Add Homebrew JSON API and bottle proxy support

README.md

@@ -40,6 +40,7 @@ Resolution order: package override, then ecosystem override, then global default
 | CRAN | R | | ✓ |
 | Julia | Julia | | ✓ |
 | Container | Docker/OCI | | ✓ |
+| Homebrew | macOS/Linux | | ✓ |
 | Debian | Debian/Ubuntu | | ✓ |
 | RPM | RHEL/Fedora | | ✓ |
 | Alpine | Alpine Linux | | ✗ |
@@ -157,6 +158,29 @@ export GOPROXY=http://localhost:8080/go,direct
 
 Or in your shell profile for persistence.
 
+### Homebrew
+
+Point Homebrew's JSON API and artifact domain at the proxy:
+
+```bash
+export HOMEBREW_API_DOMAIN=http://localhost:8080/homebrew
+export HOMEBREW_ARTIFACT_DOMAIN=http://localhost:8080
+```
+
+The artifact domain proxies manifests and bottle blobs under `/v2/homebrew/core/`. GHCR routing is limited to that repository. Source archives, cask application downloads, custom tap artifacts, and legacy flat-file bottle mirrors use Homebrew's normal fallback URLs. Keep fallback enabled by leaving `HOMEBREW_ARTIFACT_DOMAIN_NO_FALLBACK` unset.
+
+Enable `cache_metadata` or set `PROXY_CACHE_METADATA=true` to retain Homebrew JSON API responses for offline fallback. Bottle blobs and their OCI manifests are cached without this setting.
+
+The upstreams default to `https://formulae.brew.sh/api` for the JSON API and `https://ghcr.io` for artifacts. To chain this proxy to another proxy, configure its Homebrew endpoints as the upstreams:
+
+```yaml
+upstream:
+  homebrew_api: "https://upstream-proxy.example.com/homebrew"
+  homebrew_artifact: "https://upstream-proxy.example.com"
+```
+
+The equivalent environment variables are `PROXY_UPSTREAM_HOMEBREW_API` and `PROXY_UPSTREAM_HOMEBREW_ARTIFACT`.
+
 ### Hex (Elixir)
 
 Configure in `~/.hex/hex.config`:
@@ -670,7 +694,9 @@ Recently cached:
 | `GET /cran/*` | CRAN (R) protocol |
 | `GET /julia/*` | Julia Pkg server protocol |
 | `GET /helm/{repository}/*` | HTTP Helm chart repository protocol |
+| `GET /homebrew/*` | Homebrew JSON API |
 | `GET /v2/*` | OCI/Docker registry protocol |
+| `GET /v2/homebrew/core/*` | Homebrew core bottle manifests and blobs from GHCR |
 | `GET /debian/*` | Debian/APT repository protocol |
 | `GET /rpm/*` | RPM/Yum repository protocol |
 

config.example.yaml

@@ -102,6 +102,12 @@ upstream:
   # Debian/APT repository URL (used by /debian endpoint)
   debian: "http://deb.debian.org/debian"
 
+  # Homebrew JSON API URL (used by /homebrew endpoint)
+  homebrew_api: "https://formulae.brew.sh/api"
+
+  # Homebrew artifact registry URL (used for /v2/homebrew/core requests)
+  homebrew_artifact: "https://ghcr.io"
+
   # Named HTTP Helm chart repositories (used by /helm/{name}/)
   # helm:
   #   bitnami: "https://charts.bitnami.com/bitnami"

docs/configuration.md

@@ -143,6 +143,8 @@ upstream:
   gradle_plugin_portal: "https://plugins.gradle.org/m2"
   cargo: "https://index.crates.io"
   cargo_download: "https://static.crates.io/crates"
+  homebrew_api: "https://formulae.brew.sh/api"
+  homebrew_artifact: "https://ghcr.io"
 
   # Named HTTP Helm chart repositories, served at /helm/{name}/.
   helm:

internal/config/config.go

@@ -318,6 +318,14 @@ type UpstreamConfig struct {
 	// Default: http://deb.debian.org/debian
 	Debian string `json:"debian" yaml:"debian"`
 
+	// HomebrewAPI is the upstream Homebrew JSON API URL.
+	// Default: https://formulae.brew.sh/api
+	HomebrewAPI string `json:"homebrew_api" yaml:"homebrew_api"`
+
+	// HomebrewArtifact is the upstream registry URL for Homebrew artifacts.
+	// Default: https://ghcr.io
+	HomebrewArtifact string `json:"homebrew_artifact" yaml:"homebrew_artifact"`
+
 	// Helm maps repository names to HTTP Helm chart repository URLs.
 	// Requests use /helm/{name}/index.yaml and chart URLs in the index are
 	// rewritten to the same named proxy endpoint.
@@ -476,6 +484,8 @@ func Default() *Config {
 			Cargo:              "https://index.crates.io",
 			CargoDownload:      "https://static.crates.io/crates",
 			Debian:             "http://deb.debian.org/debian",
+			HomebrewAPI:        "https://formulae.brew.sh/api",
+			HomebrewArtifact:   "https://ghcr.io",
 		},
 		Gradle: GradleConfig{
 			BuildCache: GradleBuildCacheConfig{
@@ -566,6 +576,8 @@ func (c *Config) LoadFromEnv() {
 	setEnvString(&c.Upstream.Maven, "PROXY_UPSTREAM_MAVEN")
 	setEnvString(&c.Upstream.GradlePluginPortal, "PROXY_UPSTREAM_GRADLE_PLUGIN_PORTAL")
 	setEnvString(&c.Upstream.Debian, "PROXY_UPSTREAM_DEBIAN")
+	setEnvString(&c.Upstream.HomebrewAPI, "PROXY_UPSTREAM_HOMEBREW_API")
+	setEnvString(&c.Upstream.HomebrewArtifact, "PROXY_UPSTREAM_HOMEBREW_ARTIFACT")
 	setEnvString(&c.Cooldown.Default, "PROXY_COOLDOWN_DEFAULT")
 	setEnvBool(&c.CacheMetadata, "PROXY_CACHE_METADATA")
 	setEnvBool(&c.MirrorAPI, "PROXY_MIRROR_API")

internal/config/config_test.go

@@ -44,6 +44,12 @@ func TestDefault(t *testing.T) {
 	if cfg.Upstream.Debian != "http://deb.debian.org/debian" {
 		t.Errorf("Upstream.Debian = %q, want %q", cfg.Upstream.Debian, "http://deb.debian.org/debian")
 	}
+	if cfg.Upstream.HomebrewAPI != "https://formulae.brew.sh/api" {
+		t.Errorf("Upstream.HomebrewAPI = %q, want %q", cfg.Upstream.HomebrewAPI, "https://formulae.brew.sh/api")
+	}
+	if cfg.Upstream.HomebrewArtifact != "https://ghcr.io" {
+		t.Errorf("Upstream.HomebrewArtifact = %q, want %q", cfg.Upstream.HomebrewArtifact, "https://ghcr.io")
+	}
 }
 
 func TestValidate(t *testing.T) {
@@ -217,6 +223,9 @@ log:
   format: "json"
 access_log:
   path: "/var/log/proxy/access.jsonl"
+upstream:
+  homebrew_api: "https://homebrew-api.example.com"
+  homebrew_artifact: "https://homebrew-artifact.example.com"
 `
 	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
 		t.Fatalf("writing config file: %v", err)
@@ -248,6 +257,12 @@ access_log:
 	if cfg.AccessLog.Path != "/var/log/proxy/access.jsonl" {
 		t.Errorf("AccessLog.Path = %q, want %q", cfg.AccessLog.Path, "/var/log/proxy/access.jsonl")
 	}
+	if cfg.Upstream.HomebrewAPI != "https://homebrew-api.example.com" {
+		t.Errorf("Upstream.HomebrewAPI = %q, want %q", cfg.Upstream.HomebrewAPI, "https://homebrew-api.example.com")
+	}
+	if cfg.Upstream.HomebrewArtifact != "https://homebrew-artifact.example.com" {
+		t.Errorf("Upstream.HomebrewArtifact = %q, want %q", cfg.Upstream.HomebrewArtifact, "https://homebrew-artifact.example.com")
+	}
 }
 
