merged from gramsrv upstream

internal/store/postgres/blob_migration.go

@@ -0,0 +1,111 @@
+package postgres
+
+import (
+	"context"
+	"encoding/hex"
+	"fmt"
+
+	"telesrv/internal/domain"
+)
+
+// BlobMigrationObject is one immutable content-addressed object referenced by
+// one or more logical file locations on the same permanent backend.
+type BlobMigrationObject struct {
+	ObjectKey    string
+	Size         int64
+	SHA256       []byte
+	LocationRows int64
+}
+
+// ListBlobMigrationObjects keyset-pages distinct objects. Inconsistent size or
+// digest metadata for one content key is returned as an error, never guessed.
+func (s *MediaStore) ListBlobMigrationObjects(
+	ctx context.Context,
+	backend domain.MediaBackend,
+	afterObjectKey string,
+	limit int,
+) ([]BlobMigrationObject, error) {
+	if limit <= 0 {
+		return nil, nil
+	}
+	rows, err := s.db.Query(ctx, `
+SELECT
+    object_key,
+    min(size)::bigint,
+    count(DISTINCT size)::bigint,
+    min(encode(sha256, 'hex')),
+    count(DISTINCT encode(sha256, 'hex'))::bigint,
+    count(*)::bigint
+FROM file_blobs
+WHERE backend = $1 AND object_key > $2
+GROUP BY object_key
+ORDER BY object_key
+LIMIT $3`, string(backend), afterObjectKey, limit)
+	if err != nil {
+		return nil, fmt.Errorf("list %s blob migration objects: %w", backend, err)
+	}
+	defer rows.Close()
+	objects := make([]BlobMigrationObject, 0, limit)
+	for rows.Next() {
+		var (
+			object         BlobMigrationObject
+			sizeVariants   int64
+			digestHex      string
+			digestVariants int64
+		)
+		if err := rows.Scan(
+			&object.ObjectKey,
+			&object.Size,
+			&sizeVariants,
+			&digestHex,
+			&digestVariants,
+			&object.LocationRows,
+		); err != nil {
+			return nil, fmt.Errorf("scan blob migration object: %w", err)
+		}
+		if sizeVariants != 1 || digestVariants != 1 {
+			return nil, fmt.Errorf("blob %q has inconsistent persisted size or SHA-256 metadata", object.ObjectKey)
+		}
+		digest, err := hex.DecodeString(digestHex)
+		if err != nil || len(digest) != 32 {
+			return nil, fmt.Errorf("blob %q has invalid persisted SHA-256 metadata", object.ObjectKey)
+		}
+		if object.ObjectKey != digestHex {
+			return nil, fmt.Errorf("blob %q object key does not match persisted SHA-256 %q", object.ObjectKey, digestHex)
+		}
+		object.SHA256 = digest
+		objects = append(objects, object)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, fmt.Errorf("iterate blob migration objects: %w", err)
+	}
+	return objects, nil
+}
+
+// MoveFileBlobBackendForObject atomically relabels every logical location for a
+// verified immutable object. It refuses partial/racing changes.
+func (s *MediaStore) MoveFileBlobBackendForObject(
+	ctx context.Context,
+	from domain.MediaBackend,
+	to domain.MediaBackend,
+	objectKey string,
+	expectedRows int64,
+) error {
+	if expectedRows <= 0 {
+		return fmt.Errorf("blob %q expected row count must be positive", objectKey)
+	}
+	result, err := s.db.Exec(ctx, `
+UPDATE file_blobs
+SET backend = $1
+WHERE backend = $2 AND object_key = $3`, string(to), string(from), objectKey)
+	if err != nil {
+		return fmt.Errorf("move blob %q metadata from %s to %s: %w", objectKey, from, to, err)
+	}
+	if result.RowsAffected() != expectedRows {
+		return fmt.Errorf(
+			"move blob %q metadata changed %d rows, want %d",
+			objectKey, result.RowsAffected(), expectedRows,
+		)
+	}
+	return nil
+}