feat(master): suggest newer version tags for third-party images (#11) (#31)

internal/master/registry/registry.go

@@ -1,5 +1,6 @@
 // Package registry looks up the digest a tag points at in a container
-// registry, using HEAD requests only.
+// registry and lists the tags of a repository. Manifests are only ever
+// requested with HEAD.
 package registry
 
 import (
@@ -21,9 +22,10 @@ import (
 	"github.com/shcizo/package-updater/internal/imageref"
 )
 
-// Client looks up tag digests with HEAD requests only. Docker Hub counts a
-// GET of a manifest as a pull against the rate limit and a HEAD as nothing,
-// so Client never issues a manifest GET.
+// Client looks up tag digests and lists tags. Docker Hub counts a GET of a
+// manifest as a pull against the rate limit and a HEAD as nothing, so Client
+// never issues a manifest GET. The only GETs it sends are the /v2/ ping and
+// tags/list, which Docker Hub does not count as a pull.
 type Client struct {
 	keychain  authn.Keychain
 	userAgent string
@@ -65,16 +67,46 @@ func (c *Client) Digest(ctx context.Context, ref string) (string, error) {
 		remote.WithAuth(auth),
 		remote.WithUserAgent(c.userAgent))
 	if err != nil {
-		var terr *transport.Error
-		if errors.As(err, &terr) {
-			return "", fmt.Errorf("lookup %s: %s", r, describe(terr))
-		}
-		c.log.Warn("registry_lookup_failed", "ref", ref, "error", err)
-		return "", fmt.Errorf("lookup %s: %s", r, classify(err))
+		return "", c.lookupError("lookup", r.String(), ref, err)
 	}
 	return desc.Digest.String(), nil
 }
 
+// Tags returns every tag of repo ("host/path", or a Docker Hub name), in the
+// order the registry lists them. It sends GET /v2/<repo>/tags/list, following
+// the registry's pagination links. Errors are sanitised like Digest's.
+func (c *Client) Tags(ctx context.Context, repo string) ([]string, error) {
+	r, err := name.NewRepository(repo)
+	if err != nil {
+		return nil, fmt.Errorf("parse %s: %w", repo, err)
+	}
+	auth, err := c.keychain.Resolve(r)
+	if err != nil {
+		return nil, fmt.Errorf("list %s: %w", r, err)
+	}
+	tags, err := remote.List(r,
+		remote.WithContext(ctx),
+		remote.WithAuth(auth),
+		remote.WithUserAgent(c.userAgent))
+	if err != nil {
+		return nil, c.lookupError("list", r.String(), repo, err)
+	}
+	return tags, nil
+}
+
+// lookupError turns a failed registry request into an error that is safe to
+// show: a registry answer is described by its status and codes, anything
+// else by a fixed text. The full error goes to the log. verb and target
+// start the message; ref is what the log line names.
+func (c *Client) lookupError(verb, target, ref string, err error) error {
+	var terr *transport.Error
+	if errors.As(err, &terr) {
+		return fmt.Errorf("%s %s: %s", verb, target, describe(terr))
+	}
+	c.log.Warn("registry_request_failed", "ref", ref, "error", err)
+	return fmt.Errorf("%s %s: %s", verb, target, classify(err))
+}
+
 // classify returns a fixed text for an error that is not a registry answer.
 // ggcr copies registry-controlled text (token responses, authentication
 // challenges, redirect URLs, certificate names) into such errors, so none of

internal/master/registry/registry_test.go

@@ -134,6 +134,8 @@ func TestDigestIgnoresDigestSuffix(t *testing.T) {
 	assert.Equal(t, want, got)
 }
 
+// Digest asks the manifest endpoint with HEAD only; the one other request is
+// the GET /v2/ ping that every client sends first.
 func TestDigestUsesHeadOnly(t *testing.T) {
 	dockerConfig(t, "")
 	reg := newTestRegistry(t, "", "")
@@ -236,7 +238,7 @@ func TestCredsStoreWithoutHelperFailsTheLookup(t *testing.T) {
 }
 
