This project implements asynchronous HTTP client-server communication using Boost.Asio. The HTTP client generates a request message for a specific resource on the server, transmitting it over TCP. The HTTP server, upon receiving the request, parses it, retrieves the requested resource (from a file system or database), and returns it to the client in an HTTP response. This implementation focuses on asynchronous I/O operations, leveraging the capabilities of Modern C++ functionalities like Lambda Expressions, Smart Pointers, Threads and Boost.Asio for scalable and high-performance networking.
HTTPClient
Acts as a factory of HTTPRequest objects. The createRequest() method creates and returns a shared pointer to a HTTPRequest with the given request id.
HTTPClient http_client;
std::shared_ptr<HTTPRequest> http_request_one = http_client.createRequest(1);HTTPRequest
An instance of the HTTPRequest represents a single HTTP GET request. Two send a HTTP Request to steps need to be done.
Firstly, the parameters of the request and the callback function to be called when the request completes are set by calling the corresponding setter methods on the object.
http_request_one->setHost("localhost");
http_request_one->setUri("/index.html");
http_request_one->setPort(3334);
http_request_one->setCallback(handler);Then, the execute() method is invoked to initiate the request execution. When the request completes, the callback function is called.
http_request_one->request_one->execute();The execute() method begins the execution of a request by initiating a sequence of asynchronous operations. Each asynchronous operation performs one step of request execution procedure.
HTTPResponse
The HTTPResponse class does not provide much functionality. It is more like a plain data structure containing data members representing different parts of a response, with getter and setter methods defined, allowing getting and setting corresponding data member values.
Server
The Server class represents a server itself. It consists of two methods: start() and stop(). The start() method starts accepts two arguments. First argument named port_num specifies the number of the protocol port on which the server should listen for incoming connections. The second argument named thread_pool_size specifies the number of threads to add to the pool of threads running the even loop and deliver asynchronous operation completion events.
Server srv;
srv.start(port_num, thread_pool_size);
srv.stop();Acceptor
The Acceptor class is a part of the server application's infrastructure. Its constructor accepts a port number on which it will listen for the incoming connection requests as its input argument. It consists of two methods: start() and stop(). When started it puts the acceptor socket in listening mode and initiates the asynchronous accept operation, calling the asio::async_accept() method on the acceptor socket object and passing the object representing an active socket to it as an argument.
auto sock = std::make_shared<asio::ip::tcp::socket>(m_ios);
m_acceptor.async_accept(*sock.get(),
[this, sock](const boost::system::error_code &error) {onAccept(error, sock); });Service
The Service class is the key functional component in the application. While other components constitute an infrastructure of the server, this class implements the actual function provided by the server to the clients. One instance of this class is intended to handle a single connected client by reading the request, processing it, and then sending back the response message.
After an instance of the Service class has been constructed, its start_handling() method is called by the Acceptor class. From this method, the sequence of asynchronous method invocations begins, which performs request receiving, processing, and response sending. The start_handling() method immediately initiates an asynchronous reading operation calling the asio::async_read_until() function in order to receive the HTTP request line sent by the client.
asio::async_read_until(*m_sock.get(), m_request, "\r\n",
[this](const boost::system::error_code &ec, std::size_t bytes_transferred)
{on_request_line_received(ec, bytes_transferred);});sudo apt-get update
sudo apt-get install libboost-all-dev