NOISSUE Flatten gui and logic libraries into MultiMC

18 files changed, 1796 insertions, 0 deletions

diff --git a/launcher/net/ByteArraySink.h b/launcher/net/ByteArraySink.h
new file mode 100644
index 00000000..20e6764c
--- /dev/null
+++ b/launcher/net/ByteArraySink.h
@@ -0,0 +1,62 @@
+#pragma once
+
+#include "Sink.h"
+
+namespace Net {
+/*
+ * Sink object for downloads that uses an external QByteArray it doesn't own as a target.
+ */
+class ByteArraySink : public Sink
+{
+public:
+    ByteArraySink(QByteArray *output)
+        :m_output(output)
+    {
+        // nil
+    };
+
+    virtual ~ByteArraySink()
+    {
+        // nil
+    }
+
+public:
+    JobStatus init(QNetworkRequest & request) override
+    {
+        m_output->clear();
+        if(initAllValidators(request))
+            return Job_InProgress;
+        return Job_Failed;
+    };
+
+    JobStatus write(QByteArray & data) override
+    {
+        m_output->append(data);
+        if(writeAllValidators(data))
+            return Job_InProgress;
+        return Job_Failed;
+    }
+
+    JobStatus abort() override
+    {
+        m_output->clear();
+        failAllValidators();
+        return Job_Failed;
+    }
+
+    JobStatus finalize(QNetworkReply &reply) override
+    {
+        if(finalizeAllValidators(reply))
+            return Job_Finished;
+        return Job_Failed;
+    }
+
+    bool hasLocalData() override
+    {
+        return false;
+    }
+
+private:
+    QByteArray * m_output;
+};
+}
diff --git a/launcher/net/ChecksumValidator.h b/launcher/net/ChecksumValidator.h
new file mode 100644
index 00000000..0d6b19c2
--- /dev/null
+++ b/launcher/net/ChecksumValidator.h
@@ -0,0 +1,55 @@
+#pragma once
+
+#include "Validator.h"
+#include <QCryptographicHash>
+#include <memory>
+#include <QFile>
+
+namespace Net {
+class ChecksumValidator: public Validator
+{
+public: /* con/des */
+    ChecksumValidator(QCryptographicHash::Algorithm algorithm, QByteArray expected = QByteArray())
+        :m_checksum(algorithm), m_expected(expected)
+    {
+    };
+    virtual ~ChecksumValidator() {};
+
+public: /* methods */
+    bool init(QNetworkRequest &) override
+    {
+        m_checksum.reset();
+        return true;
+    }
+    bool write(QByteArray & data) override
+    {
+        m_checksum.addData(data);
+        return true;
+    }
+    bool abort() override
+    {
+        return true;
+    }
+    bool validate(QNetworkReply &) override
+    {
+        if(m_expected.size() && m_expected != hash())
+        {
+            qWarning() << "Checksum mismatch, download is bad.";
+            return false;
+        }
+        return true;
+    }
+    QByteArray hash()
+    {
+        return m_checksum.result();
+    }
+    void setExpected(QByteArray expected)
+    {
+        m_expected = expected;
+    }
+
+private: /* data */
+    QCryptographicHash m_checksum;
+    QByteArray m_expected;
+};
+}
\ No newline at end of file
diff --git a/launcher/net/Download.cpp b/launcher/net/Download.cpp
new file mode 100644
index 00000000..3f183b7d
--- /dev/null
+++ b/launcher/net/Download.cpp
@@ -0,0 +1,309 @@
+/* Copyright 2013-2021 MultiMC Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Download.h"
+
+#include "BuildConfig.h"
+#include <QFileInfo>
+#include <QDateTime>
+#include <QDebug>
+#include "Env.h"
+#include <FileSystem.h>
+#include "ChecksumValidator.h"
+#include "MetaCacheSink.h"
+#include "ByteArraySink.h"
+
+namespace Net {
+
+Download::Download():NetAction()
+{
+    m_status = Job_NotStarted;
+}
+
+Download::Ptr Download::makeCached(QUrl url, MetaEntryPtr entry, Options options)
+{
+    Download * dl = new Download();
+    dl->m_url = url;
+    dl->m_options = options;
