1258801 - Add telemetry to track malformed server records

Status: NEW

(Firefox for iOS :: Telemetry, defect)

Description

[Richard Newman [:rnewman]]

In some circumstances we drop majorly invalid records on the floor.

At point of download:

https://github.com/mozilla/firefox-ios/blob/823d11a0d2264513b06b13cdd8a2b971fe7b181b/Sync/StorageClient.swift#L679-L679

or parse:

https://github.com/mozilla/firefox-ios/blob/07d0c6f27b0991cf46e84d5dd9ac931842a41124/Sync/Record.swift#L63-L63

-- that is, if they don't parse as JSON (which should never occur), or the JSON payload doesn't pass very rudimentary validation checks.

If these checks fail, and we drop the record on the floor, we'll never insert them into the buffer.

This will manifest as a missing record when we validate structure, even though the record is present on the server.

We should measure the frequency of these states. I don't expect many, because our record validation at point of buffering is quite weak these days.

These records aren't usable, so there's not much we can do with them until another client uploads a corrected version, but having more precise numbers would be nice.