Expose permission-checked immutable asset metadata for shared depot adoption

internal/platform/assets.go

@@ -271,6 +271,51 @@ func assetReadable(r *http.Request, tx *sql.Tx, project, workspace, id, account
 	}
 	return false, nil
 }
+
+// Metadata uses the same read policy as original bytes; it is not a persistent grant.
+func (s *service) getAssetMetadata(w http.ResponseWriter, r *http.Request, project, account string) error {
+	if r.Method != http.MethodGet {
+		reject(w, 405, "method_not_allowed")
+		return nil
+	}
+	id, workspace := r.PathValue("asset"), r.PathValue("workspace")
+	if !uuidSlugPattern.MatchString(id) {
+		reject(w, 404, "not_found")
+		return nil
+	}
+	tx, err := s.db.BeginTx(r.Context(), nil)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+	var locked string
+	err = tx.QueryRowContext(r.Context(), `SELECT id::text FROM workspaces WHERE project=$1 AND id=$2 FOR UPDATE`, project, workspace).Scan(&locked)
+	if err != nil {
+		return err
+	}
+	allowed, err := assetReadable(r, tx, project, workspace, id, account)
+	if err != nil {
+		return err
+	}
+	if !allowed {
+		reject(w, 404, "not_found")
+		return nil
+	}
+	var info assetInfo
+	var digest string
+	err = tx.QueryRowContext(r.Context(), `SELECT id::text,mime_type,octet_length(bytes),width,height,digest FROM canvas_assets WHERE project=$1 AND workspace_id=$2 AND id=$3`, project, workspace, id).Scan(&info.ID, &info.MIME, &info.Bytes, &info.Width, &info.Height, &digest)
+	if err != nil {
+		return err
+	}
+	if err = tx.Commit(); err != nil {
+		return err
+	}
+	info.URL = s.assetURL(project, workspace, id)
+	w.Header().Set("Cache-Control", "private, no-store")
+	reply(w, 200, response{"metadata_version": 1, "asset": info, "sha256": digest})
+	return nil
+}
+
 func (s *service) getAsset(w http.ResponseWriter, r *http.Request, project, account string) error {
 	if r.Method != http.MethodGet {
 		reject(w, 405, "method_not_allowed")

internal/platform/http.go

@@ -151,6 +151,7 @@ func Register(mux *http.ServeMux, db *sql.DB, callbacks map[string]string, origi
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials", s.protected(callbacks, s.materials))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/assets", s.protected(callbacks, s.uploadAsset))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/assets/operations/{request}", s.protected(callbacks, s.assetOperation))
+	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/assets/{asset}/metadata", s.protected(callbacks, s.getAssetMetadata))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/assets/{asset}", s.protected(callbacks, s.getAsset))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}", s.protected(callbacks, s.material))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas", s.protected(callbacks, s.canvas))

internal/platform/integration_test.go

@@ -584,9 +584,33 @@ func TestOnboardingAndSharing(t *testing.T) {
 			t.Fatal("preview changed small original or privacy headers")
 		}
 	}
+	// Metadata discloses the same immutable identity only after a fresh read permission check.
+	metadataPath := workspacePath + "/assets/" + uploaded["id"].(string) + "/metadata"
+	for _, sample := range []struct {
+		token  string
+		status int
+	}{{tokens[0], 200}, {tokens[1], 404}, {tokens[2], 404}} {
+		request := httptest.NewRequest("GET", metadataPath, nil)
+		request.Header.Set("Authorization", "Bearer "+sample.token)
+		result := httptest.NewRecorder()
+		mux.ServeHTTP(result, request)
+		if result.Code != sample.status {
+			t.Fatalf("metadata permission got %d want %d: %s", result.Code, sample.status, result.Body.String())
+		}
+		if result.Code == 200 {
+			var metadata response
+			if err := json.Unmarshal(result.Body.Bytes(), &metadata); err != nil {
+				t.Fatal(err)
+			}
+			digest := sha256.Sum256(assetPNG.Bytes())
+			if metadata["metadata_version"] != float64(1) || metadata["sha256"] != hex.EncodeToString(digest[:]) || !modelEqual(metadata["asset"], uploaded) || result.Header().Get("Cache-Control") != "private, no-store" {
+				t.Fatalf("invalid metadata identity: %s", result.Body.String())
+			}
+		}
+	}
 	// Neither a snapshot nor an asset response may keep the workspace locked
 	// while a slow downstream consumer is accepting its body.
-	for _, path := range []string{canvasPath, workspacePath + "/assets/" + uploaded["id"].(string)} {
+	for _, path := range []string{canvasPath, workspacePath + "/assets/" + uploaded["id"].(string), metadataPath} {
 		var probeErr error
 		writer := &readLockProbe{ResponseRecorder: httptest.NewRecorder(), probe: func() {
 			lockTx, e := db.BeginTx(ctx, nil)