+    auto md5Node = new ChecksumValidator(QCryptographicHash::Md5);
+    auto cachedNode = new MetaCacheSink(entry, md5Node);
+    dl->m_sink.reset(cachedNode);
+    dl->m_target_path = entry->getFullPath();
+    return std::shared_ptr<Download>(dl);
+}
+
+Download::Ptr Download::makeByteArray(QUrl url, QByteArray *output, Options options)
+{
+    Download * dl = new Download();
+    dl->m_url = url;
+    dl->m_options = options;
+    dl->m_sink.reset(new ByteArraySink(output));
+    return std::shared_ptr<Download>(dl);
+}
+
+Download::Ptr Download::makeFile(QUrl url, QString path, Options options)
+{
+    Download * dl = new Download();
+    dl->m_url = url;
+    dl->m_options = options;
+    dl->m_sink.reset(new FileSink(path));
+    return std::shared_ptr<Download>(dl);
+}
+
+void Download::addValidator(Validator * v)
+{
+    m_sink->addValidator(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)
+    {
+        case Job_Finished:
+            emit succeeded(m_index_within_job);
+            qDebug() << "Download cache hit " << m_url.toString();
+            return;
+        case Job_InProgress:
+            qDebug() << "Downloading " << m_url.toString();
+            break;
+        case Job_Failed_Proceed: // this is meaningless in this context. We do need a sink.
+        case Job_NotStarted:
+        case Job_Failed:
+            emit failed(m_index_within_job);
+            return;
+        case Job_Aborted:
+            return;
+    }
+
+    request.setHeader(QNetworkRequest::UserAgentHeader, BuildConfig.USER_AGENT);
+
+    QNetworkReply *rep =  ENV.qnam().get(request);
+
+    m_reply.reset(rep);
+    connect(rep, SIGNAL(downloadProgress(qint64, qint64)), SLOT(downloadProgress(qint64, qint64)));
+    connect(rep, SIGNAL(finished()), SLOT(downloadFinished()));
+    connect(rep, SIGNAL(error(QNetworkReply::NetworkError)), SLOT(downloadError(QNetworkReply::NetworkError)));
+    connect(rep, &QNetworkReply::sslErrors, this, &Download::sslErrors);
+    connect(rep, &QNetworkReply::readyRead, this, &Download::downloadReadyRead);
+}
+
+void Download::downloadProgress(qint64 bytesReceived, qint64 bytesTotal)
+{
+    m_total_progress = bytesTotal;
+    m_progress = bytesReceived;
+    emit netActionProgress(m_index_within_job, bytesReceived, bytesTotal);
+}
+
+void Download::downloadError(QNetworkReply::NetworkError error)
+{
+    if(error == QNetworkReply::OperationCanceledError)
+    {
+        qCritical() << "Aborted " << m_url.toString();
+        m_status = Job_Aborted;
+    }
+    else
+    {
+        if(m_options & Option::AcceptLocalFiles)
+        {
+            if(m_sink->hasLocalData())
+            {
+                m_status = Job_Failed_Proceed;
+                return;
+            }
+        }
+        // error happened during download.
+        qCritical() << "Failed " << m_url.toString() << " with reason " << error;
+        m_status = Job_Failed;
+    }
+}
+
+void Download::sslErrors(const QList<QSslError> & errors)
+{
+    int i = 1;
+    for (auto error : errors)
+    {
+        qCritical() << "Download" << m_url.toString() << "SSL Error #" << i << " : " << error.errorString();
+        auto cert = error.certificate();
+        qCritical() << "Certificate in question:\n" << cert.toText();
+        i++;
+    }
+}
+
+bool Download::handleRedirect()
+{
+    QUrl redirect = m_reply->header(QNetworkRequest::LocationHeader).toUrl();
+    if(!redirect.isValid())
+    {
+        if(!m_reply->hasRawHeader("Location"))
+        {
+            // no redirect -> it's fine to continue
+            return false;
+        }
+        // there is a Location header, but it's not correct. we need to apply some workarounds...
