Fix outdated names and implementation details in design proposal doc

Signed-off-by: Cameron Miller <[email protected]>

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/TakeSnapshot
 ```
 
 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.
+
+* 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 `TakeSnapshot.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.
+* 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 `TakeSnapshot.srv` service interface.
 * Add `--snapshot-mode` to the `record` verb and update `StorageOptions`
 * Add keyboard shortcut for triggering a snapshot in snapshot mode