merged from gramsrv upstream

internal/updatecdn/store.go

@@ -0,0 +1,60 @@
+package updatecdn
+
+import (
+	"fmt"
+	"os"
+	"sync"
+	"time"
+)
+
+// Store atomically reloads the catalog when the manifest changes. A broken new
+// manifest is never mixed with the previous snapshot.
+type Store struct {
+	manifestPath string
+	filesDir     string
+
+	mu       sync.RWMutex
+	catalog  *Catalog
+	modTime  time.Time
+	fileSize int64
+}
+
+func NewStore(manifestPath, filesDir string) (*Store, error) {
+	store := &Store{manifestPath: manifestPath, filesDir: filesDir}
+	if _, err := store.Snapshot(); err != nil {
+		return nil, err
+	}
+	return store, nil
+}
+
+func (s *Store) Snapshot() (*Catalog, error) {
+	info, err := os.Stat(s.manifestPath)
+	if err != nil {
+		return nil, fmt.Errorf("stat manifest: %w", err)
+	}
+	s.mu.RLock()
+	if s.catalog != nil && info.ModTime().Equal(s.modTime) && info.Size() == s.fileSize {
+		catalog := s.catalog
+		s.mu.RUnlock()
+		return catalog, nil
+	}
+	s.mu.RUnlock()
+
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	info, err = os.Stat(s.manifestPath)
+	if err != nil {
+		return nil, fmt.Errorf("stat manifest: %w", err)
+	}
+	if s.catalog != nil && info.ModTime().Equal(s.modTime) && info.Size() == s.fileSize {
+		return s.catalog, nil
+	}
+	catalog, err := LoadCatalog(s.manifestPath, s.filesDir)
+	if err != nil {
+		return nil, err
+	}
+	s.catalog = catalog
+	s.modTime = info.ModTime()
+	s.fileSize = info.Size()
+	return catalog, nil
+}