GH-1726 better failure detection for updates

Instead of just checking if the new version started, make sure
it is able to write its IPC key to a file and then use the key
to connect to the process.

11 files changed, 553 insertions, 329 deletions

diff --git a/api/logic/updater/DownloadTask_test.cpp b/api/logic/updater/DownloadTask_test.cpp
index 5b88b366..e75c3ffa 100644
--- a/api/logic/updater/DownloadTask_test.cpp
+++ b/api/logic/updater/DownloadTask_test.cpp
@@ -52,8 +52,8 @@ QDebug operator<<(QDebug dbg, const Operation::Type &t)
 
 QDebug operator<<(QDebug dbg, const Operation &u)
 {
-	dbg.nospace() << "Operation(type=" << u.type << " file=" << u.file
-				  << " dest=" << u.dest << " mode=" << u.mode << ")";
+	dbg.nospace() << "Operation(type=" << u.type << " file=" << u.source
+				  << " dest=" << u.destination << " mode=" << u.destinationMode << ")";
 	return dbg.maybeSpace();
 }
 
diff --git a/api/logic/updater/GoUpdate.h b/api/logic/updater/GoUpdate.h
index b8a534de..95f26b8c 100644
--- a/api/logic/updater/GoUpdate.h
+++ b/api/logic/updater/GoUpdate.h
@@ -68,19 +68,22 @@ typedef QList<VersionFileEntry> VersionFileList;
  */
 struct MULTIMC_LOGIC_EXPORT Operation
 {
-	static Operation CopyOp(QString fsource, QString fdest, int fmode=0644)
+	static Operation CopyOp(QString from, QString to, int fmode=0644)
 	{
-		return Operation{OP_REPLACE, fsource, fdest, fmode};
+		return Operation{OP_REPLACE, from, to, fmode};
 	}
 	static Operation DeleteOp(QString file)
 	{
-		return Operation{OP_DELETE, file, "", 0644};
+		return Operation{OP_DELETE, QString(), file, 0644};
 	}
 
 	// FIXME: for some types, some of the other fields are irrelevant!
 	bool operator==(const Operation &u2) const
 	{
-		return type == u2.type && file == u2.file && dest == u2.dest && mode == u2.mode;
+		return type == u2.type &&
+			source == u2.source &&
+			destination == u2.destination &&
+			destinationMode == u2.destinationMode;
 	}
 
 	//! Specifies the type of operation that this is.
@@ -90,14 +93,14 @@ struct MULTIMC_LOGIC_EXPORT Operation
 		OP_DELETE,
 	} type;
 
-	//! The file to operate on.
-	QString file;
+	//! The source file, if any
+	QString source;
 
 	//! The destination file.
-	QString dest;
+	QString destination;
 
-	//! The mode to change the source file to.
-	int mode;
+	//! The mode to change the destination file to.
+	int destinationMode;
 };
 typedef QList<Operation> OperationList;
 
diff --git a/application/CMakeLists.txt b/application/CMakeLists.txt
index 64879e27..18351cce 100644
--- a/application/CMakeLists.txt
+++ b/application/CMakeLists.txt
@@ -85,6 +85,8 @@ SET(MULTIMC_SOURCES
 	MultiMC.cpp
 	BuildConfig.h
 	${PROJECT_BINARY_DIR}/BuildConfig.cpp
+	UpdateController.cpp
+	UpdateController.h
 
 	# GUI - general utilities
 	GuiUtil.h
diff --git a/application/MainWindow.cpp b/application/MainWindow.cpp
index e5ea81f6..4e649521 100644
--- a/application/MainWindow.cpp
+++ b/application/MainWindow.cpp
@@ -90,6 +90,7 @@
 #include "dialogs/ExportInstanceDialog.h"
 #include <FolderInstanceProvider.h>
 #include <InstanceImportTask.h>
+#include "UpdateController.h"
 
 class MainWindow::Ui
 {
@@ -952,7 +953,8 @@ void MainWindow::downloadUpdates(GoUpdate::Status status)
 	// If the task succeeds, install the updates.
 	if (updateDlg.execWithTask(&updateTask))
 	{
-		MMC->installUpdates(updateTask.updateFilesDir(), updateTask.operations());
+		UpdateController update(this, MMC->root(), updateTask.updateFilesDir(), updateTask.operations());
+		update.installUpdates();
 	}
 	else
 	{
diff --git a/application/MultiMC.cpp b/application/MultiMC.cpp
index c102e198..64c380ec 100644
--- a/application/MultiMC.cpp
+++ b/application/MultiMC.cpp
@@ -73,6 +73,8 @@
 #include <stdio.h>
 #endif
 
