WebUI: Use regular expression to check if gzip is accepted

The previous code caused a crash in case "gzip" was at the end of the
string with no quality factor (;q=*) specified.

src/core/http/connection.cpp

@@ -31,6 +31,7 @@
 
 #include <QTcpSocket>
 #include <QDebug>
+#include <QRegExp>
 #include "types.h"
 #include "requestparser.h"
 #include "responsegenerator.h"
@@ -85,26 +86,13 @@ void Connection::sendResponse(const Response &response)
 
 bool Connection::acceptsGzipEncoding(const QString &encoding)
 {
-    int pos = encoding.indexOf("gzip", 0, Qt::CaseInsensitive);
-    if (pos == -1)
-        return false;
-
-    // Let's see if there's a qvalue of 0.0 following
-    if (encoding[pos + 4] != ';') //there isn't, so it accepts gzip anyway
+    QRegExp rx("(gzip)(;q=([^,]+))?");
+    if (rx.indexIn(encoding) >= 0) {
+        if (rx.cap(2).size() > 0)
+            // check if quality factor > 0
+            return (rx.cap(3).toDouble() > 0);
+        // if quality factor is not specified, then it's 1
         return true;
-
-    //So let's find = and the next comma
-    pos = encoding.indexOf("=", pos + 4, Qt::CaseInsensitive);
-    int comma_pos = encoding.indexOf(",", pos, Qt::CaseInsensitive);
-
-    QString value;
-    if (comma_pos == -1)
-        value = encoding.mid(pos + 1, comma_pos);
-    else
-        value = encoding.mid(pos + 1, comma_pos - (pos + 1));
-
-    if (value.toDouble() == 0.0)
-        return false;
-
-    return true;
+    }
+    return false;
 }