 func TestLoadJSON(t *testing.T) {
@@ -287,6 +302,8 @@ func TestLoadFromEnv(t *testing.T) {
 	t.Setenv("PROXY_UPSTREAM_MAVEN", "https://maven.example.com/repository/maven-public")
 	t.Setenv("PROXY_UPSTREAM_GRADLE_PLUGIN_PORTAL", "https://plugins.example.com/m2")
 	t.Setenv("PROXY_UPSTREAM_DEBIAN", "http://archive.ubuntu.com/ubuntu")
+	t.Setenv("PROXY_UPSTREAM_HOMEBREW_API", "https://homebrew-api.example.com")
+	t.Setenv("PROXY_UPSTREAM_HOMEBREW_ARTIFACT", "https://homebrew-artifact.example.com")
 	t.Setenv("PROXY_GRADLE_BUILD_CACHE_READ_ONLY", "true")
 	t.Setenv("PROXY_GRADLE_BUILD_CACHE_MAX_UPLOAD_SIZE", "32MB")
 	t.Setenv("PROXY_GRADLE_BUILD_CACHE_MAX_AGE", "12h")
@@ -322,6 +339,12 @@ func TestLoadFromEnv(t *testing.T) {
 	if cfg.Upstream.Debian != "http://archive.ubuntu.com/ubuntu" {
 		t.Errorf("Upstream.Debian = %q, want %q", cfg.Upstream.Debian, "http://archive.ubuntu.com/ubuntu")
 	}
+	if cfg.Upstream.HomebrewAPI != "https://homebrew-api.example.com" {
+		t.Errorf("Upstream.HomebrewAPI = %q, want %q", cfg.Upstream.HomebrewAPI, "https://homebrew-api.example.com")
+	}
+	if cfg.Upstream.HomebrewArtifact != "https://homebrew-artifact.example.com" {
+		t.Errorf("Upstream.HomebrewArtifact = %q, want %q", cfg.Upstream.HomebrewArtifact, "https://homebrew-artifact.example.com")
+	}
 	if !cfg.Gradle.BuildCache.ReadOnly {
 		t.Error("Gradle.BuildCache.ReadOnly = false, want true")
 	}

internal/handler/container.go

@@ -26,6 +26,12 @@ type ContainerHandler struct {
 	registryURL     string
 	proxyURL        string
 	namedRegistries map[string]string
+	registries      []containerRegistry
+}
+
+type containerRegistry struct {
+	repositoryPrefix string
+	registryURL      string
 }
 
 // NewContainerHandler creates a new container registry protocol handler.
@@ -47,6 +53,36 @@ func NewContainerHandler(proxy *Proxy, proxyURL string, namedRegistries ...map[s
 	return h
 }
 
+// RegisterRegistry routes a repository and its descendants to a specific OCI
+// registry. The longest matching repository prefix wins.
+func (h *ContainerHandler) RegisterRegistry(repositoryPrefix, registryURL string) {
+	h.registries = append(h.registries, containerRegistry{
+		repositoryPrefix: strings.Trim(repositoryPrefix, "/"),
+		registryURL:      strings.TrimSuffix(registryURL, "/"),
+	})
+}
+
+// BlockRegistry prevents a repository and its descendants from falling back to
+// the default OCI registry. A more specific registered repository still wins.
+func (h *ContainerHandler) BlockRegistry(repositoryPrefix string) {
+	h.RegisterRegistry(repositoryPrefix, "")
+}
+
+func (h *ContainerHandler) registryURLFor(name string) string {
+	registryURL := h.registryURL
+	matchLength := 0
+	for _, registry := range h.registries {
+		if name != registry.repositoryPrefix && !strings.HasPrefix(name, registry.repositoryPrefix+"/") {
+			continue
+		}
+		if len(registry.repositoryPrefix) > matchLength {
+			registryURL = registry.registryURL
+			matchLength = len(registry.repositoryPrefix)
+		}
+	}
+	return registryURL
+}
+
 // Routes returns the HTTP handler for container registry requests.
 // Mount this at /v2 on your router.
 func (h *ContainerHandler) Routes() http.Handler {
@@ -114,10 +150,8 @@ func (h *ContainerHandler) handleBlobDownload(w http.ResponseWriter, r *http.Req
 	}
 	if cached != nil {
 		w.Header().Set("Docker-Content-Digest", digest)
-		if cached.ContentType != "" {
+		if cached.ContentType == "" {
-			w.Header().Set("Content-Type", cached.ContentType)
+			cached.ContentType = "application/octet-stream"
-		} else {
-			w.Header().Set("Content-Type", "application/octet-stream")
 		}
 		serveArtifact(w, r.Method, cached)
 		return
@@ -130,13 +164,14 @@ func (h *ContainerHandler) handleBlobDownload(w http.ResponseWriter, r *http.Req
 	}
 
 	// Try to get from cache, or fetch from the authentication-aware upstream client.
-	result, err := h.proxy.GetOrFetchArtifactFromURL(
+	result, err := h.proxy.GetOrFetchArtifactFromURLWithDigest(
 		r.Context(),
 		"oci",
 		cacheName,
 		digest, // use digest as version
 		filename,
 		fmt.Sprintf("%s/v2/%s/blobs/%s", registryURL, upstreamName, digest),
+		digest,
 	)
 
 	if err != nil {
@@ -144,16 +179,19 @@ func (h *ContainerHandler) handleBlobDownload(w http.ResponseWriter, r *http.Req
 			h.containerError(w, http.StatusNotFound, "BLOB_UNKNOWN", "blob unknown to registry")
 			return
 		}
+		if errors.Is(err, ErrArtifactDigestMismatch) {
+			h.proxy.Logger.Error("upstream blob failed digest verification", "error", err)
+			h.containerError(w, http.StatusBadGateway, "DIGEST_INVALID", "blob digest verification failed")
+			return
+		}
 		h.proxy.Logger.Error("failed to fetch blob", "error", err)
 		h.containerError(w, http.StatusBadGateway, "INTERNAL_ERROR", "failed to fetch blob")
 		return
 	}
 
 	w.Header().Set("Docker-Content-Digest", digest)
-	if result.ContentType != "" {
+	if result.ContentType == "" {
-		w.Header().Set("Content-Type", result.ContentType)
+		result.ContentType = "application/octet-stream"
-	} else {
-		w.Header().Set("Content-Type", "application/octet-stream")
 	}
 	ServeArtifact(w, result)
 }
@@ -241,18 +279,22 @@ func (h *ContainerHandler) proxyBlobHead(w http.ResponseWriter, r *http.Request,
 	}
 	defer func() { _ = resp.Body.Close() }()
 
-	for _, header := range []string{"Content-Type", "Content-Length", "Docker-Content-Digest"} {
+	for _, header := range []string{"Content-Type", "Content-Length", "Docker-Content-Digest", "ETag", "Last-Modified"} {
 		if v := resp.Header.Get(header); v != "" {
 			w.Header().Set(header, v)
 		}
 	}
+	if resp.StatusCode >= http.StatusOK && resp.StatusCode < http.StatusMultipleChoices && w.Header().Get("Docker-Content-Digest") == "" {
+		w.Header().Set("Docker-Content-Digest", digest)
+	}
 
 	w.WriteHeader(resp.StatusCode)
 }
 
 // registryForName resolves a client-visible OCI repository name to an upstream
 // registry and its repository name. Named upstreams use upstream/{name}/ as a
-// reserved prefix; all other names continue to target Docker Hub.
+// reserved prefix. Other names are matched against registered repository
+// prefixes, falling back to Docker Hub when no prefix matches.
 func (h *ContainerHandler) registryForName(name string) (registryURL, upstreamName, cacheName string, ok bool) {
 	parts := strings.SplitN(name, "/", registrySelectorParts)
 	if len(parts) >= 2 && parts[0] == "upstream" {
@@ -265,7 +307,11 @@ func (h *ContainerHandler) registryForName(name string) (registryURL, upstreamNa
 		}
 		return registryURL, parts[2], name, true
 	}
-	return h.registryURL, name, name, true
+	registryURL = h.registryURLFor(name)
+	if registryURL == "" {
+		return "", "", "", false
+	}
+	return registryURL, name, name, true
 }
 
 // containerError writes an OCI-compliant error response.

internal/handler/container_manifest.go

@@ -30,6 +30,7 @@ type cachedContainerManifest struct {
 	contentDigest string
 	etag          string
 	size          int64
+	lastModified  time.Time
 	fetchedAt     time.Time
 }
 
@@ -44,7 +45,7 @@ func (h *ContainerHandler) serveManifest(w http.ResponseWriter, r *http.Request,
 
 	immutable := manifestDigestReferencePattern.MatchString(reference)
 	if cached != nil && (immutable || h.containerManifestFresh(cached)) {
-		writeContainerManifest(w, r.Method, cached, false)
+		writeContainerManifest(w, r, cached, false)
 		return
 	}
 
