fix: default MIME type for WhatsApp voice messages when Baileys omits it (#14444)

src/web/inbound/media.node.test.ts

@@ -0,0 +1,101 @@
+import { describe, expect, it, vi } from "vitest";
+
+const { normalizeMessageContent, downloadMediaMessage } = vi.hoisted(() => ({
+  normalizeMessageContent: vi.fn((msg: unknown) => msg),
+  downloadMediaMessage: vi.fn().mockResolvedValue(Buffer.from("fake-media-data")),
+}));
+
+vi.mock("@whiskeysockets/baileys", () => ({
+  normalizeMessageContent,
+  downloadMediaMessage,
+}));
+
+import { downloadInboundMedia } from "./media.js";
+
+const mockSock = {
+  updateMediaMessage: vi.fn(),
+  logger: { child: () => ({}) },
+} as never;
+
+describe("downloadInboundMedia", () => {
+  it("returns undefined for messages without media", async () => {
+    const msg = { message: { conversation: "hello" } } as never;
+    const result = await downloadInboundMedia(msg, mockSock);
+    expect(result).toBeUndefined();
+  });
+
+  it("uses explicit mimetype from audioMessage when present", async () => {
+    const msg = {
+      message: { audioMessage: { mimetype: "audio/mp4", ptt: true } },
+    } as never;
+    const result = await downloadInboundMedia(msg, mockSock);
+    expect(result).toBeDefined();
+    expect(result?.mimetype).toBe("audio/mp4");
+  });
+
+  it("defaults to audio/ogg for voice messages without explicit MIME", async () => {
+    const msg = {
+      message: { audioMessage: { ptt: true } },
+    } as never;
+    const result = await downloadInboundMedia(msg, mockSock);
+    expect(result).toBeDefined();
+    expect(result?.mimetype).toBe("audio/ogg; codecs=opus");
+  });
+
+  it("defaults to audio/ogg for audio messages without MIME or ptt flag", async () => {
+    const msg = {
+      message: { audioMessage: {} },
+    } as never;
+    const result = await downloadInboundMedia(msg, mockSock);
+    expect(result).toBeDefined();
+    expect(result?.mimetype).toBe("audio/ogg; codecs=opus");
+  });
+
+  it("uses explicit mimetype from imageMessage when present", async () => {
+    const msg = {
+      message: { imageMessage: { mimetype: "image/png" } },
+    } as never;
+    const result = await downloadInboundMedia(msg, mockSock);
+    expect(result).toBeDefined();
+    expect(result?.mimetype).toBe("image/png");
+  });
+
+  it("defaults to image/jpeg for images without explicit MIME", async () => {
+    const msg = {
+      message: { imageMessage: {} },
+    } as never;
+    const result = await downloadInboundMedia(msg, mockSock);
+    expect(result).toBeDefined();
+    expect(result?.mimetype).toBe("image/jpeg");
+  });
+
+  it("defaults to video/mp4 for video messages without explicit MIME", async () => {
+    const msg = {
+      message: { videoMessage: {} },
+    } as never;
+    const result = await downloadInboundMedia(msg, mockSock);
+    expect(result).toBeDefined();
+    expect(result?.mimetype).toBe("video/mp4");
+  });
+
+  it("defaults to image/webp for sticker messages without explicit MIME", async () => {
+    const msg = {
+      message: { stickerMessage: {} },
+    } as never;
+    const result = await downloadInboundMedia(msg, mockSock);
+    expect(result).toBeDefined();
+    expect(result?.mimetype).toBe("image/webp");
+  });
+
+  it("preserves fileName from document messages", async () => {
+    const msg = {
+      message: {
+        documentMessage: { mimetype: "application/pdf", fileName: "report.pdf" },
+      },
+    } as never;
+    const result = await downloadInboundMedia(msg, mockSock);
+    expect(result).toBeDefined();
+    expect(result?.mimetype).toBe("application/pdf");
+    expect(result?.fileName).toBe("report.pdf");
+  });
+});

src/web/inbound/media.ts

@@ -8,6 +8,37 @@ function unwrapMessage(message: proto.IMessage | undefined): proto.IMessage | un
   return normalized;
 }
 
+/**
+ * Resolve the MIME type for an inbound media message.
+ * Falls back to WhatsApp's standard formats when Baileys omits the MIME.
+ */
+function resolveMediaMimetype(message: proto.IMessage): string | undefined {
+  const explicit =
+    message.imageMessage?.mimetype ??
+    message.videoMessage?.mimetype ??
+    message.documentMessage?.mimetype ??
+    message.audioMessage?.mimetype ??
+    message.stickerMessage?.mimetype ??
+    undefined;
+  if (explicit) {
+    return explicit;
+  }
+  // WhatsApp voice messages (PTT) and audio use OGG Opus by default
+  if (message.audioMessage) {
+    return "audio/ogg; codecs=opus";
+  }
+  if (message.imageMessage) {
+    return "image/jpeg";
+  }
+  if (message.videoMessage) {
+    return "video/mp4";
+  }
+  if (message.stickerMessage) {
+    return "image/webp";
+  }
+  return undefined;
+}
+
 export async function downloadInboundMedia(
   msg: proto.IWebMessageInfo,
   sock: Awaited<ReturnType<typeof createWaSocket>>,
@@ -16,13 +47,7 @@ export async function downloadInboundMedia(
   if (!message) {
     return undefined;
   }
-  const mimetype =
+  const mimetype = resolveMediaMimetype(message);
-    message.imageMessage?.mimetype ??
-    message.videoMessage?.mimetype ??
-    message.documentMessage?.mimetype ??
-    message.audioMessage?.mimetype ??
-    message.stickerMessage?.mimetype ??
-    undefined;
   const fileName = message.documentMessage?.fileName ?? undefined;
   if (
     !message.imageMessage &&