feat(agent): Add docker image update available flag (#2211)

Co-authored-by: henrygd <hank@henrygd.me>

agent/docker_registry.go

@@ -0,0 +1,222 @@
+package agent
+
+import (
+	_ "crypto/sha256"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"github.com/distribution/reference"
+	"github.com/opencontainers/go-digest"
+)
+
+const imageRegistryTimeout = 10 * time.Second
+
+const imageManifestAccept = "application/vnd.docker.distribution.manifest.list.v2+json, " +
+	"application/vnd.docker.distribution.manifest.v2+json, " +
+	"application/vnd.oci.image.manifest.v1+json, " +
+	"application/vnd.oci.image.index.v1+json"
+
+// checkImageUpdate compares the digest recorded by Docker for image with the
+// digest currently advertised by its registry. A digest-pinned reference is
+// immutable and therefore never has an update available.
+func (dm *dockerManager) checkImageUpdate(image string) (bool, error) {
+	named, err := reference.ParseNormalizedNamed(image)
+	if err != nil {
+		return false, fmt.Errorf("parse image reference %q: %w", image, err)
+	}
+	if _, pinned := named.(reference.Digested); pinned {
+		return false, nil
+	}
+	named = reference.TagNameOnly(named)
+
+	registry := reference.Domain(named)
+	repository := reference.Path(named)
+	tag := named.(reference.Tagged).Tag()
+
+	localDigest, err := dm.inspectImageDigest(image, registry, repository)
+	if err != nil {
+		return false, err
+	}
+
+	remoteDigest, err := dm.registryImageDigest(registry, repository, tag)
+	if err != nil {
+		return false, err
+	}
+
+	return remoteDigest != localDigest, nil
+}
+
+// inspectImageDigest reads Docker's image metadata without using dm.decode.
+// The checker runs in the image-discovery goroutine, so it must not hold any
+// of the container statistics locks while waiting on the Docker API.
+func (dm *dockerManager) inspectImageDigest(image, registry, repository string) (string, error) {
+	if dm.client == nil {
+		return "", fmt.Errorf("inspect image %q: Docker client is unavailable", image)
+	}
+
+	endpoint := "http://localhost/images/" + url.PathEscape(image) + "/json"
+	resp, err := dm.client.Get(endpoint)
+	if err != nil {
+		return "", fmt.Errorf("inspect image %q: %w", image, err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("inspect image %q failed: %s", image, responseStatus(resp))
+	}
+
+	var inspect struct {
+		RepoDigests []string `json:"RepoDigests"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&inspect); err != nil {
+		return "", fmt.Errorf("decode image inspect %q: %w", image, err)
+	}
+	if len(inspect.RepoDigests) == 0 {
+		return "", fmt.Errorf("inspect image %q returned no repository digests", image)
+	}
+
+	localDigest, ok := matchingRepositoryDigest(inspect.RepoDigests, registry, repository)
+	if !ok {
+		return "", fmt.Errorf("inspect image %q returned no valid digest for %s/%s", image, registry, repository)
+	}
+	return localDigest, nil
+}
+
+// matchingRepositoryDigest returns a valid digest belonging to the requested
+// repository. Docker can return multiple RepoDigests for one local image; an
+// unrelated first entry must never be used for the comparison.
+func matchingRepositoryDigest(repoDigests []string, registry, repository string) (string, bool) {
+	for _, repoDigest := range repoDigests {
+		repoDigest = strings.TrimSpace(repoDigest)
+		at := strings.LastIndexByte(repoDigest, '@')
+		if at <= 0 || at == len(repoDigest)-1 || strings.Contains(repoDigest[:at], "@") {
+			continue
+		}
+
+		repoRef, err := reference.ParseNormalizedNamed(repoDigest[:at])
+		if err != nil || reference.Path(repoRef) != repository || !sameRegistry(reference.Domain(repoRef), registry) {
