Transport-agnostic JSON-RPC 2.0 dispatch layer for the A2A protocol.

Defines a handler behaviour and a handle/3 function that parses JSON-RPC envelopes, validates params, and dispatches to the handler module.

Handler behaviour

Three callbacks are required — every A2A server answers these methods:

defmodule MyHandler do
  @behaviour A2A.JSONRPC

  @impl true
  def handle_send(message, params, context) do
    # process the message, return {:ok, task}, {:ok, message}, or
    # {:error, error} — `SendMessageResponse` is a Task/Message oneof
  end

  @impl true
  def handle_get(task_id, params, context) do
    # look up the task
  end

  @impl true
  def handle_cancel(task_id, params, context) do
    # cancel the task
  end
end

Five more are optional, and each has a defined answer when absent:

• handle_list/2 serves tasks/list. Without it that method answers -32601, method not found.
• handle_set_push_config/3, handle_get_push_config/4, handle_list_push_configs/3 and handle_delete_push_config/4 serve the four tasks/pushNotificationConfig/* methods. Without them those answer -32003, push notifications not supported.

Presence is checked per request with Code.ensure_loaded?/1 and function_exported?/3, so a handler implementing none of the optional callbacks behaves exactly as it did before they existed.

Dispatching

case A2A.JSONRPC.handle(decoded_body, MyHandler) do
  {:reply, response_map} -> send_json(response_map)
  {:stream, method, params, id} -> start_sse(method, params, id)
end

The third argument to handle/3 is a context map, threaded unchanged to every callback, which transports use to pass per-request data.