@@ -71,12 +72,12 @@ func (h *ContainerHandler) serveManifest(w http.ResponseWriter, r *http.Request,
 		if err := h.storeContainerManifest(r.Context(), cacheKey, cached); err != nil {
 			h.proxy.Logger.Warn("failed to refresh cached container manifest", "error", err)
 		}
-		writeContainerManifest(w, r.Method, cached, false)
+		writeContainerManifest(w, r, cached, false)
 		return
 	}
 	if resp.StatusCode != http.StatusOK {
 		if cached != nil && shouldServeStaleManifest(resp.StatusCode) {
-			writeContainerManifest(w, r.Method, cached, true)
+			writeContainerManifest(w, r, cached, true)
 			return
 		}
 		copyContainerManifestHeaders(w.Header(), resp.Header)
@@ -96,17 +97,27 @@ func (h *ContainerHandler) serveManifest(w http.ResponseWriter, r *http.Request,
 		h.serveStaleManifestOrError(w, r, cached, fmt.Errorf("reading manifest: %w", err))
 		return
 	}
+	computedDigest := sha256Digest(body)
+	contentDigest := resp.Header.Get("Docker-Content-Digest")
+	if contentDigest == "" {
+		contentDigest = computedDigest
+	}
+	if (immutable && reference != computedDigest) || contentDigest != computedDigest {
+		h.proxy.Logger.Error("upstream manifest failed digest verification",
+			"name", name, "reference", reference, "expected", contentDigest, "actual", computedDigest)
+		h.containerError(w, http.StatusBadGateway, "DIGEST_INVALID", "manifest digest verification failed")
+		return
+	}
+
 	manifest := &cachedContainerManifest{
 		body:          body,
 		contentType:   resp.Header.Get("Content-Type"),
-		contentDigest: resp.Header.Get("Docker-Content-Digest"),
+		contentDigest: contentDigest,
 		etag:          resp.Header.Get("ETag"),
 		size:          int64(len(body)),
+		lastModified:  parseHTTPTime(resp.Header.Get("Last-Modified")),
 		fetchedAt:     time.Now(),
 	}
-	if manifest.contentDigest == "" {
-		manifest.contentDigest = sha256Digest(body)
-	}
 	if err := h.storeContainerManifest(r.Context(), cacheKey, manifest); err != nil {
 		h.proxy.Logger.Warn("failed to cache container manifest", "error", err)
 	}
@@ -116,13 +127,13 @@ func (h *ContainerHandler) serveManifest(w http.ResponseWriter, r *http.Request,
 			h.proxy.Logger.Warn("failed to cache container manifest by digest", "error", err)
 		}
 	}
-	writeContainerManifest(w, r.Method, manifest, false)
+	writeContainerManifest(w, r, manifest, false)
 }
 
 func (h *ContainerHandler) serveStaleManifestOrError(w http.ResponseWriter, r *http.Request, cached *cachedContainerManifest, err error) {
 	if cached != nil {
 		h.proxy.Logger.Warn("upstream manifest fetch failed, serving stale cache", "error", err)
-		writeContainerManifest(w, r.Method, cached, true)
+		writeContainerManifest(w, r, cached, true)
 		return
 	}
 	h.proxy.Logger.Error("failed to fetch manifest", "error", err)
@@ -172,6 +183,9 @@ func (h *ContainerHandler) loadContainerManifest(ctx context.Context, cacheKey s
 	if entry.Size.Valid {
 		manifest.size = entry.Size.Int64
 	}
+	if entry.LastModified.Valid {
+		manifest.lastModified = entry.LastModified.Time
+	}
 	if entry.FetchedAt.Valid {
 		manifest.fetchedAt = entry.FetchedAt.Time
 	}
@@ -196,11 +210,12 @@ func (h *ContainerHandler) storeContainerManifest(ctx context.Context, cacheKey
 		ContentType:   sql.NullString{String: manifest.contentType, Valid: manifest.contentType != ""},
 		ContentDigest: sql.NullString{String: manifest.contentDigest, Valid: manifest.contentDigest != ""},
 		Size:          sql.NullInt64{Int64: size, Valid: true},
+		LastModified:  sql.NullTime{Time: manifest.lastModified, Valid: !manifest.lastModified.IsZero()},
 		FetchedAt:     sql.NullTime{Time: manifest.fetchedAt, Valid: !manifest.fetchedAt.IsZero()},
 	})
 }
 
-func writeContainerManifest(w http.ResponseWriter, method string, manifest *cachedContainerManifest, stale bool) {
+func writeContainerManifest(w http.ResponseWriter, r *http.Request, manifest *cachedContainerManifest, stale bool) {
 	if manifest.contentType != "" {
 		w.Header().Set("Content-Type", manifest.contentType)
 	}
@@ -211,11 +226,24 @@ func writeContainerManifest(w http.ResponseWriter, method string, manifest *cach
 	if manifest.etag != "" {
 		w.Header().Set("ETag", manifest.etag)
 	}
+	if !manifest.lastModified.IsZero() {
+		w.Header().Set("Last-Modified", manifest.lastModified.UTC().Format(http.TimeFormat))
+	}
 	if stale {
 		w.Header().Set("Warning", containerStaleWarning)
 	}
+	if manifest.etag != "" && r.Header.Get("If-None-Match") == manifest.etag {
+		w.WriteHeader(http.StatusNotModified)
+		return
+	}
+	if !manifest.lastModified.IsZero() {
+		if modifiedSince, err := http.ParseTime(r.Header.Get("If-Modified-Since")); err == nil && !manifest.lastModified.After(modifiedSince) {
+			w.WriteHeader(http.StatusNotModified)
+			return
+		}
+	}
 	w.WriteHeader(http.StatusOK)
-	if method != http.MethodHead {
+	if r.Method != http.MethodHead {
 		_, _ = w.Write(manifest.body)
 	}
 }
@@ -234,13 +262,18 @@ func containerManifestAccept(r *http.Request) string {
 }
 
 func copyContainerManifestHeaders(destination, source http.Header) {
-	for _, header := range []string{"Content-Type", "Content-Length", "Docker-Content-Digest", "ETag", "WWW-Authenticate"} {
+	for _, header := range []string{"Content-Type", "Content-Length", "Docker-Content-Digest", "ETag", "Last-Modified", "WWW-Authenticate"} {
 		if value := source.Get(header); value != "" {
 			destination.Set(header, value)
 		}
 	}
 }
 
+func parseHTTPTime(value string) time.Time {
+	parsed, _ := http.ParseTime(value)
+	return parsed
+}
+
 func shouldServeStaleManifest(status int) bool {
 	return status == http.StatusTooManyRequests || status >= http.StatusInternalServerError
 }

internal/handler/container_test.go

@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"strconv"
+	"strings"
 	"testing"
 	"time"
 
@@ -135,17 +136,18 @@ func TestContainerHandler_parseTagsListPath(t *testing.T) {
 }
 
 func TestContainerHandler_NamedOCIRegistryServesHelmArtifacts(t *testing.T) {
-	digest := "sha256:abc123def456abc123def456abc123def456abc123def456abc123def456abcd"
+	const blob = "chart archive"
+	digest := "sha256:" + sha256Hex(blob)
 	manifest := `{"schemaVersion":2,"config":{"mediaType":"application/vnd.cncf.helm.config.v1+json"},"layers":[{"mediaType":"application/vnd.cncf.helm.chart.content.v1.tar+gzip","digest":"` + digest + `"}]}`
 	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		switch r.URL.Path {
 		case "/v2/owner/demo/manifests/1.0.0":
 			w.Header().Set("Content-Type", "application/vnd.oci.image.manifest.v1+json")
-			w.Header().Set("Docker-Content-Digest", digest)
+			w.Header().Set("Docker-Content-Digest", "sha256:"+sha256Hex(manifest))
 			_, _ = io.WriteString(w, manifest)
 		case "/v2/owner/demo/blobs/" + digest:
 			w.Header().Set("Content-Type", "application/vnd.cncf.helm.chart.content.v1.tar+gzip")
-			_, _ = io.WriteString(w, "chart archive")
+			_, _ = io.WriteString(w, blob)
 		default:
 			http.NotFound(w, r)
 		}
@@ -180,8 +182,28 @@ func TestContainerHandler_NamedOCIRegistryServesHelmArtifacts(t *testing.T) {
 	}
 }
 