+static const QLatin1String liveCheckFile("live.check");
+
 using namespace Commandline;
 
 MultiMC::MultiMC(int &argc, char **argv) : QApplication(argc, argv)
@@ -132,6 +134,9 @@ MultiMC::MultiMC(int &argc, char **argv) : QApplication(argc, argv)
 		parser.addOption("launch");
 		parser.addShortOpt("launch", 'l');
 		parser.addDocumentation("launch", "launch the specified instance (by instance ID)");
+		// --alive
+		parser.addSwitch("alive");
+		parser.addDocumentation("alive", "write a small '" + liveCheckFile + "' file after MultiMC starts");
 
 		// parse the arguments
 		try
@@ -165,6 +170,7 @@ MultiMC::MultiMC(int &argc, char **argv) : QApplication(argc, argv)
 		}
 	}
 	m_instanceIdToLaunch = args["launch"].toString();
+	m_liveCheck = args["alive"].toBool();
 
 	QString origcwdPath = QDir::currentPath();
 	QString binPath = applicationDirPath();
@@ -242,6 +248,27 @@ MultiMC::MultiMC(int &argc, char **argv) : QApplication(argc, argv)
 		qDebug() << "ID of instance to launch   : " << m_instanceIdToLaunch;
 	}
 
+	do // once
+	{
+		if(m_liveCheck)
+		{
+			QFile check(liveCheckFile);
+			if(!check.open(QIODevice::WriteOnly | QIODevice::Truncate))
+			{
+				qWarning() << "Could not open" << liveCheckFile << "for writing!";
+				break;
+			}
+			auto payload = appID.toString().toUtf8();
+			if(check.write(payload) != payload.size())
+			{
+				qWarning() << "Could not write into" << liveCheckFile;
+				check.remove();
+				break;
+			}
+			check.close();
+		}
+	} while(false);
+
 	// load settings
 	initGlobalSettings();
 
@@ -697,319 +724,6 @@ std::shared_ptr<JavaInstallList> MultiMC::javalist()
 	return m_javalist;
 }
 
