Fix proxy statistics

[dimitar-kostadinov]

If registry is configured as pull through cache the reported proxy statistics are incorrect.
Fixes #4044.

[milosgajdos]

@dimitar-kostadinov mind rebasing?

[ialidzhikov]

@milosgajdos PR is rebased. Can you have a look? Thank you in advance!

[milosgajdos]

@ialidzhikov sorry, been swamped with work, aiming to have a proper look this week, but can't promise anything I'm afraid

[ialidzhikov]

@milosgajdos , a friendly ping. We would like to proceed with the monitoring story on our side.

[milosgajdos]

this needs a rebase @dimitar-kostadinov

[Jamstah]

Again, no tests and not a well tested area, so I'd appreciate a quick "proof of test" message.

[dimitar-kostadinov]

Again, no tests and not a well tested area, so I'd appreciate a quick "proof of test" message.

Basic unit tests added.

Here are the manual steps for validation:

• Checkout this PR gh pr checkout 4045
• Start registry as pull through cache

# build
% make binaries
# prepare configuration
% mkdir -p ~/registry-test
% export REGISTRY_STORAGE_FILESYSTEM_ROOTDIRECTORY=~/registry-test
% export REGISTRY_PROXY_REMOTEURL=https://registry-1.docker.io
% export REGISTRY_HTTP_ADDR=":5500"
% export REGISTRY_HTTP_DEBUG_ADDR=":5501"
# start the registry as proxy cache to docker.io
% ./bin/registry serve cmd/registry/config-dev.yml

• Configure docker to use registry mirror

{
  "registry-mirrors": [
    "http://test.registry.mirror:5500"
  ]
}

• Update /etc/hosts file with following record

echo '127.0.0.1 test.registry.mirror' >> /etc/host

• Pull nginx image % docker pull nginx
• Get the expvars metrics

% curl http://test.registry.mirror:5501/debug/vars | jq '.registry.proxy'
{
  "blobs": {
    "Requests": 8,
    "Hits": 0,
    "Misses": 8,
    "BytesPulled": 67238076,
    "BytesPushed": 67238076
  },
  "manifests": {
    "Requests": 3,
    "Hits": 1,
    "Misses": 2,
    "BytesPulled": 3640,
    "BytesPushed": 5502
  }
}

• Remove nginx from docker % docker rmi nginx and pull it again % docker pull nginx (from mirror)
• Get the expvars metrics again

% curl http://test.registry.mirror:5501/debug/vars | jq '.registry.proxy'
{
  "blobs": {
    "Requests": 16,
    "Hits": 8,
    "Misses": 8,
    "BytesPulled": 67238076,
    "BytesPushed": 134476152
  },
  "manifests": {
    "Requests": 6,
    "Hits": 4,
    "Misses": 2,
    "BytesPulled": 3640,
    "BytesPushed": 11004
  }
}

[ialidzhikov]

@Jamstah, can you check again?

[ialidzhikov]

HI folks,

Can someone else have a look so that we proceed with the PR? Thank in advance!

[Jamstah]

Thanks for the test results (and the rest of the PR!). Code looks good.