Enforce WhatsApp Cloud webhook body limit while reading

gateway/platforms/whatsapp_cloud.py

@@ -90,6 +90,7 @@ DEFAULT_WEBHOOK_HOST = "0.0.0.0"
 DEFAULT_WEBHOOK_PORT = 8090
 DEFAULT_WEBHOOK_PATH = "/whatsapp/webhook"
 GRAPH_API_BASE = "https://graph.facebook.com"
+WEBHOOK_MAX_BODY_BYTES = 3 * 1024 * 1024
 # Meta retries failed webhooks for up to 7 days. We don't need to remember
 # every wamid for the full retry window — the practical risk is duplicate
 # delivery within minutes, not days. 5000 entries with FIFO eviction is
@@ -144,6 +145,17 @@ _WHATSAPP_MIME_EXTENSION_OVERRIDES: Dict[str, str] = {
 }
 
 
+async def _read_limited_request_body(request: Any, max_bytes: int) -> bytes:
+    """Read at most ``max_bytes`` from an aiohttp request body."""
+    try:
+        body = await request.content.readexactly(max_bytes + 1)
+    except asyncio.IncompleteReadError as exc:
+        body = exc.partial
+    if len(body) > max_bytes:
+        raise ValueError("payload too large")
+    return body
+
+
 def _ext_for_mime(mime: str) -> Optional[str]:
     """Resolve a mime type to the file extension we want on disk.
 
@@ -1405,16 +1417,18 @@ class WhatsAppCloudAdapter(WhatsAppBehaviorMixin, BasePlatformAdapter):
              multiply downstream agent work because of a transient bug
              during dispatch.
         """
+        # Meta's documented max payload is 3MB. Read one byte past the limit
+        # so oversized chunked bodies are rejected before buffering the rest.
         try:
-            raw = await request.read()
+            raw = await _read_limited_request_body(
+                request,
+                WEBHOOK_MAX_BODY_BYTES,
+            )
+        except ValueError:
+            return web.Response(status=413)
         except Exception:
             return web.Response(status=400)
 
-        # Meta's documented max payload is 3MB. Reject earlier than aiohttp
-        # would so we don't even compute HMAC over giant junk.
-        if len(raw) > 3 * 1024 * 1024:
-            return web.Response(status=413)
-
         # Refuse to accept anything if app_secret isn't configured. Without
         # it we can't authenticate the sender, and the handler would be a
         # data-injection point. Same defensive posture as the GET verify

tests/gateway/test_whatsapp_cloud.py

@@ -12,6 +12,7 @@ exercised with synthetic ``Request`` objects.
 
 from __future__ import annotations
 
+import asyncio
 import json
 from unittest.mock import AsyncMock, MagicMock
 
@@ -405,10 +406,22 @@ def _sign(secret: str, body: bytes) -> str:
     return f"sha256={digest}"
 
 
+class _FakeRequestContent:
+    def __init__(self, body: bytes):
+        self.body = body
+        self.read_sizes: list[int] = []
+
+    async def readexactly(self, size: int) -> bytes:
+        self.read_sizes.append(size)
+        if len(self.body) < size:
+            raise asyncio.IncompleteReadError(self.body, size)
+        return self.body[:size]
+
+
 def _post_request(body: bytes, headers: dict | None = None):
     """Build a minimal aiohttp.web.Request stub for POST tests."""
     request = MagicMock()
-    request.read = AsyncMock(return_value=body)
+    request.content = _FakeRequestContent(body)
     request.headers = headers or {}
     return request
 
@@ -539,20 +552,23 @@ class TestWebhookSignature:
     @pytest.mark.asyncio
     async def test_oversize_body_rejected_before_signature(self):
         """3MB cap per Meta — refuse without computing HMAC over giant junk."""
+        from gateway.platforms.whatsapp_cloud import WEBHOOK_MAX_BODY_BYTES
+
         adapter = _make_adapter(app_secret="key")
         adapter._dispatch_payload = AsyncMock()
-        body = b"x" * (4 * 1024 * 1024)
+        body = b"x" * (WEBHOOK_MAX_BODY_BYTES + 2)
         request = _post_request(body, {"X-Hub-Signature-256": "sha256=ignored"})
 
         response = await adapter._handle_webhook(request)
         assert response.status == 413
+        assert request.content.read_sizes == [WEBHOOK_MAX_BODY_BYTES + 1]
         adapter._dispatch_payload.assert_not_called()
 
     @pytest.mark.asyncio
     async def test_unreadable_body_rejected(self):
         adapter = _make_adapter(app_secret="key")
         request = MagicMock()
-        request.read = AsyncMock(side_effect=RuntimeError("read failed"))
+        request.content.readexactly = AsyncMock(side_effect=RuntimeError("read failed"))
         request.headers = {}
 
         response = await adapter._handle_webhook(request)
@@ -2436,4 +2452,3 @@ class TestReplyContextResolution:
             rich_sent_store.lookup("15551234567", "wamid.OUT")
             == "here is your answer"
         )
-