fix(imagepin): 带 digest 的镜像引用也向 registry 确认仍存在

internal/api/images.go

@@ -270,6 +270,9 @@ func (a *API) pinImage(ctx context.Context, ref string) (string, error) {
 	}
 	pinned, err := a.Images.Pin(ctx, ref)
 	switch {
+	case errors.Is(err, imagepin.ErrNotFound) && imagepin.Pinned(ref):
+		return "", newError(http.StatusBadRequest, "image_not_in_registry",
+			"the registry no longer holds build %q (nothing referenced it, so it was pruned); pick a current tag", ref)
 	case errors.Is(err, imagepin.ErrNotFound):
 		return "", newError(http.StatusBadRequest, "image_not_in_registry",
 			"image %q is whitelisted but the registry does not hold it; build or push it first", ref)

internal/imagepin/imagepin.go

@@ -73,10 +73,23 @@ func (r Resolver) Covers(ref string) bool {
 	return r.Registry != "" && strings.HasPrefix(ref, r.Registry+"/")
 }
 
-// Pin returns ref with the digest its tag names now appended. A ref that already
-// carries a digest, or lives outside the registry, comes back unchanged.
+// Pin returns ref with the digest its tag names now appended. A ref outside the
+// registry comes back unchanged. A ref that already carries a digest comes back
+// unchanged once the registry confirms it still holds that manifest: the registry
+// pruner deletes builds nothing references, and a server set back to one of them
+// would otherwise sit in ImagePullBackOff.
 func (r Resolver) Pin(ctx context.Context, ref string) (string, error) {
-	if Pinned(ref) || !r.Covers(ref) {
+	if !r.Covers(ref) {
+		return ref, nil
+	}
+	if name, pinned, ok := strings.Cut(ref, "@"); ok {
+		repo, _ := splitTag(strings.TrimPrefix(name, r.Registry+"/"))
+		if repo == "" || !digestRE.MatchString(pinned) {
+			return "", fmt.Errorf("imagepin: %q is not a valid pinned reference", ref)
+		}
+		if _, err := r.digest(ctx, repo, pinned); err != nil {
+			return "", fmt.Errorf("imagepin: resolve %s: %w", ref, err)
+		}
 		return ref, nil
 	}
 	repo, tag := splitTag(strings.TrimPrefix(ref, r.Registry+"/"))

internal/imagepin/imagepin_test.go

@@ -13,7 +13,8 @@ import (
 
 const testDigest = "sha256:d2fcc09d2caa108678c540c99703db96d63038a5fc9e366402d7ef1712ec4d95"
 
-// fakeRegistry serves /v2/felis/paper/manifests/demo and 404s everything else.
+// fakeRegistry serves /v2/felis/paper/manifests/demo (and the same manifest by
+// its digest) and 404s everything else.
 func fakeRegistry(t *testing.T, header bool) (*httptest.Server, *[]string) {
 	t.Helper()
 	var seen []string
@@ -22,7 +23,7 @@ func fakeRegistry(t *testing.T, header bool) (*httptest.Server, *[]string) {
 		if !strings.Contains(r.Header.Get("Accept"), "application/vnd.oci.image.index.v1+json") {
 			t.Errorf("request without an OCI index Accept: %q", r.Header.Get("Accept"))
 		}
-		if r.URL.Path != "/v2/felis/paper/manifests/demo" {
+		if r.URL.Path != "/v2/felis/paper/manifests/demo" && r.URL.Path != "/v2/felis/paper/manifests/"+testDigest {
 			http.NotFound(w, r)
 			return
 		}
@@ -78,8 +79,8 @@ func TestPinLeavesOtherRefsAlone(t *testing.T) {
 	srv, seen := fakeRegistry(t, true)
 	r := resolverFor(srv)
 	for _, ref := range []string{
-		"registry.felis.svc:5000/felis/paper:demo@" + testDigest, // already pinned
 		"docker.io/itzg/minecraft-server:java21",               // external
+		"docker.io/itzg/minecraft-server:java21@" + testDigest, // external, pinned
 		"registry.felis.svc:50000/felis/paper:demo",            // a different port is a different registry
 	} {
 		got, err := r.Pin(context.Background(), ref)
@@ -92,6 +93,30 @@ func TestPinLeavesOtherRefsAlone(t *testing.T) {
 	}
 }
 
+// A pinned ref stays as it is, but only while the registry still holds that
+// manifest: the pruner deletes builds nothing references, and setting a server
+// back to one of them must fail here, not in ImagePullBackOff.
+func TestPinChecksAPinnedRefStillExists(t *testing.T) {
+	srv, seen := fakeRegistry(t, true)
+	r := resolverFor(srv)
+	ref := "registry.felis.svc:5000/felis/paper:demo@" + testDigest
+	got, err := r.Pin(context.Background(), ref)
+	if err != nil || got != ref {
+		t.Fatalf("Pin(%q) = %q, %v; want it unchanged", ref, got, err)
+	}
+	if want := "HEAD /v2/felis/paper/manifests/" + testDigest; len(*seen) != 1 || (*seen)[0] != want {
+		t.Errorf("requests = %v, want [%s]", *seen, want)
+	}
+
+	pruned := "registry.felis.svc:5000/felis/paper:demo@sha256:" + strings.Repeat("0", 64)
+	if _, err := r.Pin(context.Background(), pruned); !errors.Is(err, ErrNotFound) {
+		t.Errorf("pruned digest: err = %v, want ErrNotFound", err)
+	}
+	if _, err := r.Pin(context.Background(), "registry.felis.svc:5000/felis/paper:demo@sha256:nothex"); err == nil {
+		t.Error("malformed pinned ref accepted")
+	}
+}
+
 func TestPinImpliedLatest(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.URL.Path != "/v2/felis/paper/manifests/latest" {