-// from <sys/stat.h>
-#ifndef S_IRUSR
-#define __S_IREAD 0400         /* Read by owner.  */
-#define __S_IWRITE 0200        /* Write by owner.  */
-#define __S_IEXEC 0100         /* Execute by owner.  */
-#define S_IRUSR __S_IREAD      /* Read by owner.  */
-#define S_IWUSR __S_IWRITE     /* Write by owner.  */
-#define S_IXUSR __S_IEXEC      /* Execute by owner.  */
-
-#define S_IRGRP (S_IRUSR >> 3) /* Read by group.  */
-#define S_IWGRP (S_IWUSR >> 3) /* Write by group.  */
-#define S_IXGRP (S_IXUSR >> 3) /* Execute by group.  */
-
-#define S_IROTH (S_IRGRP >> 3) /* Read by others.  */
-#define S_IWOTH (S_IWGRP >> 3) /* Write by others.  */
-#define S_IXOTH (S_IXGRP >> 3) /* Execute by others.  */
-#endif
-static QFile::Permissions unixModeToPermissions(const int mode)
-{
-	QFile::Permissions perms;
-
-	if (mode & S_IRUSR)
-	{
-		perms |= QFile::ReadUser;
-	}
-	if (mode & S_IWUSR)
-	{
-		perms |= QFile::WriteUser;
-	}
-	if (mode & S_IXUSR)
-	{
-		perms |= QFile::ExeUser;
-	}
-
-	if (mode & S_IRGRP)
-	{
-		perms |= QFile::ReadGroup;
-	}
-	if (mode & S_IWGRP)
-	{
-		perms |= QFile::WriteGroup;
-	}
-	if (mode & S_IXGRP)
-	{
-		perms |= QFile::ExeGroup;
-	}
-
-	if (mode & S_IROTH)
-	{
-		perms |= QFile::ReadOther;
-	}
-	if (mode & S_IWOTH)
-	{
-		perms |= QFile::WriteOther;
-	}
-	if (mode & S_IXOTH)
-	{
-		perms |= QFile::ExeOther;
-	}
-	return perms;
-}
-
-void MultiMC::installUpdates(const QString updateFilesDir, GoUpdate::OperationList operations)
-{
-	qint64 pid = -1;
-	QStringList args;
-	bool started = false;
-
-	qDebug() << "Installing updates.";
-#ifdef Q_OS_WIN
-	QString finishCmd = applicationFilePath();
-#elif defined Q_OS_LINUX
-	QString finishCmd = FS::PathCombine(root(), "MultiMC");
-#elif defined Q_OS_MAC
-	QString finishCmd = applicationFilePath();
-#else
-#error Unsupported operating system.
-#endif
-
-	QString backupPath = FS::PathCombine(root(), "update", "backup");
-	QDir origin(root());
-
-	// clean up the backup folder. it should be empty before we start
-	if(!FS::deletePath(backupPath))
-	{
-		qWarning() << "couldn't remove previous backup folder" << backupPath;
-	}
-	// and it should exist.
-	if(!FS::ensureFolderPathExists(backupPath))
-	{
-		qWarning() << "couldn't create folder" << backupPath;
-		return;
-	}
-
-	struct BackupEntry
-	{
-		QString orig;
-		QString backup;
-	};
-	enum Failure
-	{
-		Replace,
-		Delete,
-		Start,
-		Nothing
-	} failedOperationType = Nothing;
-	QString failedFile;
-
-	QList <BackupEntry> backups;
-	QList <BackupEntry> trashcan;
-
-	bool useXPHack = false;
-	QString exePath;
-	QString exeOrigin;
-	QString exeBackup;
-
-	// perform the update operations
-	for(auto op: operations)
-	{
-		switch(op.type)
-		{
-			// replace = move original out to backup, if it exists, move the new file in its place
-			case GoUpdate::Operation::OP_REPLACE:
-			{
-#ifdef Q_OS_WIN32
-				// hack for people renaming the .exe because ... reasons :)
-				if(op.dest == "MultiMC.exe")
-				{
-					op.dest = QFileInfo(applicationFilePath()).fileName();
-				}
-#endif
-				QFileInfo replaced (FS::PathCombine(root(), op.dest));
-#ifdef Q_OS_WIN32
-				if(QSysInfo::windowsVersion() < QSysInfo::WV_VISTA)
-				{
-					if(replaced.fileName() == "MultiMC.exe")
-					{
-						QDir rootDir(root());
-						exeOrigin = rootDir.relativeFilePath(op.file);
-						exePath = rootDir.relativeFilePath(op.dest);
-						exeBackup = rootDir.relativeFilePath(FS::PathCombine(backupPath, replaced.fileName()));
-						useXPHack = true;
-						continue;
-					}
-				}
-#endif
-				if(replaced.exists())
-				{
-					QString backupName = op.dest;
-					backupName.replace('/', '_');
-					QString backupFilePath = FS::PathCombine(backupPath, backupName);
-					if(!QFile::rename(replaced.absoluteFilePath(), backupFilePath))
-					{
-						qWarning() << "Couldn't move:" << replaced.absoluteFilePath() << "to" << backupFilePath;
-						failedOperationType = Replace;
-						failedFile = op.dest;
-						goto FAILED;
-					}
-					BackupEntry be;
-					be.orig = replaced.absoluteFilePath();
-					be.backup = backupFilePath;
-					backups.append(be);
-				}
-				// make sure the folder we are putting this into exists
-				if(!FS::ensureFilePathExists(replaced.absoluteFilePath()))
-				{
-					qWarning() << "REPLACE: Couldn't create folder:" << replaced.absoluteFilePath();
-					failedOperationType = Replace;
-					failedFile = op.dest;
-					goto FAILED;
-				}
-				// now move the new file in
