Read indexServerAddress from Docker's /info

[bsideup]

Related to #5263
Fixes #5121

[gesellix]

You might be interested in this one: docker/cli#2819

I myself didn't have the time to adopt that change in my docker-client implementation - fetching the daemon's index server address still seems to work.

[bsideup]

@gesellix interesting, many thanks for sharing!

[kiview]

@gesellix Isn't the new approach just using a hardcoded value?
CLI is calling GetAuthConfigKey, which returns IndexServer:
https://github.com/docker/cli/blob/4cc4385075205409c835454f6e5055147d8495b4/vendor/github.com/docker/docker/registry/config.go#L406-L411

And IndexServer is just the hardcoded new format:
https://github.com/docker/cli/blob/4cc4385075205409c835454f6e5055147d8495b4/vendor/github.com/docker/docker/registry/config.go#L45

[bsideup]

FTR it looks like they hardcoded it to avoid calling /info (because it is considered expensive) but we call it anyways (to get the OS info and fail fast on Windows containers)

[gesellix]

Isn't the new approach just using a hardcoded value

Yes, that's my impression, too, and from reading the details I would assume that calling the /info endpoint was necessary in the early stages of Windows support, but has been obsolete for quite a while.

I wonder, though, if using the /info endpoint resolves the linked issues on testcontainer's side... using the daemon's indexServerAddress shouldn't hurt, but I would be surprised if the issues are resolved.

Maybe there's a little detail missing when handling the default index domains. As far as I know a client should handle both index.docker.io and docker.io as "default domain", meaning that the client should authenticate in both cases with the credentials for https://index.docker.io/v1/.

edit: I didn't find the issue before, but this is why I mentioned the "default domain": #4912 (comment) (which is related to #4474).

[thaJeztah]

👋 sorry for commenting on old PRs, but I was working on some changes in this area, and saw this PR linked to our repo.

FTR it looks like they hardcoded it to avoid calling /info (because it is considered expensive) but we call it anyways (to get the OS info and fail fast on Windows containers)

@bsideup The /info endpoint can indeed be "expensive" (depending on what's running on the daemon). If all you need is information about the daemon's platform, you could consider using the HEAD /_ping (or GET if HEAD is not an option) endpoint.

That endpoint should return some minimum amount of information in the Headers (API version supported, platform (windows / linux));

curl --unix-socket /var/run/docker.sock -I 'http://foo/_ping'
HTTP/1.1 200 OK
Api-Version: 1.43
Builder-Version: 2
Cache-Control: no-cache, no-store, must-revalidate
Content-Type: text/plain; charset=utf-8
Date: Tue, 11 Apr 2023 21:13:45 GMT
Docker-Experimental: false
Ostype: linux
Pragma: no-cache
Server: Docker/22.06.0-beta.0-926-g914b02ebaf.m (linux)
Swarm: active/manager