Cloud storage: check connection before connecting

libgit2 takes forever (a minute or so) to figure out that it can't connect
to a remote server.
So if we are using https as connection protocol, quickly check utilizing
RFCs 2324/7168 to make sure we can reach the cloud server (and not some
captive portal or something).

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

git-access.c

@@ -217,6 +217,7 @@ static int check_remote_status(git_repository *repo, git_remote *origin, const c
 
 /* from qthelper.cpp */
 extern bool getProxyString(char **proxy_string);
+extern bool canReachCloudServer();
 
 static git_repository *update_local_repo(const char *localdir, const char *remote, const char *branch)
 {
@@ -259,6 +260,8 @@ static git_repository *update_local_repo(const char *localdir, const char *remot
 		return repo;
 	}
 
+	if (rt == HTTPS && !canReachCloudServer())
+		return repo;
 #if USE_LIBGIT23_API
 	git_fetch_options opts = GIT_FETCH_OPTIONS_INIT;
 	if (rt == SSH)

qt-ui/subsurfacewebservices.cpp

@@ -944,7 +944,6 @@ QNetworkReply* UserSurveyServices::sendSurvey(QString values)
 CloudStorageAuthenticate::CloudStorageAuthenticate(QObject *parent) : QObject(parent)
 {
 	userAgent = getUserAgent();
-
 }
 
 #define CLOUDURL "https://cloud.subsurface-divelog.org/"
@@ -998,3 +997,48 @@ void CloudStorageAuthenticate::sslErrors(QList<QSslError> errorList)
 		qDebug() << err.errorString();
 	}
 }
+
+CheckCloudConnection::CheckCloudConnection(QObject *parent)
+{
+
+}
+
+#define TEAPOT "https://cloud.subsurface-divelog.org/make-latte?number-of-shots=3"
+#define HTTP_I_AM_A_TEAPOT 418
+#define MILK "Linus does not like non-fat milk"
+bool CheckCloudConnection::checkServer()
+{
+	QTimer timer;
+	timer.setSingleShot(true);
+	QEventLoop loop;
+	QNetworkRequest request;
+	request.setRawHeader("Accept", "text/plain");
+	request.setRawHeader("User-Agent", getUserAgent().toUtf8());
+	request.setUrl(QString(TEAPOT));
+	QNetworkAccessManager *mgr = new QNetworkAccessManager();
+	QNetworkReply *reply = mgr->get(request);
+	connect(&timer, SIGNAL(timeout()), &loop, SLOT(quit()));
+	connect(reply, SIGNAL(finished()), &loop, SLOT(quit()));
+	timer.start(2000); // wait two seconds
+	loop.exec();
+	if (timer.isActive()) {
+		// didn't time out, did we get the right response?
+		timer.stop();
+		if (reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt() == HTTP_I_AM_A_TEAPOT &&
+		    reply->readAll() == QByteArray(MILK)) {
+			reply->deleteLater();
+			mgr->deleteLater();
+			return true;
+		}
+		// qDebug() << "did not get expected response - server unreachable" <<
+		//	    reply->error() << reply->errorString() <<
+		//	    reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt() <<
+		//	    reply->readAll();
+	} else {
+		disconnect(reply, SIGNAL(finished()), &loop, SLOT(quit()));
+		reply->abort();
+	}
+	reply->deleteLater();
+	mgr->deleteLater();
+	return false;
+}

qt-ui/subsurfacewebservices.h

@@ -129,6 +129,13 @@ private:
 
 };
 
+class CheckCloudConnection : public QObject {
+	Q_OBJECT
+public:
+	explicit CheckCloudConnection(QObject *parent = 0);
+	static bool checkServer();
+};
+
 #ifdef __cplusplus
 extern "C" {
 #endif

qthelper.cpp

@@ -33,6 +33,7 @@
 #include <QImageReader>
 #include <QtConcurrent>
 #include "divepicturewidget.h"
+#include "subsurfacewebservices.h"
 
 #include <libxslt/documents.h>
 
@@ -1051,3 +1052,8 @@ extern "C" bool getProxyString(char **buffer)
 	}
 	return false;
 }
+
+extern "C" bool canReachCloudServer()
+{
+	return CheckCloudConnection::checkServer();
+}