+func TestContainerHandler_registryURLForUsesLongestRepositoryPrefix(t *testing.T) {
+	h := &ContainerHandler{registryURL: "https://registry-1.docker.io"}
+	h.RegisterRegistry("homebrew", "https://example.test")
+	h.RegisterRegistry("homebrew/core", "https://ghcr.io/")
+
+	tests := map[string]string{
+		"homebrew/core":            "https://ghcr.io",
+		"homebrew/core/jq":         "https://ghcr.io",
+		"homebrew/portable-ruby":   "https://example.test",
+		"homebrew-core/jq":         "https://registry-1.docker.io",
+		"library/homebrew/core/jq": "https://registry-1.docker.io",
+	}
+	for name, want := range tests {
+		if got := h.registryURLFor(name); got != want {
+			t.Errorf("registryURLFor(%q) = %q, want %q", name, got, want)
+		}
+	}
+}
+
 func TestContainerHandler_BlobDownload_DiscoversBearerChallenge(t *testing.T) {
-	digest := "sha256:abc123def456abc123def456abc123def456abc123def456abc123def456abcd"
+	blob := "upstream blob"
+	digest := sha256Digest([]byte(blob))
 	registryRequests := 0
 	tokenRequests := 0
 	var upstream *httptest.Server
@@ -202,7 +224,7 @@ func TestContainerHandler_BlobDownload_DiscoversBearerChallenge(t *testing.T) {
 				return
 			}
 			w.Header().Set("Content-Type", "application/octet-stream")
-			_, _ = io.WriteString(w, "upstream blob")
+			_, _ = io.WriteString(w, blob)
 		default:
 			http.NotFound(w, r)
 		}
@@ -233,8 +255,8 @@ func TestContainerHandler_BlobDownload_DiscoversBearerChallenge(t *testing.T) {
 		if w.Code != http.StatusOK {
 			t.Fatalf("status = %d, want %d; body: %s", w.Code, http.StatusOK, w.Body.String())
 		}
-		if got := w.Body.String(); got != "upstream blob" {
+		if got := w.Body.String(); got != blob {
-			t.Errorf("body = %q, want %q", got, "upstream blob")
+			t.Errorf("body = %q, want %q", got, blob)
 		}
 	}
 
@@ -246,10 +268,102 @@ func TestContainerHandler_BlobDownload_DiscoversBearerChallenge(t *testing.T) {
 	}
 }
 
+func TestContainerHandler_HomebrewBlobDoesNotForwardClientCredentialsToRegistryOrCDN(t *testing.T) {
+	blob := "homebrew bottle"
+	digest := sha256Digest([]byte(blob))
+	var registryAuthorization, cdnAuthorization string
+
+	cdn := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		cdnAuthorization = r.Header.Get("Authorization")
+		w.Header().Set("Content-Type", "application/vnd.homebrew.bottle")
+		_, _ = io.WriteString(w, blob)
+	}))
+	defer cdn.Close()
+
+	registry := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		registryAuthorization = r.Header.Get("Authorization")
+		http.Redirect(w, r, cdn.URL+"/bottle", http.StatusTemporaryRedirect)
+	}))
+	defer registry.Close()
+
+	defaultRequests := 0
+	defaultRegistry := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		defaultRequests++
+		http.NotFound(w, r)
+	}))
+	defer defaultRegistry.Close()
+
+	proxy, _, _, _ := setupTestProxy(t)
+	client := registry.Client()
+	artifactFetcher := fetch.NewFetcher(
+		fetch.WithHTTPClient(client),
+		fetch.WithMaxRetries(0),
+	)
+	t.Cleanup(func() { _ = artifactFetcher.Close() })
+	proxy.Fetcher = artifactFetcher
+
+	h := &ContainerHandler{proxy: proxy, registryURL: defaultRegistry.URL}
+	h.RegisterRegistry("homebrew/core", registry.URL)
+	req := httptest.NewRequest(http.MethodGet, "/homebrew/core/jq/blobs/"+digest, nil)
+	req.Header.Set("Authorization", "Bearer client-secret")
+	w := httptest.NewRecorder()
+	h.Routes().ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d; body: %s", w.Code, http.StatusOK, w.Body.String())
+	}
+	if got := w.Body.String(); got != blob {
+		t.Errorf("body = %q, want %q", got, blob)
+	}
+	if got := w.Header().Get("Content-Type"); got != "application/vnd.homebrew.bottle" {
+		t.Errorf("Content-Type = %q, want application/vnd.homebrew.bottle", got)
+	}
+	if registryAuthorization != "" {
+		t.Errorf("registry Authorization = %q, want empty", registryAuthorization)
+	}
+	if cdnAuthorization != "" {
+		t.Errorf("CDN Authorization = %q, want empty", cdnAuthorization)
+	}
+	if defaultRequests != 0 {
+		t.Errorf("default registry requests = %d, want 0", defaultRequests)
+	}
+}
+
+func TestContainerHandler_BlobDigestMismatchIsNotCached(t *testing.T) {
+	proxy, _, store, fetcher := setupTestProxy(t)
+	fetcher.artifact = &fetch.Artifact{
+		Body:        io.NopCloser(strings.NewReader("wrong bottle")),
+		ContentType: "application/octet-stream",
+	}
+	digest := sha256Digest([]byte("expected bottle"))
+	h := &ContainerHandler{proxy: proxy, registryURL: "https://registry.example.test"}
+
+	w := httptest.NewRecorder()
+	h.Routes().ServeHTTP(w, httptest.NewRequest(http.MethodGet, "/homebrew/core/jq/blobs/"+digest, nil))
+
+	if w.Code != http.StatusBadGateway {
+		t.Fatalf("status = %d, want %d; body: %s", w.Code, http.StatusBadGateway, w.Body.String())
+	}
+	if !strings.Contains(w.Body.String(), "DIGEST_INVALID") {
+		t.Errorf("body = %q, want DIGEST_INVALID", w.Body.String())
+	}
+	cached, err := proxy.GetCachedArtifact(t.Context(), "oci", "homebrew/core/jq", digest, digest)
+	if err != nil {
+		t.Fatalf("checking cache: %v", err)
+	}
+	if cached != nil {
+		t.Error("digest-mismatched blob was recorded in the cache")
+	}
+	if len(store.files) != 0 {
+		t.Errorf("stored files = %d, want 0", len(store.files))
+	}
+}
+
 func TestContainerHandler_CachedImagePullSurvivesRegistryAndTokenOutages(t *testing.T) {
-	digest := "sha256:abc123def456abc123def456abc123def456abc123def456abc123def456abcd"
 	manifest := `{"schemaVersion":2,"mediaType":"application/vnd.oci.image.manifest.v1+json"}`
 	blob := "cached image blob"
+	manifestDigest := sha256Digest([]byte(manifest))
+	blobDigest := sha256Digest([]byte(blob))
 	registryAvailable := true
 	tokenAvailable := true
 	registryRequests := 0
@@ -284,9 +398,9 @@ func TestContainerHandler_CachedImagePullSurvivesRegistryAndTokenOutages(t *test
 		switch r.URL.Path {
 		case "/v2/library/nginx/manifests/latest":
 			w.Header().Set("Content-Type", "application/vnd.oci.image.manifest.v1+json")
-			w.Header().Set("Docker-Content-Digest", digest)
+			w.Header().Set("Docker-Content-Digest", manifestDigest)
 			_, _ = io.WriteString(w, manifest)
-		case "/v2/library/nginx/blobs/" + digest:
+		case "/v2/library/nginx/blobs/" + blobDigest:
 			w.Header().Set("Content-Type", "application/octet-stream")
 			_, _ = io.WriteString(w, blob)
 		default:
@@ -316,7 +430,7 @@ func TestContainerHandler_CachedImagePullSurvivesRegistryAndTokenOutages(t *test
 		body string
 	}{
 		{path: "/library/nginx/manifests/latest", body: manifest},
-		{path: "/library/nginx/blobs/" + digest, body: blob},
+		{path: "/library/nginx/blobs/" + blobDigest, body: blob},
 	} {
 		response := httptest.NewRecorder()
 		warmHandler.ServeHTTP(response, httptest.NewRequest(http.MethodGet, request.path, nil))
@@ -349,13 +463,14 @@ func TestContainerHandler_CachedImagePullSurvivesRegistryAndTokenOutages(t *test
 	}).Routes()
 
