Introduction to QtNetworkNg

QtNetworkNg is a coroutine-based networking programming toolkit, like boost::asio but use concept of QtNetwork and gevent of Python. Compare to boost::asio and Qt’s QtNetwork, QtNetworkNg has more simpler API.

Why Coroutines

The coroutine-based paradigm is not a new thing, Python, Go, and C# was using coroutines to simplify network programming many years ago.

The traditional network programming use threads. send()/recv() is blocked, and then the Operating System switch current thread to another ready thread until data arrived. This is very straightforward, and easy for network programming. But threads use heavy resources, thousouds connections may consume many memory. More worst, threads cause data races, data currupt, even crashes.

Another choice is use callback-based paradigm. Before calling send()/recv(), use select()/poll()/epoll() to determine data arriving. Although select() is blocked, but many connections are handled in one thread. Pseudocode like this.

callback-based networking programming
class HandleRequest {
    HandleRequest() {
        state = ReadingHeader;
        fd->readyRead->addCallback(this::onReadyRead); // add fd to select() hub, if data arrived, call this::onReadRead;
    void onReadyRead() {
        const QByteArray &buf = fd->read(fd->bytesAvailable());
        if (this->state == ReadingHeader) {
        } else if (this->state == ReadingBody) {

class SelectHub {
    typedef void* context;
    typedef std::function<void(int,Context) Callback;
    void addOnRead(int fd, Callback callback, Context context) {
        fds.append(make_tuple(fd, callback, context));
    void run() {
        while(true) {
            fd, callback, context = select(fds);
            callback(fd, context);
    List<Tuple<int, Callback, Context>> fds;

Callback-based paradigm is considered “the new-age goto”, hard to understand and read/write code. But it is widely used by C++ programmer for the popularity of boost::asio and other traditional C++ networking programming frameworks.

Coroutine-based paradigm is the now and feature of network programming. Coroutine is light-weight thread which has its own stack, not managed by Operating System but QtNetworkNg. Like thread-based paradigm, send()/recv() is blocked, but switch to another coroutine in the same thread unitl data arrived. Many coroutines can be created at low cost. Because there is only one thread, no locks or other synchoronization is needed. The API is straightforward like thread-based paradigm, but avoid the complexities of using threads.

Cross platforms

QtNetworkNg is tested in Linux, Android, Windows, OpenBSD. And support gcc, clang. No dependence except Qt5 is required. If SslSocket is used, the dynmaic library file of OpenSSL above 1.0.0 is required in runtime. However, QtNetworkNg do not require OpenSSL for building.

QtCore, QtNetwork is required to build QtNetworkNg. I am working hard to remove QtNetwork dependence.

The coroutine is implemented using boost::context asm code, and support native posix ucontext and windows fiber API. Running tests is successful in ARM, ARM64, x86, amd64.

In theory, QtNetworkNg can be ran in macos and ios. But there is nothing I can do before I having macos machine. And mips architecture would be supported.

Use QtNetworkNg in qmake projects

Assume your Qt/qmake project is project foo, described in, and has a directory structure like this.

original content of project directory

Unlike other cpp library, QtNetworkNg encourages using git subrepository, clone QtNetworkNg from github and include the qtnetworkng.pri in your like this.

get qtnetworkng
git clone

Now your project’s directory structure.

contents of project directory.
    other files...

Edit your to include qtnetworkng.pri, but not, because the file is exists for dynamic library build.
QT += core network
TARGET = foo
SOURCES += main.cpp

Edit main.cpp to run simple test.

get web page.
#include "qtnetworkng/qtnetworkng.h"
#include <QtCore/QCoreApplication>

using namespace qtng;
int main(int argc, char **argv)
    QCoreApplication app(argc, argv);
    HttpSession session;
    HttpResponse resp = session.get("");
    qDebug() << resp.html();
    return 0;\

Now you can build QtNetworkNg as usual C++/Qt library.

build project

The Coroutine

QtNetworkNg is created base on the Coroutine. Make sure QtNetworkNg’s network operations is running in Coroutine. Be convenient, the main thread is converted to Coroutine implicitly. There are two ways to create Coroutine. I strong recommend using CoroutineGroup, as it use QSharedPointer to manage coroutines instead of raw pointer, and considers many corner cases.

start coroutine
void coroutine_entry()
    Coroutine::sleep(1000); // sleep 1s
    qDebug() << "I am coroutine: " << Coroutine::current().id();
// I strong recommend using CoroutineGroup.
CoroutineGroup operations;
QSharedPointer<Coroutine> coroutine = operations.spawn(coroutine_entry);

// Or manage coroutine yourself.
QSharedPointer<Coroutine> coroutine = Coroutine::spawn(coroutine_entry);

Call Coroutine::start() schedule coroutine to start. And Coroutine::kill() to send exception to coroutine. Two function return immediately, while coroutine will start or be killed later.