-				if(!QFile::rename(op.file, replaced.absoluteFilePath()))
-				{
-					qWarning() << "REPLACE: Couldn't move:" << op.file << "to" << replaced.absoluteFilePath();
-					failedOperationType = Replace;
-					failedFile = op.dest;
-					goto FAILED;
-				}
-				QFile::setPermissions(replaced.absoluteFilePath(), unixModeToPermissions(op.mode));
-			}
-			break;
-			// delete = move original to backup
-			case GoUpdate::Operation::OP_DELETE:
-			{
-				QString origFilePath = FS::PathCombine(root(), op.file);
-				if(QFile::exists(origFilePath))
-				{
-					QString backupName = op.file;
-					backupName.replace('/', '_');
-					QString trashFilePath = FS::PathCombine(backupPath, backupName);
-
-					if(!QFile::rename(origFilePath, trashFilePath))
-					{
-						qWarning() << "DELETE: Couldn't move:" << op.file << "to" << trashFilePath;
-						failedFile = op.file;
-						failedOperationType = Delete;
-						goto FAILED;
-					}
-					BackupEntry be;
-					be.orig = origFilePath;
-					be.backup = trashFilePath;
-					trashcan.append(be);
-				}
-			}
-			break;
-		}
-	}
-
-	// try to start the new binary
-	args = qApp->arguments();
-	args.removeFirst();
-
-	// on old Windows, do insane things... no error checking here, this is just to have something.
-	if(useXPHack)
-	{
-		QString script;
-		auto nativePath = QDir::toNativeSeparators(exePath);
-		auto nativeOriginPath = QDir::toNativeSeparators(exeOrigin);
-		auto nativeBackupPath = QDir::toNativeSeparators(exeBackup);
-
-		// so we write this vbscript thing...
-		QTextStream out(&script);
-		out << "WScript.Sleep 1000\n";
-		out << "Set fso=CreateObject(\"Scripting.FileSystemObject\")\n";
-		out << "Set shell=CreateObject(\"WScript.Shell\")\n";
-		out << "fso.MoveFile \"" << nativePath << "\", \"" << nativeBackupPath << "\"\n";
-		out << "fso.MoveFile \"" << nativeOriginPath << "\", \"" << nativePath << "\"\n";
-		out << "shell.Run \"" << nativePath << "\"\n";
-
-		QString scriptPath = FS::PathCombine(root(), "update", "update.vbs");
-
-		// we save it
-		QFile scriptFile(scriptPath);
-		scriptFile.open(QIODevice::WriteOnly);
-		scriptFile.write(script.toLocal8Bit().replace("\n", "\r\n"));
-		scriptFile.close();
-
-		// we run it
-		started = QProcess::startDetached("wscript", {scriptPath}, root());
-
-		// and we quit. conscious thought.
-		qApp->quit();
-		return;
-	}
-	started = QProcess::startDetached(finishCmd, args, QDir::currentPath(), &pid);
-	// failed to start... ?
-	if(!started || pid == -1)
-	{
-		qWarning() << "Couldn't start new process properly!";
-		failedOperationType = Start;
-		goto FAILED;
-	}
-	origin.rmdir(updateFilesDir);
-	qApp->quit();
-	return;
-
-FAILED:
-	qWarning() << "Update failed!";
-	bool revertOK = true;
-	// if the above failed, roll back changes
-	for(auto backup:backups)
-	{
-		qWarning() << "restoring" << backup.orig << "from" << backup.backup;
-		if(!QFile::remove(backup.orig))
-		{
-			revertOK = false;
-			qWarning() << "removing new" << backup.orig << "failed!";
-			continue;
-		}
-
-		if(!QFile::rename(backup.backup, backup.orig))
-		{
-			revertOK = false;
-			qWarning() << "restoring" << backup.orig << "failed!";
-		}
-	}
-	for(auto backup:trashcan)
-	{
-		qWarning() << "restoring" << backup.orig << "from" << backup.backup;
-		if(!QFile::rename(backup.backup, backup.orig))
-		{
-			revertOK = false;
-			qWarning() << "restoring" << backup.orig << "failed!";
-		}
-	}
-	QString msg;
-	if(!revertOK)
-	{
-		msg = tr("The update failed and then the update revert failed too.\n"
-			"You will have to repair MultiMC manually.\n"
-				"Please let us know why and how this happened.").arg(failedFile);
-	}
-	else switch (failedOperationType)
-	{
-		case Replace:
-			msg = tr("Couldn't replace file %1. Changes were reverted.\n"
-				"See the MultiMC log file for details.").arg(failedFile);
-			break;
-		case Delete:
-			msg = tr("Couldn't remove file %1. Changes were reverted.\n"
-				"See the MultiMC log file for details.").arg(failedFile);
-			break;
-		case Start:
-			msg = tr("The new version didn't start and the update was rolled back.");
-			break;
-		case Nothing:
-		default:
-			return;
-	}
-	QMessageBox::critical(nullptr, tr("Update failed!"), msg);
-}
-
 std::vector<ITheme *> MultiMC::getValidApplicationThemes()
 {
 	std::vector<ITheme *> ret;
diff --git a/application/MultiMC.h b/application/MultiMC.h
index c416b8c0..23cafdb1 100644
--- a/application/MultiMC.h
+++ b/application/MultiMC.h
@@ -132,9 +132,6 @@ public:
 		return m_rootPath;
 	}
 
