我正在尝试使用Boost beast :: websocket websocket_client_async.cpp示例，并结合websocket_server_async.cpp。
如上所述，客户端示例只是建立连接，向服务器发送一个字符串（只是回显），打印回复，关闭和存在。
我试图修改客户端以使会话保持活动状态，以便我可以重复发送/接收字符串。因此，虽然示例代码的on_handshake函数会立即通过ws_.async_write(...)发送字符串，但我将其分离为自己的write(...)函数。
以下是我修改过的session课程：
using tcp = boost::asio::ip::tcp;
namespace websocket = boost::beast::websocket;
void fail(boost::system::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<tcp::socket> ws_;
std::atomic<bool> io_in_progress_;
boost::beast::multi_buffer buffer_;
std::string host_;
public:
// Resolver and socket require an io_context
explicit session(boost::asio::io_context& ioc) : resolver_(ioc), ws_(ioc) {
io_in_progress_ = false;
}
bool io_in_progress() const {
return io_in_progress_;
}
// +---------------------+
// | The "open" sequence |
// +---------------------+
void open(char const* host, char const* port)
{
host_ = host;
// Look up the domain name
resolver_.async_resolve(host, port,
std::bind( &session::on_resolve, shared_from_this(),
std::placeholders::_1, std::placeholders::_2 )
);
}
void on_resolve(boost::system::error_code ec, tcp::resolver::results_type results)
{
if (ec)
return fail(ec, "resolve");
boost::asio::async_connect(
ws_.next_layer(), results.begin(), results.end(),
std::bind( &session::on_connect, shared_from_this(),
std::placeholders::_1 )
);
}
void on_connect(boost::system::error_code ec)
{
if (ec)
return fail(ec, "connect");
ws_.async_handshake(host_, "/",
std::bind( &session::on_handshake, shared_from_this(),
std::placeholders::_1 )
);
}
void on_handshake(boost::system::error_code ec)
{
if (ec)
return fail(ec, "handshake");
else {
std::cout << "Successful handshake with server.\n";
}
}
// +---------------------------+
// | The "write/read" sequence |
// +---------------------------+
void write(const std::string &text)
{
io_in_progress_ = true;
ws_.async_write(boost::asio::buffer(text),
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");
ws_.async_read(buffer_,
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)
{
io_in_progress_ = false; // end of write/read sequence
boost::ignore_unused(bytes_transferred);
if (ec)
return fail(ec, "read");
std::cout << boost::beast::buffers(buffer_.data()) << std::endl;
}
// +----------------------+
// | The "close" sequence |
// +----------------------+
void close()
{
io_in_progress_ = true;
ws_.async_close(websocket::close_code::normal,
std::bind( &session::on_close, shared_from_this(),
std::placeholders::_1)
);
}
void on_close(boost::system::error_code ec)
{
io_in_progress_ = false; // end of close sequence
if (ec)
return fail(ec, "close");
std::cout << "Socket closed successfully.\n";
}
};
问题是，虽然连接工作正常并且我可以发送一个字符串，但on_read回调永远不会被命中（除非我做了下面描述的丑陋黑客攻击）。
我的main看起来像这样：
void wait_for_io(std::shared_ptr<session> psession, boost::asio::io_context &ioc)
{
// Continually try to run the ioc until the callbacks are finally
// triggered (as indicated by the session::io_in_progress_ flag)
while (psession->io_in_progress()) {
std::this_thread::sleep_for(std::chrono::milliseconds(1));
ioc.run();
}
}
int main(int argc, char** argv)
{
// Check command line arguments.
if (argc != 3) {
std::cerr << "usage info goes here...\n";
return EXIT_FAILURE;
}
const char *host = argv[1], *port = argv[2];
boost::asio::io_context ioc;
std::shared_ptr<session> p = std::make_shared<session>(ioc);
p->open(host, port);
ioc.run(); // This works. Connection is established and all callbacks are executed.
p->write("Hello world"); // String is sent & received by server,
// even before calling ioc.run()
// However, session::on_read callback is never
// reached.
ioc.run(); // This seems to be ignored and returns immediately, so
wait_for_io(p, ioc); // <-- so this hack is necessary
p->close(); // session::on_close is never reached
ioc.run(); // Again, this seems to be ignored and returns immediately, so
wait_for_io(p, ioc); // <-- this is necessary
return EXIT_SUCCESS;
}
如果我这样做：
p->write("Hello world");
while(1) {
std::this_thread::sleep_for(std::chrono::milliseconds(1));
}
我可以确认该字符串已发送＆amp;服务器收到 1 ，且session::on_read回调 未到达。
与p->close()相同。
但是，如果我添加我奇怪的wait_for_io()函数，一切正常。我很肯定这是一个可怕的黑客，但我无法弄清楚发生了什么。
1 注意：我可以确认邮件是否到达服务器，因为我修改了服务器示例以将任何收到的字符串打印到控制台。这是我制作的唯一修改。回声到客户端功能没有改变。
答案 0 :(得分：2)
第一次通话后调用io_context::run()的原因无效（如下所示）：
boost::asio::io_context ioc;
std::shared_ptr<session> p = std::make_shared<session>(ioc);
p->open(host, port);
ioc.run(); // This works. Connection is established and all callbacks are executed.
是因为必须在io_context::restart()的任何后续调用之前调用函数io_context::run。
<强> io_context ::重新启动
重新启动 io_context 以准备后续的run（）调用。
必须在run（），run_one的任何第二次或更后一组调用之前调用此函数（ ），poll（）或poll_one（）函数在由于io_context停止或停止工作而返回先前调用这些函数时起作用。在调用restart（）之后，io_context对象的stopped（）函数将返回false。
答案 1 :(得分：1)
app.use( '/src', express.static( __dirname + '/src' ) );
只会在没有更多待处理工作时返回。如果您只是确保始终有io_context::run处于待处理状态的待处理呼叫，那么websocket::stream::async_read将永远不会返回，并且不会需要黑客攻击。此外，您将收到服务器发送的所有消息。