Python: Issue with MCP integration for tools that return image content

[egeozanozyedek]

Where: agent_framework/_mcp.py, function _mcp_type_to_ai_content, here

Problem:
When converting MCP ImageContent or AudioContent to DataContent, the raw base64 data from mcp_type.data is passed directly to the uri parameter:

case types.ImageContent() | types.AudioContent():
    return_types.append(
        DataContent(
            uri=mcp_type.data,  # Raw base64 string
            media_type=mcp_type.mimeType,
            raw_representation=mcp_type,
        )
    )

Per the MCP specification, ImageContent.data contains only the raw base64-encoded data, and not passed as a uri. However, DataContent expects uri to be a valid in the format data:{media_type};base64,{base64_data}.

When an MCP tool returns raw base64 data, this conversion leads to a ValueError because of the validated_uri = self._validate_uri(uri) line in DataContent.

Fix:

Use the preexisting data parameter which accepts raw bytes and builds the URI automatically (I think this is quick and graceful):

import base64
DataContent(
    data=base64.b64decode(mcp_type.data),
    media_type=mcp_type.mimeType,
    raw_representation=mcp_type,
)