feat(bridge): add support for stickers

whatsapp-bridge/main.go

@@ -1314,6 +1314,16 @@ func extractMediaInfo(msg *waProto.Message, msgTimestamp time.Time, msgID string
 			doc.GetURL(), doc.GetMediaKey(), doc.GetFileSHA256(), doc.GetFileEncSHA256(), doc.GetFileLength()
 	}
 
+	// Sticker message: WebP image, no caption, same URL+MediaKey+SHA shape as other media.
+	// On the wire stickers surface as type="media" with an <enc mediatype="sticker"> payload, e.g.:
+	//   <message id="..." type="media">
+	//     <enc mediatype="sticker" type="msg" v="2"><!-- 660 bytes --></enc>
+	//   </message>
+	if stk := msg.GetStickerMessage(); stk != nil {
+		return "sticker", "sticker_" + suffix + ".webp",
+			stk.GetURL(), stk.GetMediaKey(), stk.GetFileSHA256(), stk.GetFileEncSHA256(), stk.GetFileLength()
+	}
+
 	return "", "", "", nil, nil, nil, 0
 }
 
@@ -1669,6 +1679,8 @@ func downloadMedia(client *whatsmeow.Client, messageStore *MessageStore, message
 		ext = ".mp4"
 	case "audio":
 		ext = ".ogg"
+	case "sticker":
+		ext = ".webp"
 	case "document":
 		ext = ""
 	default:
@@ -1721,6 +1733,10 @@ func downloadMedia(client *whatsmeow.Client, messageStore *MessageStore, message
 		waMediaType = whatsmeow.MediaAudio
 	case "document":
 		waMediaType = whatsmeow.MediaDocument
+	case "sticker":
+		// whatsmeow derives sticker decryption keys from the image HKDF info string
+		// (see download.go: classToMediaType maps "StickerMessage" -> MediaImage).
+		waMediaType = whatsmeow.MediaImage
 	default:
 		return false, "", "", "", fmt.Errorf("unsupported media type: %s", mediaType)
 	}

whatsapp-bridge/main_test.go

@@ -1031,6 +1031,61 @@ func TestExtractTextContent_SurfacesMediaCaptions(t *testing.T) {
 	}
 }
 
+func TestExtractMediaInfo_Sticker(t *testing.T) {
+	ts := time.Unix(1710000000, 0).UTC()
+	msgID := "TEST_STICKER_ID"
+
+	url := "https://mmg.whatsapp.net/v/t62.7161-24/sticker.enc"
+	mediaKey := []byte{0x01, 0x02, 0x03}
+	sha := []byte{0xaa, 0xbb}
+	encSha := []byte{0xcc, 0xdd}
+	var length uint64 = 660
+
+	msg := &waProto.Message{
+		StickerMessage: &waProto.StickerMessage{
+			URL:           proto.String(url),
+			MediaKey:      mediaKey,
+			FileSHA256:    sha,
+			FileEncSHA256: encSha,
+			FileLength:    proto.Uint64(length),
+		},
+	}
+
+	gotType, gotFile, gotURL, gotKey, gotSHA, gotEncSHA, gotLen := extractMediaInfo(msg, ts, msgID)
+
+	if gotType != "sticker" {
+		t.Errorf("mediaType = %q, want %q", gotType, "sticker")
+	}
+	wantFile := "sticker_" + ts.Format("20060102_150405") + "_" + msgID + ".webp"
+	if gotFile != wantFile {
+		t.Errorf("filename = %q, want %q", gotFile, wantFile)
+	}
+	if gotURL != url {
+		t.Errorf("url = %q, want %q", gotURL, url)
+	}
+	if string(gotKey) != string(mediaKey) {
+		t.Errorf("mediaKey = %x, want %x", gotKey, mediaKey)
+	}
+	if string(gotSHA) != string(sha) {
+		t.Errorf("fileSHA256 = %x, want %x", gotSHA, sha)
+	}
+	if string(gotEncSHA) != string(encSha) {
+		t.Errorf("fileEncSHA256 = %x, want %x", gotEncSHA, encSha)
+	}
+	if gotLen != length {
+		t.Errorf("fileLength = %d, want %d", gotLen, length)
+	}
+}
+
+func TestExtractMediaInfo_NoMediaReturnsEmpty(t *testing.T) {
+	msg := &waProto.Message{Conversation: proto.String("plain text, not media")}
+	gotType, gotFile, gotURL, gotKey, _, _, gotLen := extractMediaInfo(msg, time.Unix(1710000000, 0), "X")
+	if gotType != "" || gotFile != "" || gotURL != "" || gotKey != nil || gotLen != 0 {
+		t.Errorf("non-media should return empty: type=%q file=%q url=%q keyLen=%d len=%d",
+			gotType, gotFile, gotURL, len(gotKey), gotLen)
+	}
+}
+
 func TestMigrateLegacyLIDChatsToPhoneJIDs_AggregatesByPhoneJIDDeterministically(t *testing.T) {
 	ms := newTestMessageStore(t)
 	logger := testLogger()