We are trying to setup our registry to act as a proxy to several ECR registries.
We have a registry middleware where the Repository method fetches credentials to allow pushing that specific tag.

Depending on the tag's pattern, the credentials will point to an ECR registry or another, returning a distribution.Repository struct where the baseURL is the URL to the appropriate registry and the transport contains our authentication parameters, expending on the registry proxy work.

This works well outside of a few small issues.

• Blob Resume is not implemented for repositories.
• ServeBlob is not implemented for repositories.
• httpBlobUpload's ReadFrom and Write methods don't increment the offset when writing data, making the Size method return invalid values.
• ECR doesn't return the Docker-Upload-UUID HTTP header preventing Repository Blob Create from properly reading it, and from later on generating the Location URL.

Above are linked 3 PRs providing solutions for those issues. I am happy to work toward making any changes you will see fit to be happy landing those PRs.

As a side one, I have also opened a PR adding tests for httpBlobUpload's Write method.