I'm making a TCP server by using the boost::asio library.
At this moment, I have working it with a code like this:
Note:This is a testing server for non-profit.
int main(){
const int SERVER_PORT = 60000;
try{
...
//declare the io_service, endpoint, acceptor and socket
...
{
acceptor.accept(socket);
boost::asio::write(socket, boost::asio::buffer(message));
boost::asio::streambuf received;
boost::asio::read_until(socket, received, "\r\n");
...
//all server operations
...
}
}
}
catch (std::exception& ex)
{
std::cerr << "Exception " << ex.what() << std::endl;
}
return 0;
}
Now, I wan't to improve the code and I started by organizing my code by functions like this:
void session(){
boost::asio::write(socket, boost::asio::buffer(message));
boost::asio::streambuf received;
boost::asio::read_until(socket, received, "\r\n");
...
//All server operations
...
}
void server(boost::asio::io_service& io_service, const int SERVER_PORT){
...
//declare the io_service, endpoint, acceptor and socket
...
session();//Call Session
}
int main(){
const int SERVER_PORT = 60000;
boost::asio::io_service io_service;
server(io_service, SERVER_PORT);
return 0;
}
My problem is that with the functions, it doesn't compile.
I have the Visual Studio compilation error: C2228
error C2228:The operand to the left of the period .read_some is not a
class, structure, or union
error C2228:The operand to the left of the period .write_some is not a
class, structure, or union
I don't found how to fix this problem.
Thank you very much!
EDIT: SOLUTION BASED ON THE ANSWER
Unless socket is a global vairable, void session() is not valid.
The good one is:
void session(boost::asio::ip::tcp::socket& socket)
Thanks very much to Orrkid
Where is socket defined? sounds like it isn't properly defined causing the write and read_until functions to throw the error.
read_some and write_some are called inside the write and read_until
(edit) looking at your code, unless socket is a global vairable, how is it getting passed into your session function, I see where you commented that you will declare them in your server function, but unless you have omitted more code from the example, looks like void session() is not valid.
You have defined a socket object ,The name of this object is conflict with Socket under windows,so you need to modify this name.
Related
Okay, so I might have got myself a big problem here. All this time, I've been basing my code in something I might not have wanted, that is, I'm using synchronous boost::asio functions with a server that can have multiple clients at the same time. Here it is:
void session(tcp::socket socket, std::vector<Player>* pl)
{
debug("New connection! Reading username...\n");
/* ...Username verification code removed... */
debug("Client logged in safely as ");
debug(u->name);
debug("\n");
for (;;)
{
boost::array<unsigned char, 128> buf;
size_t len = socket.read_some(boost::asio::buffer(buf), error);
if (error == boost::asio::error::eof)
{
debug("Connection ended.\n");
break; // Connection closed cleanly by peer.
}
else if (error)
throw boost::system::system_error(error); // Some other error.
DataHeader ins = static_cast<DataHeader>(buf.data()[0]);
std::vector<unsigned char> response;
/* ... Get appropiate response... */
// send response
boost::system::error_code ignored_error;
boost::asio::write(socket, boost::asio::buffer(response), ignored_error);
//debug("Sent ");
//debug(response.size());
//debug("B to client.\n");
}
}
As you can see from the code, I'm using read_some and write functions in a non-ideal scenario. Now, the question is, how did I make this code usable for multiple clients at the same time? Well, I used threads:
int main()
{
try
{
boost::asio::io_context io_context;
tcp::acceptor acceptor(io_context, tcp::endpoint(tcp::v4(), 13));
debug("Ready.\n");
for (;;)
{
std::thread(session, acceptor.accept(), &players).detach(); // Accept incoming clients
}
}
catch (std::exception& e)
{
std::cerr << e.what() << std::endl;
}
return 0;
}
Now, I've never had a problem with this setup until recently, that I started testing multiple clients at the same time on one server. This made the server crash many times, and just until now, I thought the problem were just connection issues. However, now I've started to wonder, "Might the problem be the synchronous functions?"
All the examples I've seen until now of multi-client servers use async functions, and maybe it's because they are needed. So, my final question is, do I really need async functions? Is there anything wrong with this code to make it crash? And finally, if async functions are needed, how could I implement them? Many thanks in advance!
As user VTT has pointed out, although this approach may work for a little bit, it's just better to switch to async functions due to resource exhaustion, so, I'll just redo the entire server to implement them.
I am an AspNet programmer with 57 years of age. Because I was the only one who worked a little, back in the beginning, with C ++, my bosses asked me to serve a customer who needs a communication agent with very specific characteristics. It can run as a daemon on multiple platforms and be both client and server at times. I do not know enough but I have to solve the problem and found a chance in the Boost / Asio library.
