Report start_time and end_time on empty bags

src/rosbags/rosbag1/reader.py

@@ -436,17 +436,17 @@ class Reader:
     @property
     def duration(self) -> int:
         """Duration in nanoseconds between earliest and latest messages."""
-        return self.end_time - self.start_time
+        return self.end_time - self.start_time if self.chunk_infos else 0
 
     @property
     def start_time(self) -> int:
         """Timestamp in nanoseconds of the earliest message."""
-        return min(x.start_time for x in self.chunk_infos)
+        return min(x.start_time for x in self.chunk_infos) if self.chunk_infos else 2**63 - 1
 
     @property
     def end_time(self) -> int:
         """Timestamp in nanoseconds after the latest message."""
-        return max(x.end_time for x in self.chunk_infos)
+        return max(x.end_time for x in self.chunk_infos) if self.chunk_infos else 0
 
     @property
     def message_count(self) -> int:

src/rosbags/rosbag2/reader.py

@@ -191,17 +191,18 @@ class Reader:
     def duration(self) -> int:
         """Duration in nanoseconds between earliest and latest messages."""
         nsecs: int = self.metadata['duration']['nanoseconds']
-        return nsecs + 1
+        return nsecs + 1 if self.message_count else 0
 
     @property
     def start_time(self) -> int:
         """Timestamp in nanoseconds of the earliest message."""
-        return self.metadata['starting_time']['nanoseconds_since_epoch']
+        nsecs: int = self.metadata['starting_time']['nanoseconds_since_epoch']
+        return nsecs if self.message_count else 2**63 - 1
 
     @property
     def end_time(self) -> int:
         """Timestamp in nanoseconds after the latest message."""
-        return self.start_time + self.duration
+        return self.start_time + self.duration if self.message_count else 0
 
     @property
     def message_count(self) -> int:

tests/test_reader.py

@@ -55,6 +55,22 @@ rosbag2_bagfile_information:
   compression_mode: {compression_mode}
 """
 
+METADATA_EMPTY = """
+rosbag2_bagfile_information:
+  version: 4
+  storage_identifier: sqlite3
+  relative_file_paths:
+    - db.db3
+  duration:
+    nanoseconds: 0
+  starting_time:
+    nanoseconds_since_epoch: 0
+  message_count: 0
+  topics_with_message_count: []
+  compression_format: ""
+  compression_mode: ""
+"""
+
 
 @pytest.fixture(params=['none', 'file', 'message'])
 def bag(request: SubRequest, tmp_path: Path) -> Path:
@@ -117,6 +133,21 @@ def bag(request: SubRequest, tmp_path: Path) -> Path:
     return tmp_path
 
 
+def test_empty_bag(tmp_path: Path) -> None:
+    """Test bags with broken fs layout."""
+    (tmp_path / 'metadata.yaml').write_text(METADATA_EMPTY)
+    dbpath = tmp_path / 'db.db3'
+    dbh = sqlite3.connect(dbpath)
+    dbh.executescript(Writer.SQLITE_SCHEMA)
+
+    with Reader(tmp_path) as reader:
+        assert reader.message_count == 0
+        assert reader.start_time == 2**63 - 1
+        assert reader.end_time == 0
+        assert reader.duration == 0
+        assert not list(reader.messages())
+
+
 def test_reader(bag: Path) -> None:
     """Test reader and deserializer on simple bag."""
     with Reader(bag) as reader:

tests/test_reader1.py

@@ -202,6 +202,10 @@ def test_reader(tmp_path: Path) -> None:  # pylint: disable=too-many-statements
     write_bag(bag, create_default_header())
     with Reader(bag) as reader:
         assert reader.message_count == 0
+        assert reader.start_time == 2**63 - 1
+        assert reader.end_time == 0
+        assert reader.duration == 0
+        assert not list(reader.messages())
 
     # empty bag, explicit encryptor
     bag = tmp_path / 'test.bag'