GH-352 Make OneSix instance update downloads cancellable

30 files changed, 771 insertions, 337 deletions

diff --git a/api/logic/BaseInstance.h b/api/logic/BaseInstance.h
index 9a6976cb..ebaaeb83 100644
--- a/api/logic/BaseInstance.h
+++ b/api/logic/BaseInstance.h
@@ -16,6 +16,7 @@
 #pragma once
 
 #include <QObject>
+#include "QObjectPtr.h"
 #include <QDateTime>
 #include <QSet>
 #include <QProcess>
@@ -152,7 +153,7 @@ public:
 	virtual SettingsObjectPtr settings() const;
 
 	/// returns a valid update task
-	virtual std::shared_ptr<Task> createUpdateTask() = 0;
+	virtual shared_qobject_ptr<Task> createUpdateTask() = 0;
 
 	/// returns a valid launcher (task container)
 	virtual std::shared_ptr<LaunchTask> createLaunchTask(AuthSessionPtr account) = 0;
diff --git a/api/logic/CMakeLists.txt b/api/logic/CMakeLists.txt
index 4514d8c3..415584fc 100644
--- a/api/logic/CMakeLists.txt
+++ b/api/logic/CMakeLists.txt
@@ -200,6 +200,14 @@ set(MINECRAFT_SOURCES
 	minecraft/onesix/OneSixProfileStrategy.h
 	minecraft/onesix/OneSixVersionFormat.cpp
 	minecraft/onesix/OneSixVersionFormat.h
+	minecraft/onesix/update/AssetUpdateTask.h
+	minecraft/onesix/update/AssetUpdateTask.cpp
+	minecraft/onesix/update/FMLLibrariesTask.cpp
+	minecraft/onesix/update/FMLLibrariesTask.h
+	minecraft/onesix/update/FoldersTask.cpp
+	minecraft/onesix/update/FoldersTask.h
+	minecraft/onesix/update/LibrariesTask.cpp
+	minecraft/onesix/update/LibrariesTask.h
 	minecraft/launch/CreateServerResourcePacksFolder.cpp
 	minecraft/launch/CreateServerResourcePacksFolder.h
 	minecraft/launch/ModMinecraftJar.cpp
diff --git a/api/logic/NullInstance.h b/api/logic/NullInstance.h
index d87fb6f7..4fb31854 100644
--- a/api/logic/NullInstance.h
+++ b/api/logic/NullInstance.h
@@ -48,7 +48,7 @@ public:
 	{
 		return nullptr;
 	}
-	virtual std::shared_ptr< Task > createUpdateTask() override
+	virtual shared_qobject_ptr< Task > createUpdateTask() override
 	{
 		return nullptr;
 	}
diff --git a/api/logic/QObjectPtr.h b/api/logic/QObjectPtr.h
index b81b3234..000d228d 100644
--- a/api/logic/QObjectPtr.h
+++ b/api/logic/QObjectPtr.h
@@ -48,6 +48,10 @@ public:
 		using namespace std::placeholders;
 		m_ptr.reset(wrap, std::bind(&QObject::deleteLater, _1));
 	}
+	void reset(const shared_qobject_ptr<T> &other)
+	{
+		m_ptr = other.m_ptr;
+	}
 	void reset()
 	{
 		m_ptr.reset();
diff --git a/api/logic/launch/steps/Update.cpp b/api/logic/launch/steps/Update.cpp
index 4901f001..ad0c4fc4 100644
--- a/api/logic/launch/steps/Update.cpp
+++ b/api/logic/launch/steps/Update.cpp
@@ -18,7 +18,12 @@
 
 void Update::executeTask()
 {
-	m_updateTask = m_parent->instance()->createUpdateTask();
+	if(m_aborted)
+	{
+		emitFailed(tr("Task aborted."));
+		return;
+	}
+	m_updateTask.reset(m_parent->instance()->createUpdateTask());
 	if(m_updateTask)
 	{
 		connect(m_updateTask.get(), SIGNAL(finished()), this, SLOT(updateFinished()));
@@ -39,12 +44,37 @@ void Update::updateFinished()
 {
 	if(m_updateTask->successful())
 	{
+		m_updateTask.reset();
 		emitSucceeded();
 	}
 	else
 	{
 		QString reason = tr("Instance update failed because: %1.\n\n").arg(m_updateTask->failReason());
+		m_updateTask.reset();
 		emit logLine(reason, MessageLevel::Fatal);
 		emitFailed(reason);
 	}
 }
+
+bool Update::canAbort() const
+{
+	if(m_updateTask)
+	{
+		return m_updateTask->canAbort();
+	}
+	return true;
+}
+
+
+bool Update::abort()
+{
+	m_aborted = true;
+	if(m_updateTask)
+	{
+		if(m_updateTask->canAbort())
+		{
+			return m_updateTask->abort();
+		}
+	}
+	return true;
+}
diff --git a/api/logic/launch/steps/Update.h b/api/logic/launch/steps/Update.h
index 14928253..1739de47 100644
--- a/api/logic/launch/steps/Update.h
+++ b/api/logic/launch/steps/Update.h
@@ -16,6 +16,7 @@
 #pragma once
 
 #include <launch/LaunchStep.h>
+#include <QObjectPtr.h>
 #include <launch/LoggedProcess.h>
 #include <java/JavaChecker.h>
 
@@ -27,15 +28,16 @@ public:
 	explicit Update(LaunchTask *parent):LaunchStep(parent) {};
 	virtual ~Update() {};
 
-	virtual void executeTask();
-	virtual bool canAbort() const
-	{
-		return false;
-	}
-	virtual void proceed();
+	void executeTask() override;
+	bool canAbort() const override;
+	void proceed() override;
+public slots:
+	bool abort() override;
+
 private slots:
 	void updateFinished();
 
 private:
-	std::shared_ptr<Task> m_updateTask;
+	shared_qobject_ptr<Task> m_updateTask;
+	bool m_aborted = false;
 };
diff --git a/api/logic/minecraft/MinecraftVersionList.cpp b/api/logic/minecraft/MinecraftVersionList.cpp
index 4e4eafbc..e3f416d9 100644
--- a/api/logic/minecraft/MinecraftVersionList.cpp
+++ b/api/logic/minecraft/MinecraftVersionList.cpp
@@ -61,6 +61,10 @@ public:
 	explicit MCVListVersionUpdateTask(MinecraftVersionList *vlist, std::shared_ptr<MinecraftVersion> updatedVersion);
 	virtual ~MCVListVersionUpdateTask() override{};
 	virtual void executeTask() override;
+	bool canAbort() const override;
+
+public slots:
+	bool abort() override;
 
 protected
 slots:
@@ -71,6 +75,7 @@ protected:
 	QByteArray versionIndexData;
 	std::shared_ptr<MinecraftVersion> updatedVersion;
 	MinecraftVersionList *m_list;
+	bool m_aborted = false;
 };
 
 class ListLoadError : public Exception
@@ -410,6 +415,11 @@ MCVListVersionUpdateTask::MCVListVersionUpdateTask(MinecraftVersionList *vlist,
 
 void MCVListVersionUpdateTask::executeTask()
 {
+	if(m_aborted)
+	{
+		emitFailed(tr("Task aborted."));
+		return;
+	}
 	auto job = new NetJob("Version index");
 	job->addNetAction(Net::Download::makeByteArray(QUrl(updatedVersion->getUrl()), &versionIndexData));
 	specificVersionDownloadJob.reset(job);
@@ -419,6 +429,21 @@ void MCVListVersionUpdateTask::executeTask()
 	specificVersionDownloadJob->start();
 }
 
