Demux stdout and stderr from result of attach() command

[sanathkr]

When I run container.attach(stdout=True, stderr=True, stream=True, logs=True), the resulting generator contains the output of stdout and stderr multiplexed into one string. I would like to separate to get stdout and stderr in separate generators (or) streams.

I know the Go SDK contains a stdcopy.StdCopy precisely for the purpose of demuxing the output given a raw socket. I would like to implement something similar for the Docker Python SDK as well.

I need this for my project, so I am going to implement anyway, but would you be open to the idea of my contributing the patch back to this project? Actually most of the functionality is already implemented in socket.py. Instead of discarding the frame type, I will pass it out and have the caller decide how to handle it. The attach() method will discard the type, whereas, a new docker.util.demuxSocketOutput(stdout_stream, stderr_stream) will write the output to respective the streams.

Would you be open to this idea? I send a PR.

[shin-]

I think it'd be a good feature to have, but I feel you may be overthinking the implementation a little bit. Why not add a demux parameter to attach() that, when set to True, returns a couple of (stdout_stream, stderr_stream)? That'd be simpler, more pythonic, and more in line with the way the rest of the library is written!

[sanathkr]

Love it! Instead of creating the stream inside attach(), how about letting the user pass the streams? Easier to unit test and users can pass any fancy stream they want - even sys.stdout/sys.stderr if they choose to:

def attach(**kwargs):
"""

If both `stdout_stream` and `stderr_stream` are not specified, then this method will return an iterator of output strings containing the contents of both stdout and stderr.

:param bool stdout: existing argument
:param bool stderr: existing argument
:param bool stream: existing argument
:param bool logs: existing argument
:param io.BaseIO stdout_stream: Optional stream where the stdout from Docker container is written to.
:param io.BaseIO stderr_stream: Optional stream where the stderr from Docker container is written to.
"""

[holiman]

I would really love to have this. Any progress? (for my usecase, on docker_exec )

[little-dude]

@holiman I've the same use case than yours. I've opened a PR for that if you want to try it out.