I am new to Boost-Asio and reading the documentation I created a server and a TCP socket client that exchanges messages perfectly and two-way, full duplex.
I read several posts where they asked for the same things I want, but all the answers suggested full duplex as if that meant having a client and a server in the same program. And it's not. The definition of full duplex refers to the ability to write and read from the same connection and every TCP connection is full duplex by default.
I need to make two programs can accept connections initiated by the other. There will be no permanent connection between the two programs. Sometimes one of them will ask for a connection and at other times the other will make this request and both need to be listening, accepting the connection, exchanging some messages and terminating the connection until new request is made.
The server I did seems to get stuck in the process of listening to the port to see if a connection is coming in and I can not continue with the process to be able to create a socket and request a connection with the other program. I need threads but I do not know enough about them.
It'is possible?
As I said I'm new to Boost / Asio and I tried to follow some documents of threads and Coroutines. Then I put the client codes in one method and the server in another.:
int main(int argc, char* argv[])
{
try
{
boost::thread t1(&server_agent);
boost::thread t2(&client_agent);
// wait
t1.join();
t2.join();
return 0;
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}
and two Coroutines:
void client_agent() {
parameters param;
param.load();
boost::asio::io_service io_service1;
tcp::resolver resolver(io_service1);
char port[5];
_itoa(param.getNrPortaServComunic(), port, 10);
auto endpoint_iterator = resolver.resolve({ param.getIPServComunicPrincipal(), port });
std::list<client> clients;
client c(io_service1, endpoint_iterator, param);
while (true)
{
BOOL enviada = FALSE;
while (true) {
if (!enviada) {
std::cout << "sending a message\n";
int nr = 110;
message msg(nr, param);
c.write(msg);
enviada = TRUE;
}
}
}
c.close();
}
void server_agent() {
parameters param;
param.load();
boost::asio::io_service io_service1;
std::list<server> servers;
tcp::endpoint endpoint(tcp::v4(), param.getNrPortaAgenteServ());
servers.emplace_back(io_service1, endpoint);
io_service1.run();
}
I used one port to client endpoint and other port to server endpoint. Is it correct? Required?
It starts looking like it's going to work. Each of the methods runs concurrently but then I get a thread allocation error at the io_service1.run (last line of the server_agent method):
boost::exception_detail::clone_impl > at memory location 0x0118C61C.
Any suggestion?
You are describing a UDP client/server application. But your implementation is bound to fail. Think of an asio server or client as always running in a single thread.
The following code is just so you get an idea. I haven't tried to compile it. Client is very similar, but may need a transmit buffer, depends on the app, obviously.
This is a shortened version, so you get the idea. In a final application you way want to add receive timeouts and the likes. The same principles hold for TCP servers, with the added async_listen call. Connected sockets can be stored in shared_ptr, and captured by the lambdas, will destroy almost magically.
Server is basically the same, except there is no constant reading going on. If running both server and client in the same process, you can rely on run() to be looping because of the server, but if not, you'd have to call run() for each connection. run() would exit at the end of the exchange.
using namespace boost::asio; // Or whichever way you like to shorten names
class Server
{
public:
Server(io_service& ios) : ios_(ios) {}
void Start()
{
// create socket
// Start listening
Read();
}
void Read()
{
rxBuffer.resize(1024)
s_.async_receive_from(
buffer(rxBuffer),
remoteEndpoint_,
[this](error_code ec, size_t n)
{
OnReceive(ec, n); // could be virtual, if done this way
});
}
void OnReceive(error_code ec, size_t n)
{
rxBuffer_.resize(n);
if (ec)
{
// error ... stops listen loop
return;
}
// grab data, put in txBuffer_
Read();
s_.async_send_to(
buffer(txBuffer_),
remoteEndpoint_,
[this, msg](error_code ec, size_t n)
{
OnTransmitDone(ec, n);
});
}
void OnTransmitDone(error_code ec, size_t n)
{
// check for error?
txBuffer_.clear();
}
protected:
io_service& ios_;
ip::udp::socket s_;
ip::udp::endpoint remoteEndpoint_; // the other's address/port
std::vector<char> rxBuffer_; // could be any data type you like
std::vector<char> txBuffer_; // idem All access is in one thread, so only
// one needed for simple ask/respond ops.
};
int main()
{
io_service ios;
Server server(ios); // could have both server and client run on same thread
// on same io service this way.
