Handle slow startup of the web server.

If the web server is slow to start, we may need to retry the initial
page load. Implement a retry system that will retry the initial load
4 times, after 1, 2, 3 and 4 seconds, before giving up and leaving
the user with an error message and a link to retry manually.

runtime/BrowserWindow.cpp

@@ -30,6 +30,7 @@
 // App headers
 #include "BrowserWindow.h"
 
+
 // Constructor
 BrowserWindow::BrowserWindow()
 {
@@ -39,11 +40,15 @@ BrowserWindow::BrowserWindow()
     // Create the WebKit control
     webView = new QWebView(this);
     setCentralWidget(webView);
+    connect(webView, SIGNAL(loadFinished(bool)), SLOT(finishLoading(bool)));
 
     // Display the app
-    webView->setUrl(QString("http://127.0.0.1:8080"));
+    m_initialload = true;
+    m_loadattempt = 1;
+    webView->setUrl(PGA_SERVER_URL);
 }
 
+
 // Create the actions for the window
 void BrowserWindow::createActions()
 {
@@ -65,6 +70,7 @@ void BrowserWindow::createActions()
     connect(aboutAction, SIGNAL(triggered()), this, SLOT(about()));
 }
 
+
 // Create the application menus
 void BrowserWindow::createMenus()
 {
@@ -81,12 +87,54 @@ void BrowserWindow::createMenus()
     helpMenu->addAction(aboutAction);
 }
 
+
+// Process loading finished signals from the web view.
+void BrowserWindow::finishLoading(bool ok)
+{
+    if (m_initialload && !ok)
+    {
+        // The load attempt failed. Try again up to 4 times with an
+        // incremental backoff.
+        if (m_loadattempt < 5)
+        {
+            qDebug() << "Initial load failed. Retrying in" << m_loadattempt << "seconds.";
+            webView->setHtml(QString(tr("<p>Failed to connect to the pgAdmin application server. Retrying in %1 seconds, ") +
+                                     tr("or click <a href=\"%2\">here</a> to try again now.</p>")).arg(m_loadattempt).arg(PGA_SERVER_URL));
+
+            pause(m_loadattempt);
+            webView->setUrl(PGA_SERVER_URL);
+            m_loadattempt++;
+            return;
+        }
+        else
+        {
+            qDebug() << "Initial page load failed after multiple attempts. Aborting.";
+            webView->setHtml(QString(tr("<p>Failed to connect to the pgAdmin application server. ") +
+                                     tr("Click <a href=\"%1\">here</a> to try again.</p>")).arg(PGA_SERVER_URL));
+        }
+    }
+
+    m_initialload = false;
+}
+
+
+// Pause for n seconds, without freezing the UI.
+void BrowserWindow::pause(int seconds)
+{
+    QTime dieTime = QTime::currentTime().addSecs(seconds);
+
+    while (QTime::currentTime() < dieTime)
+        QCoreApplication::processEvents(QEventLoop::AllEvents, 100);    
+}
+
+
 // Display the about box
 void BrowserWindow::about()
 {
     QMessageBox::about(this, tr("About pgAdmin 4"), tr("pgAdmin 4 - PostgreSQL Tools"));
 }
 
+
 // Open an arbitrary URL
 void BrowserWindow::openUrl()
 {

runtime/BrowserWindow.h

@@ -36,6 +36,9 @@ class BrowserWindow : public QMainWindow
 public:
     BrowserWindow();
 
+protected slots:
+    void finishLoading(bool);
+
 private slots:
     void openUrl();
     void about();
@@ -48,8 +51,12 @@ private:
     QAction *exitAction;
     QAction *aboutAction;
 
+    bool m_initialload;
+    int m_loadattempt;
+
     void createActions();
     void createMenus();
+    void pause(int seconds = 1);
 };
 
 #endif // BROWSERWINDOW_H

runtime/Server.cpp

@@ -25,7 +25,7 @@
 Server::Server()
 {
     // Initialise Python
-    Py_SetProgramName(PGA_APPNAME.toUtf8().data());
+    Py_SetProgramName(PGA_APP_NAME.toUtf8().data());
     Py_Initialize();
 }
 

runtime/pgAdmin4.h

@@ -25,7 +25,10 @@
 #include <QApplication>
 #endif
 
-// char *PGA_APPNAME = "pgAdmin 4";
-const QString PGA_APPNAME = QString("pgAdmin 4");
+// Application name
+const QString PGA_APP_NAME = QString("pgAdmin 4");
+
+// Server URL
+const QString PGA_SERVER_URL = QString("http://127.0.0.1:8080");
 
 #endif // PGADMIN4_H