Add --snapshot-mode argument to the "record" verb (ros2#851)

* Add snapshot mode parameter to record verb


Signed-off-by: Cameron Miller <cammlle@amazon.com>

docs/design/rosbag2_snapshot_mode.md

@@ -18,7 +18,7 @@ $ ros2 bag record --max-cache-size 100000 --snapshot-mode [topics [topics ...]]
 
 Triggering a snapshot via CLI:
 ```
-$ ros2 service call ~/snapshot rosbag2_interfaces/TakeSnapshot
+$ ros2 service call /rosbag2_recorder/snapshot rosbag2_interfaces/Snapshot
 ```
 
 Triggering a snapshot with a keyboard shortcut:
@@ -29,22 +29,24 @@ Triggering a snapshot with a keyboard shortcut:
 
 * Add a `--snapshot-mode` flag to the `record` verb in `ros2bag` that will be passed via `StorageOptions`.
 
-* Create a new class `CircularBufferMessageCache` which maintains two circular buffers sized according to the existing `—max-cache-size` parameter. During snapshot mode, this class will keep adding messages to the same circular buffer until triggered to switch to the secondary buffer by the `Recorder` class.
+* Create a new class `CircularMessageCache` which maintains two circular buffers, individally implemented in a class `MessageCacheCircularBuffer` and sized according to the existing `—max-cache-size` parameter. During snapshot mode, `CircularMessageCache` will keep adding messages to the same circular buffer until triggered to switch to the secondary buffer by the `Recorder` class.
 
-* Create a service `~/snapshot` in the `rosbag2_recorder` node that will listen for snapshot requests. Upon receiving a service call, it will trigger a buffer flip in `CircularBufferMessageCache` and call the new `take_snapeshot` function in `SequentialWriter` (detailed below) to write the snapshot messages to storage.
+* Create a service `~/snapshot` in the `rosbag2_recorder` node that will listen for snapshot requests. Upon receiving a service call, it will trigger a buffer flip in `CircularMessageCache` and call the new `take_snapeshot` function in `SequentialWriter` (detailed below) to write the snapshot messages to storage.
 
-* Modify `SequentialWriter` to use `CircularBufferMessageCache` when snapshot mode is enabled instead of `MessageCache` and `CacheConsumer`.
+* Modify `SequentialWriter` to use `CircularMessageCache` when snapshot mode is enabled instead of `MessageCache` and `CacheConsumer`.
 
-* Add a new `take_snapshot` function to `SequentialWriter` that will be invoked by the `rosbag2_recorder` node's snapshot service to write the snapshot data to the rosbag, close the rosbag, and open a new rosbag for a future snapshot.
+* Add a new `take_snapshot` function to `SequentialWriter` that will be invoked by the `rosbag2_recorder` node's snapshot service to write the snapshot data to the rosbag.
 
-* Implement the `~/snapshot` service interface as `TakeSnapshot.srv` in `rosbag2_interfaces`. It won’t require any arguments (similar to `Resume.srv`).
+* Modify `BaseWriterInterface` to include a pure virutal function `take_snapshot` to ensure that all future writers are compatible with snapshot mode.
+
+* Implement the `~/snapshot` service interface as `Snapshot.srv` in `rosbag2_interfaces`. It won’t require any arguments (similar to `Resume.srv`).
 
 
 ## Implementation Breakdown
 The snapshot feature implementation could be broken down into the following PRs:
 
-* Implement `CircularBufferMessageCache` and add corresponding tests.
-* Integrate `CircularBufferMessageCache` into `SequentialWriter` and update its tests.
-* Create the `~/snapshot` service in the `Recorder` class, add corresponding tests, and create the `TakeSnapshot.srv` service interface.
+* Implement `CircularMessageCache` and `MessageCacheCircularBuffer`. Then add corresponding tests.
+* Integrate `CircularMessageCache` into `SequentialWriter` and update its tests.
+* Create the `~/snapshot` service in the `Recorder` class, add corresponding tests, and create the `Snapshot.srv` service interface.
 * Add `--snapshot-mode` to the `record` verb and update `StorageOptions`
 * Add keyboard shortcut for triggering a snapshot in snapshot mode

ros2bag/ros2bag/verb/record.py

@@ -109,6 +109,11 @@ def add_arguments(self, parser, cli_name):  # noqa: D102
             help='Number of files or messages that may be compressed in parallel. '
                  'Default is 0, which will be interpreted as the number of CPU cores.'
         )
+        parser.add_argument(
+            '--snapshot-mode', action='store_true',
+            help='Enable snapshot mode. Messages will not be written to the bagfile until '
+                 'the "/rosbag2_recorder/snapshot" service is called.'
+        )
         parser.add_argument(
             '--include-hidden-topics', action='store_true',
             help='record also hidden topics.'
@@ -185,6 +190,7 @@ def main(self, *, args):  # noqa: D102
             max_cache_size=args.max_cache_size,
             storage_preset_profile=args.storage_preset_profile,
             storage_config_uri=storage_config_file,
+            snapshot_mode=args.snapshot_mode
         )
         record_options = RecordOptions()
         record_options.all = args.all

rosbag2_py/src/rosbag2_py/_storage.cpp

@@ -43,14 +43,15 @@ PYBIND11_MODULE(_storage, m) {
   pybind11::class_<rosbag2_storage::StorageOptions>(m, "StorageOptions")
   .def(
     pybind11::init<
-      std::string, std::string, uint64_t, uint64_t, uint64_t, std::string, std::string>(),
+      std::string, std::string, uint64_t, uint64_t, uint64_t, std::string, std::string, bool>(),
     pybind11::arg("uri"),
     pybind11::arg("storage_id"),
     pybind11::arg("max_bagfile_size") = 0,
     pybind11::arg("max_bagfile_duration") = 0,
     pybind11::arg("max_cache_size") = 0,
     pybind11::arg("storage_preset_profile") = "",
-    pybind11::arg("storage_config_uri") = "")
+    pybind11::arg("storage_config_uri") = "",
+    pybind11::arg("snapshot_mode") = false)
   .def_readwrite("uri", &rosbag2_storage::StorageOptions::uri)
   .def_readwrite("storage_id", &rosbag2_storage::StorageOptions::storage_id)
   .def_readwrite(
@@ -67,7 +68,10 @@ PYBIND11_MODULE(_storage, m) {
     &rosbag2_storage::StorageOptions::storage_preset_profile)
   .def_readwrite(
     "storage_config_uri",
-    &rosbag2_storage::StorageOptions::storage_config_uri);
+    &rosbag2_storage::StorageOptions::storage_config_uri)
+  .def_readwrite(
+    "snapshot_mode",
+    &rosbag2_storage::StorageOptions::snapshot_mode);
 
   pybind11::class_<rosbag2_storage::StorageFilter>(m, "StorageFilter")
   .def(