BerriAI/litellm · error · TypeError

aretrieve_container_file_content expected bytes, got {type(c

Error message

aretrieve_container_file_content expected bytes, got {type(content).__name__}

What it means

TypeError raised inside the container file-content handler in litellm/proxy/container_endpoints/handler_factory.py when aretrieve_container_file_content returns a value that is not bytes. The handler must build a FastAPI Response(content=...) with raw bytes; a str or None from the provider transformation layer violates that contract. This is an internal invariant failure, typically caused by a provider transformation or a custom/mock handler returning decoded text.

Source

Thrown at litellm/proxy/container_endpoints/handler_factory.py:248

        content_type = "application/octet-stream"
        file_id_lower: Final = file_id.lower()
        if ".png" in file_id_lower or file_id_lower.endswith("png"):
            content_type = "image/png"
        elif ".jpg" in file_id_lower or ".jpeg" in file_id_lower:
            content_type = "image/jpeg"
        elif ".gif" in file_id_lower:
            content_type = "image/gif"
        elif ".csv" in file_id_lower:
            content_type = "text/csv"
        elif ".json" in file_id_lower:
            content_type = "application/json"
        elif ".txt" in file_id_lower:
            content_type = "text/plain"
        elif ".pdf" in file_id_lower:
            content_type = "application/pdf"

        if not isinstance(content, bytes):
            raise TypeError(f"aretrieve_container_file_content expected bytes, got {type(content).__name__}")

        return Response(
            content=content,
            headers=dict(fastapi_response.headers),
            media_type=content_type,
        )

    except Exception as e:
        raise await processor._handle_llm_api_exception(
            e=e,
            user_api_key_dict=user_api_key_dict,
            proxy_logging_obj=proxy_logging_obj,
            version=version,
        )


async def _process_multipart_upload_request(
    request: Request,

View on GitHub (pinned to 77b7c6c40c)

Solutions

Check litellm version and upgrade — report the provider + file type to the LiteLLM maintainers if it reproduces on the latest release.
If you control the transformation/handler, ensure the content is encoded: content.encode('utf-8') or the raw bytes from the HTTP response.
As a workaround for binary retrieval, call the provider's file-content endpoint directly rather than through the proxy container route.

Defensive patterns

Strategy: type-guard

Validate before calling

# Server-side: verify before building the Response
content = await provider_handler.aretrieve_container_file_content(...)
if not isinstance(content, bytes):
    content = content.encode("utf-8") if isinstance(content, str) else bytes(content)

Type guard

def is_bytes_payload(content: object) -> bool:
    return isinstance(content, (bytes, bytearray, memoryview))

Try / catch

try:
    data = await client.get(f"/v1/containers/{cid}/files/{fid}/content")
except TypeError as e:
    if "expected bytes" in str(e):
        # proxy/provider contract broken: report, don't retry blindly
        capture_diagnostics(cid, fid, litellm_version)
    raise

Prevention

Pin the LiteLLM version in production and test container file retrieval after upgrades.
In custom provider transformations, always return response.content (bytes) from the upstream HTTP response.
Report reproducible type errors upstream with provider, file type, and version instead of working around them silently.

When it happens

Trigger: GET /v1/containers/{container_id}/files/{file_id}/content where the underlying provider handler returns str (e.g. text decoded upstream) or None instead of bytes; a custom handler_factory wrapper that transforms the provider response; Azure/OpenAI file-content transformation returning the wrong type in a specific LiteLLM version.

Common situations: Hitting the bug after a LiteLLM upgrade changed a transformation's return type; mocking aretrieve_container_file_content in tests with a string payload; a provider returning an empty/JSON-encoded body that the transformation layer passes through un-decoded.

Related errors

AI-assisted analysis of BerriAI/litellm@77b7c6c40c (2026-08-18). Data as JSON: /api/errors/c80db9411a0eea6a. Report an issue: GitHub.