fix(fcm): Add ability to override default FCM endpoint via ClientOptions (#373)

* Add FIREBASE_MESSAGING_ENDPOINT environment variable to override default FCM endpoint

* Use endpoint while creating new messaging client

* Add tests for custom endpoint

* Simplify setting default endpoint

* Remove redundant code

* Fix formatting

* Fix imports order

Co-authored-by: Hiranya Jayathilaka <hiranya911@gmail.com>

Author: slirx

firebase_test.go

@@ -29,6 +29,7 @@ import (
 	"testing"
 	"time"
 
+	"firebase.google.com/go/messaging"
 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/google"
 	"google.golang.org/api/option"
@@ -361,6 +362,43 @@ func TestMessaging(t *testing.T) {
 	}
 }
 
+func TestMessagingSendWithCustomEndpoint(t *testing.T) {
+	name := "custom-endpoint-ok"
+
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.Write([]byte("{ \"name\":\"" + name + "\" }"))
+	}))
+	defer ts.Close()
+
+	ctx := context.Background()
+
+	tokenSource := &testTokenSource{AccessToken: "mock-token-from-custom"}
+	app, err := NewApp(
+		ctx,
+		nil,
+		option.WithCredentialsFile("testdata/service_account.json"),
+		option.WithTokenSource(tokenSource),
+		option.WithEndpoint(ts.URL),
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	c, err := app.Messaging(ctx)
+	if c == nil || err != nil {
+		t.Fatalf("Messaging() = (%v, %v); want (iid, nil)", c, err)
+	}
+
+	msg := &messaging.Message{
+		Token: "...",
+	}
+	n, err := c.Send(ctx, msg)
+	if n != name || err != nil {
+		t.Errorf("Send() = (%q, %v); want (%q, nil)", n, err, name)
+	}
+}
+
 func TestCustomTokenSource(t *testing.T) {
 	ctx := context.Background()
 	ts := &testTokenSource{AccessToken: "mock-token-from-custom"}

messaging/messaging.go

@@ -913,13 +913,17 @@ func NewClient(ctx context.Context, c *internal.MessagingConfig) (*Client, error
 		return nil, errors.New("project ID is required to access Firebase Cloud Messaging client")
 	}
 
-	hc, _, err := transport.NewHTTPClient(ctx, c.Opts...)
+	hc, endpoint, err := transport.NewHTTPClient(ctx, c.Opts...)
 	if err != nil {
 		return nil, err
 	}
 
+	if endpoint == "" {
+		endpoint = messagingEndpoint
+	}
+
 	return &Client{
-		fcmClient: newFCMClient(hc, c),
+		fcmClient: newFCMClient(hc, c, endpoint),
 		iidClient: newIIDClient(hc),
 	}, nil
 }
@@ -932,7 +936,7 @@ type fcmClient struct {
 	httpClient    *internal.HTTPClient
 }
 
-func newFCMClient(hc *http.Client, conf *internal.MessagingConfig) *fcmClient {
+func newFCMClient(hc *http.Client, conf *internal.MessagingConfig, endpoint string) *fcmClient {
 	client := internal.WithDefaultRetryConfig(hc)
 	client.CreateErrFn = handleFCMError
 	client.SuccessFn = internal.HasSuccessStatus
@@ -944,7 +948,7 @@ func newFCMClient(hc *http.Client, conf *internal.MessagingConfig) *fcmClient {
 	}
 
 	return &fcmClient{
-		fcmEndpoint:   messagingEndpoint,
+		fcmEndpoint:   endpoint,
 		batchEndpoint: batchEndpoint,
 		project:       conf.ProjectID,
 		version:       version,

messaging/messaging_test.go

@@ -1126,6 +1126,43 @@ func TestSend(t *testing.T) {
 	}
 }
 
+func TestSendWithCustomEndpoint(t *testing.T) {
+	var tr *http.Request
+	var b []byte
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		tr = r
+		b, _ = ioutil.ReadAll(r.Body)
+		w.Header().Set("Content-Type", "application/json")
+		w.Write([]byte("{ \"name\":\"" + testMessageID + "\" }"))
+	}))
+	defer ts.Close()
+
+	ctx := context.Background()
+
+	conf := *testMessagingConfig
+	optEndpoint := option.WithEndpoint(ts.URL)
+	conf.Opts = append(conf.Opts, optEndpoint)
+
+	client, err := NewClient(ctx, &conf)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if ts.URL != client.fcmEndpoint {
+		t.Errorf("client.fcmEndpoint = %q; want = %q", client.fcmEndpoint, ts.URL)
+	}
+
+	for _, tc := range validMessages {
+		t.Run(tc.name, func(t *testing.T) {
+			name, err := client.Send(ctx, tc.req)
+			if name != testMessageID || err != nil {
+				t.Errorf("Send(%s) = (%q, %v); want = (%q, nil)", tc.name, name, err, testMessageID)
+			}
+			checkFCMRequest(t, b, tr, tc.want, false)
+		})
+	}
+}
+
 func TestSendDryRun(t *testing.T) {
 	var tr *http.Request
 	var b []byte