mesh-catalog/modules/distribution/internal/holder/platforms.go

package holder

// **An index's platform manifests go with it, unless a kept index names them** (CAT-AS1: what the artifact sweep did
// over the store's door, ADR 0257, is the holder's now that the sweep asks `remove`). A removal for retention of an
// index removes first every platform manifest it names that no other kept index of the repository names, then the
// index; a kept index is one a tag names or one held (`hold`). A manifest a kept index names is never removed for
// retention, so holding an index keeps its platforms too.

import (
	"encoding/json"
	"fmt"
	"net/http"
	"strings"
)

// spared is every manifest of name a kept index keeps on seat, but the one being removed (except): each tagged
// manifest and held digest, and the platform manifests each of those names.
func (v *Verbs) spared(seat, name, except string) (map[string]string, error) {
	keepers := map[string]string{} // digest -> why it is kept
	tags, err := v.Catalog.Versions(name)
	if err != nil {
		return nil, err
	}
	for _, t := range tags {
		d, err := v.Catalog.Digest(name, t)
		if err != nil {
			return nil, err
		}
		if d != "" {
			keepers[d] = "the tag " + t
		}
	}
	holds, err := v.Holds.List()
	if err != nil {
		return nil, err
	}
	for _, h := range holds {
		if h.Seat == seat && h.Name == name {
			keepers[h.Digest] = "the hold of " + h.Digest
		}
	}
	out := map[string]string{}
	for d, why := range keepers {
		if d == except {
			continue
		}
		out[d] = why
		children, err := v.Catalog.Platforms(name, d)
		if err != nil {
			return nil, fmt.Errorf("reading the kept %s@%s: %w", name, d, err)
		}
		for _, c := range children {
			out[c] = "the index " + d + ", kept by " + why
		}
	}
	return out, nil
}

// removeForRetention removes name@digest and, for an index, the platform manifests no kept index names; a manifest a
// kept index names is refused. Any read that fails removes nothing.
func (v *Verbs) removeForRetention(seat, name, digest string) error {
	children, err := v.Catalog.Platforms(name, digest)
	if err != nil {
		return fmt.Errorf("remove: the store cannot read %s@%s, so nothing is removed: %w", name, digest, err)
	}
	spared, err := v.spared(seat, name, digest)
	if err != nil {
		return fmt.Errorf("remove: which manifests a kept index of %s names cannot be read, so nothing is removed: %w", name, err)
	}
	if why, kept := spared[digest]; kept {
		return fmt.Errorf("remove: refused: %s@%s is kept by %s", name, digest, why)
	}
	for _, c := range children {
		if _, kept := spared[c]; kept {
			continue
		}
		if err := v.Catalog.RemoveDigest(name, c); err != nil {
			return fmt.Errorf("remove: the store did not remove %s@%s, a platform of %s: %w", name, c, digest, err)
		}
	}
	if err := v.Catalog.RemoveDigest(name, digest); err != nil {
		return fmt.Errorf("remove: the store did not remove %s@%s: %w", name, digest, err)
	}
	return nil
}

// Platforms is the manifests an index names, by digest: none for a manifest that is not an index, or one the store
// does not hold.
func (o *OCI) Platforms(name, digest string) ([]string, error) {
	resp, b, err := o.do(http.MethodGet, "/v2/"+name+"/manifests/"+digest, "", nil,
		"application/vnd.oci.image.index.v1+json", "application/vnd.docker.distribution.manifest.list.v2+json",
		mediaManifest, "application/vnd.docker.distribution.manifest.v2+json")
	if err != nil {
		return nil, err
	}
	if resp.StatusCode == http.StatusNotFound {
		return nil, nil
	}
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("the store answered %d for %s@%s", resp.StatusCode, name, digest)
	}
	var doc struct {
		Manifests []struct {
			Digest string `json:"digest"`
		} `json:"manifests"`
	}
	if err := json.Unmarshal(b, &doc); err != nil {
		return nil, fmt.Errorf("%s@%s is not a manifest: %w", name, digest, err)
	}
	var out []string
	for _, m := range doc.Manifests {
		if strings.HasPrefix(m.Digest, "sha256:") {
			out = append(out, m.Digest)
		}
	}
	return out, nil
}