Behaviour definition for MCP transport implementations.

A transport is responsible for sending and receiving MCP protocol messages over a specific communication channel. ExMCP includes implementations for the standard MCP transports and provides this behaviour for custom implementations.

Built-in Transports

ExMCP provides these standard transports:

• :stdio - Standard I/O communication (MCP specification)
• :http - HTTP with optional SSE streaming (MCP specification)
• :test - In-memory transport for testing
• :beam - JSON-compliant transport for BEAM-to-BEAM communication.
• :native - High-performance transport for BEAM-to-BEAM communication using raw Elixir terms.

Using Transports

Transports are specified when starting clients or servers:

# stdio transport
{:ok, client} = ExMCP.Client.start_link(
  transport: :stdio,
  command: ["python", "mcp-server.py"]
)

# HTTP transport
{:ok, client} = ExMCP.Client.start_link(
  transport: :http,
  url: "https://api.example.com"
)

Custom Transport Implementation

To implement a custom transport, create a module that implements all the callbacks defined in this behaviour:

defmodule MyTransport do
  @behaviour ExMCP.Transport

  @impl true
  def connect(opts) do
    # Establish connection
    {:ok, state}
  end

  @impl true
  def send_message(message, state) do
    # Send the message
    {:ok, state}
  end

  @impl true
  def receive_message(state) do
    # Receive a message (blocking)
    {:ok, message, state}
  end

  @impl true
  def close(state) do
    # Clean up
    :ok
  end
end