Description

Docker attach API do use application/vnd.docker.raw-stream content type, which has two implementations:

• multiplexed stdout/stderr streams
• raw tty output

from API response there's no way (afaict) to determine which one is used
I suggest a header is introduced to document which mode is being used

Steps to reproduce the issue:

1. ask a friend to create a container, setting tty= to a random value kept secret
2. invoke containers/{id}/attach
3. try to guess the raw.stream format in use

Describe the results you received:

have to try parsing a multiplexed frame, then admit I was wrong.

Describe the results you expected:

simple way to determine the parsing logic to use