google ADK a2a SSE

Question

I implemented an agent to be called by an orchestrator using a2a. Both agents are running and the ADK works well with it, however since I have a long-lasting session on the sub-agent (called through a2a), I would like to send SSE messages about the progression of the task. I couldn't find examples of this application, although it is supported by a2a protocol using SSE ... from my investigation:

The A2A protocol fully supports streaming progress via Server-Sent Events (SSE):

• Method: message/stream RPC initiates a streaming connection
• Transport: Uses Content-Type: text/event-stream for SSE
• Event Types:
• TaskStatusUpdateEvent: Task state changes (submitted, working, completed, failed)
• TaskArtifactUpdateEvent: Incremental result delivery
• Event Structure: Each SSE event contains a JSON-RPC 2.0 Response with task updates
• Capability Flag: Agent cards must indicate capabilities.streaming: true The protocol is designed for this exact use case - real-time progress updates during long-running tasks.

Anyone tried this before? Any feedback of when this is going to be supported on ADK?

Answer 1

1. Custom SSE Implementation:
   You can implement a lightweight SSE endpoint on your sub-agent to stream task updates back to the orchestrator. The orchestrator can then subscribe to these updates using a simple HTTP EventSource. This works well as an interim solution until ADK provides native support.

2. Polling Workaround:
   Another workaround is to periodically poll the sub-agent for progress updates through a standard A2A message. While less efficient, it maintains compatibility with the current ADK.