56 lines
1.9 KiB
Go
56 lines
1.9 KiB
Go
// Package registry looks up the digest a tag points at in a container
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// registry, using HEAD requests only.
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package registry
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import (
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"context"
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"fmt"
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"github.com/google/go-containerregistry/pkg/authn"
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"github.com/google/go-containerregistry/pkg/name"
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"github.com/google/go-containerregistry/pkg/v1/remote"
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"github.com/shcizo/package-updater/internal/imageref"
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)
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// Client looks up tag digests with HEAD requests only. Docker Hub counts a
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// GET of a manifest as a pull against the rate limit and a HEAD as nothing,
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// so Client never issues a manifest GET.
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type Client struct {
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keychain authn.Keychain
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userAgent string
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}
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// New returns a Client that finds credentials the way the Docker CLI does:
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// in $DOCKER_CONFIG/config.json, else ~/.docker/config.json. Registries
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// without an entry are accessed anonymously. userAgent is added to the
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// User-Agent header of every request.
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func New(userAgent string) *Client {
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return &Client{keychain: authn.DefaultKeychain, userAgent: userAgent}
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}
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// Digest returns the digest that "repo:tag" points at, as the registry
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// reports it: for a multi-arch image that is the digest of the index, the
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// same one `docker inspect` shows in RepoDigests. A digest suffix in ref is
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// ignored. It sends HEAD /v2/<repo>/manifests/<tag> and nothing else to the
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// manifest endpoint; it does not fall back to GET when the registry omits
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// the digest header.
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func (c *Client) Digest(ctx context.Context, ref string) (string, error) {
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p := imageref.Parse(ref)
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if p.Tag == "" {
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return "", fmt.Errorf("image %q has no tag", ref)
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}
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r, err := name.ParseReference(p.Repo + ":" + p.Tag)
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if err != nil {
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return "", fmt.Errorf("parse %s: %w", ref, err)
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}
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desc, err := remote.Head(r,
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remote.WithContext(ctx),
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remote.WithAuthFromKeychain(c.keychain),
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remote.WithUserAgent(c.userAgent))
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if err != nil {
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return "", fmt.Errorf("head %s: %w", r, err)
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}
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return desc.Digest.String(), nil
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}
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