-	// install updates now.
-	void installUpdates(const QString updateFilesDir, GoUpdate::OperationList operations);
-
 	/*!
 	 * Opens a json file using either a system default editor, or, if not empty, the editor
 	 * specified in the settings
@@ -223,5 +220,6 @@ private:
 	LocalPeer * m_peerInstance = nullptr;
 public:
 	QString m_instanceIdToLaunch;
+	bool m_liveCheck = false;
 	std::unique_ptr<QFile> logFile;
 };
diff --git a/application/UpdateController.cpp b/application/UpdateController.cpp
new file mode 100644
index 00000000..e3d8f2fb
--- /dev/null
+++ b/application/UpdateController.cpp
@@ -0,0 +1,431 @@
+#include <QFile>
+#include <QMessageBox>
+#include <FileSystem.h>
+#include <updater/GoUpdate.h>
+#include "UpdateController.h"
+#include <QApplication>
+#include <thread>
+#include <chrono>
+#include <LocalPeer.h>
+
+// from <sys/stat.h>
+#ifndef S_IRUSR
+#define __S_IREAD 0400         /* Read by owner.  */
+#define __S_IWRITE 0200        /* Write by owner.  */
+#define __S_IEXEC 0100         /* Execute by owner.  */
+#define S_IRUSR __S_IREAD      /* Read by owner.  */
+#define S_IWUSR __S_IWRITE     /* Write by owner.  */
+#define S_IXUSR __S_IEXEC      /* Execute by owner.  */
+
+#define S_IRGRP (S_IRUSR >> 3) /* Read by group.  */
+#define S_IWGRP (S_IWUSR >> 3) /* Write by group.  */
+#define S_IXGRP (S_IXUSR >> 3) /* Execute by group.  */
+
+#define S_IROTH (S_IRGRP >> 3) /* Read by others.  */
+#define S_IWOTH (S_IWGRP >> 3) /* Write by others.  */
+#define S_IXOTH (S_IXGRP >> 3) /* Execute by others.  */
+#endif
+static QFile::Permissions unixModeToPermissions(const int mode)
+{
+	QFile::Permissions perms;
+
+	if (mode & S_IRUSR)
+	{
+		perms |= QFile::ReadUser;
+	}
+	if (mode & S_IWUSR)
+	{
+		perms |= QFile::WriteUser;
+	}
+	if (mode & S_IXUSR)
+	{
+		perms |= QFile::ExeUser;
+	}
+
+	if (mode & S_IRGRP)
+	{
+		perms |= QFile::ReadGroup;
+	}
+	if (mode & S_IWGRP)
+	{
+		perms |= QFile::WriteGroup;
+	}
+	if (mode & S_IXGRP)
+	{
+		perms |= QFile::ExeGroup;
+	}
+
+	if (mode & S_IROTH)
+	{
+		perms |= QFile::ReadOther;
+	}
+	if (mode & S_IWOTH)
+	{
+		perms |= QFile::WriteOther;
+	}
+	if (mode & S_IXOTH)
+	{
+		perms |= QFile::ExeOther;
+	}
+	return perms;
+}
+
+static const QLatin1String liveCheckFile("live.check");
+
+UpdateController::UpdateController(QWidget * parent, const QString& root, const QString updateFilesDir, GoUpdate::OperationList operations)
+{
+	m_parent = parent;
+	m_root = root;
+	m_updateFilesDir = updateFilesDir;
+	m_operations = operations;
+}
+
+
+void UpdateController::installUpdates()
+{
+	qint64 pid = -1;
+	QStringList args;
+	bool started = false;
+
+	qDebug() << "Installing updates.";
+#ifdef Q_OS_WIN
+	QString finishCmd = QApplication::applicationFilePath();
+#elif defined Q_OS_LINUX
+	QString finishCmd = FS::PathCombine(m_root, "MultiMC");
+#elif defined Q_OS_MAC
+	QString finishCmd = QApplication::applicationFilePath();
+#else
+#error Unsupported operating system.
+#endif
+
+	QString backupPath = FS::PathCombine(m_root, "update", "backup");
+	QDir origin(m_root);
+
+	// clean up the backup folder. it should be empty before we start
+	if(!FS::deletePath(backupPath))
+	{
+		qWarning() << "couldn't remove previous backup folder" << backupPath;
+	}
+	// and it should exist.
+	if(!FS::ensureFolderPathExists(backupPath))
+	{
+		qWarning() << "couldn't create folder" << backupPath;
+		return;
+	}
+
+	bool useXPHack = false;
+	QString exePath;
+	QString exeOrigin;
+	QString exeBackup;
+
+	// perform the update operations
+	for(auto op: m_operations)
+	{
+		switch(op.type)
+		{
+			// replace = move original out to backup, if it exists, move the new file in its place
+			case GoUpdate::Operation::OP_REPLACE:
+			{
+#ifdef Q_OS_WIN32
+				// hack for people renaming the .exe because ... reasons :)
+				if(op.destination == "MultiMC.exe")
+				{
+					op.destination = QFileInfo(QApplication::applicationFilePath()).fileName();
+				}
+#endif
+				QFileInfo destination (FS::PathCombine(m_root, op.destination));
+#ifdef Q_OS_WIN32
+				if(QSysInfo::windowsVersion() < QSysInfo::WV_VISTA)
+				{
+					if(destination.fileName() == "MultiMC.exe")
+					{
+						QDir rootDir(m_root);
+						exeOrigin = rootDir.relativeFilePath(op.source);
+						exePath = rootDir.relativeFilePath(op.destination);
+						exeBackup = rootDir.relativeFilePath(FS::PathCombine(backupPath, destination.fileName()));
+						useXPHack = true;
+						continue;
+					}
+				}
+#endif
+				if(destination.exists())
+				{