 	for _, request := range []struct {
-		name string
+		name   string
-		path string
+		path   string
-		body string
+		body   string
+		digest string
 	}{
-		{name: "tag manifest", path: "/library/nginx/manifests/latest", body: manifest},
+		{name: "tag manifest", path: "/library/nginx/manifests/latest", body: manifest, digest: manifestDigest},
-		{name: "digest manifest", path: "/library/nginx/manifests/" + digest, body: manifest},
+		{name: "digest manifest", path: "/library/nginx/manifests/" + manifestDigest, body: manifest, digest: manifestDigest},
-		{name: "blob", path: "/library/nginx/blobs/" + digest, body: blob},
+		{name: "blob", path: "/library/nginx/blobs/" + blobDigest, body: blob, digest: blobDigest},
 	} {
 		t.Run(request.name, func(t *testing.T) {
 			response := httptest.NewRecorder()
@@ -366,8 +481,8 @@ func TestContainerHandler_CachedImagePullSurvivesRegistryAndTokenOutages(t *test
 			if got := response.Body.String(); got != request.body {
 				t.Errorf("body = %q, want %q", got, request.body)
 			}
-			if got := response.Header().Get("Docker-Content-Digest"); got != digest {
+			if got := response.Header().Get("Docker-Content-Digest"); got != request.digest {
-				t.Errorf("Docker-Content-Digest = %q, want %q", got, digest)
+				t.Errorf("Docker-Content-Digest = %q, want %q", got, request.digest)
 			}
 		})
 	}
@@ -495,8 +610,9 @@ func TestContainerHandler_BlobHead_DirectServeRedirects(t *testing.T) {
 }
 
 func TestContainerHandler_ManifestByDigest_CacheHitSkipsUpstream(t *testing.T) {
-	digest := "sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
 	manifest := `{"schemaVersion":2,"mediaType":"application/vnd.oci.image.manifest.v1+json"}`
+	digest := sha256Digest([]byte(manifest))
+	lastModified := time.Date(2026, time.August, 14, 9, 30, 0, 0, time.UTC)
 	upstreamAvailable := true
 	upstreamRequests := 0
 	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -512,6 +628,7 @@ func TestContainerHandler_ManifestByDigest_CacheHitSkipsUpstream(t *testing.T) {
 		w.Header().Set("Content-Type", "application/vnd.oci.image.manifest.v1+json")
 		w.Header().Set("Docker-Content-Digest", digest)
 		w.Header().Set("ETag", `"manifest-etag"`)
+		w.Header().Set("Last-Modified", lastModified.Format(http.TimeFormat))
 		if r.Method != http.MethodHead {
 			_, _ = io.WriteString(w, manifest)
 		}
@@ -543,6 +660,23 @@ func TestContainerHandler_ManifestByDigest_CacheHitSkipsUpstream(t *testing.T) {
 	if got := second.Header().Get("Docker-Content-Digest"); got != digest {
 		t.Errorf("cached Docker-Content-Digest = %q, want %q", got, digest)
 	}
+	if got := second.Header().Get("Last-Modified"); got != lastModified.Format(http.TimeFormat) {
+		t.Errorf("cached Last-Modified = %q, want %q", got, lastModified.Format(http.TimeFormat))
+	}
+
+	conditionalRequest := httptest.NewRequest(http.MethodGet, "/library/nginx/manifests/"+digest, nil)
+	conditionalRequest.Header.Set("If-None-Match", `"manifest-etag"`)
+	conditional := httptest.NewRecorder()
+	h.Routes().ServeHTTP(conditional, conditionalRequest)
+	if conditional.Code != http.StatusNotModified {
+		t.Fatalf("conditional status = %d, want %d", conditional.Code, http.StatusNotModified)
+	}
+	if got := conditional.Header().Get("ETag"); got != `"manifest-etag"` {
+		t.Errorf("conditional ETag = %q, want %q", got, `"manifest-etag"`)
+	}
+	if conditional.Body.Len() != 0 {
+		t.Errorf("conditional body length = %d, want 0", conditional.Body.Len())
+	}
 
 	head := httptest.NewRecorder()
 	h.Routes().ServeHTTP(head, httptest.NewRequest(http.MethodHead, "/library/nginx/manifests/"+digest, nil))
@@ -561,9 +695,72 @@ func TestContainerHandler_ManifestByDigest_CacheHitSkipsUpstream(t *testing.T) {
 	}
 }
 
+func TestContainerHandler_ManifestDigestMismatchIsNotCached(t *testing.T) {
+	manifest := `{"schemaVersion":2}`
+	digest := sha256Digest([]byte("different manifest"))
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/vnd.oci.image.manifest.v1+json")
+		w.Header().Set("Docker-Content-Digest", digest)
+		_, _ = io.WriteString(w, manifest)
+	}))
+	defer upstream.Close()
+
+	proxy, db, _, _ := setupTestProxy(t)
+	proxy.HTTPClient = upstream.Client()
+	h := &ContainerHandler{proxy: proxy, registryURL: upstream.URL}
+	req := httptest.NewRequest(http.MethodGet, "/homebrew/core/jq/manifests/"+digest, nil)
+	w := httptest.NewRecorder()
+	h.Routes().ServeHTTP(w, req)
+
+	if w.Code != http.StatusBadGateway {
+		t.Fatalf("status = %d, want %d; body: %s", w.Code, http.StatusBadGateway, w.Body.String())
+	}
+	if !strings.Contains(w.Body.String(), "DIGEST_INVALID") {
+		t.Errorf("body = %q, want DIGEST_INVALID", w.Body.String())
+	}
+	cacheKey := h.containerManifestCacheKey(upstream.URL, "homebrew/core/jq", digest, containerManifestAccept(req))
+	entry, err := db.GetMetadataCache(containerManifestCacheEcosystem, cacheKey)
+	if err != nil {
+		t.Fatalf("checking manifest cache: %v", err)
+	}
+	if entry != nil {
+		t.Error("digest-mismatched manifest was recorded in the cache")
+	}
+}
+
+func TestContainerHandler_ManifestTagWithInvalidDigestIsNotAliased(t *testing.T) {
+	manifest := `{"schemaVersion":2}`
+	invalidDigest := sha256Digest([]byte("different manifest"))
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/vnd.oci.image.manifest.v1+json")
+		w.Header().Set("Docker-Content-Digest", invalidDigest)
+		_, _ = io.WriteString(w, manifest)
+	}))
+	defer upstream.Close()
+
+	proxy, db, _, _ := setupTestProxy(t)
+	proxy.HTTPClient = upstream.Client()
+	h := &ContainerHandler{proxy: proxy, registryURL: upstream.URL}
+	req := httptest.NewRequest(http.MethodGet, "/homebrew/core/jq/manifests/latest", nil)
+	w := httptest.NewRecorder()
+	h.Routes().ServeHTTP(w, req)
+
+	if w.Code != http.StatusBadGateway {
+		t.Fatalf("status = %d, want %d; body: %s", w.Code, http.StatusBadGateway, w.Body.String())
+	}
+	cacheKey := h.containerManifestCacheKey(upstream.URL, "homebrew/core/jq", invalidDigest, containerManifestAccept(req))
+	entry, err := db.GetMetadataCache(containerManifestCacheEcosystem, cacheKey)
+	if err != nil {
+		t.Fatalf("checking manifest cache: %v", err)
+	}
+	if entry != nil {
+		t.Error("tag manifest was cached under an unverified digest")
+	}
+}
+
 func TestContainerHandler_ManifestByTag_UsesStaleCacheOnUpstreamFailure(t *testing.T) {
-	digest := "sha256:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"
 	manifest := `{"schemaVersion":2,"mediaType":"application/vnd.oci.image.index.v1+json"}`
+	digest := sha256Digest([]byte(manifest))
 	upstreamAvailable := true
 	upstreamRequests := 0
 	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
@@ -610,8 +807,8 @@ func TestContainerHandler_ManifestByTag_UsesStaleCacheOnUpstreamFailure(t *testi
 }
 
 func TestContainerHandler_ManifestByTag_CachesDigestAlias(t *testing.T) {
-	digest := "sha256:cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc"
 	manifest := `{"schemaVersion":2,"mediaType":"application/vnd.oci.image.manifest.v1+json"}`
+	digest := sha256Digest([]byte(manifest))
 	upstreamAvailable := true
 	upstreamRequests := 0
 	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -658,7 +855,8 @@ func TestContainerHandler_ManifestByTag_CachesDigestAlias(t *testing.T) {
 }
 
 func TestContainerHandler_ManifestByTag_StaleHeadChecksUpstream(t *testing.T) {
-	oldDigest := "sha256:dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd"
+	manifest := `{"schemaVersion":2}`
+	oldDigest := sha256Digest([]byte(manifest))
 	newDigest := "sha256:eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee"
 	currentDigest := oldDigest
 	upstreamRequests := 0
@@ -668,7 +866,7 @@ func TestContainerHandler_ManifestByTag_StaleHeadChecksUpstream(t *testing.T) {
 		w.Header().Set("Docker-Content-Digest", currentDigest)
 		w.Header().Set("ETag", `"`+currentDigest+`"`)
 		if r.Method != http.MethodHead {
-			_, _ = io.WriteString(w, `{"schemaVersion":2}`)
+			_, _ = io.WriteString(w, manifest)
 		}
 	}))
 	defer upstream.Close()

internal/handler/handler.go

@@ -633,6 +633,8 @@ func (p *Proxy) fetchUpstreamMetadata(ctx context.Context, upstreamURL string, e
 
 	if entry != nil && entry.ETag.Valid {
 		req.Header.Set("If-None-Match", entry.ETag.String)
+	} else if entry != nil && entry.LastModified.Valid {
+		req.Header.Set("If-Modified-Since", entry.LastModified.Time.UTC().Format(http.TimeFormat))
 	}
 
 	resp, err := p.HTTPClient.Do(req)
@@ -775,6 +777,12 @@ func (p *Proxy) ProxyCached(w http.ResponseWriter, r *http.Request, upstreamURL,
 func (p *Proxy) writeMetadataCachedResponse(w http.ResponseWriter, r *http.Request, ecosystem, cacheKey string, body []byte, contentType string) {
 	cm := p.lookupCachedMeta(ecosystem, cacheKey)
 
