A2A Protocol Guardrail Translation Handler

Handler for processing A2A (Agent-to-Agent) Protocol messages with guardrails.

Overview

This handler processes A2A JSON-RPC 2.0 input/output by:

Extracting text from message parts (kind: "text")
Applying guardrails to text content
Mapping guardrailed text back to original structure

A2A Protocol Format

Input Format (JSON-RPC 2.0)

{
  "jsonrpc": "2.0",
  "id": "request-id",
  "method": "message/send",
  "params": {
    "message": {
      "kind": "message",
      "messageId": "...",
      "role": "user",
      "parts": [
        {"kind": "text", "text": "Hello, my SSN is 123-45-6789"}
      ]
    },
    "metadata": {
      "guardrails": ["block-ssn"]
    }
  }
}

Output Formats

The handler supports multiple A2A response formats:

Direct message:

{
  "result": {
    "kind": "message",
    "parts": [{"kind": "text", "text": "Response text"}]
  }
}

Nested message:

{
  "result": {
    "message": {
      "parts": [{"kind": "text", "text": "Response text"}]
    }
  }
}

Task with artifacts:

{
  "result": {
    "kind": "task",
    "artifacts": [
      {"parts": [{"kind": "text", "text": "Artifact text"}]}
    ]
  }
}

Task with status message:

{
  "result": {
    "kind": "task",
    "status": {
      "message": {
        "parts": [{"kind": "text", "text": "Status message"}]
      }
    }
  }
}

Streaming artifact-update:

{
  "result": {
    "kind": "artifact-update",
    "artifact": {
      "parts": [{"kind": "text", "text": "Streaming text"}]
    }
  }
}

Usage

The handler is automatically discovered and applied when guardrails are used with A2A endpoints.

Via LiteLLM Proxy

curl -X POST 'http://localhost:4000/a2a/my-agent' \
-H 'Content-Type: application/json' \
-H 'Authorization: Bearer your-api-key' \
-d '{
  "jsonrpc": "2.0",
  "id": "1",
  "method": "message/send",
  "params": {
    "message": {
      "kind": "message",
      "messageId": "msg-1",
      "role": "user",
      "parts": [{"kind": "text", "text": "Hello, my SSN is 123-45-6789"}]
    },
    "metadata": {
      "guardrails": ["block-ssn"]
    }
  }
}'

Specifying Guardrails

Guardrails can be specified in the A2A request via the metadata.guardrails field:

{
  "params": {
    "message": {...},
    "metadata": {
      "guardrails": ["block-ssn", "pii-filter"]
    }
  }
}

Extension

Override these methods to customize behavior:

_extract_texts_from_result(): Custom text extraction from A2A responses
_extract_texts_from_parts(): Custom text extraction from message parts
_apply_text_to_path(): Custom application of guardrailed text

Call Types

This handler is registered for:

CallTypes.send_message: Synchronous A2A message sending
CallTypes.asend_message: Asynchronous A2A message sending