🐛 Avoid mutating milestone snapshots when building from ops #651
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
ericyhwang
approved these changes
May 14, 2024
| next(); | ||
| }, | ||
| function(next) { | ||
| connection.fetchSnapshot('books', 'mocking-bird', 3, next); |
There was a problem hiding this comment.
Let's add a comment indicating that this test case is making sure the client-facing connection.fetchSnapshot doesn't cause an in-place mutation to the stored milestone snapshot returned by the internal milestoneDb.getMilestoneSnapshot.
It took me a bit to realize where the mutation would formerly have occurred.
At the moment, we directly pass our milestone snapshot to `ot.applyOps()`, which [mutates the snapshot][1]. In most Production-grade implementations of the `MilestoneDb`, this is fine, since mutating the in-memory `Snapshot` will have no effect on the underlying database representation. However, this does break the `MemoryMilestoneDb` (eg in tests). In order to fix this, and generally be defensive (eg if db adapters decide to implement an in-memory cache), this change clones the snapshot before calling `ot.applyOps()` on it. [1]: https://github.com/share/sharedb/blob/a5c19b986d65c93abbc9ed11f7a25c0dbaf0788c/lib/ot.js#L172
alecgibson
force-pushed
the
milestone-mutation
branch
from
8a52f10 to
1683efa
Compare
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
At the moment, we directly pass our milestone snapshot to
ot.applyOps(), which mutates the snapshot.In most Production-grade implementations of the
MilestoneDb, this is fine, since mutating the in-memorySnapshotwill have no effect on the underlying database representation.However, this does break the
MemoryMilestoneDb(eg in tests).In order to fix this, and generally be defensive (eg if db adapters decide to implement an in-memory cache), this change clones the snapshot before calling
ot.applyOps()on it.