+	if cm.etag != "" {
+		w.Header().Set("ETag", cm.etag)
+	}
+	if !cm.lastModified.IsZero() {
+		w.Header().Set("Last-Modified", cm.lastModified.UTC().Format(http.TimeFormat))
+	}
 	if cm.etag != "" {
 		if match := r.Header.Get("If-None-Match"); match != "" && match == cm.etag {
 			w.WriteHeader(http.StatusNotModified)
@@ -792,23 +800,19 @@ func (p *Proxy) writeMetadataCachedResponse(w http.ResponseWriter, r *http.Reque
 
 	w.Header().Set("Content-Type", contentType)
 	w.Header().Set("Content-Length", strconv.Itoa(len(body)))
-	if cm.etag != "" {
-		w.Header().Set("ETag", cm.etag)
-	}
-	if !cm.lastModified.IsZero() {
-		w.Header().Set("Last-Modified", cm.lastModified.UTC().Format(http.TimeFormat))
-	}
 	if cm.stale {
 		w.Header().Set("Warning", `110 - "Response is Stale"`)
 	}
 	w.WriteHeader(http.StatusOK)
-	_, _ = w.Write(body)
+	if r.Method != http.MethodHead {
+		_, _ = w.Write(body)
+	}
 }
 
 // proxyMetadataStream forwards an upstream metadata response by streaming it to the client
 // without buffering the full body in memory.
 func (p *Proxy) proxyMetadataStream(w http.ResponseWriter, r *http.Request, upstreamURL string, acceptHeaders ...string) {
-	req, err := http.NewRequestWithContext(r.Context(), http.MethodGet, upstreamURL, nil)
+	req, err := http.NewRequestWithContext(r.Context(), r.Method, upstreamURL, nil)
 	if err != nil {
 		http.Error(w, "failed to create request", http.StatusInternalServerError)
 		return
@@ -841,7 +845,9 @@ func (p *Proxy) proxyMetadataStream(w http.ResponseWriter, r *http.Request, upst
 	}
 
 	w.WriteHeader(resp.StatusCode)
-	_, _ = io.Copy(w, resp.Body)
+	if r.Method != http.MethodHead {
+		_, _ = io.Copy(w, resp.Body)
+	}
 }
 
 func (p *Proxy) applyUpstreamAuth(req *http.Request) {
@@ -858,12 +864,22 @@ func (p *Proxy) applyUpstreamAuth(req *http.Request) {
 // GetOrFetchArtifactFromURL retrieves an artifact from cache or fetches from a specific URL.
 // This is useful for registries where download URLs are determined from metadata.
 func (p *Proxy) GetOrFetchArtifactFromURL(ctx context.Context, ecosystem, name, version, filename, downloadURL string) (*CacheResult, error) {
-	return p.GetOrFetchArtifactFromURLWithHeaders(ctx, ecosystem, name, version, filename, downloadURL, nil)
+	return p.getOrFetchArtifactFromURL(ctx, ecosystem, name, version, filename, downloadURL, nil, "")
 }
 
 // GetOrFetchArtifactFromURLWithHeaders retrieves an artifact from cache or fetches from a URL
 // with additional request-specific HTTP headers.
 func (p *Proxy) GetOrFetchArtifactFromURLWithHeaders(ctx context.Context, ecosystem, name, version, filename, downloadURL string, headers http.Header) (*CacheResult, error) {
+	return p.getOrFetchArtifactFromURL(ctx, ecosystem, name, version, filename, downloadURL, headers, "")
+}
+
+// GetOrFetchArtifactFromURLWithDigest retrieves an artifact and verifies its
+// SHA-256 digest before adding a newly fetched response to the cache.
+func (p *Proxy) GetOrFetchArtifactFromURLWithDigest(ctx context.Context, ecosystem, name, version, filename, downloadURL, digest string) (*CacheResult, error) {
+	return p.getOrFetchArtifactFromURL(ctx, ecosystem, name, version, filename, downloadURL, nil, digest)
+}
+
+func (p *Proxy) getOrFetchArtifactFromURL(ctx context.Context, ecosystem, name, version, filename, downloadURL string, headers http.Header, digest string) (*CacheResult, error) {
 	if cached, err := p.GetCachedArtifact(ctx, ecosystem, name, version, filename); err != nil {
 		return nil, err
 	} else if cached != nil {
@@ -873,10 +889,10 @@ func (p *Proxy) GetOrFetchArtifactFromURLWithHeaders(ctx context.Context, ecosys
 
 	pkgPURL := purl.MakePURLString(ecosystem, name, "")
 	versionPURL := purl.MakePURLString(ecosystem, name, version)
-	return p.fetchAndCacheFromURL(ctx, ecosystem, name, version, filename, pkgPURL, versionPURL, downloadURL, headers)
+	return p.fetchAndCacheFromURL(ctx, ecosystem, name, version, filename, pkgPURL, versionPURL, downloadURL, headers, digest)
 }
 
-func (p *Proxy) fetchAndCacheFromURL(ctx context.Context, ecosystem, name, version, filename, pkgPURL, versionPURL, downloadURL string, headers http.Header) (*CacheResult, error) {
+func (p *Proxy) fetchAndCacheFromURL(ctx context.Context, ecosystem, name, version, filename, pkgPURL, versionPURL, downloadURL string, headers http.Header, expectedDigest string) (*CacheResult, error) {
 	p.Logger.Info("fetching from upstream",
 		"ecosystem", ecosystem, "name", name, "version", version, "url", downloadURL)
 
@@ -894,6 +910,12 @@ func (p *Proxy) fetchAndCacheFromURL(ctx context.Context, ecosystem, name, versi
 	if err != nil {
 		return nil, fmt.Errorf("storing artifact: %w", err)
 	}
+	if expectedDigest != "" && expectedDigest != "sha256:"+hash {
+		if deleteErr := p.Storage.Delete(ctx, storagePath); deleteErr != nil {
+			p.Logger.Warn("failed to remove artifact with invalid digest", "path", storagePath, "error", deleteErr)
+		}
+		return nil, fmt.Errorf("%w: expected %s, got sha256:%s", ErrArtifactDigestMismatch, expectedDigest, hash)
+	}
 
 	if err := p.updateCacheDB(ecosystem, name, filename, pkgPURL, versionPURL, downloadURL, storagePath, hash, size, artifact.ContentType); err != nil {
 		p.Logger.Warn("failed to update cache database", "error", err)
@@ -912,3 +934,7 @@ func (p *Proxy) fetchAndCacheFromURL(ctx context.Context, ecosystem, name, versi
 		Cached:      false,
 	}, nil
 }
+
+// ErrArtifactDigestMismatch indicates that fetched bytes did not match their
+// digest-addressed URL and were not recorded in the cache database.
+var ErrArtifactDigestMismatch = errors.New("artifact digest mismatch")

