fix(discord): bound REST response reads

Refs NousResearch/hermes-agent#54745

tests/tools/test_discord_tool.py

@@ -142,6 +142,41 @@ class TestDiscordRequest:
         assert exc_info.value.status == 403
         assert "Missing Access" in exc_info.value.body
 
+    @patch("tools.discord_tool.urllib.request.urlopen")
+    def test_response_body_size_limit(self, mock_urlopen_fn, monkeypatch):
+        monkeypatch.setattr("tools.discord_tool._DISCORD_RESPONSE_BODY_MAX_BYTES", 8)
+        mock_resp = MagicMock()
+        mock_resp.status = 200
+        mock_resp.read.return_value = b"x" * 9
+        mock_resp.__enter__ = MagicMock(return_value=mock_resp)
+        mock_resp.__exit__ = MagicMock(return_value=False)
+        mock_urlopen_fn.return_value = mock_resp
+
+        with pytest.raises(DiscordAPIError) as exc_info:
+            _discord_request("GET", "/test", "tok")
+
+        assert exc_info.value.status == 502
+        assert "response body exceeded 8 bytes" in exc_info.value.body
+        mock_resp.read.assert_called_once_with(9)
+
+    @patch("tools.discord_tool.urllib.request.urlopen")
+    def test_http_error_body_size_limit(self, mock_urlopen_fn, monkeypatch):
+        monkeypatch.setattr("tools.discord_tool._DISCORD_ERROR_BODY_MAX_BYTES", 8)
+        http_error = urllib.error.HTTPError(
+            url="https://discord.com/api/v10/test",
+            code=403,
+            msg="Forbidden",
+            hdrs={},
+            fp=BytesIO(b"x" * 9),
+        )
+        mock_urlopen_fn.side_effect = http_error
+
+        with pytest.raises(DiscordAPIError) as exc_info:
+            _discord_request("GET", "/test", "tok")
+
+        assert exc_info.value.status == 403
+        assert "error body exceeded 8 bytes" in exc_info.value.body
+
 
 # ---------------------------------------------------------------------------
 # Main handler: validation

tools/discord_tool.py

@@ -42,6 +42,8 @@ if TYPE_CHECKING:
 logger = logging.getLogger(__name__)
 
 DISCORD_API_BASE = "https://discord.com/api/v10"
+_DISCORD_RESPONSE_BODY_MAX_BYTES = 4 * 1024 * 1024
+_DISCORD_ERROR_BODY_MAX_BYTES = 64 * 1024
 
 # Application flag bits (from GET /applications/@me → "flags").
 # Source: https://discord.com/developers/docs/resources/application#application-object-application-flags
@@ -54,6 +56,21 @@ _FLAG_GATEWAY_MESSAGE_CONTENT_LIMITED = 1 << 19
 # Helpers
 # ---------------------------------------------------------------------------
 
+class DiscordAPIError(Exception):
+    """Raised when a Discord API call fails."""
+    def __init__(self, status: int, body: str):
+        self.status = status
+        self.body = body
+        super().__init__(f"Discord API error {status}: {body}")
+
+
+def _read_limited_response_body(source: Any, limit: int, *, label: str) -> bytes:
+    body = source.read(limit + 1)
+    if len(body) > limit:
+        raise DiscordAPIError(502, f"Discord API {label} exceeded {limit} bytes.")
+    return body
+
+
 def _get_bot_token() -> Optional[str]:
     """Resolve the Discord bot token from environment."""
     return os.getenv("DISCORD_BOT_TOKEN", "").strip() or None
@@ -91,24 +108,28 @@ def _discord_request(
         with urllib.request.urlopen(req, timeout=timeout) as resp:
             if resp.status == 204:
                 return None
-            return json.loads(resp.read().decode("utf-8"))
+            response_body = _read_limited_response_body(
+                resp,
+                _DISCORD_RESPONSE_BODY_MAX_BYTES,
+                label="response body",
+            )
+            return json.loads(response_body.decode("utf-8"))
     except urllib.error.HTTPError as e:
         error_body = ""
         try:
-            error_body = e.read().decode("utf-8", errors="replace")
+            raw_error_body = _read_limited_response_body(
+                e,
+                _DISCORD_ERROR_BODY_MAX_BYTES,
+                label="error body",
+            )
+            error_body = raw_error_body.decode("utf-8", errors="replace")
+        except DiscordAPIError as too_large:
+            error_body = too_large.body
         except Exception:
             pass
         raise DiscordAPIError(e.code, error_body) from e
 
 
-class DiscordAPIError(Exception):
-    """Raised when a Discord API call fails."""
-    def __init__(self, status: int, body: str):
-        self.status = status
-        self.body = body
-        super().__init__(f"Discord API error {status}: {body}")
-
-
 # ---------------------------------------------------------------------------
 # Channel type mapping
 # ---------------------------------------------------------------------------