* Under the hood, SQLite creates surrogate keys (ROWID) anyway. We may as well take advantage of this and use the surrogates for foreign keys as well, since they are simpler and more efficient than compound foreign keys.
* Create indexes for efficient eviction queries
When inserting an cached resource, or removing a region, remove least-recently used resources and tiles, not used by offline regions, until the used database size, as calculated by multiplying the number of in-use pages by the page size, is less than the maximum cache size minus 5 times the page size.
In addition, OfflineDatabase may be configured to ignore cache puts of individual resources larger than a certain size.
This policy is similar but not identical to the former SQLiteCache policy:
* It accounts for offline, by exempting resources required by offline regions from eviction.
* It must delete from two tables (resources and tiles), rather than one. Currently the strategy is naive: evict 50 rows at a time from each table.
* It makes maximumCacheSize and maximumCacheEntrySize completely independent. The SQLiteCache implementation evicted when `usedSize > maximumCacheSize - 2 * maximumCacheEntrySize`. This evicts when `usedSize > maximumCacheSize - 5 * pageSize`.
* It uses a non-unlimited default value for maximumCacheSize: 50 MB. We should have always had a limit in place; "a cache without an eviction policy is a resource leak".
There is no such thing as a cancelled response, only cancelled requests. A request that is cancelled does not have its callback called with a Response.
This allows the FileSource interface itself to support revalidation. We could (and probably should) now rewrite HTTPContextBase implementations as FileSource implementations.
Updating glyphs is still unsupported, and there's no good use case for doing so. When we're using a stale glyph PBF, and the fresh answer contains changed to that glyph, we will continue to use the old glyph.
This is a naïve implementation that essentially merges updated data into existing data. It will *not* remove icons from the stale sprite if they aren't present in the fresh sprite (we aren't tracking the source of a sprite, and the user could have changed it as well). Similarly, it will not update icons that have changed in dimension. This is a rare edge case and probably not worth implementing.
We're now supporting using stale TileJSON and GeoJSON data. When we receive a new answer with an updated TileJSON file, we're replacing the Source's metadata with the new one and trigger updates to make sure we're loading the correct tiles. Similarly, GeoJSON data will be reparsed.
This adds support for using cached styles that are stale. They're treated like changing styles; when the refreshed style changed compared to the one we've already had, we're swapping out the entire style, which might cause a slight flicker.
If you use many different caches, expired weak_ptrs will pile up in the unordered_map, but that is an edge case, and you probably shouldn't do that anyway.
I regenerated assets.zip so that all file paths have an `assets/` prefix, as the Android AssetFileSource implementation asserts, and removed `TEST_DATA` from the paths.
* Move asset:// URL handling to DefaultFileSource.
* AssetFileSource implements FileSource interface and follows familiar implementation patterns.
* Move default implementation to platform/default, zip implementation to platform/android.
* Don't bother with modified / expires / etag -- assets are not cached so it doesn't matter.
* Don't bother with interleaving individual IO calls on the implementation thread. That adds a lot of complexity for very little benefit.
The cache `accessed` field resolution is 1s, so we
need to sleep a little bit more in order to make
sure that the cache entries we are refreshing will have
a different `accessed` time than the other entries.
Added aliases for std::chrono typedefs (eg. 'Seconds' for
std::chrono::seconds). These aliases are used together with templated
helper functions to replace time_t with std::chrono::seconds for most
cases, in particular for 'modified' and 'expires' values in Response.
