with a mutation derived from m, populating the response into it.
 // m should be a pointer to struct that corresponds to the GraphQL schema.
 func (c *Client) Mutate(ctx context.Context, m interface{}, variables map[string]interface{}) error {
-	return c.do(ctx, mutationOperation, m, variables)
+	return c.do(ctx, mutationOperation, m, variables, nil)
+}
+
+// MutateWithExtensions executes a single GraphQL mutation request,
+// with a mutation derived from m, populating the response into it.
+// m should be a pointer to struct that corresponds to the GraphQL schema.
+// Additionally, this will capture the extensions from the response.
+// extensions should be a pointer that corresponds to the extensions schema.
+func (c *Client) MutateWithExtensions(ctx context.Context, m interface{}, variables map[string]interface{}, extensions interface{}) error {
+	return c.do(ctx, mutationOperation, m, variables, extensions)
 }
 
 // do executes a single GraphQL operation.
-func (c *Client) do(ctx context.Context, op operationType, v interface{}, variables map[string]interface{}) error {
+func (c *Client) do(ctx context.Context, op operationType, v interface{}, variables map[string]interface{}, extensions interface{}) error {
 	var query string
 	switch op {
 	case queryOperation:
@@ -75,9 +93,9 @@ func (c *Client) do(ctx context.Context, op operationType, v interface{}, variab
 		return fmt.Errorf("non-200 OK status code: %v body: %q", resp.Status, body)
 	}
 	var out struct {
-		Data   *json.RawMessage
-		Errors errors
-		//Extensions interface{} // Unused.
+		Data       *json.RawMessage
+		Errors     errors
+		Extensions *json.RawMessage
 	}
 	err = json.NewDecoder(resp.Body).Decode(&out)
 	if err != nil {
@@ -91,6 +109,13 @@ func (c *Client) do(ctx context.Context, op operationType, v interface{}, variab
 			return err
 		}
 	}
+	if extensions != nil && out.Extensions != nil {
+		err := jsonutil.UnmarshalGraphQL(*out.Extensions, extensions)
+		if err != nil {
+			// TODO: Consider including response body in returned error, if deemed helpful.
+			return err
+		}
+	}
 	if len(out.Errors) > 0 {
 		return out.Errors
 	}

graphql_test.go

@@ -153,6 +153,40 @@ func TestClient_Query_emptyVariables(t *testing.T) {
 	}
 }
 
+func TestClient_QueryWithExtensions(t *testing.T) {
+	mux := http.NewServeMux()
+	mux.HandleFunc("/graphql", func(w http.ResponseWriter, req *http.Request) {
+		body := mustRead(req.Body)
+		if got, want := body, `{"query":"{user{name}}"}`+"\n"; got != want {
+			t.Errorf("got body: %v, want %v", got, want)
+		}
+		w.Header().Set("Content-Type", "application/json")
+		mustWrite(w, `{"data": {"user": {"name": "Gopher"}}, "extensions": {"cost": {"actualQueryCost":50}}}`)
+	})
+	client := graphql.NewClient("/graphql", &http.Client{Transport: localRoundTripper{handler: mux}})
+
+	var q struct {
+		User struct {
+			Name string
+		}
+	}
+	var e struct {
+		Cost struct {
+			ActualQueryCost int
+		}
+	}
+	err := client.QueryWithExtensions(context.Background(), &q, map[string]interface{}{}, &e)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got, want := q.User.Name, "Gopher"; got != want {
+		t.Errorf("got q.User.Name: %q, want: %q", got, want)
+	}
+	if got, want := e.Cost.ActualQueryCost, 50; got != want {
+		t.Errorf("got e.QueryCost: %q, want: %q", got, want)
+	}
+}
+
 // localRoundTripper is an http.RoundTripper that executes HTTP transactions
 // by using handler directly, instead of going over an HTTP connection.
 type localRoundTripper struct {