+					QString backupName = op.destination;
+					backupName.replace('/', '_');
+					QString backupFilePath = FS::PathCombine(backupPath, backupName);
+					if(!QFile::rename(destination.absoluteFilePath(), backupFilePath))
+					{
+						qWarning() << "Couldn't move:" << destination.absoluteFilePath() << "to" << backupFilePath;
+						m_failedOperationType = Replace;
+						m_failedFile = op.destination;
+						fail();
+						return;
+					}
+					BackupEntry be;
+					be.original = destination.absoluteFilePath();
+					be.backup = backupFilePath;
+					be.update = op.source;
+					m_replace_backups.append(be);
+				}
+				// make sure the folder we are putting this into exists
+				if(!FS::ensureFilePathExists(destination.absoluteFilePath()))
+				{
+					qWarning() << "REPLACE: Couldn't create folder:" << destination.absoluteFilePath();
+					m_failedOperationType = Replace;
+					m_failedFile = op.destination;
+					fail();
+					return;
+				}
+				// now move the new file in
+				if(!QFile::rename(op.source, destination.absoluteFilePath()))
+				{
+					qWarning() << "REPLACE: Couldn't move:" << op.source << "to" << destination.absoluteFilePath();
+					m_failedOperationType = Replace;
+					m_failedFile = op.destination;
+					fail();
+					return;
+				}
+				QFile::setPermissions(destination.absoluteFilePath(), unixModeToPermissions(op.destinationMode));
+			}
+			break;
+			// delete = move original to backup
+			case GoUpdate::Operation::OP_DELETE:
+			{
+				QString destFilePath = FS::PathCombine(m_root, op.destination);
+				if(QFile::exists(destFilePath))
+				{
+					QString backupName = op.destination;
+					backupName.replace('/', '_');
+					QString trashFilePath = FS::PathCombine(backupPath, backupName);
+
+					if(!QFile::rename(destFilePath, trashFilePath))
+					{
+						qWarning() << "DELETE: Couldn't move:" << op.destination << "to" << trashFilePath;
+						m_failedFile = op.destination;
+						m_failedOperationType = Delete;
+						fail();
+						return;
+					}
+					BackupEntry be;
+					be.original = destFilePath;
+					be.backup = trashFilePath;
+					m_delete_backups.append(be);
+				}
+			}
+			break;
+		}
+	}
+
+	// try to start the new binary
+	args = qApp->arguments();
+	args.removeFirst();
+
+	// on old Windows, do insane things... no error checking here, this is just to have something.
+	if(useXPHack)
+	{
+		QString script;
+		auto nativePath = QDir::toNativeSeparators(exePath);
+		auto nativeOriginPath = QDir::toNativeSeparators(exeOrigin);
+		auto nativeBackupPath = QDir::toNativeSeparators(exeBackup);
+
+		// so we write this vbscript thing...
+		QTextStream out(&script);
+		out << "WScript.Sleep 1000\n";
+		out << "Set fso=CreateObject(\"Scripting.FileSystemObject\")\n";
+		out << "Set shell=CreateObject(\"WScript.Shell\")\n";
+		out << "fso.MoveFile \"" << nativePath << "\", \"" << nativeBackupPath << "\"\n";
+		out << "fso.MoveFile \"" << nativeOriginPath << "\", \"" << nativePath << "\"\n";
+		out << "shell.Run \"" << nativePath << "\"\n";
+
+		QString scriptPath = FS::PathCombine(m_root, "update", "update.vbs");
+
+		// we save it
+		QFile scriptFile(scriptPath);
+		scriptFile.open(QIODevice::WriteOnly);
+		scriptFile.write(script.toLocal8Bit().replace("\n", "\r\n"));
+		scriptFile.close();
+
+		// we run it
+		started = QProcess::startDetached("wscript", {scriptPath}, m_root);
+
+		// and we quit. conscious thought.
+		qApp->quit();
+		return;
+	}
+	bool doLiveCheck = true;
+	bool startFailed = false;
+
+	// remove live check file, if any
+	if(QFile::exists(liveCheckFile))
+	{
+		if(!QFile::remove(liveCheckFile))
+		{
+			qWarning() << "Couldn't remove the" << liveCheckFile << "file! We will proceed without :(";
+			doLiveCheck = false;
+		}
+	}
+
+	if(doLiveCheck)
+	{
+		if(!args.contains("--alive"))
+		{
+			args.append("--alive");
+		}
+	}
+
+	// start the updated application
+	started = QProcess::startDetached(finishCmd, args, QDir::currentPath(), &pid);
+	// much dumber check - just find out if the call
+	if(!started || pid == -1)
+	{
+		qWarning() << "Couldn't start new process properly!";
+		startFailed = true;
+	}
+	if(!startFailed && doLiveCheck)
+	{
+		int attempts = 0;
+		while(attempts < 10)
+		{
+			attempts++;
+			QString key;
+			std::this_thread::sleep_for(std::chrono::milliseconds(250));
+			if(!QFile::exists(liveCheckFile))
+			{
+				qWarning() << "Couldn't find the" << liveCheckFile << "file!";
+				startFailed = true;
+				continue;
+			}
+			try
+			{