+bool MCVListVersionUpdateTask::canAbort() const
+{
+	return true;
+}
+
+bool MCVListVersionUpdateTask::abort()
+{
+	m_aborted = true;
+	if(specificVersionDownloadJob)
+	{
+		return specificVersionDownloadJob->abort();
+	}
+	return true;
+}
+
 void MCVListVersionUpdateTask::json_downloaded()
 {
 	specificVersionDownloadJob.reset();
diff --git a/api/logic/minecraft/forge/ForgeXzDownload.cpp b/api/logic/minecraft/forge/ForgeXzDownload.cpp
index adf96552..8b762866 100644
--- a/api/logic/minecraft/forge/ForgeXzDownload.cpp
+++ b/api/logic/minecraft/forge/ForgeXzDownload.cpp
@@ -35,6 +35,12 @@ ForgeXzDownload::ForgeXzDownload(QString relative_path, MetaEntryPtr entry) : Ne
 
 void ForgeXzDownload::start()
 {
+	if(m_status == Job_Aborted)
+	{
+		qWarning() << "Attempt to start an aborted Download:" << m_url.toString();
+		emit aborted(m_index_within_job);
+		return;
+	}
 	m_status = Job_InProgress;
 	if (!m_entry->isStale())
 	{
@@ -76,9 +82,17 @@ void ForgeXzDownload::downloadProgress(qint64 bytesReceived, qint64 bytesTotal)
 
 void ForgeXzDownload::downloadError(QNetworkReply::NetworkError error)
 {
-	// error happened during download.
-	// TODO: log the reason why
-	m_status = Job_Failed;
+	if(error == QNetworkReply::OperationCanceledError)
+	{
+		qCritical() << "Aborted " << m_url.toString();
+		m_status = Job_Aborted;
+	}
+	else
+	{
+		// error happened during download.
+		qCritical() << "Failed " << m_url.toString() << " with reason " << error;
+		m_status = Job_Failed;
+	}
 }
 
 void ForgeXzDownload::failAndTryNextMirror()
@@ -90,7 +104,7 @@ void ForgeXzDownload::failAndTryNextMirror()
 void ForgeXzDownload::downloadFinished()
 {
 	// if the download succeeded
-	if (m_status != Job_Failed)
+	if (m_status != Job_Failed && m_status != Job_Aborted)
 	{
 		// nothing went wrong...
 		m_status = Job_Finished;
@@ -110,6 +124,14 @@ void ForgeXzDownload::downloadFinished()
 			return;
 		}
 	}
+	else if(m_status == Job_Aborted)
+	{
+		m_pack200_xz_file.remove();
+		m_reply.reset();
+		emit failed(m_index_within_job);
+		emit aborted(m_index_within_job);
+		return;
+	}
 	// else the download failed
 	else
 	{
@@ -147,6 +169,7 @@ void ForgeXzDownload::downloadReadyRead()
 
 const size_t buffer_size = 8196;
 
+// NOTE: once this gets here, it can't be aborted anymore. we don't care.
 void ForgeXzDownload::decompressAndInstall()
 {
 	// rewind the downloaded temp file
@@ -356,3 +379,16 @@ void ForgeXzDownload::decompressAndInstall()
 	m_reply.reset();
 	emit succeeded(m_index_within_job);
 }
+
+bool ForgeXzDownload::abort()
+{
+	if(m_reply)
+		m_reply->abort();
+	m_status = Job_Aborted;
+	return true;
+}
+
+bool ForgeXzDownload::canAbort()
+{
+	return true;
+}
diff --git a/api/logic/minecraft/forge/ForgeXzDownload.h b/api/logic/minecraft/forge/ForgeXzDownload.h
index 67524405..e51ff9e5 100644
--- a/api/logic/minecraft/forge/ForgeXzDownload.h
+++ b/api/logic/minecraft/forge/ForgeXzDownload.h
@@ -41,17 +41,19 @@ public:
 		return ForgeXzDownloadPtr(new ForgeXzDownload(relative_path, entry));
 	}
 	virtual ~ForgeXzDownload(){};
+	bool canAbort() override;
 
 protected
 slots:
-	virtual void downloadProgress(qint64 bytesReceived, qint64 bytesTotal);
-	virtual void downloadError(QNetworkReply::NetworkError error);
-	virtual void downloadFinished();
-	virtual void downloadReadyRead();
+	void downloadProgress(qint64 bytesReceived, qint64 bytesTotal) override;
+	void downloadError(QNetworkReply::NetworkError error) override;
+	void downloadFinished() override;
+	void downloadReadyRead() override;
 
 public
 slots:
-	virtual void start();
+	void start() override;
+	bool abort() override;
 
 private:
 	void decompressAndInstall();
diff --git a/api/logic/minecraft/ftb/OneSixFTBInstance.cpp b/api/logic/minecraft/ftb/OneSixFTBInstance.cpp
index 81e939a1..5edad080 100644
--- a/api/logic/minecraft/ftb/OneSixFTBInstance.cpp
+++ b/api/logic/minecraft/ftb/OneSixFTBInstance.cpp
@@ -125,7 +125,7 @@ void OneSixFTBInstance::createProfile()
 	m_profile.reset(new MinecraftProfile(new FTBProfileStrategy(this)));
 }
 
-std::shared_ptr<Task> OneSixFTBInstance::createUpdateTask()
+shared_qobject_ptr<Task> OneSixFTBInstance::createUpdateTask()
 {
 	return OneSixInstance::createUpdateTask();
 }
diff --git a/api/logic/minecraft/ftb/OneSixFTBInstance.h b/api/logic/minecraft/ftb/OneSixFTBInstance.h
index e7f8f485..a5621685 100644
--- a/api/logic/minecraft/ftb/OneSixFTBInstance.h
+++ b/api/logic/minecraft/ftb/OneSixFTBInstance.h
@@ -13,7 +13,7 @@ public:
 
 	virtual void createProfile() override;
 
-	virtual std::shared_ptr<Task> createUpdateTask() override;
+	virtual shared_qobject_ptr<Task> createUpdateTask() override;
 
 	virtual QString id() const override;
 
diff --git a/api/logic/minecraft/legacy/LegacyInstance.cpp b/api/logic/minecraft/legacy/LegacyInstance.cpp
index 7c552369..7ed2041c 100644
--- a/api/logic/minecraft/legacy/LegacyInstance.cpp
+++ b/api/logic/minecraft/legacy/LegacyInstance.cpp
@@ -87,12 +87,12 @@ bool LegacyInstance::shouldUseCustomBaseJar() const
 }
 
 
-std::shared_ptr<Task> LegacyInstance::createUpdateTask()
+shared_qobject_ptr<Task> LegacyInstance::createUpdateTask()
 {
 	// make sure the jar mods list is initialized by asking for it.
 	auto list = jarModList();
 	// create an update task
-	return std::shared_ptr<Task>(new LegacyUpdate(this, this));
+	return shared_qobject_ptr<Task>(new LegacyUpdate(this, this));
 }
 
 std::shared_ptr<Task> LegacyInstance::createJarModdingTask()
diff --git a/api/logic/minecraft/legacy/LegacyInstance.h b/api/logic/minecraft/legacy/LegacyInstance.h
index f1cefbcc..1d95340b 100644
--- a/api/logic/minecraft/legacy/LegacyInstance.h
+++ b/api/logic/minecraft/legacy/LegacyInstance.h
@@ -113,7 +113,7 @@ public:
 
 	virtual bool shouldUpdate() const override;
 	virtual void setShouldUpdate(bool val) override;
-	virtual std::shared_ptr<Task> createUpdateTask() override;
+	virtual shared_qobject_ptr<Task> createUpdateTask() override;
 	virtual std::shared_ptr<Task> createJarModdingTask() override;
 	virtual QString createLaunchScript(AuthSessionPtr session) override;
 
diff --git a/api/logic/minecraft/onesix/OneSixInstance.cpp b/api/logic/minecraft/onesix/OneSixInstance.cpp
index 8b5491e2..1bf75bdb 100644
--- a/api/logic/minecraft/onesix/OneSixInstance.cpp
+++ b/api/logic/minecraft/onesix/OneSixInstance.cpp
@@ -60,9 +60,9 @@ QSet<QString> OneSixInstance::traits()
 	}
 }
 