Server.Start();
ios_run();
// or std::thread ioThread([&](){ ios_.run(); });
return 0;
}
I have an UDP Server set up with boost/asio (I copied the example and just changed a few things). Below is the code:
udp_server.hpp
using boost::asio::ip::udp;
class udp_server {
public:
udp_server(boost::asio::io_service&, int);
private:
boost::array<char, 256> recBuffer;
udp::socket socket_;
udp::endpoint remote_endpoint_;
void start_receive();
void handle_receive(const boost::system::error_code&, std::size_t);
void handle_send(boost::shared_ptr<std::string> /*message*/,
const boost::system::error_code& /*error*/,
std::size_t /*bytes_transferred*/)
{}
};
and udp_server.cpp
udp_server::udp_server( boost::asio::io_service& io_service,
int port)
: socket_(io_service, udp::endpoint(udp::v4(), port)) {
serverNotifications.push_back("UDP Server class initialized.");
start_receive();
}
void udp_server::start_receive() {
socket_.async_receive_from(
boost::asio::buffer(recBuffer),
remote_endpoint_,
boost::bind(&udp_server::handle_receive,
this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
serverNotifications.push_back("Starting to receive UDP Messages.");
}
void udp_server::handle_receive(const boost::system::error_code& error,
std::size_t size) {
serverNotifications.push_back("RecFrom: " + remote_endpoint_.address().to_string());
if (!error) {
// I do data stuff here
} else {
errors.push_back("Handle Receive error: " + error.message());
}
}
After initializing the Server with:
try {
udp_server server(io_service, ApplData.PORT, (size_t)ApplData.BUFLEN);
} catch (std::exception& e) {
// error handling
}
and running it with io_service.run() in a seperate try catch in another function I get some problems:
My Callback function handle_receive gets called without any UDP message getting send in the whole network (aka only my laptop without connection)
error.message() returns "Operation canceled"
remote_endpoint_.address().to_string() returns "acfc:4000:0:0:7800::%2885986016" which I can't identify as something useful
Also I recognized that my io_service is stopping all the time, but in my understanding it should run all the time, right?
I already thought about referencing this in the callback function bind with a shared_from_this ptr, but since I have a real instance of the udp_server class until I leave my program I can't think of a good reason to do that.
Can someone explain thy this failure occurs, what these errors tell me about my code or what I can do to avoid them?
Nevermind, Rubberduck debugging was enough. I just read the line
but since I have a real instance of the udp_server class until I leave my program I can't think of a good reason to do that.
and noticed, that I actually didn't have this and this was the error.
I am working on a project where I need to be able to use a few persistent to talk to different servers over long periods of time. This server will have a fairly high throughput. I am having trouble figuring out a way to setup the persistent connections correctly. The best way I could think of to do this is create a persistent connection class. Ideally I would connect to the server one time, and do async_writes as information comes into me. And read information as it comes back to me. I don't think I am structuring my class correctly though.
Here is what I have built right now:
persistent_connection::persistent_connection(std::string ip, std::string port):
io_service_(), socket_(io_service_), strand_(io_service_), is_setup_(false), outbox_()
{
boost::asio::ip::tcp::resolver resolver(io_service_);
boost::asio::ip::tcp::resolver::query query(ip,port);
boost::asio::ip::tcp::resolver::iterator iterator = resolver.resolve(query);
boost::asio::ip::tcp::endpoint endpoint = *iterator;
socket_.async_connect(endpoint, boost::bind(&persistent_connection::handler_connect, this, boost::asio::placeholders::error, iterator));
io_service_.poll();
}
void persistent_connection::handler_connect(const boost::system::error_code &ec, boost::asio::ip::tcp::resolver::iterator endpoint_iterator)
{
if(ec)
{
std::cout << "Couldn't connect" << ec << std::endl;
return;
}
else
{
boost::asio::socket_base::keep_alive option(true);
socket_.set_option(option);
boost::asio::async_read_until(socket_, buf_ ,"\r\n\r\n", boost::bind(&persistent_connection::handle_read_headers, this, boost::asio::placeholders::error));
}
}
void persistent_connection::write(const std::string &message)
{
write_impl(message);
//strand_.post(boost::bind(&persistent_connection::write_impl, this, message));
}
void persistent_connection::write_impl(const std::string &message)
{
outbox_.push_back(message);
if(outbox_.size() > 1)
{
return;
}
this->write_to_socket();
}
void persistent_connection::write_to_socket()
{
std::string message = "GET /"+ outbox_[0] +" HTTP/1.0\r\n";
message += "Host: 10.1.10.120\r\n";
message += "Accept: */*\r\n";
boost::asio::async_write(socket_, boost::asio::buffer(message.c_str(), message.size()), strand_.wrap(
boost::bind(&persistent_connection::handle_write, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred)));
}
void persistent_connection::handle_write(const boost::system::error_code& ec, std::size_t bytes_transfered)
{
outbox_.pop_front();
if(ec)
{
std::cout << "Send error" << boost::system::system_error(ec).what() << std::endl;
}
if(!outbox_.empty())
{
this->write_to_socket();
}
boost::asio::async_read_until(socket_, buf_ ,"\r\n\r\n",boost::bind(&persistent_connection::handle_read_headers, this, boost::asio::placeholders::error));
}
The first message I will send from this seems to send out fine, the server gets it, and responds with a valid response. I see two problem unfortunately:
1) My handle_write is never called after doing the async_write command, I have no clue why.
