- Qt 6.10
- Qt HTTP Server
- C++ Classes
- QHttpServer
- Qt 6.10.2 Reference Documentation

# QHttpServer Class

QHttpServer is a simplified API for QAbstractHttpServer and QHttpServerRouter. More...

Header: | `#include <QHttpServer>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS HttpServer)` `target_link_libraries(mytarget PRIVATE Qt6::HttpServer)`
qmake: | `QT += httpserver`
Since: | Qt 6.4
Inherits: | QAbstractHttpServer

- List of all members, including inherited members

## Public Functions

| QHttpServer(QObject *parent = nullptr)
virtual | ~QHttpServer() override
void | addAfterRequestHandler(const QObject *context, Functor &&slot)
void | clearMissingHandler()
Rule * | route(const QString &pathPattern, QHttpServerRequest::Methods method, const QObject *context, Functor &&slot)
Rule * | route(const QString &pathPattern, Functor &&handler)
Rule * | route(const QString &pathPattern, QHttpServerRequest::Methods method, Functor &&handler)
Rule * | route(const QString &pathPattern, const QObject *context, Functor &&slot)
QHttpServerRouter * | router()
const QHttpServerRouter * | router() const
void | setMissingHandler(const QObject *context, Functor &&slot)

## Detailed Description

QHttpServer is used to create a simple HTTP server by registering a range of request handlers.

The route function can be used to conveniently add rules to the server's QHttpServerRouter. To register a handler that is called after every request to further process the response use addAfterRequestHandler, but this mechanism only works for routes returning QHttpServerResponse or `QFuture<QHttpServerResponse>`. To register a handler for all unhandled requests use setMissingHandler.

Minimal example:

     QHttpServer server;

     server.route("/", [] () {
         return "hello world";
     });

     auto tcpserver = new QTcpServer();
     if (!tcpserver->listen() || !server.bind(tcpserver)) {
         delete tcpserver;
         return -1;
     }
     qDebug() << "Listening on port" << tcpserver->serverPort();

## Member Function Documentation

### `[explicit]` QHttpServer::QHttpServer(QObject *parent = nullptr)

Creates an instance of QHttpServer with parent parent.

### `[override virtual noexcept]` QHttpServer::~QHttpServer()

Destroys a QHttpServer.

### template <typename Functor> void QHttpServer::addAfterRequestHandler(const QObject *context, Functor &&slot)

Register a context and slot to be called after each request is handled.

The slot has to implement the signature `void (*)(const QHttpServerRequest &, QHttpServerResponse &)`.

The slot can also be a function pointer, non-mutable lambda, or any other copyable callable with const call operator. In that case the context will be a context object and the handler will be valid until the context object is destroyed.

Example:

     server.addAfterRequestHandler(&server, [] (const QHttpServerRequest &req, QHttpServerResponse &resp) {
         auto h = resp.headers();
         h.append(QHttpHeaders::WellKnownHeader::Cookie, "PollyWants=Cracker");
         resp.setHeaders(std::move(h));
     }

Note: These handlers will only be called for requests that are processed by route handlers that either return QHttpServerResponse or QFuture<QHttpServerResponse>, and therefore do not take a QHttpServerResponder argument.

### void QHttpServer::clearMissingHandler()

Resets the handler to the default one that produces replies with status `404 Not Found`.

See also setMissingHandler.

### template <typename Rule = QHttpServerRouterRule, typename Functor> Rule *QHttpServer::route(const QString &pathPattern, QHttpServerRequest::Methods method, const QObject *context, Functor &&slot)

This method adds a new routing `Rule` to the server's QHttpServerRouter member. The `Rule` template parameter can be any class derived from QHttpServerRouterRule. The parameters are passed to `Rule`. The server matches incoming HTTP requests against registered rules based on the URL path and HTTP method, and the first match of both is executed.

The pathPattern parameter is compared with the path() of the URL of the incoming request. The method parameter is compared with the HTTP method of the incoming request. The slot parameter is the request handler. It can be a member function pointer of context, a function pointer, non-mutable lambda, or any copyable callable with a const call operator. If context is provided, the rule remains valid as long as context exists. The context must share the same thread affinity as QHttpServer.

The slot takes as arguments any number of parsed arguments, that are extracted from the pathPattern by matching the `"<arg>"` placeholders, followed by an optional QHttpServerRequest and optional QHttpServerResponder. These two classes are called specials.