-std::shared_ptr<Task> OneSixInstance::createUpdateTask()
+shared_qobject_ptr<Task> OneSixInstance::createUpdateTask()
 {
-	return std::shared_ptr<Task>(new OneSixUpdate(this));
+	return shared_qobject_ptr<Task>(new OneSixUpdate(this));
 }
 
 QString replaceTokensIn(QString text, QMap<QString, QString> with)
diff --git a/api/logic/minecraft/onesix/OneSixInstance.h b/api/logic/minecraft/onesix/OneSixInstance.h
index 1a917e79..c857075f 100644
--- a/api/logic/minecraft/onesix/OneSixInstance.h
+++ b/api/logic/minecraft/onesix/OneSixInstance.h
@@ -52,7 +52,7 @@ public:
 	QString worldDir() const;
 	virtual QString instanceConfigFolder() const override;
 
-	virtual std::shared_ptr<Task> createUpdateTask() override;
+	virtual shared_qobject_ptr<Task> createUpdateTask() override;
 	virtual std::shared_ptr<Task> createJarModdingTask() override;
 	virtual QString createLaunchScript(AuthSessionPtr session) override;
 	QStringList verboseDescription(AuthSessionPtr session) override;
diff --git a/api/logic/minecraft/onesix/OneSixUpdate.cpp b/api/logic/minecraft/onesix/OneSixUpdate.cpp
index d3cd197d..02a6f561 100644
--- a/api/logic/minecraft/onesix/OneSixUpdate.cpp
+++ b/api/logic/minecraft/onesix/OneSixUpdate.cpp
@@ -18,332 +18,138 @@
 #include "OneSixUpdate.h"
 #include "OneSixInstance.h"
 
-#include <QtNetwork>
-
 #include <QFile>
 #include <QFileInfo>
 #include <QTextStream>
 #include <QDataStream>
-#include <JlCompress.h>
 
 #include "BaseInstance.h"
 #include "minecraft/MinecraftVersionList.h"
 #include "minecraft/MinecraftProfile.h"
 #include "minecraft/Library.h"
 #include "net/URLConstants.h"
-#include "net/ChecksumValidator.h"
-#include "minecraft/AssetsUtils.h"
-#include "Exception.h"
-#include "MMCZip.h"
 #include <FileSystem.h>
 
-OneSixUpdate::OneSixUpdate(OneSixInstance *inst, QObject *parent) : Task(parent), m_inst(inst)
-{
-}
+#include "update/FoldersTask.h"
+#include "update/LibrariesTask.h"
+#include "update/FMLLibrariesTask.h"
+#include "update/AssetUpdateTask.h"
 
-void OneSixUpdate::executeTask()
+OneSixUpdate::OneSixUpdate(OneSixInstance *inst, QObject *parent) : Task(parent), m_inst(inst)
 {
-	// Make directories
-	QDir mcDir(m_inst->minecraftRoot());
-	if (!mcDir.exists() && !mcDir.mkpath("."))
+	// create folders
 	{
-		emitFailed(tr("Failed to create folder for minecraft binaries."));
-		return;
+		m_tasks.append(std::make_shared<FoldersTask>(m_inst));
 	}
 
-	// Get a pointer to the version object that corresponds to the instance's version.
-	targetVersion = std::dynamic_pointer_cast<MinecraftVersion>(ENV.getVersion("net.minecraft", m_inst->intendedVersionId()));
-	if (targetVersion == nullptr)
-	{
-		// don't do anything if it was invalid
-		emitFailed(tr("The specified Minecraft version is invalid. Choose a different one."));
-		return;
-	}
-	if (m_inst->providesVersionFile() || !targetVersion->needsUpdate())
+	// add a version update task, if necessary
 	{
-		qDebug() << "Instance either provides a version file or doesn't need an update.";
-		jarlibStart();
-		return;
+		auto list = std::dynamic_pointer_cast<MinecraftVersionList>(ENV.getVersionList("net.minecraft"));
+		auto version = std::dynamic_pointer_cast<MinecraftVersion>(list->findVersion(m_inst->intendedVersionId()));
+		if (version == nullptr)
+		{
+			// don't do anything if it was invalid
+			m_preFailure = tr("The specified Minecraft version is invalid. Choose a different one.");
+		}
+		else if (m_inst->providesVersionFile() || !version->needsUpdate())
+		{
+			qDebug() << "Instance either provides a version file or doesn't need an update.";
+		}
+		else
+		{
+			auto versionUpdateTask = list->createUpdateTask(m_inst->intendedVersionId());
+			if (!versionUpdateTask)
+			{
+				qDebug() << "Didn't spawn an update task.";
+			}
+			else
+			{
+				m_tasks.append(versionUpdateTask);
+			}
+		}
 	}
-	versionUpdateTask = std::dynamic_pointer_cast<MinecraftVersionList>(ENV.getVersionList("net.minecraft"))->createUpdateTask(m_inst->intendedVersionId());
-	if (!versionUpdateTask)
+
+	// libraries download
 	{
-		qDebug() << "Didn't spawn an update task.";
-		jarlibStart();
-		return;
+		m_tasks.append(std::make_shared<LibrariesTask>(m_inst));
 	}
-	connect(versionUpdateTask.get(), SIGNAL(succeeded()), SLOT(jarlibStart()));
-	connect(versionUpdateTask.get(), &NetJob::failed, this, &OneSixUpdate::versionUpdateFailed);
-	connect(versionUpdateTask.get(), SIGNAL(progress(qint64, qint64)), SIGNAL(progress(qint64, qint64)));
-	setStatus(tr("Getting the version files from Mojang..."));
-	versionUpdateTask->start();
-}
 
-void OneSixUpdate::versionUpdateFailed(QString reason)
-{
-	emitFailed(reason);
-}
-
-void OneSixUpdate::assetIndexStart()
-{
-	setStatus(tr("Updating assets index..."));
-	OneSixInstance *inst = (OneSixInstance *)m_inst;
-	auto profile = inst->getMinecraftProfile();
-	auto assets = profile->getMinecraftAssets();
-	QUrl indexUrl = assets->url;
-	QString localPath = assets->id + ".json";
-	auto job = new NetJob(tr("Asset index for %1").arg(inst->name()));
-
-	auto metacache = ENV.metacache();
-	auto entry = metacache->resolveEntry("asset_indexes", localPath);
-	entry->setStale(true);
-	auto hexSha1 = assets->sha1.toLatin1();
-	qDebug() << "Asset index SHA1:" << hexSha1;
-	auto dl = Net::Download::makeCached(indexUrl, entry);
-	auto rawSha1 = QByteArray::fromHex(assets->sha1.toLatin1());
-	dl->addValidator(new Net::ChecksumValidator(QCryptographicHash::Sha1, rawSha1));
-	job->addNetAction(dl);
-
-	jarlibDownloadJob.reset(job);
-
-	connect(jarlibDownloadJob.get(), SIGNAL(succeeded()), SLOT(assetIndexFinished()));
-	connect(jarlibDownloadJob.get(), &NetJob::failed, this, &OneSixUpdate::assetIndexFailed);
-	connect(jarlibDownloadJob.get(), SIGNAL(progress(qint64, qint64)), SIGNAL(progress(qint64, qint64)));
-
-	qDebug() << m_inst->name() << ": Starting asset index download";
-	jarlibDownloadJob->start();
-}
-
-void OneSixUpdate::assetIndexFinished()
-{
-	AssetsIndex index;
-	qDebug() << m_inst->name() << ": Finished asset index download";
-
-	OneSixInstance *inst = (OneSixInstance *)m_inst;
-	auto profile = inst->getMinecraftProfile();
-	auto assets = profile->getMinecraftAssets();
-
-	QString asset_fname = "assets/indexes/" + assets->id + ".json";
-	// FIXME: this looks like a job for a generic validator based on json schema?
-	if (!AssetsUtils::loadAssetsIndexJson(assets->id, asset_fname, &index))
+	// FML libraries download and copy into the instance
 	{
-		auto metacache = ENV.metacache();
-		auto entry = metacache->resolveEntry("asset_indexes", assets->id + ".json");
-		metacache->evictEntry(entry);
-		emitFailed(tr("Failed to read the assets index!"));
+		m_tasks.append(std::make_shared<FMLLibrariesTask>(m_inst));
 	}
 
