Upgrade: tcp (HTTP)

[1] Docker Remote API v1.19 - Docker (2016-11-17 10:13:12 +09:00) <https://docs.docker.com/engine/reference/api/docker_remote_api_v1.19/>

Example request:
GET /containers/4fa6e0f0c678/logs?stderr=1&stdout=1&timestamps=1&follow=1&tail=10&since=1428990821 HTTP/1.1
Example response:
HTTP/1.1 101 UPGRADED
Content-Type: application/vnd.docker.raw-stream
Connection: Upgrade
Upgrade: tcp
{{ STREAM }}

[2] Docker Remote API v1.19 - Docker (2016-11-17 10:13:12 +09:00) <https://docs.docker.com/engine/reference/api/docker_remote_api_v1.19/>

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 }}

[3] Docker Remote API v1.19 - Docker (2016-11-17 10:13:12 +09:00) <https://docs.docker.com/engine/reference/api/docker_remote_api_v1.19/>

In this version of the API, /attach, uses hijacking to transport stdin, stdout, and stderr on the same socket.
To hint potential proxies about connection hijacking, Docker client sends connection upgrade headers similarly to websocket.
Upgrade: tcp
Connection: Upgrade
When Docker daemon detects the Upgrade header, it switches its status code from 200 OK to 101 UPGRADED and resends the same headers.