QHttpServer: Web Apps in Qt

Posted on Feb 6, 2011

Qt is a great GUI toolkit, but it is also an entire C++ standard library waiting to be used for other tasks. In addition the network module is really powerful. I’ve been playing around with node.js for a while now, and realized that Qt’s default asynchronous nature maps over perfectly to create a event-based web server. To make things better, Ryan Dahl’s small and fast http-parser is freely available. So I just combined the two, and here is QHttpServer.

Here is a ‘web-application’ written completely in C++/Qt. You can even try it out.

#!cpp
#include "greeting.h"

#include <QCoreApplication>
#include <QRegExp>
#include <QStringList>

#include <qhttpserver.h>
#include <qhttprequest.h>
#include <qhttpresponse.h>

Greeting::Greeting()
{
    QHttpServer *server = new QHttpServer;
    server->listen(QHostAddress::Any, 5000);
    connect(server, SIGNAL(newRequest(QHttpRequest*, QHttpResponse*)),
            this, SLOT(handle(QHttpRequest*, QHttpResponse*)));
}

void Greeting::handle(QHttpRequest *req, QHttpResponse *resp)
{
    QRegExp exp("^/user/([a-z]+)$");
    if( exp.indexIn(req->path()) != -1 )
    {
        resp->setHeader("Content-Type", "text/html");
        resp->writeHead(200);
        QString name = exp.capturedTexts()[1];

        QString reply = tr("<html><head><title>Greeting App</title></head><body><h1>Hello  %1!</h1></body></html>");
        resp->end(reply.arg(name).toAscii());
    }
    else
    {
        resp->writeHead(403);
        resp->end("You aren't allowed here!");
    }
}

int main(int argc, char **argv)
{
    QCoreApplication app(argc, argv);

    Greeting hello;
    
    app.exec();
}

Awesome isn’t it? You launch an instance of QHttpServer, it emits a signal whenever a new request comes in, you can handle and respond to it. The code is fully documented, so you can do a git clone and run doxygen in the docs/ folder to get API documentation. For now it doesn’t deal with everything that can happen in HTTP, but it does know about keep-alives (no chunked encoding though). QHttpServer is streaming, see the body data example.

Here is a simple ApacheBench run comparing qhttpserver and node.

QHttpServer Greeting app:

> ab -n 1000 -c 100 http://localhost:5000/user/nikhil
This is ApacheBench, Version 2.3 <$Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking localhost (be patient)


Server Software:        
Server Hostname:        localhost
Server Port:            5000

Document Path:          /user/nikhil
Document Length:        88 bytes

Concurrency Level:      100
Time taken for tests:   0.467 seconds
Complete requests:      1000
Failed requests:        0
Write errors:           0
Total transferred:      151000 bytes
HTML transferred:       88000 bytes
Requests per second:    2142.47 [#/sec] (mean)
Time per request:       46.675 [ms] (mean)
Time per request:       0.467 [ms] (mean, across all concurrent requests)
Transfer rate:          315.93 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    2   4.7      0      23
Processing:    14   43  18.9     40     123
Waiting:       13   43  18.9     40     123
Total:         14   45  18.9     41     130

Percentage of the requests served within a certain time (ms)
  50%     41
  66%     48
  75%     53
  80%     58
  90%     69
  95%     80
  98%     98
  99%    117
 100%    130 (longest request)

node.js greeting app:

> ab -n 1000 -c 100 http://localhost:5000/user/nikhil
This is ApacheBench, Version 2.3 <$Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking localhost (be patient)


Server Software:        
Server Hostname:        localhost
Server Port:            5000

Document Path:          /user/nikhil
Document Length:        88 bytes

Concurrency Level:      100
Time taken for tests:   0.441 seconds
Complete requests:      1000
Failed requests:        0
Write errors:           0
Total transferred:      151000 bytes
HTML transferred:       88000 bytes
Requests per second:    2267.94 [#/sec] (mean)
Time per request:       44.093 [ms] (mean)
Time per request:       0.441 [ms] (mean, across all concurrent requests)
Transfer rate:          334.43 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    2   4.4      0      18
Processing:     4   40  22.7     37     101
Waiting:        4   40  22.9     37     101
Total:          4   42  21.7     39     101

Percentage of the requests served within a certain time (ms)
  50%     39
  66%     50
  75%     57
  80%     63
  90%     73
  95%     83
  98%     91
  99%     95
 100%    101 (longest request)

While not a very scientific benchmark, this does show them pretty close. C++ is compiled, but I believe node has less ‘layers’ and a particularly efficient I/O infrastructure which allows it to be better even with an interpreted language.

I would really like to see this being used in Qt apps that need a web interface for remote control, or for simple delivery of files.

In addition, if you will be attending conf.kde.in in Bangalore, India on March 9th-13th, my talk on Qt Scripting will involve writing a thin JavaScript wrapper over this and doing some other cool stuff! So be there.