Initial public release of birdwatch-relay

internal/fcm/sender.go

@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+package fcm
+
+import (
+	"context"
+	"encoding/base64"
+
+	firebase "firebase.google.com/go/v4"
+	"firebase.google.com/go/v4/messaging"
+	"google.golang.org/api/option"
+)
+
+type Sender struct {
+	client *messaging.Client
+}
+
+func New(ctx context.Context, keyPath string) (*Sender, error) {
+	app, err := firebase.NewApp(ctx, nil, option.WithCredentialsFile(keyPath))
+	if err != nil {
+		return nil, err
+	}
+	mc, err := app.Messaging(ctx)
+	if err != nil {
+		return nil, err
+	}
+	return &Sender{client: mc}, nil
+}
+
+// SendCiphertext delivers a ciphertext to a single FCM token as a data-only
+// push (no `notification` field) so the phone decrypts and renders locally —
+// Google never sees plaintext.
+func (s *Sender) SendCiphertext(ctx context.Context, fcmToken string, ciphertext []byte) error {
+	msg := &messaging.Message{
+		Token: fcmToken,
+		Data: map[string]string{
+			"ciphertext": base64.StdEncoding.EncodeToString(ciphertext),
+		},
+		Android: &messaging.AndroidConfig{
+			Priority: "high",
+		},
+	}
+	_, err := s.client.Send(ctx, msg)
+	return err
+}