Complete refactor of Browser Integration classes

* Removed option to attach KeePassXC to the browser extension. Users must use the proxy application to communicate with KeePassXC.
* Significantly streamlined proxy code. Used same implementation of stdin/stdout interface across all platforms.
* Moved browser service entry point to BrowserService class instead of NativeMessagingHost. BrowserService now coordinates the communication to/from clients.
* Moved settings page definition out of MainWindow
* Decoupled BrowserService from DatabaseTabWidget
* Reduced complexity of various functions and cleaned the ABI (public vs private).
* Eliminated BrowserClients class, moved functionality into the BrowserService
* Renamed HostInstaller to NativeMessageInstaller and renamed NativeMessageHost to BrowserHost.
* Recognize XDG_CONFIG_HOME when installing native message file on Linux. Fix #4121 and fix #4123.

src/browser/BrowserHost.cpp

@@ -0,0 +1,107 @@
+/*
+ *  Copyright (C) 2020 KeePassXC Team <team@keepassxc.org>
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "BrowserHost.h"
+#include "BrowserSettings.h"
+#include "BrowserShared.h"
+
+#include <QJsonDocument>
+#include <QLocalServer>
+#include <QLocalSocket>
+#include <QMutexLocker>
+#include <QtNetwork>
+
+#include "sodium.h"
+#include <iostream>
+
+BrowserHost::BrowserHost(QObject* parent)
+    : QObject(parent)
+{
+    m_localServer = new QLocalServer(this);
+    m_localServer->setSocketOptions(QLocalServer::UserAccessOption);
+    connect(m_localServer.data(), SIGNAL(newConnection()), this, SLOT(proxyConnected()));
+}
+
+BrowserHost::~BrowserHost()
+{
+    stop();
+}
+
+void BrowserHost::start()
+{
+    if (sodium_init() == -1) {
+        qWarning() << "Failed to start browser service: libsodium failed to initialize!";
+        return;
+    }
+
+    if (!m_localServer->isListening()) {
+        m_localServer->listen(BrowserShared::localServerPath());
+    }
+}
+
+void BrowserHost::stop()
+{
+    m_socketList.clear();
+    m_localServer->close();
+}
+
+void BrowserHost::proxyConnected()
+{
+    auto socket = m_localServer->nextPendingConnection();
+    if (socket) {
+        m_socketList.append(socket);
+        connect(socket, SIGNAL(readyRead()), this, SLOT(readProxyMessage()));
+        connect(socket, SIGNAL(disconnected()), this, SLOT(proxyDisconnected()));
+    }
+}
+
+void BrowserHost::readProxyMessage()
+{
+    QLocalSocket* socket = qobject_cast<QLocalSocket*>(QObject::sender());
+    if (!socket || socket->bytesAvailable() <= 0) {
+        return;
+    }
+
+    socket->setReadBufferSize(BrowserShared::NATIVEMSG_MAX_LENGTH);
+
+    QJsonParseError error;
+    auto json = QJsonDocument::fromJson(socket->readAll(), &error);
+    if (json.isNull()) {
+        qWarning() << "Failed to read proxy message: " << error.errorString();
+        return;
+    }
+
+    emit clientMessageReceived(json.object());
+}
+
+void BrowserHost::sendClientMessage(const QJsonObject& json)
+{
+    QString reply(QJsonDocument(json).toJson(QJsonDocument::Compact));
+    for (const auto socket : m_socketList) {
+        if (socket && socket->isValid() && socket->state() == QLocalSocket::ConnectedState) {
+            QByteArray arr = reply.toUtf8();
+            socket->write(arr.constData(), arr.length());
+            socket->flush();
+        }
+    }
+}
+
+void BrowserHost::proxyDisconnected()
+{
+    auto socket = qobject_cast<QLocalSocket*>(QObject::sender());
+    m_socketList.removeOne(socket);
+}