Docker export could break post-hooks

[lukemarsden]

It's a sad fact that you can't encode arbitrary binary data as a JSON string (because JSON strings are UTF-8-encoded unicode and some binary isn't valid UTF-8... right?) so any responses which could include arbitrary binary data could break the post-hooks, such as docker export which claims to respond with application/tar.

This is a limitation of the v1 powerstrip protocol. A workaround could be to detect the content-type and skip the post-hooks.