Is there a reason why `client.images.build` doesn't stream output logs ?

Seems to be a recurrent question. I looked at the code and it seems to me there is no reason why the higher-level API generator couldn't return the output logs as they come. This could be achieved by using a sort of fake future for the image object returned by the build function. Something like that (very rough sketch) :

    def build(self, **kwargs):
        resp = self.client.api.build(**kwargs)
        if isinstance(resp, six.string_types):
            return self.get(resp)
        last_event = None
        image_id = None
        result_stream, internal_stream = itertools.tee(json_stream(resp))
        
        result = {}

        def gen():
            for chunk in internal_stream:
                if 'error' in chunk:
                    raise BuildError(chunk['error'], result_stream)
                if 'stream' in chunk:
                    match = re.search(
                        r'(^Successfully built |sha256:)([0-9a-f]+)$',
                        chunk['stream']
                    )
                    if match:
                        image_id = match.group(2)
                    else:
                        yield chunk
                last_event = chunk
            
            if image_id:
                result['image'] = self.get(image_id)
            else:
                raise BuildError(last_event or 'Unknown', result_stream)

        return result, gen()

Maybe this could be switched-on by adding an option to build for example stream_output ?

And this can be used like this :

    image, output_iter = docker_client.images.build(fileobj=fd, tag=args.tag)

    for line in output_iter:
        print(line)
    
    print(image)

Of course the nicer solution for that would be to use asyncio but that's then becoming more complicated :P

Start by reviewing the higher-level client.images.build path and the client.api.build response handling described in the issue. Determine how output can be yielded while retaining the final image result and BuildError details; done means build logs are available incrementally without breaking existing image retrieval behavior.