+        QByteArray redirectBA = m_reply->rawHeader("Location");
+        if(redirectBA.size() == 0)
+        {
+            // empty, yet present redirect header? WTF?
+            return false;
+        }
+        QString redirectStr = QString::fromUtf8(redirectBA);
+
+        if(redirectStr.startsWith("//"))
+        {
+            /*
+             * IF the URL begins with //, we need to insert the URL scheme.
+             * See: https://bugreports.qt.io/browse/QTBUG-41061
+             * See: http://tools.ietf.org/html/rfc3986#section-4.2
+             */
+            redirectStr = m_reply->url().scheme() + ":" + redirectStr;
+        }
+        else if(redirectStr.startsWith("/"))
+        {
+            /*
+             * IF the URL begins with /, we need to process it as a relative URL
+             */
+            auto url = m_reply->url();
+            url.setPath(redirectStr, QUrl::TolerantMode);
+            redirectStr = url.toString();
+        }
+
+        /*
+         * Next, make sure the URL is parsed in tolerant mode. Qt doesn't parse the location header in tolerant mode, which causes issues.
+         * FIXME: report Qt bug for this
+         */
+        redirect = QUrl(redirectStr, QUrl::TolerantMode);
+        if(!redirect.isValid())
+        {
+            qWarning() << "Failed to parse redirect URL:" << redirectStr;
+            downloadError(QNetworkReply::ProtocolFailure);
+            return false;
+        }
+        qDebug() << "Fixed location header:" << redirect;
+    }
+    else
+    {
+        qDebug() << "Location header:" << redirect;
+    }
+
+    m_url = QUrl(redirect.toString());
+    qDebug() << "Following redirect to " << m_url.toString();
+    start();
+    return true;
+}
+
+
+void Download::downloadFinished()
+{
+    // handle HTTP redirection first
+    if(handleRedirect())
+    {
+        qDebug() << "Download redirected:" << m_url.toString();
+        return;
+    }
+
+    // if the download failed before this point ...
+    if (m_status == Job_Failed_Proceed)
+    {
+        qDebug() << "Download failed but we are allowed to proceed:" << m_url.toString();
+        m_sink->abort();
+        m_reply.reset();
+        emit succeeded(m_index_within_job);
+        return;
+    }
+    else if (m_status == Job_Failed)
+    {
+        qDebug() << "Download failed in previous step:" << m_url.toString();
+        m_sink->abort();
+        m_reply.reset();
+        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();
+    if(data.size())
+    {
+        qDebug() << "Writing extra" << data.size() << "bytes to" << m_target_path;
+        m_status = m_sink->write(data);
+    }
+
+    // otherwise, finalize the whole graph
+    m_status = m_sink->finalize(*m_reply.get());
+    if (m_status != Job_Finished)
+    {
+        qDebug() << "Download failed to finalize:" << m_url.toString();
+        m_sink->abort();
+        m_reply.reset();
+        emit failed(m_index_within_job);
+        return;
+    }
+    m_reply.reset();
+    qDebug() << "Download succeeded:" << m_url.toString();
+    emit succeeded(m_index_within_job);
+}
+
+void Download::downloadReadyRead()
+{
+    if(m_status == Job_InProgress)
+    {
+        auto data = m_reply->readAll();
+        m_status = m_sink->write(data);
+        if(m_status == Job_Failed)
+        {
+            qCritical() << "Failed to process response chunk for " << m_target_path;
+        }
+        // qDebug() << "Download" << m_url.toString() << "gained" << data.size() << "bytes";
+    }
+    else
+    {
+        qCritical() << "Cannot write to " << m_target_path << ", illegal status" << m_status;
+    }
+}
+
+}
+
+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/launcher/net/Download.h b/launcher/net/Download.h
new file mode 100644
index 00000000..a224bb86
--- /dev/null
+++ b/launcher/net/Download.h
@@ -0,0 +1,75 @@