+			continue
+		}
+		if _, hasTag := repoRef.(reference.Tagged); hasTag {
+			continue
+		}
+
+		d, err := digest.Parse(repoDigest[at+1:])
+		if err != nil {
+			continue
+		}
+		return d.String(), true
+	}
+	return "", false
+}
+
+func sameRegistry(left, right string) bool {
+	left = canonicalRegistry(left)
+	right = canonicalRegistry(right)
+	return left == right ||
+		(left == "ghcr.io" && right == "lscr.io") ||
+		(left == "lscr.io" && right == "ghcr.io")
+}
+
+func canonicalRegistry(registry string) string {
+	if registry == "index.docker.io" {
+		return "docker.io"
+	}
+	return registry
+}
+
+func (dm *dockerManager) registryImageDigest(registry, repository, tag string) (string, error) {
+	client := dm.registryClient
+	if client == nil {
+		client = &http.Client{Timeout: imageRegistryTimeout}
+	}
+
+	token, err := dm.registryToken(client, registry, repository)
+	if err != nil {
+		return "", err
+	}
+
+	host := registry
+	if registry == "docker.io" {
+		host = "registry-1.docker.io"
+	}
+	manifestURL := "https://" + host + "/v2/" + repository + "/manifests/" + url.PathEscape(tag)
+	req, err := http.NewRequest(http.MethodHead, manifestURL, nil)
+	if err != nil {
+		return "", fmt.Errorf("create manifest request: %w", err)
+	}
+	req.Header.Set("Accept", imageManifestAccept)
+	if token != "" {
+		req.Header.Set("Authorization", "Bearer "+token)
+	}
+
+	resp, err := client.Do(req)
+	if err != nil {
+		return "", fmt.Errorf("fetch manifest %s:%s: %w", registry, repository, err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("manifest request for %s:%s failed: %s", repository, tag, responseStatus(resp))
+	}
+
+	remote := strings.TrimSpace(resp.Header.Get("Docker-Content-Digest"))
+	d, err := digest.Parse(remote)
+	if err != nil {
+		return "", fmt.Errorf("manifest request for %s:%s returned invalid digest: %w", repository, tag, err)
+	}
+	return d.String(), nil
+}
+
+func (dm *dockerManager) registryToken(client *http.Client, registry, repository string) (string, error) {
+	var authURL string
+	switch registry {
+	case "docker.io":
+		authURL = "https://auth.docker.io/token?service=registry.docker.io&scope=" + url.QueryEscape("repository:"+repository+":pull")
+	case "ghcr.io", "lscr.io":
+		// lscr.io is the LinuxServer alias for its GHCR-backed images.
+		authURL = "https://ghcr.io/token?service=ghcr.io&scope=" + url.QueryEscape("repository:"+repository+":pull")
+	default:
+		// Anonymous registries remain supported, as they were before the
+		// authenticated Docker Hub and GHCR paths were added.
+		return "", nil
+	}
+
+	req, err := http.NewRequest(http.MethodGet, authURL, nil)
+	if err != nil {
+		return "", fmt.Errorf("create registry auth request: %w", err)
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		return "", fmt.Errorf("fetch registry auth token for %s: %w", repository, err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("registry auth request for %s failed: %s", repository, responseStatus(resp))
+	}
+
+	var tokenResponse struct {
+		Token       string `json:"token"`
+		AccessToken string `json:"access_token"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&tokenResponse); err != nil {
+		return "", fmt.Errorf("decode registry auth response for %s: %w", repository, err)
+	}
+	token := strings.TrimSpace(tokenResponse.Token)
+	if token == "" {
+		token = strings.TrimSpace(tokenResponse.AccessToken)
+	}
+	if token == "" {
+		return "", fmt.Errorf("registry auth response for %s contained no token", repository)
+	}
+	return token, nil
+}
+
+func responseStatus(resp *http.Response) string {
+	if resp.Status != "" {
+		return resp.Status
+	}
+	return http.StatusText(resp.StatusCode)
+}