Implementing Http service to receive POST request in Qt

Hello, everyone! I will make a simple record of the following knowledge points and share them with my friends!

First, let's understand a few concepts:

The difference between websocket server and http server

WebSocket servers and HTTP servers are two different types of servers, which differ in terms of protocols, connection methods, and communication modes.

1. Protocol: HTTP servers use the HTTP protocol for communication, while WebSocket servers use the WebSocket protocol. The HTTP protocol is stateless. The client initiates a request, and the server closes the connection immediately after responding to the request. The WebSocket protocol allows for a persistent connection and two-way communication between the client and the server.
2. Connection mode: HTTP server adopts "request-response" mode, that is, the client sends a request to the server, and the server disconnects after responding. Each request needs to re-establish the connection. After the initial handshake, the WebSocket server establishes a persistent connection, allowing two-way communication, and the client and server can send messages at any time.
3. Communication mode: HTTP server is based on request-response mode, the client initiates the request and the server responds. Each request and response is independent and has no persistence. WebSocket server supports two-way communication, the client and server can interact in real time by sending messages, and the server can actively push messages to the client.

In general, HTTP servers are suitable for traditional client-server communication, where each request requires a new connection, and are suitable for request-response scenarios. WebSocket servers are suitable for scenarios that require real-time two-way communication, such as chat applications, real-time data updates, etc.

It should be noted that the WebSocket protocol uses the HTTP protocol for the initial handshake when establishing a connection, so a WebSocket server can be implemented on an HTTP server. However, the WebSocket server provides more features and optimizations to support real-time communication needs.

Common HTTP request methods

In the HTTP protocol, common HTTP request methods (also called HTTP verbs) include the following:

• GET: used to obtain resources from the server, it specifies the URL of the resource to be obtained in the request. GET requests usually have no side effects on server data and are idempotent, that is, multiple identical GET requests should produce the same results.
• POST: used to submit data to the server and request the server to process the data. The data of the POST request is included in the message body of the request and is used to create, update, or delete resources. POST requests are usually not idempotent, that is, multiple identical POST requests may produce different results.
• PUT: Used to upload data to the server and request the server to store it at the specified URL. The PUT request is similar to the POST request, but it is usually used to replace or update resources.
• DELETE: used to request the server to delete the specified resource.
• HEAD: Similar to a GET request, but the server only returns the response header information, not the actual resource content. HEAD requests are often used to obtain resource metadata or check the existence and status of resources.
• OPTIONS: Used to request the server to provide information about supported request methods, response headers, and other options.
• PATCH: used to partially update resources, that is, to modify only part of the resource content.

In addition to the common HTTP request methods above, HTTP/1.1 also introduces some extended request methods, such as TRACE, CONNECT, PROPFIND, etc. These methods are rarely used in specific application scenarios.

In actual applications, developers choose appropriate HTTP request methods according to their needs to interact with the server to achieve different operations and functions.

POST request

The POST request is one of the request methods used in the HTTP protocol. It is used to submit data to the server for processing, storage, or other operations.

When using a POST request, the data is included in the request body, rather than being appended to the query string of the URL as with a GET request. This means that the data of a POST request will not be directly displayed in the URL and is not visible to the user.

POST requests are usually used in the following situations:

Create resources: When you need to create a new resource on the server, you can use a POST request. For example, submitting a form to create a new user or publish a blog post.

Updating resources: When you need to update an existing resource on the server, you can use a POST request. For example, editing a user profile or modifying article content.

Deleting resources: When you need to delete resources from the server, you can use a POST request, for example, to delete a user account or a file.

Processing form data: When you need to submit form data to the server for processing, you can use a POST request. Form data can contain various fields and values, such as a user registration form or a search form.

The data of the POST request will be wrapped in the request body and can be transmitted using various encoding methods, such as application/x-www-form-urlencoded, multipart/form-data, etc.

In Web development, the server needs to process POST requests accordingly and parse the data in the request body to perform corresponding operations. In this way, data processing, verification, persistence and other operations can be performed on the server, thereby realizing interaction with the client and data transmission.

Implementing http service receiving POST request in Qt

To receive HTTP POST protocol data in Qt, you can use Qt's network module and HTTP class to handle the request. Here is a simple example showing how to use Qt to receive HTTP POST request data:

 #include <QtNetwork> #include <QTcpServer> #include <QTcpSocket> #include <QTextStream> class HttpServer : public QTcpServer { Q_OBJECT public: explicit HttpServer(QObject *parent = nullptr) : QTcpServer(parent) {} protected: void incomingConnection(qintptr socketDescriptor) override { QTcpSocket *socket = new QTcpSocket(this); socket->setSocketDescriptor(socketDescriptor); connect(socket, &QTcpSocket::readyRead, this, &HttpServer::socketReadyRead); connect(socket, &QTcpSocket::disconnected, this, &HttpServer::socketDisconnected); } private slots: void socketReadyRead() { QTcpSocket *socket = qobject_cast<QTcpSocket *>(sender()); if (socket) { // Read the request from the socket QByteArray requestData = socket->readAll(); // Parse the request // In this example, we assume the request is in plain text format QString request = QString::fromUtf8(requestData); // Check if it's a POST request if (request.startsWith("POST")) { // Extract the POST data QString postData = request.split("\r\n\r\n").last(); // Process the POST data processPostData(postData); // Send a response back to the client QString response = "HTTP/1.1 200 OK\r\n" "Content-Type: text/plain\r\n" "\r\n" "POST data received!"; socket->write(response.toUtf8()); socket->flush(); socket->waitForBytesWritten(); } socket->close(); } } void socketDisconnected() { QTcpSocket *socket = qobject_cast<QTcpSocket *>(sender()); if (socket) { socket->deleteLater(); } } private: void processPostData(const QString &postData) { // Process the POST data here qDebug() << "POST data received:" << postData; } }; int main(int argc, char *argv[]) { QCoreApplication app(argc, argv); HttpServer server; if (!server.listen(QHostAddress::Any, 8080)) { qDebug() << "Failed to start server."; return 1; } qDebug() << "Server started on port 8080."; return app.exec(); } #include "main.moc"

In this example, we create an HttpServer class that inherits from QTcpServer to handle HTTP requests. When a new connection request arrives, the incomingConnection function is called, in which a QTcpSocket is created to handle the connection. Then, the socket's readyRead and disconnected signals are connected to the corresponding slot functions.

In the socketReadyRead slot function, read the request and process it. If the request starts with "POST", we extract the POST data and call the processPostData function to process the data. You can process the POST data in the processPostData function.

Finally, we send a simple response to the client and close the connection.

In the main function, we create an HttpServer instance and call the listen function to start listening for connections. If the listening fails, an error message will be output.

This is a simple example that demonstrates how to use Qt to receive HTTP POST request data. You can extend and modify it according to your specific needs, such as adding routing processing, validation, and parsing POST data.