internal/handler/homebrew.go

@@ -0,0 +1,70 @@
+package handler
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"net/http"
+	"strings"
+)
+
+const (
+	homebrewArtifactNamespace  = "homebrew"
+	homebrewArtifactRepository = "homebrew/core"
+	homebrewMetadataEcosystem  = "homebrew"
+)
+
+// HomebrewHandler proxies Homebrew's JSON API without modifying signed files.
+type HomebrewHandler struct {
+	proxy       *Proxy
+	apiUpstream string
+}
+
+// NewHomebrewHandler creates a Homebrew JSON API handler.
+func NewHomebrewHandler(proxy *Proxy, apiUpstream string) *HomebrewHandler {
+	return &HomebrewHandler{
+		proxy:       proxy,
+		apiUpstream: strings.TrimSuffix(apiUpstream, "/"),
+	}
+}
+
+// RegisterHomebrewArtifacts routes homebrew/core OCI requests to its configured
+// registry and blocks other homebrew repositories from reaching the default
+// OCI registry.
+func RegisterHomebrewArtifacts(container *ContainerHandler, artifactUpstream string) {
+	container.BlockRegistry(homebrewArtifactNamespace)
+	container.RegisterRegistry(homebrewArtifactRepository, artifactUpstream)
+}
+
+// Routes returns the Homebrew JSON API handler. Mount this at /homebrew.
+func (h *HomebrewHandler) Routes() http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodGet && r.Method != http.MethodHead {
+			w.Header().Set("Allow", "GET, HEAD")
+			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+			return
+		}
+
+		requestPath := strings.TrimPrefix(r.URL.EscapedPath(), "/")
+		if requestPath == "" || containsPathTraversal(requestPath) {
+			http.NotFound(w, r)
+			return
+		}
+
+		upstreamURL := h.apiUpstream + "/" + requestPath
+		if r.URL.RawQuery != "" {
+			upstreamURL += "?" + r.URL.RawQuery
+		}
+
+		accept := r.Header.Get("Accept")
+		if r.Method == http.MethodHead {
+			h.proxy.proxyMetadataStream(w, r, upstreamURL, accept)
+			return
+		}
+		h.proxy.ProxyCached(w, r, upstreamURL, homebrewMetadataEcosystem, homebrewMetadataCacheKey(requestPath, r.URL.RawQuery), accept)
+	})
+}
+
+func homebrewMetadataCacheKey(requestPath, rawQuery string) string {
+	sum := sha256.Sum256([]byte(requestPath + "\x00" + rawQuery))
+	return hex.EncodeToString(sum[:])
+}

