feat(agent): job runner, compose override executor and swarm executor (#7)

internal/agent/updater/resolve.go

@@ -0,0 +1,49 @@
+package updater
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/docker/docker/api/types/registry"
+
+	"github.com/shcizo/package-updater/internal/imageref"
+)
+
+// DistributionClient is the subset of the Docker SDK the Resolver needs.
+// *client.Client satisfies it.
+type DistributionClient interface {
+	DistributionInspect(ctx context.Context, imageRef, encodedRegistryAuth string) (registry.DistributionInspect, error)
+}
+
+// Resolver turns "repo:tag" into "repo:tag@digest" by asking the local
+// daemon, which contacts the registry.
+type Resolver struct {
+	cli  DistributionClient
+	auth *RegistryAuth
+}
+
+// NewResolver returns a Resolver. auth may be nil (anonymous access).
+func NewResolver(cli DistributionClient, auth *RegistryAuth) *Resolver {
+	return &Resolver{cli: cli, auth: auth}
+}
+
+// Resolve returns ref pinned to the digest its tag currently points at. It
+// fails for a ref without a tag or with a digest already.
+func (r *Resolver) Resolve(ctx context.Context, ref string) (string, error) {
+	p := imageref.Parse(ref)
+	switch {
+	case p.Digest != "":
+		return "", fmt.Errorf("image %q already has a digest", ref)
+	case p.Tag == "":
+		return "", fmt.Errorf("image %q has no tag to resolve", ref)
+	}
+	info, err := r.cli.DistributionInspect(ctx, ref, r.auth.For(p.Repo))
+	if err != nil {
+		return "", fmt.Errorf("resolve %s: %w", ref, err)
+	}
+	if info.Descriptor.Digest == "" {
+		return "", errors.New("resolve " + ref + ": registry returned no digest")
+	}
+	return ref + "@" + info.Descriptor.Digest.String(), nil
+}