multi-transport-agent

Multi-Transport Agent

This sample exposes a single A2A agent over all three transports supported by the SDK simultaneously:

Transport	URL
JSON-RPC	http://localhost:41241/a2a/jsonrpc
HTTP+JSON/REST	http://localhost:41241/a2a/rest (then <operation>, e.g. message:send)
gRPC	localhost:41242
Agent Card	http://localhost:41241/.well-known/agent-card.json

The same DefaultRequestHandler instance backs every transport, so the business logic is written exactly once. The agent card declares all three interfaces in supportedInterfaces, allowing ClientFactory to pick whichever transport the client prefers.

Running

npm run agents:multi-transport-agent

You should see:

[MultiTransportAgent] HTTP server started on http://localhost:41241
  JSON-RPC : http://localhost:41241/a2a/jsonrpc
  REST     : http://localhost:41241/a2a/rest
  Card     : http://localhost:41241/.well-known/agent-card.json
[MultiTransportAgent] gRPC server started on localhost:41242

Talking to the agent

Using the bundled CLI (auto-discovery)

The cli.ts sample inspects the agent card and picks the first matching transport. Force a specific one with --transport=:

# JSON-RPC (default preference order)
npm run a2a:cli http://localhost:41241

# REST
npm run a2a:cli http://localhost:41241 -- --transport=HTTP+JSON

# gRPC
npm run a2a:cli http://localhost:41241 -- --transport=GRPC

Direct REST request

REST routes are exposed by the SDK's restHandler at the operation paths defined in A2A Specification §11.3 (URL Patterns and HTTP Methods) — for example POST /message:send, POST /message:stream, GET /tasks/{id}, POST /tasks/{id}:cancel. There is no version prefix: mounting restHandler at /a2a/rest therefore yields full paths such as /a2a/rest/message:send. The body is the JSON wire form of SendMessageRequest. REST returns the bare result object — there is no JSON-RPC envelope. The A2A-Version header is required; if it is omitted the binding defaults to 0.3 and the agent rejects the request with VERSION_NOT_SUPPORTED.

curl -sS -X POST http://localhost:41241/a2a/rest/message:send \
  -H 'Content-Type: application/json' \
  -H 'A2A-Version: 1.0' \
  -d '{
    "message": {
      "messageId": "demo-1",
      "role": "ROLE_USER",
      "parts": [{ "text": "hello", "mediaType": "text/plain" }]
    }
  }'

Direct JSON-RPC request

curl -sS -X POST http://localhost:41241/a2a/jsonrpc \
  -H 'Content-Type: application/json' \
  -H 'A2A-Version: 1.0' \
  -d '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "SendMessage",
    "params": {
      "message": {
        "messageId": "demo-2",
        "role": "ROLE_USER",
        "parts": [{ "text": "hello", "mediaType": "text/plain" }]
      }
    }
  }'

Configuration

Variable	Default	Description
HTTP_PORT	41241	JSON-RPC + REST + AgentCard
GRPC_PORT	41242	gRPC service