2.x TTL doesn't purge expired documents

[borrrden]

Library Version

Iridium

.NET Runtime

All

Operating System / Device Details

All

Log Output

n/a

Expected behavior

An expired document should be purged

Actual behavior

No purge occurs

Steps To Reproduce

1. Set TTL to something small (e.g. 2 seconds)
2. Wait for more than the TTL
3. Observe that the document is still present

Reproduction Project

[borrrden]

@Sandychuang8 I blanked on this when reviewing the PR. When document expiration is set, a timer needs to be set up for the next expiration (unless a timer is already set for a point in time sooner than the new expiration). The timer's job is to then run the LiteCore c4db_purgeExpiredDocs method, and reschedule if there is another document that will be expiring. But be careful not to exceed the maximum allowed time for a timer (see #1029 )