+/* Copyright 2013-2021 MultiMC Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include "NetAction.h"
+#include "HttpMetaCache.h"
+#include "Validator.h"
+#include "Sink.h"
+
+namespace Net {
+class Download : public NetAction
+{
+    Q_OBJECT
+
+public: /* types */
+    typedef std::shared_ptr<class Download> Ptr;
+    enum class Option
+    {
+        NoOptions = 0,
+        AcceptLocalFiles = 1
+    };
+    Q_DECLARE_FLAGS(Options, Option)
+
+protected: /* con/des */
+    explicit Download();
+public:
+    virtual ~Download(){};
+    static Download::Ptr makeCached(QUrl url, MetaEntryPtr entry, Options options = Option::NoOptions);
+    static Download::Ptr makeByteArray(QUrl url, QByteArray *output, Options options = Option::NoOptions);
+    static Download::Ptr makeFile(QUrl url, QString path, Options options = Option::NoOptions);
+
+public: /* methods */
+    QString getTargetFilepath()
+    {
+        return m_target_path;
+    }
+    void addValidator(Validator * v);
+    bool abort() override;
+    bool canAbort() override;
+
+private: /* methods */
+    bool handleRedirect();
+
+protected slots:
+    void downloadProgress(qint64 bytesReceived, qint64 bytesTotal) override;
+    void downloadError(QNetworkReply::NetworkError error) override;
+    void sslErrors(const QList<QSslError> & errors);
+    void downloadFinished() override;
+    void downloadReadyRead() override;
+
+public slots:
+    void start() override;
+
+private: /* data */
+    // FIXME: remove this, it has no business being here.
+    QString m_target_path;
+    std::unique_ptr<Sink> m_sink;
+    Options m_options;
+};
+}
+
+Q_DECLARE_OPERATORS_FOR_FLAGS(Net::Download::Options)
diff --git a/launcher/net/FileSink.cpp b/launcher/net/FileSink.cpp
new file mode 100644
index 00000000..8b3e917d
--- /dev/null
+++ b/launcher/net/FileSink.cpp
@@ -0,0 +1,115 @@
+#include "FileSink.h"
+#include <QFile>
+#include <QFileInfo>
+#include "Env.h"
+#include "FileSystem.h"
+
+namespace Net {
+
+FileSink::FileSink(QString filename)
+    :m_filename(filename)
+{
+    // nil
+}
+
+FileSink::~FileSink()
+{
+    // nil
+}
+
+JobStatus FileSink::init(QNetworkRequest& request)
+{
+    auto result = initCache(request);
+    if(result != Job_InProgress)
+    {
+        return result;
+    }
+    // create a new save file and open it for writing
+    if (!FS::ensureFilePathExists(m_filename))
+    {
+        qCritical() << "Could not create folder for " + m_filename;
+        return Job_Failed;
+    }
+    wroteAnyData = false;
+    m_output_file.reset(new QSaveFile(m_filename));
+    if (!m_output_file->open(QIODevice::WriteOnly))
+    {
+        qCritical() << "Could not open " + m_filename + " for writing";
+        return Job_Failed;
+    }
+
+    if(initAllValidators(request))
+        return Job_InProgress;
+    return Job_Failed;
+}
+
+JobStatus FileSink::initCache(QNetworkRequest &)
+{
+    return Job_InProgress;
+}
+
+JobStatus FileSink::write(QByteArray& data)
+{
+    if (!writeAllValidators(data) || m_output_file->write(data) != data.size())
+    {
+        qCritical() << "Failed writing into " + m_filename;
+        m_output_file->cancelWriting();
+        m_output_file.reset();
+        wroteAnyData = false;
+        return Job_Failed;
+    }
+    wroteAnyData = true;
+    return Job_InProgress;
+}
+
+JobStatus FileSink::abort()
+{
+    m_output_file->cancelWriting();
+    failAllValidators();
+    return Job_Failed;
+}
+
+JobStatus FileSink::finalize(QNetworkReply& reply)
+{
+    bool gotFile = false;
+    QVariant statusCodeV = reply.attribute(QNetworkRequest::HttpStatusCodeAttribute);
+    bool validStatus = false;
+    int statusCode = statusCodeV.toInt(&validStatus);
+    if(validStatus)
+    {
+        // this leaves out 304 Not Modified
+        gotFile = statusCode == 200 || statusCode == 203;
+    }
+    // if we wrote any data to the save file, we try to commit the data to the real file.