-	auto job = index.getDownloadJob();
-	if(job)
+	// assets update
 	{
-		setStatus(tr("Getting the assets files from Mojang..."));
-		jarlibDownloadJob = job;
-		connect(jarlibDownloadJob.get(), SIGNAL(succeeded()), SLOT(assetsFinished()));
-		connect(jarlibDownloadJob.get(), &NetJob::failed, this, &OneSixUpdate::assetsFailed);
-		connect(jarlibDownloadJob.get(), SIGNAL(progress(qint64, qint64)), SIGNAL(progress(qint64, qint64)));
-		jarlibDownloadJob->start();
-		return;
+		m_tasks.append(std::make_shared<AssetUpdateTask>(m_inst));
 	}
-	assetsFinished();
-}
-
-void OneSixUpdate::assetIndexFailed(QString reason)
-{
-	qDebug() << m_inst->name() << ": Failed asset index download";
-	emitFailed(tr("Failed to download the assets index:\n%1").arg(reason));
-}
-
-void OneSixUpdate::assetsFinished()
-{
-	emitSucceeded();
-}
-
-void OneSixUpdate::assetsFailed(QString reason)
-{
-	emitFailed(tr("Failed to download assets:\n%1").arg(reason));
 }
 
-void OneSixUpdate::jarlibStart()
+void OneSixUpdate::executeTask()
 {
-	setStatus(tr("Getting the library files from Mojang..."));
-	qDebug() << m_inst->name() << ": downloading libraries";
-	OneSixInstance *inst = (OneSixInstance *)m_inst;
-	inst->reloadProfile();
-	if(inst->flags() & BaseInstance::VersionBrokenFlag)
+	if(!m_preFailure.isEmpty())
 	{
-		emitFailed(tr("Failed to load the version description files - check the instance for errors."));
+		emitFailed(m_preFailure);
 		return;
 	}
+	next();
+}
 
-	// Build a list of URLs that will need to be downloaded.
-	std::shared_ptr<MinecraftProfile> profile = inst->getMinecraftProfile();
-	// minecraft.jar for this version
+void OneSixUpdate::next()
+{
+	if(m_abort)
 	{
-		QString version_id = profile->getMinecraftVersion();
-		QString localPath = version_id + "/" + version_id + ".jar";
-		QString urlstr = profile->getMainJarUrl();
-
-		auto job = new NetJob(tr("Libraries for instance %1").arg(inst->name()));
-
-		auto metacache = ENV.metacache();
-		auto entry = metacache->resolveEntry("versions", localPath);
-		job->addNetAction(Net::Download::makeCached(QUrl(urlstr), entry));
-		jarlibDownloadJob.reset(job);
+		emitFailed(tr("Aborted by user."));
+		return;
 	}
-
-	auto libs = profile->getLibraries();
-
-	auto metacache = ENV.metacache();
-	QList<LibraryPtr> brokenLocalLibs;
-
-	QStringList failedFiles;
-	for (auto lib : libs)
+	m_currentTask ++;
+	if(m_currentTask > 0)
 	{
-		auto dls = lib->getDownloads(currentSystem, metacache.get(), failedFiles);
-		for(auto dl : dls)
-		{
-			jarlibDownloadJob->addNetAction(dl);
-		}
+		auto task = m_tasks[m_currentTask - 1];
+		disconnect(task.get(), &Task::succeeded, this, &OneSixUpdate::subtaskSucceeded);
+		disconnect(task.get(), &Task::failed, this, &OneSixUpdate::subtaskFailed);
+		disconnect(task.get(), &Task::progress, this, &OneSixUpdate::progress);
+		disconnect(task.get(), &Task::status, this, &OneSixUpdate::setStatus);
 	}
-	if (!brokenLocalLibs.empty())
+	if(m_currentTask == m_tasks.size())
 	{
-		jarlibDownloadJob.reset();
-
-		QString failed_all = failedFiles.join("\n");
-		emitFailed(tr("Some libraries marked as 'local' are missing their jar "
-					  "files:\n%1\n\nYou'll have to correct this problem manually. If this is "
-					  "an externally tracked instance, make sure to run it at least once "
-					  "outside of MultiMC.").arg(failed_all));
+		emitSucceeded();
 		return;
 	}
-
-	connect(jarlibDownloadJob.get(), SIGNAL(succeeded()), SLOT(jarlibFinished()));
-	connect(jarlibDownloadJob.get(), &NetJob::failed, this, &OneSixUpdate::jarlibFailed);
-	connect(jarlibDownloadJob.get(), SIGNAL(progress(qint64, qint64)),
-			SIGNAL(progress(qint64, qint64)));
-
-	jarlibDownloadJob->start();
+	auto task = m_tasks[m_currentTask];
+	connect(task.get(), &Task::succeeded, this, &OneSixUpdate::subtaskSucceeded);
+	connect(task.get(), &Task::failed, this, &OneSixUpdate::subtaskFailed);
+	connect(task.get(), &Task::progress, this, &OneSixUpdate::progress);
+	connect(task.get(), &Task::status, this, &OneSixUpdate::setStatus);
+	task->start();
 }
 
-void OneSixUpdate::jarlibFinished()
+void OneSixUpdate::subtaskSucceeded()
 {
-	OneSixInstance *inst = (OneSixInstance *)m_inst;
-	std::shared_ptr<MinecraftProfile> profile = inst->getMinecraftProfile();
-
-	if (profile->hasTrait("legacyFML"))
-	{
-		fmllibsStart();
-	}
-	else
-	{
-		assetIndexStart();
-	}
+	next();
 }
 
-void OneSixUpdate::jarlibFailed(QString reason)
+void OneSixUpdate::subtaskFailed(QString error)
 {
-	QStringList failed = jarlibDownloadJob->getFailedFiles();
-	QString failed_all = failed.join("\n");
-	emitFailed(
-		tr("Failed to download the following files:\n%1\n\nReason:%2\nPlease try again.").arg(failed_all, reason));
+	emitFailed(error);
 }
 
-void OneSixUpdate::fmllibsStart()
-{
-	// Get the mod list
-	OneSixInstance *inst = (OneSixInstance *)m_inst;
-	std::shared_ptr<MinecraftProfile> profile = inst->getMinecraftProfile();
-	bool forge_present = false;
-
-	QString version = inst->intendedVersionId();
-	auto &fmlLibsMapping = g_VersionFilterData.fmlLibsMapping;
-	if (!fmlLibsMapping.contains(version))
-	{
-		assetIndexStart();
-		return;
-	}
-
-	auto &libList = fmlLibsMapping[version];
-
-	// determine if we need some libs for FML or forge
-	setStatus(tr("Checking for FML libraries..."));
-	forge_present = (profile->versionPatch("net.minecraftforge") != nullptr);
-	// we don't...
-	if (!forge_present)
-	{
-		assetIndexStart();
-		return;
-	}
-
-	// now check the lib folder inside the instance for files.
-	for (auto &lib : libList)
-	{
-		QFileInfo libInfo(FS::PathCombine(inst->libDir(), lib.filename));
-		if (libInfo.exists())
-			continue;
-		fmlLibsToProcess.append(lib);
-	}
 