+				key = QString::fromUtf8(FS::read(liveCheckFile));
+				auto id = ApplicationId::fromRawString(key);
+				LocalPeer peer(nullptr, id);
+				if(peer.isClient())
+				{
+					startFailed = false;
+					qDebug() << "Found process started with key " << key;
+					break;
+				}
+				else
+				{
+					startFailed = true;
+					qDebug() << "Process started with key " << key << "apparently died or is not reponding...";
+					break;
+				}
+			}
+			catch(Exception e)
+			{
+				qWarning() << "Couldn't read the" << liveCheckFile << "file!";
+				startFailed = true;
+				continue;
+			}
+		}
+	}
+	if(startFailed)
+	{
+		m_failedOperationType = Start;
+		fail();
+		return;
+	}
+	else
+	{
+		origin.rmdir(m_updateFilesDir);
+		qApp->quit();
+		return;
+	}
+}
+
+void UpdateController::fail()
+{
+	qWarning() << "Update failed!";
+
+	QString msg;
+	bool doRollback = false;
+	QString failTitle = QObject::tr("Update failed!");
+	QString rollFailTitle = QObject::tr("Rollback failed!");
+	switch (m_failedOperationType)
+	{
+		case Replace:
+		{
+			msg = QObject::tr("Couldn't replace file %1. Changes will be reverted.\n"
+				"See the MultiMC log file for details.").arg(m_failedFile);
+			doRollback = true;
+			QMessageBox::critical(m_parent, failTitle, msg);
+			break;
+		}
+		case Delete:
+		{
+			msg = QObject::tr("Couldn't remove file %1. Changes will be reverted.\n"
+				"See the MultiMC log file for details.").arg(m_failedFile);
+			doRollback = true;
+			QMessageBox::critical(m_parent, failTitle, msg);
+			break;
+		}
+		case Start:
+		{
+			msg = QObject::tr("The new version didn't start or is too old and doesn't respond to startup checks.\n"
+				"\n"
+				"Roll back to previous version?");
+			auto result = QMessageBox::critical(
+				m_parent,
+				failTitle,
+				msg,
+				QMessageBox::Yes | QMessageBox::No,
+				QMessageBox::Yes
+			);
+			doRollback = (result == QMessageBox::Yes);
+			break;
+		}
+		case Nothing:
+		default:
+			return;
+	}
+	if(doRollback)
+	{
+		auto rollbackOK = rollback();
+		if(!rollbackOK)
+		{
+			msg = QObject::tr("The rollback failed too.\n"
+				"You will have to repair MultiMC manually.\n"
+				"Please let us know why and how this happened.").arg(m_failedFile);
+			QMessageBox::critical(m_parent, rollFailTitle, msg);
+			qApp->quit();
+		}
+	}
+	else
+	{
+		qApp->quit();
+	}
+}
+
+bool UpdateController::rollback()
+{
+	bool revertOK = true;
+	// if the above failed, roll back changes
+	for(auto backup:m_replace_backups)
+	{
+		qWarning() << "restoring" << backup.original << "from" << backup.backup;
+		if(!QFile::rename(backup.original, backup.update))
+		{
+			revertOK = false;
+			qWarning() << "moving new" << backup.original << "back to" << backup.update << "failed!";
+			continue;
+		}
+
+		if(!QFile::rename(backup.backup, backup.original))
+		{
+			revertOK = false;
+			qWarning() << "restoring" << backup.original << "failed!";
+		}
+	}
+	for(auto backup:m_delete_backups)
+	{
+		qWarning() << "restoring" << backup.original << "from" << backup.backup;
+		if(!QFile::rename(backup.backup, backup.original))
+		{
+			revertOK = false;
+			qWarning() << "restoring" << backup.original << "failed!";
+		}
+	}
+	return revertOK;
+}
diff --git a/application/UpdateController.h b/application/UpdateController.h
new file mode 100644
index 00000000..2b258701
--- /dev/null
+++ b/application/UpdateController.h
@@ -0,0 +1,44 @@
+#pragma once
+
+#include <QString>
+#include <QList>
+#include <updater/GoUpdate.h>
+
+class QWidget;
+
+class UpdateController
+{
+public:
+	UpdateController(QWidget * parent, const QString &root, const QString updateFilesDir, GoUpdate::OperationList operations);
+	void installUpdates();
+
+private:
+	void fail();
+	bool rollback();
+
+private:
+	QString m_root;
+	QString m_updateFilesDir;
+	GoUpdate::OperationList m_operations;
+	QWidget * m_parent;
+
+	struct BackupEntry
+	{
+		// path where we got the new file from
+		QString update;
+		// path of what is being actually updated
+		QString original;
+		// path where the backup of the updated file was placed
+		QString backup;
+	};
+	QList <BackupEntry> m_replace_backups;
+	QList <BackupEntry> m_delete_backups;
+	enum Failure
+	{
+		Replace,
+		Delete,
+		Start,
+		Nothing
+	} m_failedOperationType = Nothing;
+	QString m_failedFile;
+};
diff --git a/application/main.cpp b/application/main.cpp
index 61771f6e..0fd9f089 100644
--- a/application/main.cpp
+++ b/application/main.cpp
@@ -4,8 +4,30 @@
 #include <InstanceList.h>
 #include <QDebug>
 