+    // if it actually got a proper file, we write it even if it was empty
+    if (gotFile || wroteAnyData)
+    {
+        // ask validators for data consistency
+        // we only do this for actual downloads, not 'your data is still the same' cache hits
+        if(!finalizeAllValidators(reply))
+            return Job_Failed;
+        // nothing went wrong...
+        if (!m_output_file->commit())
+        {
+            qCritical() << "Failed to commit changes to " << m_filename;
+            m_output_file->cancelWriting();
+            return Job_Failed;
+        }
+    }
+    // then get rid of the save file
+    m_output_file.reset();
+
+    return finalizeCache(reply);
+}
+
+JobStatus FileSink::finalizeCache(QNetworkReply &)
+{
+    return Job_Finished;
+}
+
+bool FileSink::hasLocalData()
+{
+    QFileInfo info(m_filename);
+    return info.exists() && info.size() != 0;
+}
+}
diff --git a/launcher/net/FileSink.h b/launcher/net/FileSink.h
new file mode 100644
index 00000000..875fe511
--- /dev/null
+++ b/launcher/net/FileSink.h
@@ -0,0 +1,28 @@
+#pragma once
+#include "Sink.h"
+#include <QSaveFile>
+
+namespace Net {
+class FileSink : public Sink
+{
+public: /* con/des */
+    FileSink(QString filename);
+    virtual ~FileSink();
+
+public: /* methods */
+    JobStatus init(QNetworkRequest & request) override;
+    JobStatus write(QByteArray & data) override;
+    JobStatus abort() override;
+    JobStatus finalize(QNetworkReply & reply) override;
+    bool hasLocalData() override;
+
+protected: /* methods */
+    virtual JobStatus initCache(QNetworkRequest &);
+    virtual JobStatus finalizeCache(QNetworkReply &reply);
+
+protected: /* data */
+    QString m_filename;
+    bool wroteAnyData = false;
+    std::unique_ptr<QSaveFile> m_output_file;
+};
+}
diff --git a/launcher/net/HttpMetaCache.cpp b/launcher/net/HttpMetaCache.cpp
new file mode 100644
index 00000000..4bc8fbc8
--- /dev/null
+++ b/launcher/net/HttpMetaCache.cpp
@@ -0,0 +1,273 @@
+/* Copyright 2013-2021 MultiMC Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Env.h"
+#include "HttpMetaCache.h"
+#include "FileSystem.h"
+
+#include <QFileInfo>
+#include <QFile>
+#include <QDateTime>
+#include <QCryptographicHash>
+
+#include <QDebug>
+
+#include <QJsonDocument>
+#include <QJsonArray>
+#include <QJsonObject>
+
+QString MetaEntry::getFullPath()
+{
+    // FIXME: make local?