-	// if everything is in place, there's nothing to do here...
-	if (fmlLibsToProcess.isEmpty())
-	{
-		assetIndexStart();
-		return;
-	}
-
-	// download missing libs to our place
-	setStatus(tr("Dowloading FML libraries..."));
-	auto dljob = new NetJob("FML libraries");
-	auto metacache = ENV.metacache();
-	for (auto &lib : fmlLibsToProcess)
-	{
-		auto entry = metacache->resolveEntry("fmllibs", lib.filename);
-		QString urlString = lib.ours ? URLConstants::FMLLIBS_OUR_BASE_URL + lib.filename
-									 : URLConstants::FMLLIBS_FORGE_BASE_URL + lib.filename;
-		dljob->addNetAction(Net::Download::makeCached(QUrl(urlString), entry));
-	}
-
-	connect(dljob, SIGNAL(succeeded()), SLOT(fmllibsFinished()));
-	connect(dljob, &NetJob::failed, this, &OneSixUpdate::fmllibsFailed);
-	connect(dljob, SIGNAL(progress(qint64, qint64)), SIGNAL(progress(qint64, qint64)));
-	legacyDownloadJob.reset(dljob);
-	legacyDownloadJob->start();
-}
-
-void OneSixUpdate::fmllibsFinished()
+bool OneSixUpdate::abort()
 {
-	legacyDownloadJob.reset();
-	if (!fmlLibsToProcess.isEmpty())
+	if(!m_abort)
 	{
-		setStatus(tr("Copying FML libraries into the instance..."));
-		OneSixInstance *inst = (OneSixInstance *)m_inst;
-		auto metacache = ENV.metacache();
-		int index = 0;
-		for (auto &lib : fmlLibsToProcess)
+		m_abort = true;
+		auto task = m_tasks[m_currentTask];
+		if(task->canAbort())
 		{
-			progress(index, fmlLibsToProcess.size());
-			auto entry = metacache->resolveEntry("fmllibs", lib.filename);
-			auto path = FS::PathCombine(inst->libDir(), lib.filename);
-			if (!FS::ensureFilePathExists(path))
-			{
-				emitFailed(tr("Failed creating FML library folder inside the instance."));
-				return;
-			}
-			if (!QFile::copy(entry->getFullPath(), FS::PathCombine(inst->libDir(), lib.filename)))
-			{
-				emitFailed(tr("Failed copying Forge/FML library: %1.").arg(lib.filename));
-				return;
-			}
-			index++;
+			return task->abort();
 		}
-		progress(index, fmlLibsToProcess.size());
 	}
-	assetIndexStart();
+	return true;
 }
 
-void OneSixUpdate::fmllibsFailed(QString reason)
+bool OneSixUpdate::canAbort() const
 {
-	emitFailed(tr("Game update failed: it was impossible to fetch the required FML libraries.\nReason:\n%1").arg(reason));
-	return;
+	return true;
 }
-
diff --git a/api/logic/minecraft/onesix/OneSixUpdate.h b/api/logic/minecraft/onesix/OneSixUpdate.h
index b5195364..3780ef2e 100644
--- a/api/logic/minecraft/onesix/OneSixUpdate.h
+++ b/api/logic/minecraft/onesix/OneSixUpdate.h
@@ -32,36 +32,22 @@ class OneSixUpdate : public Task
 	Q_OBJECT
 public:
 	explicit OneSixUpdate(OneSixInstance *inst, QObject *parent = 0);
-	virtual void executeTask();
+	void executeTask() override;
+	bool canAbort() const override;
 
 private
 slots:
-	void versionUpdateFailed(QString reason);
-
-	void jarlibStart();
-	void jarlibFinished();
-	void jarlibFailed(QString reason);
-
-	void fmllibsStart();
-	void fmllibsFinished();
-	void fmllibsFailed(QString reason);
-
-	void assetIndexStart();
-	void assetIndexFinished();
-	void assetIndexFailed(QString reason);
-
-	void assetsFinished();
-	void assetsFailed(QString reason);
+	bool abort() override;
+	void subtaskSucceeded();
+	void subtaskFailed(QString error);
 
 private:
-	NetJobPtr jarlibDownloadJob;
-	NetJobPtr legacyDownloadJob;
-
-	/// target version, determined during this task
-	std::shared_ptr<MinecraftVersion> targetVersion;
-	/// the task that is spawned for version updates
-	std::shared_ptr<Task> versionUpdateTask;
+	void next();
 
