fix: Truncate HttpError message to first 8192 characters (#5020)

Signed-off-by: Phillippe Siclait <546332+siclait@users.noreply.github.com>

lib/bindings/python/rust/http.rs

@@ -138,6 +138,12 @@ impl HttpAsyncEngine {
     }
 }
 
+#[derive(FromPyObject)]
+struct HttpError {
+    code: u16,
+    message: String,
+}
+
 #[async_trait]
 impl<Req, Resp> AsyncEngine<SingleIn<Req>, ManyOut<Annotated<Resp>>, Error> for HttpAsyncEngine
 where
@@ -153,18 +159,10 @@ where
             Err(e) => {
                 if let Some(py_err) = e.downcast_ref::<PyErr>() {
                     Python::with_gil(|py| {
-                        let err_val = py_err.clone_ref(py).into_value(py);
-                        let bound_err = err_val.bind(py);
-
-                        // check: Py03 exceptions cannot be cross-compiled, so we duck-type by name
-                        // and fields.
-                        if let Ok(type_name) = bound_err.get_type().name()
-                            && type_name.to_string().contains("HttpError")
-                            && let (Ok(code), Ok(message)) =
-                                (bound_err.getattr("code"), bound_err.getattr("message"))
-                            && let (Ok(code), Ok(message)) =
-                                (code.extract::<u16>(), message.extract::<String>())
-                        {
+                        // With the Stable ABI, we can't subclass Python's built-in exceptions in PyO3, so instead we
+                        // implement the exception in Python and assume that it's an HttpError if the code and message
+                        // are present.
+                        if let Ok(HttpError { code, message }) = py_err.value(py).extract() {
                             // SSE panics if there are carriage returns or newlines
                             let message = message.replace(['\r', '\n'], "");
                             return Err(http_error::HttpError { code, message })?;

lib/bindings/python/src/dynamo/llm/exceptions.py

@@ -3,13 +3,33 @@
 
 # flake8: noqa
 
+import logging
+
+logger = logging.getLogger(__name__)
+
+_MAX_MESSAGE_LENGTH = 8192
+
 
 class HttpError(Exception):
     def __init__(self, code: int, message: str):
-        if not (isinstance(code, int) and 0 <= code < 600):
+        # These ValueErrors are easier to trace to here than the TypeErrors that
+        # would be raised otherwise.
+        if not isinstance(code, int) or isinstance(code, bool):
+            raise ValueError("HttpError status code must be an integer")
+
+        if not isinstance(message, str):
+            raise ValueError("HttpError message must be a string")
+
+        if not (0 <= code < 600):
             raise ValueError("HTTP status code must be an integer between 0 and 599")
-        if not (isinstance(message, str) and 0 < len(message) <= 8192):
-            raise ValueError("HTTP error message must be a string of length <= 8192")
+
+        if len(message) > _MAX_MESSAGE_LENGTH:
+            logger.warning(
+                f"HttpError message length {len(message)} exceeds max length {_MAX_MESSAGE_LENGTH}, truncating..."
+            )
+            message = message[: (_MAX_MESSAGE_LENGTH - 3)] + "..."
+
         self.code = code
         self.message = message
+
         super().__init__(f"HTTP {code}: {message}")

lib/bindings/python/tests/test_http_error.py

@@ -18,3 +18,19 @@ def test_raise_http_error():
 def test_invalid_http_error_code():
     with pytest.raises(ValueError):
         HttpError(1700, "Invalid Code")
+
+
+def test_invalid_http_error_message():
+    with pytest.raises(ValueError):
+        # The second argument must be a string, not bytes.
+        HttpError(400, b"Bad Request")
+
+
+def test_long_http_error_message():
+    message = ("A" * 8192) + "B"
+    error = HttpError(400, message)
+    assert len(error.message) == 8192
+
+    # Ensure the exception string uses the truncated message too.
+    assert message[:8189] in str(error)
+    assert "B" not in str(error)