+    return FS::PathCombine(basePath, relativePath);
+}
+
+HttpMetaCache::HttpMetaCache(QString path) : QObject()
+{
+    m_index_file = path;
+    saveBatchingTimer.setSingleShot(true);
+    saveBatchingTimer.setTimerType(Qt::VeryCoarseTimer);
+    connect(&saveBatchingTimer, SIGNAL(timeout()), SLOT(SaveNow()));
+}
+
+HttpMetaCache::~HttpMetaCache()
+{
+    saveBatchingTimer.stop();
+    SaveNow();
+}
+
+MetaEntryPtr HttpMetaCache::getEntry(QString base, QString resource_path)
+{
+    // no base. no base path. can't store
+    if (!m_entries.contains(base))
+    {
+        // TODO: log problem
+        return MetaEntryPtr();
+    }
+    EntryMap &map = m_entries[base];
+    if (map.entry_list.contains(resource_path))
+    {
+        return map.entry_list[resource_path];
+    }
+    return MetaEntryPtr();
+}
+
+MetaEntryPtr HttpMetaCache::resolveEntry(QString base, QString resource_path, QString expected_etag)
+{
+    auto entry = getEntry(base, resource_path);
+    // it's not present? generate a default stale entry
+    if (!entry)
+    {
+        return staleEntry(base, resource_path);
+    }
+
+    auto &selected_base = m_entries[base];
+    QString real_path = FS::PathCombine(selected_base.base_path, resource_path);
+    QFileInfo finfo(real_path);
+
+    // is the file really there? if not -> stale
+    if (!finfo.isFile() || !finfo.isReadable())
+    {
+        // if the file doesn't exist, we disown the entry
+        selected_base.entry_list.remove(resource_path);
+        return staleEntry(base, resource_path);
+    }
+
+    if (!expected_etag.isEmpty() && expected_etag != entry->etag)
+    {
+        // if the etag doesn't match expected, we disown the entry
+        selected_base.entry_list.remove(resource_path);
+        return staleEntry(base, resource_path);
+    }
+
+    // if the file changed, check md5sum
+    qint64 file_last_changed = finfo.lastModified().toUTC().toMSecsSinceEpoch();
+    if (file_last_changed != entry->local_changed_timestamp)
+    {
+        QFile input(real_path);
+        input.open(QIODevice::ReadOnly);
+        QString md5sum = QCryptographicHash::hash(input.readAll(), QCryptographicHash::Md5)
+                             .toHex()
+                             .constData();
+        if (entry->md5sum != md5sum)
+        {
+            selected_base.entry_list.remove(resource_path);
+            return staleEntry(base, resource_path);
+        }
+        // md5sums matched... keep entry and save the new state to file
+        entry->local_changed_timestamp = file_last_changed;
+        SaveEventually();
+    }
+
+    // entry passed all the checks we cared about.
+    entry->basePath = getBasePath(base);
+    return entry;
+}
+
+bool HttpMetaCache::updateEntry(MetaEntryPtr stale_entry)
+{
+    if (!m_entries.contains(stale_entry->baseId))
+    {
+        qCritical() << "Cannot add entry with unknown base: "
+                     << stale_entry->baseId.toLocal8Bit();
+        return false;
+    }
+    if (stale_entry->stale)
+    {
+        qCritical() << "Cannot add stale entry: " << stale_entry->getFullPath().toLocal8Bit();
+        return false;
+    }
+    m_entries[stale_entry->baseId].entry_list[stale_entry->relativePath] = stale_entry;
+    SaveEventually();
+    return true;
+}
+
+bool HttpMetaCache::evictEntry(MetaEntryPtr entry)
+{
+    if(entry)
+    {
+        entry->stale = true;
+        SaveEventually();
+        return true;
+    }
+    return false;
+}
+
+MetaEntryPtr HttpMetaCache::staleEntry(QString base, QString resource_path)
+{
+    auto foo = new MetaEntry();
+    foo->baseId = base;
+    foo->basePath = getBasePath(base);
+    foo->relativePath = resource_path;
+    foo->stale = true;
+    return MetaEntryPtr(foo);
+}
+
+void HttpMetaCache::addBase(QString base, QString base_root)
+{
+    // TODO: report error
