如何使用 boost beast websocket 客户端收听 websocket 提要？
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【中文标题】如何使用 boost beast websocket 客户端收听 websocket 提要？【英文标题】：How to listen to websocket feed using boost beast websocket client? 【发布时间】：2020-06-13 12:44:21 【问题描述】：我是野兽新手，正在尝试创建一个 websocket 客户端，它将订阅远程服务器中的 websocket 事件并开始永远监听传入的消息，除非我或服务器明确关闭连接。
目前，我正在使用野兽的 github repository 中的 async_sll_websocket_client 示例。
#include "example/common/root_certificates.hpp"
#include <boost/beast/core.hpp>
#include <boost/beast/ssl.hpp>
#include <boost/beast/websocket.hpp>
#include <boost/beast/websocket/ssl.hpp>
#include <boost/asio/strand.hpp>
#include <cstdlib>
#include <functional>
#include <iostream>
#include <memory>
#include <string>
namespace beast = boost::beast; // from <boost/beast.hpp>
namespace http = beast::http; // from <boost/beast/http.hpp>
namespace websocket = beast::websocket; // from <boost/beast/websocket.hpp>
namespace net = boost::asio; // from <boost/asio.hpp>
namespace ssl = boost::asio::ssl; // from <boost/asio/ssl.hpp>
using tcp = boost::asio::ip::tcp; // from <boost/asio/ip/tcp.hpp>
//------------------------------------------------------------------------------
// Report a failure
void
fail(beast::error_code ec, char const* what)
std::cerr << what << ": " << ec.message() << "\n";
// Sends a WebSocket message and prints the response
class session : public std::enable_shared_from_this<session>
tcp::resolver resolver_;
websocket::stream<
beast::ssl_stream<beast::tcp_stream>> ws_;
beast::flat_buffer buffer_;
std::string host_;
std::string text_;
public:
// Resolver and socket require an io_context
explicit
session(net::io_context& ioc, ssl::context& ctx)
: resolver_(net::make_strand(ioc))
, ws_(net::make_strand(ioc), ctx)
// Start the asynchronous operation
void
run(
char const* host,
char const* port,
char const* text)
// Save these for later
host_ = host;
text_ = text;
// Look up the domain name
resolver_.async_resolve(
host,
port,
beast::bind_front_handler(
&session::on_resolve,
shared_from_this()));
void
on_resolve(
beast::error_code ec,
tcp::resolver::results_type results)
if(ec)
return fail(ec, "resolve");
// Set a timeout on the operation
beast::get_lowest_layer(ws_).expires_after(std::chrono::seconds(30));
// Make the connection on the IP address we get from a lookup
beast::get_lowest_layer(ws_).async_connect(
results,
beast::bind_front_handler(
&session::on_connect,
shared_from_this()));
void
on_connect(beast::error_code ec, tcp::resolver::results_type::endpoint_type ep)
if(ec)
return fail(ec, "connect");
// Update the host_ string. This will provide the value of the
// Host HTTP header during the WebSocket handshake.
// See https://tools.ietf.org/html/rfc7230#section-5.4
host_ += ':' + std::to_string(ep.port());
// Set a timeout on the operation
beast::get_lowest_layer(ws_).expires_after(std::chrono::seconds(30));
// Perform the SSL handshake
ws_.next_layer().async_handshake(
ssl::stream_base::client,
beast::bind_front_handler(
&session::on_ssl_handshake,
shared_from_this()));
void
on_ssl_handshake(beast::error_code ec)
if(ec)
return fail(ec, "ssl_handshake");
// Turn off the timeout on the tcp_stream, because
// the websocket stream has its own timeout system.
beast::get_lowest_layer(ws_).expires_never();
// Set suggested timeout settings for the websocket
ws_.set_option(
websocket::stream_base::timeout::suggested(
beast::role_type::client));
// Set a decorator to change the User-Agent of the handshake
ws_.set_option(websocket::stream_base::decorator(
[](websocket::request_type& req)
req.set(http::field::user_agent,
std::string(BOOST_BEAST_VERSION_STRING) +
" websocket-client-async-ssl");
));
// Perform the websocket handshake
ws_.async_handshake(host_, "/",
beast::bind_front_handler(
&session::on_handshake,
shared_from_this()));
void
on_handshake(beast::error_code ec)
if(ec)
return fail(ec, "handshake");
// Send the message
ws_.async_write(
net::buffer(text_),
beast::bind_front_handler(
&session::on_write,
shared_from_this()));
void
on_write(
beast::error_code ec,
std::size_t bytes_transferred)
boost::ignore_unused(bytes_transferred);
if(ec)
return fail(ec, "write");
// Read a message into our buffer
ws_.async_read(
buffer_,
beast::bind_front_handler(
&session::on_read,
shared_from_this()));
void
on_read(
beast::error_code ec,
std::size_t bytes_transferred)
boost::ignore_unused(bytes_transferred);
if(ec)
return fail(ec, "read");
//here I try to read the buffer again instead of ccalling the async_close.
ws_.async_read(
buffer_,
beast::bind_front_handler(
&session::on_read,
shared_from_this()));
// Close the WebSocket connection
//ws_.async_close(websocket::close_code::normal,
// beast::bind_front_handler(
// &session::on_close,
// shared_from_this()));
void
on_close(beast::error_code ec)
if(ec)
return fail(ec, "close");
// If we get here then the connection is closed gracefully
// The make_printable() function helps print a ConstBufferSequence
std::cout << beast::make_printable(buffer_.data()) << std::endl;
;
//------------------------------------------------------------------------------
int main(int argc, char** argv)
// Check command line arguments.
if(argc != 4)
std::cerr <<
"Usage: websocket-client-async-ssl <host> <port> <text>\n" <<
"Example:\n" <<
" websocket-client-async-ssl echo.websocket.org 443 \"Hello, world!\"\n";
return EXIT_FAILURE;
auto const host = argv[1];
auto const port = argv[2];
auto const text = argv[3];
// The io_context is required for all I/O
net::io_context ioc;
// The SSL context is required, and holds certificates
ssl::context ctxssl::context::tlsv12_client;
// This holds the root certificate used for verification
load_root_certificates(ctx);
// Launch the asynchronous operation
std::make_shared<session>(ioc, ctx)->run(host, port, text);
// Run the I/O service. The call will return when
// the socket is closed.
ioc.run();
return EXIT_SUCCESS;
到目前为止，我尝试在on_read 函数中再次调用async_read 并递归调用on_read。连接不会以这种方式关闭，但不会第二次调用“on_read”。有没有我可以应用的模式来持续收听来自服务器的传入消息？
编辑：显然我的方法是正确的，我只需要在第一次on_readcall 之后再发送一次订阅消息。
【问题讨论】：
【参考方案1】：此函数可能在第一次读取后立即终止，这是对写入的响应 (code)。 试试这个代码，只要套接字打开就继续寻找消息。
net::io_context ioc;
auto const host = "localhost";
auto const port = "1234";
auto const port = "SOME TEXT";
// Launch the asynchronous operation
std::shared_ptr<session> p = std::make_shared<session>(ioc);
p->run(host, port, text);
ioc.run();
while (p->is_socket_open())
ioc.restart();
p->enable_async_read();
ioc.run();
enable_async_read & is_socket_open 的实现
void session::enable_async_read()
ws_.async_read(
buffer_,
beast::bind_front_handler(
&session::on_read,
shared_from_this()));
bool session::is_socket_open()
return ws_.is_open();
【讨论】：
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