glb + docker 20.10.2 errors

[matti]

invalid from flag value my-glb-host.name.com/libjpeg-turbo:2020-08-25-1: missing or empty Content-Length header

if I downgrade to 19.03 docker it works fine.

[tobias-kuendig]

It looks like Cloud Run removes the Content-Length header by default, which Docker 20.10 does no longer accept.

[tobias-kuendig]

By looking at the relevant Docker code, I did stumble upon these lines:
https://github.com/docker/distribution/blob/master/registry/client/repository.go#L333

It looks like Google Cloud Run strips the Content-Length header for HEAD requests, but not GET. By returning an error on HEAD requests, we force Docker to re-try using a GET request.

Definitely not a nice workaround, but it works for the time being:
OFFLINE-GmbH@6c98a08

Optimized implementation:
OFFLINE-GmbH/serverless-registry-proxy@445a0e2...OFFLINE-GmbH:932d954875fc798486ddfe5f4909f1f06761665b