之前工作中用到websocket,用boost.beast实现了客户端,原则上可以用了。不过既然涉及到这个问题,于是顺便研究了一下服务端如何实现。下面同样给出同步的版本和异步的版本。
先看看同步的版本
server.cpp
#include <boost/beast/core.hpp>
#include <boost/beast/websocket.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <cstdlib>
#include <functional>
#include <iostream>
#include <string>
#include <thread>
using tcp = boost::asio::ip::tcp;
namespace websocket = boost::beast::websocket;
// echoes back all received WebSocket messages
void do_session(tcp::socket& socket)
{
try {
// Construct the stream by moving in the socket
websocket::stream<tcp::socket> ws{std::move(socket)};
// Accept the websocket handshake
ws.accept();
for (;;) {
// This buffer will hold the incoming message
boost::beast::multi_buffer buffer;
// Read a message
ws.read(buffer);
// Echo the message back
ws.text(ws.got_text());
ws.write(buffer.data());
}
} catch (boost::system::system_error const& se) {
// This indicates that the session was closed
if (se.code() != websocket::error::closed)
std::cerr << "Error: " << se.code().message() << std::endl;
} catch (std::exception const& e) {
std::cerr << "Error: " << e.what() << std::endl;
}
}
int main(int argc, char* argv[])
{
try {
// Check command line arguments
if (argc != 3) {
std::cerr <<
"Usage: server <address> <port>\n" <<
"Example:\n" <<
" server 0.0.0.0 8080\n";
return EXIT_FAILURE;
}
auto const address = boost::asio::ip::make_address(argv[1]);
auto const port = static_cast<unsigned short>(std::atoi(argv[2]));
// The io_context is required for all I/O
boost::asio::io_context ioc{1};
// The acceptor receives incoming connections
tcp::acceptor acceptor{ioc, {address, port}};
for (;;) {
// This will receive the new connection
tcp::socket socket{ioc};
// Block until we get a connection
acceptor.accept(socket);
// Launch the session, transferring ownership of the socket
std::thread{std::bind(&do_session, std::move(socket))}.detach();
}
} catch (const std::exception& e) {
std::cerr << "Error: " << e.what() << std::endl;
return EXIT_FAILURE;
}
}
可以看到这是一个非常简单的服务器,通过不断处理socket连接并在do_session中进行处理,将客户端发送过来的内容再返回给客户端。
接下来看看异步的版本
async_server.cpp
#include <boost/beast/core.hpp>
#include <boost/beast/websocket.hpp>
#include <boost/asio/bind_executor.hpp>
#include <boost/asio/strand.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <algorithm>
#include <cstdlib>
#include <functional>
#include <iostream>
#include <memory>
#include <string>
#include <thread>
#include <vector>
using tcp = boost::asio::ip::tcp;
namespace websocket = boost::beast::websocket;
//------------------------------------------------------------------------------
// Report a failure
void fail(boost::system::error_code ec, char const* what)
{
std::cerr << what << ": " << ec.message() << "\n";
}
// Echoes back all received WebSocket messages
class session : public std::enable_shared_from_this<session>
{
websocket::stream<tcp::socket> ws_;
boost::asio::strand<
boost::asio::io_context::executor_type> strand_;
boost::beast::multi_buffer buffer_;
public:
// Take ownership of the socket
explicit session(tcp::socket socket)
: ws_(std::move(socket))
, strand_(ws_.get_executor())
{
}
// Start the asynchronous operation
void run()
{
// Accept the websocket handshake
ws_.async_accept(
boost::asio::bind_executor(
strand_,
std::bind(
&session::on_accept,
shared_from_this(),
std::placeholders::_1)));
}
void on_accept(boost::system::error_code ec)
{
if(ec) return fail(ec, "accept");
// Read a message
do_read();
}
void do_read()
{
// Read a message into our buffer
ws_.async_read(
buffer_,
boost::asio::bind_executor(
strand_,
std::bind(
&session::on_read,
shared_from_this(),
std::placeholders::_1,
std::placeholders::_2)));
}
void on_read(
boost::system::error_code ec,
std::size_t bytes_transferred)
{
boost::ignore_unused(bytes_transferred);
// This indicates that the session was closed
if(ec == websocket::error::closed) return;
if(ec) fail(ec, "read");
// Echo the message
ws_.text(ws_.got_text());
ws_.async_write(
buffer_.data(),
boost::asio::bind_executor(
strand_,
std::bind(
&session::on_write,
shared_from_this(),
std::placeholders::_1,
std::placeholders::_2)));
}
void on_write(
boost::system::error_code ec,
std::size_t bytes_transferred)
{
boost::ignore_unused(bytes_transferred);
if(ec) return fail(ec, "write");
// Clear the buffer
buffer_.consume(buffer_.size());
// Do another read
do_read();
}
};
//------------------------------------------------------------------------------
// Accepts incoming connections and launches the sessions
class listener : public std::enable_shared_from_this<listener>
{
tcp::acceptor acceptor_;
tcp::socket socket_;
public:
listener(
boost::asio::io_context& ioc,
tcp::endpoint endpoint)
: acceptor_(ioc)
, socket_(ioc)
{
boost::system::error_code ec;
// Open the acceptor
acceptor_.open(endpoint.protocol(), ec);
if(ec)
{
fail(ec, "open");
return;
}
// Allow address reuse
acceptor_.set_option(boost::asio::socket_base::reuse_address(true), ec);
if(ec)
{
fail(ec, "set_option");
return;
}
// Bind to the server address
acceptor_.bind(endpoint, ec);
if(ec)
{
fail(ec, "bind");
return;
}
// Start listening for connections
acceptor_.listen(
boost::asio::socket_base::max_listen_connections, ec);
if(ec)
{
fail(ec, "listen");
return;
}
}
// Start accepting incoming connections
void run()
{
if(! acceptor_.is_open())
return;
do_accept();
}
void do_accept()
{
acceptor_.async_accept(
socket_,
std::bind(
&listener::on_accept,
shared_from_this(),
std::placeholders::_1));
}
void on_accept(boost::system::error_code ec)
{
if(ec)
{
fail(ec, "accept");
}
else
{
// Create the session and run it
std::make_shared<session>(std::move(socket_))->run();
}
// Accept another connection
do_accept();
}
};
//------------------------------------------------------------------------------
int main(int argc, char* argv[])
{
// Check command line arguments.
if (argc != 4)
{
std::cerr <<
"Usage: async_server <address> <port> <threads>\n" <<
"Example:\n" <<
" async_server 0.0.0.0 8080 1\n";
return EXIT_FAILURE;
}
auto const address = boost::asio::ip::make_address(argv[1]);
auto const port = static_cast<unsigned short>(std::atoi(argv[2]));
auto const threads = std::max<int>(1, std::atoi(argv[3]));
// The io_context is required for all I/O
boost::asio::io_context ioc{threads};
// Create and launch a listening port
std::make_shared<listener>(ioc, tcp::endpoint{address, port})->run();
// Run the I/O service on the requested number of threads
std::vector<std::thread> v;
v.reserve(threads - 1);
for(auto i = threads - 1; i > 0; --i)
v.emplace_back(
[&ioc]
{
ioc.run();
});
ioc.run();
return EXIT_SUCCESS;
}
可以看到异步服务器端和异步客户端类似,均是层层异步调用,只是session write后没有结束,又接着调用do_read。此外增加了一个监听器listener,在建立连接后,让session处理接下来的工作,读取socket内容,通过websocket流再写回去。