Behaviour for handling MCP server notifications and requests.

When a server sends notifications (like list_changed events) or requests (like ping or sampling), they are dispatched to a notification handler if one is configured.

Implementing a Handler

defmodule MyApp.MCPHandler do
  @behaviour Hermolaos.Client.NotificationHandler

  @impl true
  def handle_notification({:notification, "notifications/tools/list_changed", _params}, state) do
    IO.puts("Tools list changed!")
    {:ok, state}
  end

  def handle_notification({:notification, method, params}, state) do
    IO.puts("Got notification: #{method}")
    {:ok, state}
  end

  def handle_notification({:request, "ping", _params}, state) do
    # ping is handled automatically, but you can observe it
    {:ok, state}
  end

  def handle_notification(_event, state) do
    {:ok, state}
  end
end

Using the Handler

{:ok, conn} = Hermolaos.Client.Connection.start_link(
  transport: :stdio,
  command: "my-server",
  notification_handler: {MyApp.MCPHandler, %{}}
)

Event Types

Events are tuples with one of these formats:

• {:notification, method, params} - Server notification
• {:request, method, params} - Server request (ping, sampling, etc.)

Common Notifications

• notifications/tools/list_changed - Available tools changed
• notifications/resources/list_changed - Available resources changed
• notifications/resources/updated - A specific resource was updated
• notifications/prompts/list_changed - Available prompts changed
• notifications/progress - Progress update for long operation
• notifications/message - Log message from server