Restore: the warning for a blob read again says how the first read differed (zeros, shifted, other bytes)

2026-10-22 19:50:27 +02:00
parent b4f20cb070
commit 8032411789
1 changed files with 20 additions and 1 deletions
@@ -918,12 +918,31 @@ final class Repository {
 			}
 			$data = $this->decodeBlob($id, $again);
 			if (function_exists('OCP\Log\logger')) {
-				\OCP\Log\logger('ng_backup')->warning('NG Backup: blob ' . $id . ' did not decrypt as first read from pack ' . $pack . '; read again, it is fine');
+				\OCP\Log\logger('ng_backup')->warning('NG Backup: blob ' . $id . ' did not decrypt as first read from pack ' . $pack . ' at ' . $offset . '; read again, it is fine. First read: ' . self::howItDiffered($encrypted, $again));
 			}
 			return $data;
 		}
 	}

+	/**
+	 * What a read that went wrong looked like next to the right bytes, for the log: where it starts
+	 * to differ, and whether the rest is zeros or the right bytes from another place (a stream that
+	 * lost its place).
+	 */
+	private static function howItDiffered(string $wrong, string $right): string {
+		$at = strspn($wrong ^ $right, "\0");
+		$text = strlen($wrong) . ' bytes, differ from byte ' . $at . ' of ' . strlen($right);
+		$tail = substr($wrong, $at, 64);
+		if ($tail === '') {
+			return $text . ' (too short)';
+		}
+		if (trim($tail, "\0") === '') {
+			return $text . ' (zeros)';
+		}
+		$found = strpos($right, $tail);
+		return $text . ($found !== false ? ' (the right bytes from ' . ($found - $at) . ' bytes further on)' : ' (other bytes)');
+	}
+
 	/** Decrypts and checks a blob read from its pack; throws when it is corrupted or tampered with. */
 	private function decodeBlob(string $id, string $encrypted): string {
 		[, , , $raw, $flags] = $this->index->get($id);