+private:
 	OneSixInstance *m_inst = nullptr;
-	QList<FMLlib> fmlLibsToProcess;
+	QList<std::shared_ptr<Task>> m_tasks;
+	QString m_preFailure;
+	int m_currentTask = -1;
+	bool m_abort = false;
 };
diff --git a/api/logic/minecraft/onesix/update/AssetUpdateTask.cpp b/api/logic/minecraft/onesix/update/AssetUpdateTask.cpp
new file mode 100644
index 00000000..21600ff0
--- /dev/null
+++ b/api/logic/minecraft/onesix/update/AssetUpdateTask.cpp
@@ -0,0 +1,99 @@
+#include "Env.h"
+#include "AssetUpdateTask.h"
+#include "minecraft/onesix/OneSixInstance.h"
+#include "net/ChecksumValidator.h"
+#include "minecraft/AssetsUtils.h"
+
+AssetUpdateTask::AssetUpdateTask(OneSixInstance * inst)
+{
+	m_inst = inst;
+}
+void AssetUpdateTask::executeTask()
+{
+	setStatus(tr("Updating assets index..."));
+	auto profile = m_inst->getMinecraftProfile();
+	auto assets = profile->getMinecraftAssets();
+	QUrl indexUrl = assets->url;
+	QString localPath = assets->id + ".json";
+	auto job = new NetJob(tr("Asset index for %1").arg(m_inst->name()));
+
+	auto metacache = ENV.metacache();
+	auto entry = metacache->resolveEntry("asset_indexes", localPath);
+	entry->setStale(true);
+	auto hexSha1 = assets->sha1.toLatin1();
+	qDebug() << "Asset index SHA1:" << hexSha1;
+	auto dl = Net::Download::makeCached(indexUrl, entry);
+	auto rawSha1 = QByteArray::fromHex(assets->sha1.toLatin1());
+	dl->addValidator(new Net::ChecksumValidator(QCryptographicHash::Sha1, rawSha1));
+	job->addNetAction(dl);
+
+	downloadJob.reset(job);
+
+	connect(downloadJob.get(), &NetJob::succeeded, this, &AssetUpdateTask::assetIndexFinished);
+	connect(downloadJob.get(), &NetJob::failed, this, &AssetUpdateTask::assetIndexFailed);
+	connect(downloadJob.get(), &NetJob::progress, this, &AssetUpdateTask::progress);
+
+	qDebug() << m_inst->name() << ": Starting asset index download";
+	downloadJob->start();
+}
+
+bool AssetUpdateTask::canAbort() const
+{
+	return true;
+}
+
+void AssetUpdateTask::assetIndexFinished()
+{
+	AssetsIndex index;
+	qDebug() << m_inst->name() << ": Finished asset index download";
+
+	auto profile = m_inst->getMinecraftProfile();
+	auto assets = profile->getMinecraftAssets();
+
+	QString asset_fname = "assets/indexes/" + assets->id + ".json";
+	// FIXME: this looks like a job for a generic validator based on json schema?
+	if (!AssetsUtils::loadAssetsIndexJson(assets->id, asset_fname, &index))
+	{
+		auto metacache = ENV.metacache();
+		auto entry = metacache->resolveEntry("asset_indexes", assets->id + ".json");
+		metacache->evictEntry(entry);
+		emitFailed(tr("Failed to read the assets index!"));
+	}
+
+	auto job = index.getDownloadJob();
+	if(job)
+	{
+		setStatus(tr("Getting the assets files from Mojang..."));
+		downloadJob = job;
+		connect(downloadJob.get(), &NetJob::succeeded, this, &AssetUpdateTask::emitSucceeded);
+		connect(downloadJob.get(), &NetJob::failed, this, &AssetUpdateTask::assetsFailed);
+		connect(downloadJob.get(), &NetJob::progress, this, &AssetUpdateTask::progress);
+		downloadJob->start();
+		return;
+	}
+	emitSucceeded();
+}
+
+void AssetUpdateTask::assetIndexFailed(QString reason)
+{
+	qDebug() << m_inst->name() << ": Failed asset index download";
+	emitFailed(tr("Failed to download the assets index:\n%1").arg(reason));
+}
+
+void AssetUpdateTask::assetsFailed(QString reason)
+{
+	emitFailed(tr("Failed to download assets:\n%1").arg(reason));
+}
+
+bool AssetUpdateTask::abort()
+{
+	if(downloadJob)
+	{
+		return downloadJob->abort();
+	}
+	else
+	{
+		qWarning() << "Prematurely aborted FMLLibrariesTask";
+	}
+	return true;
+}
diff --git a/api/logic/minecraft/onesix/update/AssetUpdateTask.h b/api/logic/minecraft/onesix/update/AssetUpdateTask.h
new file mode 100644
index 00000000..dff72571
--- /dev/null
+++ b/api/logic/minecraft/onesix/update/AssetUpdateTask.h
@@ -0,0 +1,25 @@
+#pragma once
+#include "tasks/Task.h"
+#include "net/NetJob.h"
+class OneSixInstance;
+
+class AssetUpdateTask : public Task
+{
+public:
+	AssetUpdateTask(OneSixInstance * inst);
+	void executeTask() override;
+
+	bool canAbort() const override;
+
+private slots:
+	void assetIndexFinished();
+	void assetIndexFailed(QString reason);
+	void assetsFailed(QString reason);
+
+public slots:
+	bool abort() override;
+
+private:
+	OneSixInstance *m_inst;
+	NetJobPtr downloadJob;
+};
diff --git a/api/logic/minecraft/onesix/update/FMLLibrariesTask.cpp b/api/logic/minecraft/onesix/update/FMLLibrariesTask.cpp
new file mode 100644
index 00000000..1cbee95e
--- /dev/null
+++ b/api/logic/minecraft/onesix/update/FMLLibrariesTask.cpp
@@ -0,0 +1,132 @@
+#include "Env.h"
+#include <FileSystem.h>
+#include <minecraft/VersionFilterData.h>
+#include "FMLLibrariesTask.h"
+#include "minecraft/onesix/OneSixInstance.h"
+
+
+FMLLibrariesTask::FMLLibrariesTask(OneSixInstance * inst)
+{
+	m_inst = inst;
+}
+void FMLLibrariesTask::executeTask()
+{
+	// Get the mod list
+	OneSixInstance *inst = (OneSixInstance *)m_inst;
+	std::shared_ptr<MinecraftProfile> profile = inst->getMinecraftProfile();
+	bool forge_present = false;
+
+	if (!profile->hasTrait("legacyFML"))
+	{
+		emitSucceeded();
+	}
+
+	QString version = inst->intendedVersionId();
+	auto &fmlLibsMapping = g_VersionFilterData.fmlLibsMapping;
+	if (!fmlLibsMapping.contains(version))
+	{
+		emitSucceeded();
+		return;
+	}
+
+	auto &libList = fmlLibsMapping[version];
+
+	// determine if we need some libs for FML or forge
+	setStatus(tr("Checking for FML libraries..."));
+	forge_present = (profile->versionPatch("net.minecraftforge") != nullptr);
+	// we don't...
+	if (!forge_present)
+	{
+		emitSucceeded();
+		return;
+	}
+
+	// now check the lib folder inside the instance for files.
+	for (auto &lib : libList)
+	{
+		QFileInfo libInfo(FS::PathCombine(inst->libDir(), lib.filename));
+		if (libInfo.exists())
+			continue;
+		fmlLibsToProcess.append(lib);
+	}
+
+	// if everything is in place, there's nothing to do here...
+	if (fmlLibsToProcess.isEmpty())
+	{
+		emitSucceeded();
+		return;
+	}
+
+	// download missing libs to our place
+	setStatus(tr("Dowloading FML libraries..."));
+	auto dljob = new NetJob("FML libraries");
+	auto metacache = ENV.metacache();
+	for (auto &lib : fmlLibsToProcess)
+	{
+		auto entry = metacache->resolveEntry("fmllibs", lib.filename);
+		QString urlString = lib.ours ? URLConstants::FMLLIBS_OUR_BASE_URL + lib.filename
+									: URLConstants::FMLLIBS_FORGE_BASE_URL + lib.filename;
+		dljob->addNetAction(Net::Download::makeCached(QUrl(urlString), entry));
+	}
+
+	connect(dljob, &NetJob::succeeded, this, &FMLLibrariesTask::fmllibsFinished);
+	connect(dljob, &NetJob::failed, this, &FMLLibrariesTask::fmllibsFailed);
+	connect(dljob, &NetJob::progress, this, &FMLLibrariesTask::progress);
+	downloadJob.reset(dljob);
+	downloadJob->start();
+}
+
+bool FMLLibrariesTask::canAbort() const
+{
+	return true;
+}
+
+void FMLLibrariesTask::fmllibsFinished()
+{
+	downloadJob.reset();
+	if (!fmlLibsToProcess.isEmpty())
+	{