The CoroutineGroup can spawn coroutines, and kill or get coroutines by name.

manage many coroutines
CoroutineGroup operations;
operations.spawnWithName("coroutine1", coroutine_entry);

Killing coroutine safely is a big advanced feature of coroutine compare to thread and process. If coroutine is killed by other coroutine, is will throw a CoroutineExit exception. At your will, any exception based on CoroutineException can be thrown. Coroutine is killed and joined before deleted.

how to kill coroutine
coroutine.kill(new MyCoroutineException());

void coroutine_entry()
    try {
    } catch (MyCoroutineException const &e) {
        // deal with exception.

The CoroutineExit exception is handled by QtNetworkNg silently.

The Socket and SslSocket

The main purpose to create QtNetworkNg is to simplify C++ network programming. There are many great networking programming toolkits already, like boost::asio, libco, libgo, poco, QtNetowrk and others. Many of them has complex callback-style API, or just simple coroutine implementations without Object Oriented socket API.

The Socket class is a straightforward transliteration of the bsd socket interface to object-oriented interface. It was designed to support any network families but now ipv4 and ipv6 is supported only, because QtNetworkNg is using QHostAddress now.

SslSocket has the same interface as Socket, but do ssl handshake after connection established.

Socket and SslSocket objects can be converted to SocketLike objects, which are useful for functions accept both Socket and SslSocket parameter.

Create Socket client

Socket class has two constructors. One accpets plain unix socket descriptor and another accpets protocol family and socket type.

connect to remote host
Socket s(Socket::AnyIPProtocol, Socket::TcpSocket);
bool ok = s.connect(remoteHost, 80);

Socket s(socketDescriptor); // socketDescriptor is set to nonblocking.
bool ok = s.connect(remoteHost, 80);

The SslSocket has similar constructors which accpet an extra SslConfiguration

connect to remote ssl server.
SslConfiguration config;
SslSocket s(Socket::AnyIPProtocol, config);
bool ok = s.connect(remoteHost, 443);

SslSocket s(socketDescriptor, config);
bool ok = s.connect(remoteHost, 443);

Create socket server

Combine Socket and Coroutine, you can create socket server in few lines of code.

tcp server
Socket s;
CoroutineGroup operations;
s.bind(QHostAddress::Any, 8000);
while(true) {
    QSharedPointer<Socket> request(s.accept());
    if(request.isNull()) {
    operations.spawn([request] {

Http Client

QtNetworkNg provides a HTTP client support http 1.1 and https, can handle socks5 proxies, cookies, redirection and many data types such as JSON, form-data, etc..

HTTP 2.0 is planned.

Many concepts are inspired by requests module of Python.

Get url from HTTP server

QtNetworkNg implement HTTP client in HttpSession class. To fetch data from or send data to HTTP server, you should create HttpSession object first.

get web page
qtng::HttpSession session;
HttpResponse resp = session.get(url);

The HttpSession accept and store cookies from data, so sessions is persisted among HTTP requests.

Send data to HTTP server

The most common method to send data to HTTP server is making HTTP POST form data request.

post query
FormData data;
data.addQuery("name", "fish");
HttpResponse resp =, data.toByteArray());

Or send json data.

post file
QJsonObject obj;
obj.insert("name", "fish");
HttpResponse resp =, obj);

Get data from HttpResponse

HttpResponse contains all the data from HTTP server, such as headers, content, and status code.

get response information
HttpResponse resp = session.get(url);
qDebug() << resp.getContentType();  // the content type of response.
qDebug() << resp.statusCode;  // the status code of response: 200
qDebug() << resp.statusText;  // the status text of response: OK

HttpResponse can handle many data types.

get response content
qDebug() << resp.text();  // as QString
qDebug() << resp.json();  // as QJsonDocument
qDebug() << resp.html();  // as QString
qDebug() << resp.body;  // as QByteArray

As crypto library

QtNetworkNg can load OpenSSL dynamically, and provide many crypto routines.

Message Digest

QtNetworkNg support most OpenSSL Message Digest.

hash message using sha512
MessageDigest m(MessageDigest::SHA512);
qDebug() << m.hexDigest();

Symmetrical encryption and decryption

QtNetworNg support many ciphers, such as AES, Blowfish, and ChaCha20.

encrypt message using aes256_ecb
Cipher ciph(Cihper::AES256, Cipher::ECB);
qDebug() << ciph.saltHeader() << ciph.finalData();

Cipher::setPassword() generate initial vector using PBKDF2 method. You should save Cipher::saltHeader() before save the final data.

Public Key Algorithm

QtNetworkNg can generate and manipulate RSA/DSA keys.

generate rsa key
PrivateKey key = PrivateKey::generate(PrivateKey::Rsa, 2048);
qDebug() << key.sign("fish is here.", MessageDigest::SHA512);
qDebug() <<;
PrivateKey clonedKey = PrivateKey::load(;

Certificate and CertificateRequest

QtNetworkNg can manipulate Certificate from ssl socket, or new-generated certificates.

get ssl connection certificate.
Certificate cert = sslSocket.peerCertificate();
qDebug() << cert.subjectInfo(Certificate::CommonName);
Certificate clonedCert = Certificate::load(;