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/proxy/NativeMessagingProxy.cpp

@@ -0,0 +1,110 @@
+/*
+ *  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 "NativeMessagingProxy.h"
+#include "browser/BrowserShared.h"
+
+#include <QCoreApplication>
+#include <QtConcurrent/QtConcurrent>
+
+#include <iostream>
+
+#ifdef Q_OS_WIN
+#include <fcntl.h>
+#include <windows.h>
+#endif
+
+NativeMessagingProxy::NativeMessagingProxy()
+    : QObject()
+{
+    connect(this,
+            &NativeMessagingProxy::stdinMessage,
+            this,
+            &NativeMessagingProxy::transferStdinMessage,
+            Qt::QueuedConnection);
+
+    setupStandardInput();
+    setupLocalSocket();
+}
+
+void NativeMessagingProxy::setupStandardInput()
+{
+#ifdef Q_OS_WIN
+    setmode(fileno(stdin), _O_BINARY);
+    setmode(fileno(stdout), _O_BINARY);
+#endif
+
+    QtConcurrent::run([this] {
+        while (std::cin.good()) {
+            if (std::cin.peek() != EOF) {
+                uint length = 0;
+                for (uint i = 0; i < sizeof(uint); ++i) {
+                    length |= getchar() << (i * 8);
+                }
+
+                QString msg;
+                msg.reserve(length);
+                for (uint i = 0; i < length; ++i) {
+                    msg.append(getchar());
+                }
+
+                if (msg.length() > 0) {
+                    emit stdinMessage(msg);
+                }
+            }
+            QThread::msleep(100);
+        }
+        QCoreApplication::quit();
+    });
+}
+
+void NativeMessagingProxy::transferStdinMessage(const QString& msg)
+{
+    if (m_localSocket && m_localSocket->state() == QLocalSocket::ConnectedState) {
+        m_localSocket->write(msg.toUtf8(), msg.length());
+        m_localSocket->flush();
+    }
+}
+
+void NativeMessagingProxy::setupLocalSocket()
+{
+    m_localSocket.reset(new QLocalSocket());
+    m_localSocket->connectToServer(BrowserShared::localServerPath());
+    m_localSocket->setReadBufferSize(BrowserShared::NATIVEMSG_MAX_LENGTH);
+
+    connect(m_localSocket.data(), SIGNAL(readyRead()), this, SLOT(transferSocketMessage()));
+    connect(m_localSocket.data(), SIGNAL(disconnected()), this, SLOT(socketDisconnected()));
+}
+
+void NativeMessagingProxy::transferSocketMessage()
+{
+    auto msg = m_localSocket->readAll();
+    if (!msg.isEmpty()) {
+        // Explicitly write the message length as 1 byte chunks
+        uint len = msg.size();
+        std::cout.write(reinterpret_cast<char*>(&len), sizeof(len));
+
+        // Write the message and flush the stream
+        std::cout << msg.toStdString() << std::flush;
+    }
+}
+
+void NativeMessagingProxy::socketDisconnected()
+{
+    // Shutdown the proxy when disconnected from the application
+    QCoreApplication::quit();
+}