[英]c++: BOOST_ASIO Server reply isn't as expected?
Basically I have a client where I send a string of 10 bytes hellohello
to a server and within the server I expect the reply to be 0123456789
back to the client but instead I get hellohello
again? 基本上,我有一个客户端,我在其中向服务器发送10字节的字符串
hellohello
,并且在服务器内,我希望返回0123456789
回复给客户端,但是我又得到了hellohello
? I changed the char data_
to char data_out
on line 58 in the tcp_server.cpp because I thought that was the place to send packet data out? 我改变了
char data_
到char data_out
上的tcp_server.cpp 58行,因为我认为这是发送数据包出去的地方? I'm pretty sure that gets called but for some reason things aren't working like I thought. 我很确定会打电话给我,但是由于某些原因,事情并没有按照我的想法工作。
This is the server output, 这是服务器的输出,
handle read: bytes_transferred10
10
handle write:
0123456789
handle read: bytes_transferred0
I also wonder why did handle read: bytes_transferred0
get called again? 我也想知道为什么
handle read: bytes_transferred0
再次被调用?
This is the client output, 这是客户端输出,
Enter message: hellohello
Reply is: hellohello
Process returned 0 (0x0) execution time : 6.484 s
Press any key to continue.
This is the tcp_server.cpp 这是tcp_server.cpp
#include <cstdlib>
#include <iostream>
#include <boost/bind.hpp>
#include <boost/asio.hpp>
using boost::asio::ip::tcp;
class session
{
public:
session(boost::asio::io_service& io_service)
: socket_(io_service)
{
}
tcp::socket& socket()
{
return socket_;
}
void start()
{
socket_.async_read_some(boost::asio::buffer(data_, max_length),
boost::bind(&session::handle_read, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
void read_handler(const boost::system::error_code& ec, std::size_t bytes_transferred);
private:
void handle_read(const boost::system::error_code& error,
size_t bytes_transferred)
{
std::cout<<"handle read: bytes_transferred"<<bytes_transferred<<std::endl;
if (!error)
{
read_handler(error, bytes_transferred);
boost::asio::async_write(socket_,
boost::asio::buffer(data_, bytes_transferred),
boost::bind(&session::handle_write, this,
boost::asio::placeholders::error));
}
else
{
delete this;
}
}
void handle_write(const boost::system::error_code& error)
{
std::cout<<"handle write: "<<std::endl;
data_out = {'0','1','2','3','4','5','6','7','8','9'};
if (!error)
{
std::cout<<data_out<<std::endl;
socket_.async_read_some(boost::asio::buffer(data_out, max_length),
boost::bind(&session::handle_read, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
else
{
delete this;
}
}
tcp::socket socket_;
enum { max_length = 1024 };
char data_[max_length];
char data_out[max_length];
};
void session::read_handler(const boost::system::error_code& ec, std::size_t bytes_transferred)
{
std::cout<<bytes_transferred<<std::endl;
}
class server
{
public:
server(boost::asio::io_service& io_service, short port)
: io_service_(io_service),
acceptor_(io_service, tcp::endpoint(tcp::v4(), port))
{
start_accept();
}
private:
void start_accept()
{
session* new_session = new session(io_service_);
acceptor_.async_accept(new_session->socket(),
boost::bind(&server::handle_accept, this, new_session,
boost::asio::placeholders::error));
}
void handle_accept(session* new_session,
const boost::system::error_code& error)
{
if (!error)
{
new_session->start();
}
else
{
delete new_session;
}
start_accept();
}
boost::asio::io_service& io_service_;
tcp::acceptor acceptor_;
};
int main()
{
try
{
boost::asio::io_service io_service;
server s(io_service, 4000);
io_service.run();
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}
tcp_client.cpp tcp_client.cpp
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <boost/asio.hpp>
using boost::asio::ip::tcp;
enum { max_length = 1024 };
int main(int argc, char* argv[])
{
try
{
boost::asio::io_service io_service;
tcp::resolver resolver(io_service);
tcp::resolver::query query(tcp::v4(), "127.0.0.1", "4000");
tcp::resolver::iterator iterator = resolver.resolve(query);
tcp::socket s(io_service);
s.connect(*iterator);
using namespace std; // For strlen.
std::cout << "Enter message: ";
char request[max_length];
std::cin.getline(request, max_length);
size_t request_length = strlen(request);
boost::asio::write(s, boost::asio::buffer(request, request_length));
char reply[max_length];
size_t reply_length = boost::asio::read(s,boost::asio::buffer(reply, request_length));
std::cout << "Reply is: ";
std::cout.write(reply, reply_length);
std::cout << "\n";
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}
Your comment 你的评论
I think
handle_read()
callshandle_write()
recursively?我认为
handle_read()
handle_write()
递归调用handle_write()
吗?
is close but not quite correct as there is no recursion here. 接近但不太正确,因为此处没有递归。 The documentation explains this nicely:
该文档很好地解释了这一点:
Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function .
无论异步操作是否立即完成, 都不会从此函数内调用处理程序。 Invocation of the handler will be performed in a manner equivalent to using
boost::asio::io_service::post()
.处理程序的调用将以与使用
boost::asio::io_service::post()
等效的方式执行。
Added emphasis is mine. 重点是我的。 Instead of recursion, It is better to think of these concepts as chaining since one operation such as
async_write()
is initiated in the handler of another, such as async_read()
. 最好将这些概念视为链接,而不是递归,因为一个操作(例如
async_write()
是在另一个操作(例如async_read()
的处理程序中启动的。 The exact specifics depend on the protocol in use. 具体细节取决于所使用的协议。
If you want the server to send the string 0123456789 to the client, fill your buffer before invoking async_write()
. 如果要服务器将字符串0123456789发送到客户端,请在调用
async_write()
之前填充缓冲区。
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