2) The program never reads the response, I am guessing this is related to #1, since asyn_read_until is not called until that function happens.
3) I was also wondering if someone could tell me why my commented out strand_.post call would not work.
I am guessing most of this has to due with my lack of knowledge of how I should be using my io_service, so if somebody could give me any pointer that would be greatly appreciated. And if you need any additional information, I would be glad to provide some more.
Thank you
Edit call to write:
int main()
{
persistent_connection p("10.1.10.220", "80");
p.write("100");
p.write("200");
barrier b(1,30000); //Timed mutex, waits for 300 seconds.
b.wait();
}
and
void persistent_connection::handle_read_headers(const boost::system::error_code &ec)
{
std::istream is(&buf_);
std::string read_stuff;
std::getline(is,read_stuff);
std::cout << read_stuff << std::endl;
}
The behavior described is the result of the io_service_'s event loop no longer being processed.
The constructor invokes io_service::poll() which will run handlers that are ready to run and will not block waiting for work to finish, where as io_service::run() will block until all work has finished. Thus, when polling, if the other side of the connection has not written any data, then no handlers may be ready to run, and execution will return from poll().
With regards to threading, if each connection will have its own thread, and the communication is a half-duplex protocol, such as HTTP, then the application code may be simpler if it is written synchronously. On the other hand, if it each connection will have its own thread, but the code is written asynchronously, then consider handling exceptions being thrown from within the event loop. It may be worth reading Boost.Asio's
effect of exceptions thrown from handlers.
Also, persistent_connection::write_to_socket() introduces undefined behavior. When invoking boost::asio::async_write(), it is documented that the caller retains ownership of the buffer and must guarantee that the buffer remains valid until the handler is called. In this case, the message buffer is an automatic variable, whose lifespan may end before the persistent_connection::handle_write handler is invoked. One solution could be to change the lifespan of message to match that of persistent_connection by making it a member variable.
Alright, this is my current code snippet:
namespace bai = boost::asio::ip;
bai::tcp::socket tcp_connect(std::string hostname, std::string port) {
try {
boost::asio::io_service io_service;
bai::tcp::resolver resolver(io_service);
// we now try to get a list of endpoints to the server
bai::tcp::resolver::query query(hostname, port);
bai::tcp::resolver::iterator endpoint_iterator = resolver.resolve(query);
bai::tcp::resolver::iterator end;
// looking for a successful endpoint connection
bai::tcp::socket socket(io_service);
boost::system::error_code error = boost::asio::error::host_not_found;
while (error && endpoint_iterator != end) {
socket.close();
socket.connect(*endpoint_iterator++ , error);
}
if (error) throw boost::system::system_error(error);
return socket;
} catch (std::exception &ex) {
std::cout << "Exception: " << ex.what() << "\n";
}
}
Which should return a boost::asio::ip::tcp::socket connected to hostname on port. However I get presented with a shitload of incomprehensible boost::noncopyable errors. But my question is, how should I pass around these sockets then? What's wrong with this?
socket can't be copied. Use a boost::shared_ptr<bai::tcp::socket> instead. If you could copy a socket you'd have all sorts of funny issues if you ended up with two socket instances representing the same underlying OS socket - so it makes sense that copying (and therefore return by value, pass by value) is not allowed.
The code:
return socket;
attempts to make a copy of socket to return, and then destroy the original socket when the function exits. Unfortunately, sockets cannot be copied (they manage an underlying operating system resource that must be closed, so the system must ensure only one reference to that resource exists, otherwise things would go badly wrong when the first copy went out of scope).
As suggested in the other answer, you could use a pointer to return an object created on the heap (which should be managed either with a shared_ptr, or more efficiently if you are only using it in a single place a unique_ptr), or if you are using C++11 you could use the move constructor for the return value:
return std::move (socket);
This would avoid the necessity to use heap allocation and pointers, so is probably the preferable solution.