microsoft/autogen · error · ValueError

Unsupported message content type: {message_content_type}

Error message

Unsupported message content type: {message_content_type}

What it means

When a CloudEvent arrives, GrpcWorkerAgentRuntime._process_event deserializes the payload according to the event's datacontenttype. Only JSON_DATA_CONTENT_TYPE and PROTOBUF_DATA_CONTENT_TYPE are recognized; any other content type raises ValueError('Unsupported message content type: ...') and the event is dropped (logged as a read-loop/background-task error).

Source

Thrown at python/packages/autogen-ext/src/autogen_ext/runtimes/grpc/_worker_runtime.py:634

        topic_id = TopicId(event.type, event.source)
        # Get the recipients for the topic.
        recipients = await self._subscription_manager.get_subscribed_recipients(topic_id)

        message_content_type = event_attributes[_constants.DATA_CONTENT_TYPE_ATTR].ce_string
        message_type = event_attributes[_constants.DATA_SCHEMA_ATTR].ce_string

        if message_content_type == JSON_DATA_CONTENT_TYPE:
            message = self._serialization_registry.deserialize(
                event.binary_data, type_name=message_type, data_content_type=message_content_type
            )
        elif message_content_type == PROTOBUF_DATA_CONTENT_TYPE:
            # TODO: find a way to prevent the roundtrip serialization
            proto_binary_data = event.proto_data.SerializeToString()
            message = self._serialization_registry.deserialize(
                proto_binary_data, type_name=message_type, data_content_type=message_content_type
            )
        else:
            raise ValueError(f"Unsupported message content type: {message_content_type}")

        # TODO: dont read these values in the runtime
        topic_type_suffix = topic_id.type.split(":", maxsplit=1)[1] if ":" in topic_id.type else ""
        is_rpc = topic_type_suffix == _constants.MESSAGE_KIND_VALUE_RPC_REQUEST
        is_marked_rpc_type = (
            _constants.MESSAGE_KIND_ATTR in event_attributes
            and event_attributes[_constants.MESSAGE_KIND_ATTR].ce_string == _constants.MESSAGE_KIND_VALUE_RPC_REQUEST
        )
        if is_rpc and not is_marked_rpc_type:
            warnings.warn("Received RPC request with topic type suffix but not marked as RPC request.", stacklevel=2)

        # Send the message to each recipient.
        responses: List[Awaitable[Any]] = []
        for agent_id in recipients:
            if agent_id == sender:
                continue
            message_context = MessageContext(
                sender=sender,

View on GitHub (pinned to 027ecf0a37)

Solutions

Make all producers use one of the supported formats: configure payload_serialization_format with the JSON_DATA_CONTENT_TYPE or PROTOBUF_DATA_CONTENT_TYPE constant, not a free-form string
Pin all workers to compatible autogen-ext versions so content types agree
If external systems inject CloudEvents, convert their payloads to application/json before they reach subscribed workers

Example fix

# before (producer side)
runtime = GrpcWorkerAgentRuntime(host, payload_serialization_format="application/vnd.custom")

# after
from autogen_ext.runtimes.grpc._constants import JSON_DATA_CONTENT_TYPE
runtime = GrpcWorkerAgentRuntime(host, payload_serialization_format=JSON_DATA_CONTENT_TYPE)

Defensive patterns

Strategy: validation

Validate before calling

from autogen_ext.runtimes.grpc._constants import JSON_DATA_CONTENT_TYPE, PROTOBUF_DATA_CONTENT_TYPE

SUPPORTED = {JSON_DATA_CONTENT_TYPE, PROTOBUF_DATA_CONTENT_TYPE}

# verify config of every producer before start
assert runtime_payload_format in SUPPORTED, "all workers must use a supported content type"

Try / catch

try:
    await runtime.publish_message(msg, topic)
except ValueError as e:
    # note: content-type rejection happens on the receiving worker; catch there:
    # errors surface via background-task logging — monitor logs for 'Unsupported message content type'
    raise

Prevention

Standardize payload_serialization_format across all workers via shared config
Use the module constants instead of literal strings
Pin all workers and the host to the same autogen-ext version
Monitor worker logs for read-loop errors to catch mismatched producers

When it happens

Trigger: Another worker or host publishes a CloudEvent with datacontenttype set to something other than application/json or application/x-protobuf while this worker is subscribed to the topic — e.g. a producer with a different payload_serialization_format, or an external event injected into the host.

Common situations: Mixing worker versions or configs where one uses JSON and another a custom/protobuf-ish MIME string; publishing events into the host from non-AutoGen producers; typos in content-type strings.

Related errors

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/1b3859217f8c8428. Report an issue: GitHub.