[core] Modularize FileSource codebase (#15768)

* [core] Introduce FileSourceManager and use it for default platform impl

  - Add `FileSourceManager` interface that provides access to `FileSource`
    instances and means of registering / unregistering `FileSource` factories
  - Split `DefaultFileSource` into smaller parts
  - Add `DatabaseFileSource` interface and it's default implementation
  - Remove inter-dependencies between concrete `FileSource` classes

* [build] Add files to next build system

* [core] Add generic property setters / getters

* [core] Remove setOnlineStatus from OnlineFileSource interface

* [core] Hide threading implementation details from DatabaseFileSource interface

* [core] Make DB file source methods virtual

* [core] Add documentation for DatabaseFileSource and rename one method

* [core] Use simple callback instead of ActorRef

* [core] Remove ActorRef from OnlineFileSource public header

* [core] Add callback to FileSource::forward async API

* [core] Pass OfflineRegionDefinition by value

* [core] Update tests to use modular file sources

* [core] Update unit tests

* [core] Update unit tests after rebase

* [core] Backport low prio fix for cached requests

* [core] Backport pack database

* [core] Return removed factory from unRegisterFileSourceFactory

* [core] Rename shadowed args in onlinefilesource

* [core] Remove simple std::function callback aliases

* [core] Expose online file source property keys in public header file

* [test-runner] Add proxy file source test runner

* [cache] Update mbgl-cache utility to use new file source

* [metrics] Rebaseline binary size metrics

* [offline] Update offline utility

* [core] Update changelog

1 files changed, 31 insertions, 13 deletions

diff --git a/platform/glfw/main.cpp b/platform/glfw/main.cpp
index 8f134804f0..ded8ee3e1f 100644
--- a/platform/glfw/main.cpp
+++ b/platform/glfw/main.cpp
@@ -3,13 +3,14 @@
 #include "settings_json.hpp"
 
 #include <mbgl/gfx/backend.hpp>
+#include <mbgl/renderer/renderer.hpp>
+#include <mbgl/storage/database_file_source.hpp>
+#include <mbgl/storage/file_source_manager.hpp>
+#include <mbgl/style/style.hpp>
 #include <mbgl/util/default_styles.hpp>
 #include <mbgl/util/logging.hpp>
 #include <mbgl/util/platform.hpp>
 #include <mbgl/util/string.hpp>
-#include <mbgl/storage/default_file_source.hpp>
-#include <mbgl/style/style.hpp>
-#include <mbgl/renderer/renderer.hpp>
 
 #include <args.hxx>
 
@@ -106,10 +107,16 @@ int main(int argc, char *argv[]) {
     mbgl::ResourceOptions resourceOptions;
     resourceOptions.withCachePath(cacheDB).withAccessToken(token);
 
-    auto fileSource = std::static_pointer_cast<mbgl::DefaultFileSource>(mbgl::FileSource::getSharedFileSource(resourceOptions));
+    auto onlineFileSource =
+        mbgl::FileSourceManager::get()->getFileSource(mbgl::FileSourceType::Network, resourceOptions);
     if (!settings.online) {
-        fileSource->setOnlineStatus(false);
-        mbgl::Log::Warning(mbgl::Event::Setup, "Application is offline. Press `O` to toggle online status.");
+        if (onlineFileSource) {
+            onlineFileSource->setProperty("online-status", false);
+            mbgl::Log::Warning(mbgl::Event::Setup, "Application is offline. Press `O` to toggle online status.");
+        } else {
+            mbgl::Log::Warning(mbgl::Event::Setup,
+                               "Network resource provider is not available, only local requests are supported.");
+        }
     }
 
     GLFWRendererFrontend rendererFrontend { std::make_unique<mbgl::Renderer>(view->getRendererBackend(), view->getPixelRatio()), *view };
@@ -132,9 +139,14 @@ int main(int argc, char *argv[]) {
 
     if (testDirValue) view->setTestDirectory(args::get(testDirValue));
 
-    view->setOnlineStatusCallback([&settings, fileSource]() {
+    view->setOnlineStatusCallback([&settings, onlineFileSource]() {
+        if (!onlineFileSource) {
+            mbgl::Log::Warning(mbgl::Event::Setup,
+                               "Cannot change online status. Network resource provider is not available.");
+            return;
+        }
         settings.online = !settings.online;
-        fileSource->setOnlineStatus(settings.online);
+        onlineFileSource->setProperty("online-status", settings.online);
         mbgl::Log::Info(mbgl::Event::Setup, "Application is %s. Press `O` to toggle online status.", settings.online ? "online" : "offline");
     });
 
@@ -152,20 +164,26 @@ int main(int argc, char *argv[]) {
         mbgl::Log::Info(mbgl::Event::Setup, "Changed style to: %s", newStyle.name);
     });
 
-    view->setPauseResumeCallback([fileSource] () {
+    // Resource loader controls top-level request processing and can resume / pause all managed sources simultaneously.
+    auto resourceLoader =
+        mbgl::FileSourceManager::get()->getFileSource(mbgl::FileSourceType::ResourceLoader, resourceOptions);
+    view->setPauseResumeCallback([resourceLoader]() {
         static bool isPaused = false;
 
         if (isPaused) {
-            fileSource->resume();
+            resourceLoader->resume();
         } else {
-            fileSource->pause();
+            resourceLoader->pause();
         }
 
         isPaused = !isPaused;
     });
 
-    view->setResetCacheCallback([fileSource] () {
-        fileSource->resetDatabase([](std::exception_ptr ex) {
+    // Database file source.
+    auto databaseFileSource = std::static_pointer_cast<mbgl::DatabaseFileSource>(
+        mbgl::FileSourceManager::get()->getFileSource(mbgl::FileSourceType::Database, resourceOptions));
+    view->setResetCacheCallback([databaseFileSource]() {
+        databaseFileSource->resetDatabase([](std::exception_ptr ex) {
             if (ex) {
                 mbgl::Log::Error(mbgl::Event::Database, "Failed to reset cache:: %s", mbgl::util::toString(ex).c_str());
             }