+// #define BREAK_INFINITE_LOOP
+// #define BREAK_EXCEPTION
+// #define BREAK_RETURN
+
+#ifdef BREAK_INFINITE_LOOP
+#include <thread>
+#include <chrono>
+#endif
+
 int main(int argc, char *argv[])
 {
+#ifdef BREAK_INFINITE_LOOP
+	while(true)
+	{
+		std::this_thread::sleep_for(std::chrono::milliseconds(250));
+	}
+#endif
+#ifdef BREAK_EXCEPTION
+	throw 42;
+#endif
+#ifdef BREAK_RETURN
+	return 42;
+#endif
+
 	// initialize Qt
 	MultiMC app(argc, argv);
 
diff --git a/libraries/LocalPeer/include/LocalPeer.h b/libraries/LocalPeer/include/LocalPeer.h
index 940bfcbd..7558f18e 100644
--- a/libraries/LocalPeer/include/LocalPeer.h
+++ b/libraries/LocalPeer/include/LocalPeer.h
@@ -54,8 +54,11 @@ public: /* methods */
 	static ApplicationId fromTraditionalApp();
 	// ID based on a path with all the application data (no two instances with the same data path should run)
 	static ApplicationId fromPathAndVersion(const QString & dataPath, const QString & version);
-	// fully custom ID
+	// custom ID
 	static ApplicationId fromCustomId(const QString & id);
+	// custom ID, based on a raw string previously acquired from 'toString'
+	static ApplicationId fromRawString(const QString & id);
+
 
 	QString toString()
 	{
diff --git a/libraries/LocalPeer/src/LocalPeer.cpp b/libraries/LocalPeer/src/LocalPeer.cpp
index db0c73e5..f71c62d8 100644
--- a/libraries/LocalPeer/src/LocalPeer.cpp
+++ b/libraries/LocalPeer/src/LocalPeer.cpp
@@ -108,6 +108,11 @@ ApplicationId ApplicationId::fromCustomId(const QString& id)
 	return ApplicationId(QLatin1String("qtsingleapp-") + id);
 }
 
+ApplicationId ApplicationId::fromRawString(const QString& id)
+{
+	return ApplicationId(id);
+}
+
 LocalPeer::LocalPeer(QObject * parent, const ApplicationId &appId)
 	: QObject(parent), id(appId)
 {