internal/handler/homebrew_test.go

@@ -0,0 +1,307 @@
+package handler
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/git-pkgs/registries/fetch"
+)
+
+func TestHomebrewHandler_PreservesSignedResponseAndClientValidators(t *testing.T) {
+	body := " {\n  \"payload\": \"signed bytes\",\n  \"signatures\": []\n}\n"
+	etag := `"homebrew-api-etag"`
+	lastModified := time.Date(2026, time.August, 14, 9, 30, 0, 0, time.UTC)
+	requests := 0
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		requests++
+		if r.Method != http.MethodGet {
+			t.Errorf("upstream method = %s, want GET", r.Method)
+		}
+		if r.URL.Path != "/api/internal/packages.arm64_tahoe.jws.json" {
+			t.Errorf("upstream path = %q", r.URL.Path)
+		}
+		if got := r.Header.Get("Authorization"); got != "" {
+			t.Errorf("upstream Authorization = %q, want empty", got)
+		}
+		if got := r.Header.Get("Cookie"); got != "" {
+			t.Errorf("upstream Cookie = %q, want empty", got)
+		}
+		w.Header().Set("Content-Type", "application/json")
+		w.Header().Set("ETag", etag)
+		w.Header().Set("Last-Modified", lastModified.Format(http.TimeFormat))
+		_, _ = io.WriteString(w, body)
+	}))
+	defer upstream.Close()
+
+	proxy, _, _, _ := setupTestProxy(t)
+	proxy.CacheMetadata = true
+	proxy.MetadataTTL = time.Hour
+	proxy.HTTPClient = upstream.Client()
+	h := NewHomebrewHandler(proxy, upstream.URL+"/api").Routes()
+
+	req := httptest.NewRequest(http.MethodGet, "/internal/packages.arm64_tahoe.jws.json", nil)
+	req.Header.Set("Authorization", "Bearer client-secret")
+	req.Header.Set("Cookie", "session=client-secret")
+	w := httptest.NewRecorder()
+	h.ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d; body: %s", w.Code, http.StatusOK, w.Body.String())
+	}
+	if got := w.Body.String(); got != body {
+		t.Errorf("body = %q, want byte-for-byte %q", got, body)
+	}
+	if got := w.Header().Get("Content-Type"); got != "application/json" {
+		t.Errorf("Content-Type = %q, want application/json", got)
+	}
+	wantContentLength := strconv.Itoa(len(body))
+	if got := w.Header().Get("Content-Length"); got != wantContentLength {
+		t.Errorf("Content-Length = %q, want %q", got, wantContentLength)
+	}
+	if got := w.Header().Get("ETag"); got != etag {
+		t.Errorf("ETag = %q, want %q", got, etag)
+	}
+	if got := w.Header().Get("Last-Modified"); got != lastModified.Format(http.TimeFormat) {
+		t.Errorf("Last-Modified = %q, want %q", got, lastModified.Format(http.TimeFormat))
+	}
+
+	conditionalRequest := httptest.NewRequest(http.MethodGet, "/internal/packages.arm64_tahoe.jws.json", nil)
+	conditionalRequest.Header.Set("If-None-Match", etag)
+	conditional := httptest.NewRecorder()
+	h.ServeHTTP(conditional, conditionalRequest)
+	if conditional.Code != http.StatusNotModified {
+		t.Fatalf("conditional status = %d, want %d", conditional.Code, http.StatusNotModified)
+	}
+	if got := conditional.Header().Get("ETag"); got != etag {
+		t.Errorf("conditional ETag = %q, want %q", got, etag)
+	}
+	if conditional.Body.Len() != 0 {
+		t.Errorf("conditional body length = %d, want 0", conditional.Body.Len())
+	}
+
+	modifiedSinceRequest := httptest.NewRequest(http.MethodGet, "/internal/packages.arm64_tahoe.jws.json", nil)
+	modifiedSinceRequest.Header.Set("If-Modified-Since", lastModified.Format(http.TimeFormat))
+	modifiedSince := httptest.NewRecorder()
+	h.ServeHTTP(modifiedSince, modifiedSinceRequest)
+	if modifiedSince.Code != http.StatusNotModified {
+		t.Fatalf("If-Modified-Since status = %d, want %d", modifiedSince.Code, http.StatusNotModified)
+	}
+	if got := modifiedSince.Header().Get("Last-Modified"); got != lastModified.Format(http.TimeFormat) {
+		t.Errorf("conditional Last-Modified = %q, want %q", got, lastModified.Format(http.TimeFormat))
+	}
+	if requests != 1 {
+		t.Errorf("upstream requests = %d, want 1", requests)
+	}
+}
+
+func TestHomebrewHandler_HeadPreservesUpstreamMethodWithMetadataCacheEnabled(t *testing.T) {
+	body := `{"payload":"signed bytes","signatures":[]}`
+	upstreamMethod := ""
+	upstreamAuthorization := ""
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		upstreamMethod = r.Method
+		upstreamAuthorization = r.Header.Get("Authorization")
+		w.Header().Set("Content-Type", "application/json")
+		w.Header().Set("Content-Length", strconv.Itoa(len(body)))
+		w.Header().Set("ETag", `"head-etag"`)
+		if r.Method != http.MethodHead {
+			_, _ = io.WriteString(w, body)
+		}
+	}))
+	defer upstream.Close()
+
+	proxy, _, _, _ := setupTestProxy(t)
+	proxy.CacheMetadata = true
+	proxy.MetadataTTL = time.Hour
+	proxy.HTTPClient = upstream.Client()
+	h := NewHomebrewHandler(proxy, upstream.URL+"/api").Routes()
+
+	headRequest := httptest.NewRequest(http.MethodHead, "/formula.jws.json", nil)
+	headRequest.Header.Set("Authorization", "Bearer client-secret")
+	head := httptest.NewRecorder()
+	h.ServeHTTP(head, headRequest)
+
+	if head.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d", head.Code, http.StatusOK)
+	}
+	if upstreamMethod != http.MethodHead {
+		t.Errorf("upstream method = %q, want HEAD", upstreamMethod)
+	}
+	if upstreamAuthorization != "" {
+		t.Errorf("upstream Authorization = %q, want empty", upstreamAuthorization)
+	}
+	if head.Body.Len() != 0 {
+		t.Errorf("body length = %d, want 0", head.Body.Len())
+	}
+	if got := head.Header().Get("Content-Length"); got != strconv.Itoa(len(body)) {
+		t.Errorf("Content-Length = %q, want %d", got, len(body))
+	}
+	if got := head.Header().Get("ETag"); got != `"head-etag"` {
+		t.Errorf("ETag = %q, want %q", got, `"head-etag"`)
+	}
+}
+
+func TestHomebrewHandler_ServesStaleCachedResponseWhenUpstreamFails(t *testing.T) {
+	body := `{"payload":"signed bytes","signatures":[]}`
+	available := true
+	requests := 0
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		requests++
+		if !available {
+			http.Error(w, "unavailable", http.StatusServiceUnavailable)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		w.Header().Set("ETag", `"stale-etag"`)
+		_, _ = io.WriteString(w, body)
+	}))
+	defer upstream.Close()
+
+	proxy, _, _, _ := setupTestProxy(t)
+	proxy.CacheMetadata = true
+	proxy.MetadataTTL = 5 * time.Millisecond
+	proxy.HTTPClient = upstream.Client()
+	h := NewHomebrewHandler(proxy, upstream.URL+"/api").Routes()
+
+	first := httptest.NewRecorder()
+	h.ServeHTTP(first, httptest.NewRequest(http.MethodGet, "/formula.jws.json", nil))
+	if first.Code != http.StatusOK {
+		t.Fatalf("warm status = %d, want %d", first.Code, http.StatusOK)
+	}
+
+	time.Sleep(10 * time.Millisecond)
+	available = false
+	stale := httptest.NewRecorder()
+	h.ServeHTTP(stale, httptest.NewRequest(http.MethodGet, "/formula.jws.json", nil))
+	if stale.Code != http.StatusOK {
+		t.Fatalf("stale status = %d, want %d; body: %s", stale.Code, http.StatusOK, stale.Body.String())
+	}
+	if got := stale.Body.String(); got != body {
+		t.Errorf("stale body = %q, want %q", got, body)
+	}
+	if got := stale.Header().Get("Warning"); got != containerStaleWarning {
+		t.Errorf("Warning = %q, want %q", got, containerStaleWarning)
+	}
+	if requests != 2 {
+		t.Errorf("upstream requests = %d, want 2", requests)
+	}
+}
+
+func TestHomebrewHandler_ProxiesSupportedAPIPaths(t *testing.T) {
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, _ = io.WriteString(w, r.URL.RequestURI())
+	}))
+	defer upstream.Close()
+
+	proxy, _, _, _ := setupTestProxy(t)
+	proxy.HTTPClient = upstream.Client()
+	h := NewHomebrewHandler(proxy, upstream.URL+"/api").Routes()
+
+	paths := []string{
+		"/formula.jws.json",
+		"/cask.jws.json",
+		"/formula/jq.json",
+		"/cask/firefox.json",
+		"/internal/packages.arm64_tahoe.jws.json?download=1",
+	}
+	for _, requestPath := range paths {
+		t.Run(requestPath, func(t *testing.T) {
+			w := httptest.NewRecorder()
+			h.ServeHTTP(w, httptest.NewRequest(http.MethodGet, requestPath, nil))
+			if w.Code != http.StatusOK {
+				t.Fatalf("status = %d, want %d", w.Code, http.StatusOK)
+			}
+			if got, want := w.Body.String(), "/api"+requestPath; got != want {
+				t.Errorf("upstream request = %q, want %q", got, want)
+			}
+		})
+	}
+}
+
+func TestHomebrewHandler_RejectsUnsupportedRequests(t *testing.T) {
+	proxy, _, _, _ := setupTestProxy(t)
+	h := NewHomebrewHandler(proxy, "https://example.test/api").Routes()
+
+	method := httptest.NewRecorder()
+	h.ServeHTTP(method, httptest.NewRequest(http.MethodPost, "/formula.jws.json", nil))
+	if method.Code != http.StatusMethodNotAllowed {
+		t.Errorf("POST status = %d, want %d", method.Code, http.StatusMethodNotAllowed)
+	}
+	if got := method.Header().Get("Allow"); got != "GET, HEAD" {
+		t.Errorf("Allow = %q, want GET, HEAD", got)
+	}
+
+	root := httptest.NewRecorder()
+	h.ServeHTTP(root, httptest.NewRequest(http.MethodGet, "/", nil))
+	if root.Code != http.StatusNotFound {
+		t.Errorf("root status = %d, want %d", root.Code, http.StatusNotFound)
+	}
+
+	traversal := httptest.NewRecorder()
+	h.ServeHTTP(traversal, httptest.NewRequest(http.MethodGet, "/%2e%2e/secret", nil))
+	if traversal.Code != http.StatusNotFound {
+		t.Errorf("traversal status = %d, want %d", traversal.Code, http.StatusNotFound)
+	}
+}
+
+func TestRegisterHomebrewArtifacts(t *testing.T) {
+	h := &ContainerHandler{registryURL: dockerHubRegistry}
+	artifactUpstream := "https://homebrew-proxy.example.com"
+	RegisterHomebrewArtifacts(h, artifactUpstream+"/")
+
+	if got := h.registryURLFor("homebrew/core/jq"); got != artifactUpstream {
+		t.Errorf("homebrew/core registry = %q, want %q", got, artifactUpstream)
+	}
+	if got := h.registryURLFor("homebrew/cask/firefox"); got != "" {
+		t.Errorf("other Homebrew registry = %q, want blocked", got)
+	}
+	if got := h.registryURLFor("library/nginx"); got != dockerHubRegistry {
+		t.Errorf("unrelated registry = %q, want %q", got, dockerHubRegistry)
+	}
+}
+
+func TestRegisterHomebrewArtifactsRejectsOtherHomebrewRoutes(t *testing.T) {
+	upstreamRequests := 0
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		upstreamRequests++
+		_, _ = io.WriteString(w, "unexpected upstream response")
+	}))
+	defer upstream.Close()
+
+	proxy, _, _, fetcher := setupTestProxy(t)
+	proxy.HTTPClient = upstream.Client()
+	fetcher.artifact = &fetch.Artifact{
+		Body:        io.NopCloser(strings.NewReader("unexpected upstream blob")),
+		ContentType: "application/octet-stream",
+	}
+	h := &ContainerHandler{proxy: proxy, registryURL: upstream.URL}
+	RegisterHomebrewArtifacts(h, "https://ghcr.io")
+
+	const digest = "sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+	paths := []string{
+		"/homebrew/cask/firefox/blobs/" + digest,
+		"/homebrew/cask/firefox/manifests/latest",
+		"/homebrew/cask/firefox/tags/list",
+	}
+	for _, path := range paths {
+		t.Run(path, func(t *testing.T) {
+			w := httptest.NewRecorder()
+			h.Routes().ServeHTTP(w, httptest.NewRequest(http.MethodGet, path, nil))
+			if w.Code != http.StatusNotFound {
+				t.Errorf("status = %d, want %d; body: %s", w.Code, http.StatusNotFound, w.Body.String())
+			}
+		})
+	}
+
+	if fetcher.fetchCalled {
+		t.Error("blocked Homebrew blob reached the artifact fetcher")
+	}
+	if upstreamRequests != 0 {
+		t.Errorf("blocked Homebrew routes made %d upstream requests, want 0", upstreamRequests)
+	}
+}

internal/server/server.go

@@ -259,7 +259,9 @@ func (s *Server) Start() error {
 	condaHandler := handler.NewCondaHandler(proxy, s.cfg.BaseURL)
 	cranHandler := handler.NewCRANHandler(proxy, s.cfg.BaseURL)
 	juliaHandler := handler.NewJuliaHandler(proxy, s.cfg.BaseURL)
+	homebrewHandler := handler.NewHomebrewHandler(proxy, s.cfg.Upstream.HomebrewAPI)
 	containerHandler := handler.NewContainerHandler(proxy, s.cfg.BaseURL, s.cfg.Upstream.OCI)
+	handler.RegisterHomebrewArtifacts(containerHandler, s.cfg.Upstream.HomebrewArtifact)
 	helmHandler := handler.NewHelmHandler(proxy, s.cfg.BaseURL, s.cfg.Upstream.Helm)
 	debianHandler := handler.NewDebianHandler(proxy, s.cfg.BaseURL, s.cfg.Upstream.Debian)
 	rpmHandler := handler.NewRPMHandler(proxy, s.cfg.BaseURL)
@@ -279,6 +281,7 @@ func (s *Server) Start() error {
 	r.Mount("/conda", http.StripPrefix("/conda", condaHandler.Routes()))
 	r.Mount("/cran", http.StripPrefix("/cran", cranHandler.Routes()))
 	r.Mount("/julia", http.StripPrefix("/julia", juliaHandler.Routes()))
+	r.Mount("/homebrew", http.StripPrefix("/homebrew", homebrewHandler.Routes()))
 	r.Mount("/v2", http.StripPrefix("/v2", containerHandler.Routes()))
 	r.Mount("/helm", http.StripPrefix("/helm", helmHandler.Routes()))
 	r.Mount("/debian", http.StripPrefix("/debian", debianHandler.Routes()))