src/socketpair.*: log all connection errors

QTcpSocket and QTcpServer emit an Qt signal on error, so we create slots
to receive those signals, and print the error that ocurred to stderr
through qCritical. qCritical gives the admin flexibility in choosing
whether or not to make those errors fatal or not through setting or not
the environment variable `QT_FATAL_CRITICALS`. See
https://doc.qt.io/qt-5/qtglobal.html#qCritical

src/socketpair.cpp

@@ -1,6 +1,7 @@
 #include "socketpair.h"
-#include <QIODevice>
 #include <QDebug>
+#include <QIODevice>
+#include <QtGlobal>
 
 SocketPair::SocketPair(QObject *parent)
         : QObject(parent)
@@ -14,6 +15,9 @@ bool SocketPair::create()
     connect(dataCheck, SIGNAL(timeout()), this, SLOT(readServerData()));
     connect(&server, SIGNAL(newConnection()), this, SLOT(newConnection()), Qt::QueuedConnection);
 
+    connect(&server, SIGNAL(acceptError()), this, SLOT(logServerError()));
+    connect(&clientConnection, SIGNAL(error()), this, SLOT(logClientConnectionError()));
+
     int tries = 5;
     while (tries) {
         if (!server.isListening()) {
@@ -40,6 +44,12 @@ bool SocketPair::create()
 void SocketPair::newConnection()
 {
     serverConnection = server.nextPendingConnection();
+    if(serverConnection != nullptr) {
+        connect(serverConnection, SIGNAL(error()), this, SLOT(logServerConnectionError()));
+    } else {
+        qFatal("%s:%d:%s, server.nextPendingConnection() was NULL.", __FILE__,
+                __LINE__, __func__);
+    }
 
     serverConnection->setSocketOption( QAbstractSocket::LowDelayOption, 1 );
     serverConnection->setSocketOption( QAbstractSocket::KeepAliveOption, 1 );
@@ -81,3 +91,24 @@ QTcpSocket* SocketPair::output()
 {
     return serverConnection;
 }
+
+void SocketPair::logServerError(QAbstractSocket::SocketError socketError) {
+    qCritical("%s:%d:%s, server.serverError() is: '%d', and server.errorString() "
+            "is: '%s', and socketError is: '%d'", __FILE__, __LINE__, __func__,
+            server.serverError(), qUtf8Printable(server.errorString()),
+            socketError);
+}
+
+void SocketPair::logServerConnectionError(QAbstractSocket::SocketError socketError) {
+    qCritical("%s:%d:%s, serverConnection->error() is: '%d', and "
+           "serverConnection->errorString() is: '%s', and socketError is: '%d'",
+           __FILE__, __LINE__, __func__, serverConnection->error(),
+            qUtf8Printable(serverConnection->errorString()), socketError);
+}
+
+void SocketPair::logClientConnectionError(QAbstractSocket::SocketError socketError) {
+    qCritical("%s:%d:%s, clientConnection.error() is: '%d', and "
+           "clientConnection.errorString() is: '%s', and socketError is: '%d'",
+           __FILE__, __LINE__, __func__, clientConnection.error(),
+            qUtf8Printable(clientConnection.errorString()), socketError);
+}

src/socketpair.h

@@ -34,6 +34,12 @@ public slots:
     QTcpSocket *serverConnection;
     QTcpSocket clientConnection;
     QTcpServer server;
+
+private slots:
+    void logServerError(QAbstractSocket::SocketError);
+    void logServerConnectionError(QAbstractSocket::SocketError);
+    void logClientConnectionError(QAbstractSocket::SocketError);
+
 };
 
 #endif // SOCKETPAIR_H