I am running a contianer I did not build that writes a binary to standard output. For this situation, it would be very useful to add a filename field to the Docker build step that standard output/error/other file descriptors can be redirected to.

Furthermore, since container output may not be desirable in the build log (in my case it is an ELF binary, which will just bloat the log size for no reason, but you could say the same about outputs that contain secrets or other sensitive information) it would also be nice to have a toggle to enable/disable showing the output of that FD in the build log. In my case, stderr contains the build output, while stdout contains the binary, so I would still want to see the former.

The alternative of this is of course mounting the Docker socket and running docker manually, but this may not be optimal for all users. If that's the recommended path however, it should be clarified in the docs.

Regards.

P.S.: I originally sent this as an email but it looks like it didn't go through.