 // A registry that leaves out Docker-Content-Digest must not make the client
-// retry with a manifest download, which Docker Hub counts as a pull.
+// retry with a manifest GET, which Docker Hub counts as a pull.
 func TestMissingDigestHeaderDoesNotFallBackToDownload(t *testing.T) {
 	dockerConfig(t, "")
 	var mu sync.Mutex
@@ -334,3 +336,101 @@ func TestClassify(t *testing.T) {
 		})
 	}
 }
+
+// pushTags stores a random index under each tag of repo.
+func (tr *testRegistry) pushTags(t *testing.T, repo string, tags ...string) {
+	t.Helper()
+	for _, tag := range tags {
+		tr.pushIndex(t, repo, tag)
+	}
+}
+
+// Digest and Tags together never GET a manifest: every manifest request is a
+// HEAD, and the only other requests are the /v2/ ping and tags/list.
+func TestNoManifestGet(t *testing.T) {
+	dockerConfig(t, "")
+	reg := newTestRegistry(t, "", "")
+	reg.pushTags(t, "team/app", "1.2", "1.3")
+	reg.reset()
+
+	_, err := newClient().Digest(context.Background(), reg.host+"/team/app:1.2")
+	require.NoError(t, err)
+	_, err = newClient().Tags(context.Background(), reg.host+"/team/app")
+	require.NoError(t, err)
+
+	reg.mu.Lock()
+	defer reg.mu.Unlock()
+	for _, r := range reg.requests {
+		switch {
+		case strings.Contains(r.path, "/manifests/"):
+			assert.Equal(t, http.MethodHead, r.method, r.path)
+		case r.path == "/v2/", r.path == "/v2/team/app/tags/list":
+			assert.Equal(t, http.MethodGet, r.method, r.path)
+		default:
+			assert.Failf(t, "unexpected request", "%s %s", r.method, r.path)
+		}
+	}
+}
+
+func TestTagsListsAllTags(t *testing.T) {
+	dockerConfig(t, "")
+	reg := newTestRegistry(t, "", "")
+	reg.pushTags(t, "team/app", "1.2", "1.3", "latest")
+
+	got, err := newClient().Tags(context.Background(), reg.host+"/team/app")
+
+	require.NoError(t, err)
+	assert.ElementsMatch(t, []string{"1.2", "1.3", "latest"}, got)
+}
+
+// ggcr's in-memory registry sends no Link header, so pagination is tested
+// against a handler that does.
+func TestTagsFollowsLinkPagination(t *testing.T) {
+	dockerConfig(t, "")
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch {
+		case r.URL.Path == "/v2/":
+		case r.URL.Path == "/v2/a/b/tags/list" && r.URL.Query().Get("last") == "":
+			w.Header().Set("Link", `</v2/a/b/tags/list?last=1.3&n=2>; rel="next"`)
+			_, _ = w.Write([]byte(`{"name":"a/b","tags":["1.2","1.3"]}`))
+		case r.URL.Path == "/v2/a/b/tags/list":
+			_, _ = w.Write([]byte(`{"name":"a/b","tags":["1.4"]}`))
+		default:
+			w.WriteHeader(http.StatusNotFound)
+		}
+	}))
+	t.Cleanup(srv.Close)
+
+	got, err := newClient().Tags(context.Background(), strings.TrimPrefix(srv.URL, "http://")+"/a/b")
+
+	require.NoError(t, err)
+	assert.Equal(t, []string{"1.2", "1.3", "1.4"}, got)
+}
+
+func TestTagsUsesDockerConfigCredentials(t *testing.T) {
+	reg := newTestRegistry(t, "bot", "s3cret")
+	reg.pushIndex(t, "team/app", "1.2", remote.WithAuth(&authn.Basic{Username: "bot", Password: "s3cret"}))
+	auth := base64.StdEncoding.EncodeToString([]byte("bot:s3cret"))
+	dockerConfig(t, `{"auths":{"`+reg.host+`":{"auth":"`+auth+`"}}}`)
+
+	got, err := newClient().Tags(context.Background(), reg.host+"/team/app")
+
+	require.NoError(t, err)
+	assert.Equal(t, []string{"1.2"}, got)
+}
+
+func TestTagsErrorBodyDoesNotLeak(t *testing.T) {
+	dockerConfig(t, "")
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusBadRequest)
+		_, _ = w.Write([]byte(`{"errors":[{"code":"NAME_UNKNOWN","message":"internal-secret-body"}]}`))
+	}))
+	t.Cleanup(srv.Close)
+	host := strings.TrimPrefix(srv.URL, "http://")
+
+	_, err := newClient().Tags(context.Background(), host+"/a/b")
+
+	require.Error(t, err)
+	assert.NotContains(t, err.Error(), "internal-secret-body")
+	assert.ErrorContains(t, err, "list "+host+"/a/b: registry answered 400 Bad Request")
+}