# `Anubis.Transport`

Functional behaviour for MCP transport implementations.

Unlike `Anubis.Transport.Behaviour` (which defines a GenServer-oriented transport
interface), this behaviour defines a **functional** transport interface for
parsing, encoding, sending messages, and extracting metadata.

Transport modules implementing this behaviour provide pure functions for
message framing — the actual I/O process (Port, Plug conn, SSE handler) already
exists and calls these functions internally.

## Adapters

- `Anubis.Transport.STDIO` — newline-delimited JSON over stdin/stdout (client)
- `Anubis.Transport.StreamableHTTP` — JSON over HTTP request/response bodies (client)
- `Anubis.Transport.SSE` — JSON wrapped in SSE event format (client)

## Example

    {:ok, state} = MyTransport.transport_init(opts)
    {:ok, message, state} = MyTransport.parse(raw_data, state)
    {:ok, encoded, state} = MyTransport.encode(response, state)

# `raw_message`

```elixir
@type raw_message() :: binary()
```

# `transport_state`

```elixir
@type transport_state() :: term()
```

# `encode`

```elixir
@callback encode(message :: map(), transport_state()) ::
  {:ok, raw_message(), transport_state()} | {:error, term()}
```

Encode an MCP message map for this transport's wire format.

Returns the encoded binary ready to be sent.

# `extract_metadata`

```elixir
@callback extract_metadata(raw_input :: term(), transport_state()) :: map()
```

Extract transport-specific metadata from raw input.

For HTTP, this extracts session_id from headers, request context, etc.
For STDIO, this returns basic process metadata.

# `parse`

```elixir
@callback parse(raw_message() | map(), transport_state()) ::
  {:ok, [map()], transport_state()} | {:error, term()}
```

Parse raw input into decoded MCP message(s).

For STDIO, raw input is newline-delimited JSON.
For HTTP, raw input is a JSON body string or already-parsed map.
For SSE, raw input is SSE event data.

# `transport_init`

```elixir
@callback transport_init(keyword()) :: {:ok, transport_state()} | {:error, term()}
```

Initialize transport-specific state (parse options, configure connection).

---

*Consult [api-reference.md](api-reference.md) for complete listing*