The slot can return a QHttpServerResponse or a convertible type:

     QHttpServer server;
     server.route("/test/", this, [] () { return ""; });

Alternatively, if an optional QHttpServerResponder& argument is provided, the response has to be written using it and the function must return `void`.

     server.route("/test2", this, [] (QHttpServerResponder &responder) {
                                     responder.write(QHttpServerResponder::StatusCode::Forbidden); });

The QHttpServerRequest object can be used to access the body of the request:

     server.route("/test3", QHttpServerRequest::Method::Post, this,
                  [] (const QHttpServerRequest &request, QHttpServerResponder &responder) {
                      responder.write(request.body(), "text/plain"_ba);
                  });

Any placeholder ( `"<arg>"` ) in pathPattern is automatically converted to match the handler's argument types. Supported types include integers, floating point numbers, QString, QByteArray, and QUrl. The QUrl class can be used as the last parameter to handle the end of the pathPattern, and by splitting it an arbitrary number of arguments can be supported. Custom converters can be added using QHttpServerRouter::addConverter().

Each registered type has an associated regex that is used to match and convert placeholders in the pathPattern. These regex patterns are combined to construct a parser for the entire path. The resulting parser is then used to verify if the path matches the pattern. If parsing succeeds, the corresponding function is called with the converted parameters. If parsing fails, the next registered callback is attempted. If parsing fails for all callbacks, the missingHandler is called.

In the example below, the value in the request path replacing `"<arg>"` is converted to an `int` because the lambda expects an `int` parameter. When an HTTP request matches the route, the converted value is passed to the lambda's `page` argument:

     QHttpServer server;
     server.route("/showpage/<arg>", this, [] (int page) { return getPage(page); });

This function returns, if successful, a pointer to the newly created Rule, otherwise a `nullptr`. The pointer can be used to set parameters on any custom QHttpServerRouter class:

     auto rule = server.route<MyRule>("/test4", this, [] () {return "";});
     rule->setParameter("test");

Note: This function, route(), must not be called from slot, so no route handlers can register other route handlers.

Note: If a request was processed by a slot accepting QHttpServerResponder& as an argument, none of the after request handlers (see addAfterRequestHandler) will be called.

Requests are processed sequentially inside the QHttpServer's thread by default. The request handler may return `QFuture<QHttpServerResponse>` if concurrent processing is desired:

     server.route("/feature/<arg>", [] (int ms) {
         return QtConcurrent::run([ms] () {
             QThread::msleep(ms);
             return QHttpServerResponse("the future is coming");
         });
     });

The lambda of the QtConcurrent::run() is executed concurrently, but all the network communication is executed sequentially in the thread the `QHttpServer` belongs to after the QFuture is done. Be aware that any QHttpServerRequest object is passed by reference to the callback. Extract all needed content before QtConcurrent::run() is called.

The QHttpServerResponder& special argument is only available for routes returning `void`. When using a responder object the response is returned using it.

See also QHttpServerRouter::addRule and addAfterRequestHandler.

### template <typename Rule = QHttpServerRouterRule, typename Functor> Rule *QHttpServer::route(const QString &pathPattern, Functor &&handler)

Overload of QHttpServer::route to create a Rule for pathPattern and QHttpServerRequest::Method::AnyKnown. All requests are forwarded to handler, which can be a function pointer, a non-mutable lambda, or any other copyable callable with const call operator. The rule will be valid until the QHttpServer is destroyed.

This is an overloaded function.

### template <typename Rule = QHttpServerRouterRule, typename Functor> Rule *QHttpServer::route(const QString &pathPattern, QHttpServerRequest::Methods method, Functor &&handler)

Overload of QHttpServer::route to create a Rule for pathPattern and method. All requests are forwarded to handler, which can be a function pointer, a non-mutable lambda, or any other copyable callable with const call operator. The rule will be valid until the QHttpServer is destroyed.

This is an overloaded function.

### template <typename Rule = QHttpServerRouterRule, typename Functor> Rule *QHttpServer::route(const QString &pathPattern, const QObject *context, Functor &&slot)

Overload of QHttpServer::route to create a Rule for pathPattern and the method QHttpServerRequest::Method::AnyKnown. All requests are forwarded to context and slot.

This is an overloaded function.

### QHttpServerRouter *QHttpServer::router()

Returns a pointer to the router object.

### const QHttpServerRouter *QHttpServer::router() const

Returns a pointer to the constant router object.

### template <typename Functor> void QHttpServer::setMissingHandler(const QObject *context, Functor &&slot)

Set a handler for unhandled requests.

All unhandled requests will be forwarded to the context's slot.

The slot has to implement the signature `void (*)(const QHttpServerRequest &, QHttpServerResponder &)`. The slot can also be a function pointer, non-mutable lambda, or any other copyable callable with const call operator. In that case the context will be a context object. The handler will be valid until the context object is destroyed.

The default handler replies with status `404 Not Found`.

See also clearMissingHandler.