Asio provides off-the-shelf support for the internet protocols TCP, UDP and ICMP.
Hostname resolution is performed using a resolver, where host and service names are looked up and converted into one or more endpoints:
ip::tcp::resolver resolver(my_io_context); ip::tcp::resolver::query query("www.boost.org", "http"); ip::tcp::resolver::iterator iter = resolver.resolve(query); ip::tcp::resolver::iterator end; // End marker. while (iter != end) { ip::tcp::endpoint endpoint = *iter++; std::cout << endpoint << std::endl; }
The list of endpoints obtained above could contain both IPv4 and IPv6 endpoints, so a program should try each of them until it finds one that works. This keeps the client program independent of a specific IP version.
To simplify the development of protocol-independent programs, TCP clients may establish connections using the free functions connect() and async_connect(). These operations try each endpoint in a list until the socket is successfully connected. For example, a single call:
ip::tcp::socket socket(my_io_context); asio::connect(socket, resolver.resolve(query));
will synchronously try all endpoints until one is successfully connected. Similarly, an asynchronous connect may be performed by writing:
asio::async_connect(socket_, iter, boost::bind(&client::handle_connect, this, asio::placeholders::error)); // ... void handle_connect(const error_code& error) { if (!error) { // Start read or write operations. } else { // Handle error. } }
When a specific endpoint is available, a socket can be created and connected:
ip::tcp::socket socket(my_io_context); socket.connect(endpoint);
Data may be read from or written to a connected TCP socket using the receive(), async_receive(), send() or async_send() member functions. However, as these could result in short writes or reads, an application will typically use the following operations instead: read(), async_read(), write() and async_write().
A program uses an acceptor to accept incoming TCP connections:
ip::tcp::acceptor acceptor(my_io_context, my_endpoint); ... ip::tcp::socket socket(my_io_context); acceptor.accept(socket);
After a socket has been successfully accepted, it may be read from or written to as illustrated for TCP clients above.
UDP hostname resolution is also performed using a resolver:
ip::udp::resolver resolver(my_io_context); ip::udp::resolver::query query("localhost", "daytime"); ip::udp::resolver::iterator iter = resolver.resolve(query); ...
A UDP socket is typically bound to a local endpoint. The following code
will create an IP version 4 UDP socket and bind it to the "any"
address on port 12345
:
ip::udp::endpoint endpoint(ip::udp::v4(), 12345); ip::udp::socket socket(my_io_context, endpoint);
Data may be read from or written to an unconnected UDP socket using the receive_from(), async_receive_from(), send_to() or async_send_to() member functions. For a connected UDP socket, use the receive(), async_receive(), send() or async_send() member functions.
As with TCP and UDP, ICMP hostname resolution is performed using a resolver:
ip::icmp::resolver resolver(my_io_context); ip::icmp::resolver::query query("localhost", ""); ip::icmp::resolver::iterator iter = resolver.resolve(query); ...
An ICMP socket may be bound to a local endpoint. The following code will create an IP version 6 ICMP socket and bind it to the "any" address:
ip::icmp::endpoint endpoint(ip::icmp::v6(), 0); ip::icmp::socket socket(my_io_context, endpoint);
The port number is not used for ICMP.
Data may be read from or written to an unconnected ICMP socket using the receive_from(), async_receive_from(), send_to() or async_send_to() member functions.
ip::tcp, ip::udp, ip::icmp, daytime protocol tutorials, ICMP ping example.