+		setStatus(tr("Copying FML libraries into the instance..."));
+		OneSixInstance *inst = (OneSixInstance *)m_inst;
+		auto metacache = ENV.metacache();
+		int index = 0;
+		for (auto &lib : fmlLibsToProcess)
+		{
+			progress(index, fmlLibsToProcess.size());
+			auto entry = metacache->resolveEntry("fmllibs", lib.filename);
+			auto path = FS::PathCombine(inst->libDir(), lib.filename);
+			if (!FS::ensureFilePathExists(path))
+			{
+				emitFailed(tr("Failed creating FML library folder inside the instance."));
+				return;
+			}
+			if (!QFile::copy(entry->getFullPath(), FS::PathCombine(inst->libDir(), lib.filename)))
+			{
+				emitFailed(tr("Failed copying Forge/FML library: %1.").arg(lib.filename));
+				return;
+			}
+			index++;
+		}
+		progress(index, fmlLibsToProcess.size());
+	}
+	emitSucceeded();
+}
+void FMLLibrariesTask::fmllibsFailed(QString reason)
+{
+	QStringList failed = downloadJob->getFailedFiles();
+	QString failed_all = failed.join("\n");
+	emitFailed(tr("Failed to download the following files:\n%1\n\nReason:%2\nPlease try again.").arg(failed_all, reason));
+}
+
+bool FMLLibrariesTask::abort()
+{
+	if(downloadJob)
+	{
+		return downloadJob->abort();
+	}
+	else
+	{
+		qWarning() << "Prematurely aborted FMLLibrariesTask";
+	}
+	return true;
+}
diff --git a/api/logic/minecraft/onesix/update/FMLLibrariesTask.h b/api/logic/minecraft/onesix/update/FMLLibrariesTask.h
new file mode 100644
index 00000000..d1c250e4
--- /dev/null
+++ b/api/logic/minecraft/onesix/update/FMLLibrariesTask.h
@@ -0,0 +1,27 @@
+#pragma once
+#include "tasks/Task.h"
+#include "net/NetJob.h"
+class OneSixInstance;
+
+class FMLLibrariesTask : public Task
+{
+public:
+	FMLLibrariesTask(OneSixInstance * inst);
+
+	void executeTask() override;
+
+	bool canAbort() const override;
+
+private slots:
+	void fmllibsFinished();
+	void fmllibsFailed(QString reason);
+
+public slots:
+	bool abort() override;
+
+private:
+	OneSixInstance *m_inst;
+	NetJobPtr downloadJob;
+	QList<FMLlib> fmlLibsToProcess;
+};
+
diff --git a/api/logic/minecraft/onesix/update/FoldersTask.cpp b/api/logic/minecraft/onesix/update/FoldersTask.cpp
new file mode 100644
index 00000000..239a2675
--- /dev/null
+++ b/api/logic/minecraft/onesix/update/FoldersTask.cpp
@@ -0,0 +1,20 @@
+#include "FoldersTask.h"
+#include "minecraft/onesix/OneSixInstance.h"
+#include <QDir>
+
+FoldersTask::FoldersTask(OneSixInstance * inst)
+{
+	m_inst = inst;
+}
+
+void FoldersTask::executeTask()
+{
+	// Make directories
+	QDir mcDir(m_inst->minecraftRoot());
+	if (!mcDir.exists() && !mcDir.mkpath("."))
+	{
+		emitFailed(tr("Failed to create folder for minecraft binaries."));
+		return;
+	}
+	emitSucceeded();
+}
diff --git a/api/logic/minecraft/onesix/update/FoldersTask.h b/api/logic/minecraft/onesix/update/FoldersTask.h
new file mode 100644
index 00000000..552d3098
--- /dev/null
+++ b/api/logic/minecraft/onesix/update/FoldersTask.h
@@ -0,0 +1,14 @@
+#pragma once
+
+#include "tasks/Task.h"
+
+class OneSixInstance;
+class FoldersTask : public Task
+{
+public:
+	FoldersTask(OneSixInstance * inst);
+	void executeTask() override;
+private:
+	OneSixInstance *m_inst;
+};
+
diff --git a/api/logic/minecraft/onesix/update/LibrariesTask.cpp b/api/logic/minecraft/onesix/update/LibrariesTask.cpp
new file mode 100644
index 00000000..123b14a3
--- /dev/null
+++ b/api/logic/minecraft/onesix/update/LibrariesTask.cpp
@@ -0,0 +1,89 @@
+#include "Env.h"
+#include "LibrariesTask.h"
+#include "minecraft/onesix/OneSixInstance.h"
+
+LibrariesTask::LibrariesTask(OneSixInstance * inst)
+{
+	m_inst = inst;
+}
+
+void LibrariesTask::executeTask()
+{
+	setStatus(tr("Getting the library files from Mojang..."));
+	qDebug() << m_inst->name() << ": downloading libraries";
+	OneSixInstance *inst = (OneSixInstance *)m_inst;
+	inst->reloadProfile();
+	if(inst->flags() & BaseInstance::VersionBrokenFlag)
+	{
+		emitFailed(tr("Failed to load the version description files - check the instance for errors."));
+		return;
+	}
+
+	// Build a list of URLs that will need to be downloaded.
+	std::shared_ptr<MinecraftProfile> profile = inst->getMinecraftProfile();
+	// minecraft.jar for this version
+	{
+		QString version_id = profile->getMinecraftVersion();
+		QString localPath = version_id + "/" + version_id + ".jar";
+		QString urlstr = profile->getMainJarUrl();
+
+		auto job = new NetJob(tr("Libraries for instance %1").arg(inst->name()));
+
+		auto metacache = ENV.metacache();
+		auto entry = metacache->resolveEntry("versions", localPath);
+		job->addNetAction(Net::Download::makeCached(QUrl(urlstr), entry));
+		downloadJob.reset(job);
+	}
+
+	auto libs = profile->getLibraries();
+
+	auto metacache = ENV.metacache();
+	QList<LibraryPtr> brokenLocalLibs;
+	QStringList failedFiles;
+	for (auto lib : libs)
+	{
+		auto dls = lib->getDownloads(currentSystem, metacache.get(), failedFiles);
+		for(auto dl : dls)
+		{
+			downloadJob->addNetAction(dl);
+		}
+	}
+	// FIXME: this is never filled!!!!
+	if (!brokenLocalLibs.empty())
+	{
+		downloadJob.reset();
+		QString failed_all = failedFiles.join("\n");
+		emitFailed(tr("Some libraries marked as 'local' are missing their jar "
+					"files:\n%1\n\nYou'll have to correct this problem manually. If this is "
+					"an externally tracked instance, make sure to run it at least once "
+					"outside of MultiMC.").arg(failed_all));
+		return;
+	}
+	connect(downloadJob.get(), &NetJob::succeeded, this, &LibrariesTask::emitSucceeded);
+	connect(downloadJob.get(), &NetJob::failed, this, &LibrariesTask::jarlibFailed);
+	connect(downloadJob.get(), &NetJob::progress, this, &LibrariesTask::progress);
+	downloadJob->start();
+}
+
+bool LibrariesTask::canAbort() const
+{
+	return true;
+}
+
+void LibrariesTask::jarlibFailed(QString reason)
+{
+	emitFailed(tr("Game update failed: it was impossible to fetch the required libraries.\nReason:\n%1").arg(reason));
+}
+
+bool LibrariesTask::abort()
+{
+	if(downloadJob)
+	{
+		return downloadJob->abort();
+	}
+	else
+	{
+		qWarning() << "Prematurely aborted LibrariesTask";
+	}
+	return true;
+}
diff --git a/api/logic/minecraft/onesix/update/LibrariesTask.h b/api/logic/minecraft/onesix/update/LibrariesTask.h
new file mode 100644
index 00000000..80cf0d2a
--- /dev/null
+++ b/api/logic/minecraft/onesix/update/LibrariesTask.h
@@ -0,0 +1,24 @@
+#pragma once
+#include "tasks/Task.h"
+#include "net/NetJob.h"
+class OneSixInstance;
+
+class LibrariesTask : public Task
+{
+public:
+	LibrariesTask(OneSixInstance * inst);
+
+	void executeTask() override;
+
+	bool canAbort() const override;
+
+private slots:
+	void jarlibFailed(QString reason);
+
+public slots:
+	bool abort() override;
+
+private:
+	OneSixInstance *m_inst;
+	NetJobPtr downloadJob;
+};
diff --git a/api/logic/net/Download.cpp b/api/logic/net/Download.cpp
index 70fe7608..7610cae3 100644
--- a/api/logic/net/Download.cpp
+++ b/api/logic/net/Download.cpp
@@ -65,6 +65,12 @@ void Download::addValidator(Validator * v)
 
