WebDAV + GTK sync-ui: avoid long delays when accessing configs

The GTK sync-ui does CheckSource() calls on all configured sources,
even when not directly opening a config in the UI. This was
problematic for a CalDAV/CardDAV source because it ended up talking to
the server in WebDAVSource::open().

This violates the principle that open() should be a fast, local
operation. Reorganized the code so that the expensive code is done as
part of WebDAVSource::beginSync() -> WebDAVSource::contactServer()
(for CardDAV) resp. MapSyncSource::beginSync() ->
SubSyncSource::begin() -> WebDAVSource::contactServer() (for CalDAV).

src/backends/webdav/CalDAVSource.h

@@ -32,6 +32,7 @@ class CalDAVSource : public WebDAVSource,
     virtual std::string getMimeVersion() const { return "2.0"; }
 
     /* implementation of SubSyncSource interface */
+    virtual void begin() { contactServer(); }
     virtual void listAllSubItems(SubRevisionMap_t &revisions);
     virtual SubItemResult insertSubItem(const std::string &uid, const std::string &subid,
                                         const std::string &item);

src/backends/webdav/WebDAVSource.cpp

@@ -280,6 +280,11 @@ void WebDAVSource::replaceHTMLEntities(std::string &item)
 }
 
 void WebDAVSource::open()
+{
+    // Nothing to do here, expensive initialization is in contactServer().
+}
+
+void WebDAVSource::contactServer()
 {
     int timeoutSeconds = m_settings->timeoutSeconds();
     int retrySeconds = m_settings->retrySeconds();

src/backends/webdav/WebDAVSource.h

@@ -47,6 +47,13 @@ class WebDAVSource : public TrackingSyncSource, private boost::noncopyable
     static void replaceHTMLEntities(std::string &item);
 
  protected:
+    /**
+     * Initialize HTTP session and locate the right collection.
+     * To be called after open() to do the heavy initializtion
+     * work.
+     */
+    void contactServer();
+
     /* implementation of SyncSource interface */
     virtual void open();
     virtual bool isEmpty();
@@ -55,6 +62,12 @@ class WebDAVSource : public TrackingSyncSource, private boost::noncopyable
     void getSynthesisInfo(SynthesisInfo &info,
                           XMLConfigFragments &fragments);
 
+    /** intercept TrackingSyncSource::beginSync() to do the expensive initialization */
+    virtual void beginSync(const std::string &lastToken, const std::string &resumeToken) {
+        contactServer();
+        TrackingSyncSource::beginSync(lastToken, resumeToken);
+    }
+
     /* implementation of TrackingSyncSource interface */
     virtual void listAllItems(RevisionMap_t &revisions);
     virtual InsertItemResult insertItem(const string &luid, const std::string &item, bool raw);

src/syncevo/MapSyncSource.h

@@ -94,6 +94,9 @@ class SubSyncSource : virtual public SyncSourceBase
      */
     typedef map<string, pair<string, set<string> > > SubRevisionMap_t;
 
+    /** called after open() and before any of the following methods */
+    virtual void begin() = 0;
+
     virtual void listAllSubItems(SubRevisionMap_t &revisions) = 0;
     virtual SubItemResult insertSubItem(const std::string &uid, const std::string &subid,
                                         const std::string &item) = 0;
@@ -177,6 +180,7 @@ class MapSyncSource : public TrackingSyncSource,
 
     virtual Databases getDatabases() { return dynamic_cast<SyncSource &>(*m_sub).getDatabases(); }
     virtual void open() { dynamic_cast<SyncSource &>(*m_sub).open(); }
+    virtual void beginSync(const std::string &lastToken, const std::string &resumeToken) { m_sub->begin(); TrackingSyncSource::beginSync(lastToken, resumeToken); }
     virtual bool isEmpty() { return dynamic_cast<SyncSource &>(*m_sub).getOperations().m_isEmpty(); }
     virtual void listAllItems(SyncSourceRevisions::RevisionMap_t &revisions);
     virtual InsertItemResult insertItem(const std::string &luid, const std::string &item, bool raw);