+    if (m_entries.contains(base))
+        return;
+    // TODO: check if the base path is valid
+    EntryMap foo;
+    foo.base_path = base_root;
+    m_entries[base] = foo;
+}
+
+QString HttpMetaCache::getBasePath(QString base)
+{
+    if (m_entries.contains(base))
+    {
+        return m_entries[base].base_path;
+    }
+    return QString();
+}
+
+void HttpMetaCache::Load()
+{
+    if(m_index_file.isNull())
+        return;
+
+    QFile index(m_index_file);
+    if (!index.open(QIODevice::ReadOnly))
+        return;
+
+    QJsonDocument json = QJsonDocument::fromJson(index.readAll());
+    if (!json.isObject())
+        return;
+    auto root = json.object();
+    // check file version first
+    auto version_val = root.value("version");
+    if (!version_val.isString())
+        return;
+    if (version_val.toString() != "1")
+        return;
+
+    // read the entry array
+    auto entries_val = root.value("entries");
+    if (!entries_val.isArray())
+        return;
+    QJsonArray array = entries_val.toArray();
+    for (auto element : array)
+    {
+        if (!element.isObject())
+            return;
+        auto element_obj = element.toObject();
+        QString base = element_obj.value("base").toString();
+        if (!m_entries.contains(base))
+            continue;
+        auto &entrymap = m_entries[base];
+        auto foo = new MetaEntry();
+        foo->baseId = base;
+        QString path = foo->relativePath = element_obj.value("path").toString();
+        foo->md5sum = element_obj.value("md5sum").toString();
+        foo->etag = element_obj.value("etag").toString();
+        foo->local_changed_timestamp = element_obj.value("last_changed_timestamp").toDouble();
+        foo->remote_changed_timestamp =
+            element_obj.value("remote_changed_timestamp").toString();
+        // presumed innocent until closer examination
+        foo->stale = false;
+        entrymap.entry_list[path] = MetaEntryPtr(foo);
+    }
+}
+
+void HttpMetaCache::SaveEventually()
+{
+    // reset the save timer
+    saveBatchingTimer.stop();
+    saveBatchingTimer.start(30000);
+}
+
+void HttpMetaCache::SaveNow()
+{
+    if(m_index_file.isNull())
+        return;
+    QJsonObject toplevel;
+    toplevel.insert("version", QJsonValue(QString("1")));
+    QJsonArray entriesArr;
+    for (auto group : m_entries)
+    {
+        for (auto entry : group.entry_list)
+        {
+            // do not save stale entries. they are dead.
+            if(entry->stale)
+            {
+                continue;
+            }
+            QJsonObject entryObj;
+            entryObj.insert("base", QJsonValue(entry->baseId));
+            entryObj.insert("path", QJsonValue(entry->relativePath));
+            entryObj.insert("md5sum", QJsonValue(entry->md5sum));
+            entryObj.insert("etag", QJsonValue(entry->etag));
+            entryObj.insert("last_changed_timestamp",
+                            QJsonValue(double(entry->local_changed_timestamp)));
+            if (!entry->remote_changed_timestamp.isEmpty())
+                entryObj.insert("remote_changed_timestamp",
+                                QJsonValue(entry->remote_changed_timestamp));
+            entriesArr.append(entryObj);
+        }
+    }
+    toplevel.insert("entries", entriesArr);
+
+    QJsonDocument doc(toplevel);
+    try
+    {
+        FS::write(m_index_file, doc.toJson());
+    }
+    catch (const Exception &e)
+    {
+        qWarning() << e.what();
+    }
+}
diff --git a/launcher/net/HttpMetaCache.h b/launcher/net/HttpMetaCache.h
new file mode 100644
index 00000000..1c10e8c7
--- /dev/null
+++ b/launcher/net/HttpMetaCache.h
@@ -0,0 +1,123 @@
+/* Copyright 2013-2021 MultiMC Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+#include <QString>
+#include <QMap>
+#include <qtimer.h>
+#include <memory>
+
+clas