 void Download::start()
 {
+	if(m_status == Job_Aborted)
+	{
+		qWarning() << "Attempt to start an aborted Download:" << m_url.toString();
+		emit aborted(m_index_within_job);
+		return;
+	}
 	QNetworkRequest request(m_url);
 	m_status = m_sink->init(request);
 	switch(m_status)
@@ -80,6 +86,8 @@ void Download::start()
 		case Job_Failed:
 			emit failed(m_index_within_job);
 			return;
+		case Job_Aborted:
+			return;
 	}
 
 	request.setHeader(QNetworkRequest::UserAgentHeader, "MultiMC/5.0");
@@ -103,9 +111,17 @@ void Download::downloadProgress(qint64 bytesReceived, qint64 bytesTotal)
 
 void Download::downloadError(QNetworkReply::NetworkError error)
 {
-	// error happened during download.
-	qCritical() << "Failed " << m_url.toString() << " with reason " << error;
-	m_status = Job_Failed;
+	if(error == QNetworkReply::OperationCanceledError)
+	{
+		qCritical() << "Aborted " << m_url.toString();
+		m_status = Job_Aborted;
+	}
+	else
+	{
+		// error happened during download.
+		qCritical() << "Failed " << m_url.toString() << " with reason " << error;
+		m_status = Job_Failed;
+	}
 }
 
 bool Download::handleRedirect()
@@ -154,6 +170,14 @@ void Download::downloadFinished()
 		emit failed(m_index_within_job);
 		return;
 	}
+	else if(m_status == Job_Aborted)
+	{
+		qDebug() << "Download aborted in previous step:" << m_url.toString();
+		m_sink->abort();
+		m_reply.reset();
+		emit aborted(m_index_within_job);
+		return;
+	}
 
 	// make sure we got all the remaining data, if any
 	auto data = m_reply->readAll();
@@ -197,3 +221,21 @@ void Download::downloadReadyRead()
 }
 
 }
+
+bool Net::Download::abort()
+{
+	if(m_reply)
+	{
+		m_reply->abort();
+	}
+	else
+	{
+		m_status = Job_Aborted;
+	}
+	return true;
+}
+
+bool Net::Download::canAbort()
+{
+	return true;
+}
diff --git a/api/logic/net/Download.h b/api/logic/net/Download.h
index 8e38dfc9..fab39ffe 100644
--- a/api/logic/net/Download.h
+++ b/api/logic/net/Download.h
@@ -38,25 +38,25 @@ public:
 	static Download::Ptr makeFile(QUrl url, QString path);
 
 public: /* methods */
-	// FIXME: remove this
 	QString getTargetFilepath()
 	{
 		return m_target_path;
 	}
-	// FIXME: remove this
 	void addValidator(Validator * v);
+	bool abort() override;
+	bool canAbort() override;
 
 private: /* methods */
 	bool handleRedirect();
 
 protected slots:
-	virtual void downloadProgress(qint64 bytesReceived, qint64 bytesTotal);
-	virtual void downloadError(QNetworkReply::NetworkError error);
-	virtual void downloadFinished();
-	virtual void downloadReadyRead();
+	void downloadProgress(qint64 bytesReceived, qint64 bytesTotal) override;
+	void downloadError(QNetworkReply::NetworkError error) override;
+	void downloadFinished() override;
+	void downloadReadyRead() override;
 
 public slots:
-	virtual void start();
+	void start() override;
 
 private: /* data */
 	// FIXME: remove this, it has no business being here.
diff --git a/api/logic/net/NetAction.h b/api/logic/net/NetAction.h
index 2b3f1b7b..07456ce1 100644
--- a/api/logic/net/NetAction.h
+++ b/api/logic/net/NetAction.h
@@ -28,7 +28,8 @@ enum JobStatus
 	Job_NotStarted,
 	Job_InProgress,
 	Job_Finished,
-	Job_Failed
+	Job_Failed,
+	Job_Aborted
 };
 
 typedef std::shared_ptr<class NetAction> NetActionPtr;
@@ -54,6 +55,14 @@ public:
 	{
 		return m_failures;
 	}
+	virtual bool abort()
+	{
+		return false;
+	}
+	virtual bool canAbort()
+	{
+		return false;
+	}
 
 public:
 	/// the network reply
@@ -79,6 +88,7 @@ signals:
 	void netActionProgress(int index, qint64 current, qint64 total);
 	void succeeded(int index);
 	void failed(int index);
+	void aborted(int index);
 
 protected
 slots:
diff --git a/api/logic/net/NetJob.cpp b/api/logic/net/NetJob.cpp
index ca86242a..2e375760 100644
--- a/api/logic/net/NetJob.cpp
+++ b/api/logic/net/NetJob.cpp
@@ -47,6 +47,15 @@ void NetJob::partFailed(int index)
 	startMoreParts();
 }
 
+void NetJob::partAborted(int index)
+{
+	m_aborted = true;
+	m_doing.remove(index);
+	m_failed.insert(index);
+	downloads[index].get()->disconnect(this);
+	startMoreParts();
+}
+
 void NetJob::partProgress(int index, qint64 bytesReceived, qint64 bytesTotal)
 {
 	auto &slot = parts_progress[index];
@@ -85,6 +94,11 @@ void NetJob::startMoreParts()
 				qDebug() << m_job_name << "succeeded.";
 				emitSucceeded();
 			}
+			else if(m_aborted)
+			{
+				qDebug() << m_job_name << "aborted.";
+				emitFailed(tr("Job '%1' aborted.").arg(m_job_name));
+			}
 			else
 			{
 				qCritical() << m_job_name << "failed.";
@@ -104,6 +118,7 @@ void NetJob::startMoreParts()
 		// connect signals :D
 		connect(part.get(), SIGNAL(succeeded(int)), SLOT(partSucceeded(int)));
 		connect(part.get(), SIGNAL(failed(int)), SLOT(partFailed(int)));
+		connect(part.get(), SIGNAL(aborted(int)), SLOT(partAborted(int)));
 		connect(part.get(), SIGNAL(netActionProgress(int, qint64, qint64)),
 				SLOT(partProgress(int, qint64, qint64)));
 		part->start();
@@ -121,3 +136,37 @@ QStringList NetJob::getFailedFiles()
 	failed.sort();
 	return failed;
 }
+
+bool NetJob::canAbort() const
+{
+	bool canFullyAbort = true;
+	// can abort the waiting?
+	for(auto index: m_todo)
+	{
+		auto part = downloads[index];
+		canFullyAbort &= part->canAbort();
+	}
+	// can abort the active?
+	for(auto index: m_doing)
+	{
+		auto part = downloads[index];
+		canFullyAbort &= part->canAbort();
+	}
+	return canFullyAbort;
+}
+
+bool NetJob::abort()
+{
+	bool fullyAborted = true;
+	// fail all waiting
+	m_failed.unite(m_todo.toSet());
+	m_todo.clear();
+	// abort active
+	auto toKill = m_doing.toList();
+	for(auto index: toKill)
+	{
+		auto part = downloads[index];
+		fullyAborted &= part->abort();
+	}
+	return fullyAborted;
+}
diff --git a/api/logic/net/NetJob.h b/api/logic/net/NetJob.h
index 3d16b21f..e1c266dd 100644
--- a/api/logic/net/NetJob.h
+++ b/api/logic/net/NetJob.h
@@ -75,24 +75,26 @@ public:
 	{
 		return downloads.size();
 	}
-	virtual bool isRunning() const
+	virtual bool isRunning() const override
 	{
 		return m_running;
 	}
 	QStringList getFailedFiles();
 
+	bool canAbort() const override;
+
 private slots:
 	void startMoreParts();
 
 public slots:
-	virtual void executeTask();
-	// FIXME: implement
-	virtual bool abort() {return false;};
+	virtual void executeTask() override;
+	virtual bool abort() override;
 
 private slots:
 	void partProgress(int index, qint64 bytesReceived, qint64 bytesTotal);
 	void partSucceeded(int index);
 	void partFailed(int index);
+	void partAborted(int index);
 
 private:
 	struct part_info
@@ -112,4 +114,5 @@ private:
 	qint64 current_progress = 0;
 	qint64 total_progress = 0;
 	bool m_running = false;
+	bool m_aborted = false;
 };