RemoteTagCache: new glue class for integrating RemoteTagScanner

This commit also puts an instance of RemoteTagScanner into the
Instance class, and hooks it into the "add" and "addid" commands.

src/Instance.hxx

@@ -26,6 +26,10 @@
 #include "event/MaskMonitor.hxx"
 #include "Compiler.h"
 
+#ifdef ENABLE_CURL
+#include "RemoteTagCacheHandler.hxx"
+#endif
+
 #ifdef ENABLE_NEIGHBOR_PLUGINS
 #include "neighbor/Listener.hxx"
 class NeighborGlue;
@@ -38,11 +42,13 @@ class Storage;
 class UpdateService;
 #endif
 
+#include <memory>
 #include <list>
 
 class ClientList;
 struct Partition;
 class StateFile;
+class RemoteTagCache;
 
 /**
  * A utility class which, when used as the first base class, ensures
@@ -66,6 +72,9 @@ struct Instance final
 #ifdef ENABLE_NEIGHBOR_PLUGINS
 	public NeighborListener
 #endif
+#ifdef ENABLE_CURL
+	, public RemoteTagCacheHandler
+#endif
 {
 	EventThread io_thread;
 
@@ -87,6 +96,10 @@ struct Instance final
 	UpdateService *update = nullptr;
 #endif
 
+#ifdef ENABLE_CURL
+	std::unique_ptr<RemoteTagCache> remote_tag_cache;
+#endif
+
 	ClientList *client_list;
 
 	std::list<Partition> partitions;
@@ -139,6 +152,14 @@ struct Instance final
 	void FinishShutdownUpdate() noexcept;
 	void ShutdownDatabase() noexcept;
 
+#ifdef ENABLE_CURL
+	void LookupRemoteTag(const char *uri) noexcept;
+#else
+	void LookupRemoteTag(const char *) noexcept {
+		/* no-op */
+	}
+#endif
+
 private:
 #ifdef ENABLE_DATABASE
 	void OnDatabaseModified() override;
@@ -151,6 +172,11 @@ private:
 	void LostNeighbor(const NeighborInfo &info) noexcept override;
 #endif
 
+#ifdef ENABLE_CURL
+	/* virtual methods from class RemoteTagCacheHandler */
+	void OnRemoteTag(const char *uri, const Tag &tag) noexcept override;
+#endif
+
 	/* callback for #idle_monitor */
 	void OnIdle(unsigned mask);
 };