# Attach to a container

`POST /containers/(id)/attach`

Attach to the container `id`

**Example request**:

```
POST /containers/16253994b7c4/attach?logs=1&stream=0&stdout=1 HTTP/1.1
```

**Example response**:

```
HTTP/1.1 101 UPGRADED
Content-Type: application/vnd.docker.raw-stream
Connection: Upgrade
Upgrade: tcp

{{ STREAM }}
```

Query Parameters:

* **detachKeys** – Override the key sequence for detaching a container. 
* **logs** – 1/True/true or 0/False/false, return logs. Default `false`.
* **stream** – 1/True/true or 0/False/false, return stream.  Default `false`.
* **stdin** – 1/True/true or 0/False/false, if `stream=true`, attach to `stdin`. Default `false`.
* **stdout** – 1/True/true or 0/False/false, if `logs=true`, return `stdout` log, if `stream=true`, attach to `stdout`. Default `false`.
* **stderr** – 1/True/true or 0/False/false, if `logs=true`, return `stderr` log, if `stream=true`, attach to `stderr`. Default `false`.

Status Codes:

* **101** – no error, hints proxy about hijacking
* **200** – no error, no upgrade header found
* **400** – bad parameter
* **404** – no such container
* **500** – server error

  **Stream details**:

  When using the TTY setting is enabled in [`POST /containers/create` ](#create-a-container), the stream is the raw data from the process PTY and client's `stdin`. When the TTY is disabled, then the stream is multiplexed to separate `stdout` and `stderr`.

  The format is a **Header** and a **Payload** (frame).

  **HEADER**

  The header contains the information which the stream writes (`stdout` or `stderr`). It also contains the size of the associated frame encoded in the last four bytes (`uint32`).

  It is encoded on the first eight bytes like this:

  ```
  header := [8]byte{STREAM_TYPE, 0, 0, 0, SIZE1, SIZE2, SIZE3, SIZE4}
  ```

  `STREAM_TYPE` can be:
* 0: `stdin` (is written on `stdout`)
* 1: `stdout`
* 2: `stderr`

  `SIZE1, SIZE2, SIZE3, SIZE4` are the four bytes of the `uint32` size encoded as big endian.

  **PAYLOAD**

  The payload is the raw stream.

  **IMPLEMENTATION**

  The simplest way to implement the Attach protocol is the following:

  1. Read eight bytes.
  2. Choose `stdout` or `stderr` depending on the first byte.
  3. Extract the frame size from the last four bytes.
  4. Read the extracted size and output it on the correct output.
  5. Goto 1.