Related
I'm trying to write a very simple client/server app with boost::socket. I need a server to run and a single client to connect, send data, disconnect and possibly reconnect later and repeat.
The code reduced to the minimum is here:
Server app:
#include <iostream>
#include <boost/asio.hpp>
#include <boost/thread.hpp>
using boost::asio::ip::tcp;
class TheServer
{
public:
TheServer(int port) : m_port(port)
{
m_pIOService = new boost::asio::io_service;
m_pThread = new boost::thread(boost::bind<void>(&TheServer::run, this));
listenForNewConnection();
}
~TheServer()
{
m_bContinueReading = false;
m_pIOService->stop();
m_pThread->join();
delete m_pThread;
delete m_pSocket;
delete m_pAcceptor;
delete m_pIOService;
}
void listenForNewConnection()
{
if (m_pSocket)
delete m_pSocket;
if (m_pAcceptor)
delete m_pAcceptor;
// start new acceptor operation
m_pSocket = new tcp::socket(*m_pIOService);
m_pAcceptor = new tcp::acceptor(*m_pIOService, tcp::endpoint(tcp::v4(), m_port));
std::cout << "Starting async_accept" << std::endl;
m_pAcceptor->async_accept(*m_pSocket,
boost::bind<void>(&TheServer::readSession, this, boost::asio::placeholders::error));
}
void readSession(boost::system::error_code error)
{
if (!error)
{
std::cout << "Connection established" << std::endl;
while ( m_bContinueReading )
{
static unsigned char buffer[1000];
boost::system::error_code error;
size_t length = m_pSocket->read_some(boost::asio::buffer(&buffer, 1000), error);
if (!error && length != 0)
{
std::cout << "Received " << buffer << std::endl;
}
else
{
std::cout << "Received error, connection likely closed by peer" << std::endl;
break;
}
}
std::cout << "Connection closed" << std::endl;
listenForNewConnection();
}
else
{
std::cout << "Connection error" << std::endl;
}
std::cout << "Ending readSession" << std::endl;
}
void run()
{
while (m_bContinueReading)
m_pIOService->run_one();
std::cout << "Exiting run thread" << std::endl;
}
bool m_bContinueReading = true;
boost::asio::io_service* m_pIOService = NULL;
tcp::socket* m_pSocket = NULL;
tcp::acceptor* m_pAcceptor = NULL;
boost::thread* m_pThread = NULL;
int m_port;
};
int main(int argc, char* argv[])
{
TheServer* server = new TheServer(1900);
std::cout << "Press Enter to quit" << std::endl;
std::string sGot;
getline(std::cin, sGot);
delete server;
return 0;
}
Client app:
#include <iostream>
#include <boost/asio.hpp>
#include <boost/thread.hpp>
int main(int argc, char* argv[])
{
std::cout << std::endl;
std::cout << "Starting client" << std::endl;
using boost::asio::ip::tcp;
boost::asio::io_service* m_pIOService = NULL;
tcp::socket* m_pSocket = NULL;
try
{
m_pIOService = new boost::asio::io_service;
std::stringstream sPort;
sPort << 1900;
tcp::resolver resolver(*m_pIOService);
tcp::resolver::query query(tcp::v4(), "localhost", sPort.str());
tcp::resolver::iterator iterator = resolver.resolve(query);
m_pSocket = new tcp::socket(*m_pIOService);
m_pSocket->connect(*iterator);
std::cout << "Client conected" << std::endl;
std::string hello = "Hello World";
boost::asio::write( *m_pSocket, boost::asio::buffer(hello.data(), hello.size()) );
boost::this_thread::sleep(boost::posix_time::milliseconds(100));
hello += "(2)";
boost::asio::write(*m_pSocket, boost::asio::buffer(hello.data(), hello.size()));
}
catch (std::exception& e)
{
delete m_pSocket;
m_pSocket = NULL;
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}
Note that I use non-blocking async_accept to be able to cleanly stop the server when Enter is pressed.
Under Windows, it works perfectly fine, I run the server, it outputs:
Starting async_accept
Press Enter to quit
For each client app run, it outpts:
Starting client
Client conected
and server app outputs:
Connection established
Received Hello World
Received Hello World(2)
Received error, connection likely closed by peer
Connection closed
Starting async_accept
Ending readSession
Then when I press Enter in server app console, it outputs Exiting run thread and cleanly stops.
Now, when I compile this same code under Linux, the client outputs the same as under Windows, but nothing happens on the server side...
Any idea what's wrong?
There are many questionable elements.
There is a classical data race on m_bContinueReading. You write from another thread, but the other thread may never see the change because of the data race.
The second race condition is likely your problem:
m_pThread = new boost::thread(boost::bind<void>(&TheServer::run, this));
listenForNewConnection();
Here the run thread may complete before you ever post the first work. You can use a work-guard to prevent this. In your specific code you would already fix it by reordering the lines:
listenForNewConnection();
m_pThread = new boost::thread(boost::bind<void>(&TheServer::run, this));
I would not do this, because I would not have those statements in my constructor body. See below for the work guard solution
There is a lot of raw pointer handling and new/delete going on, which merely invites errors.
You use the buffer assuming that it is NUL-terminated. This is especially unwarranted because you use read_some which will read partial messages as they arrive on the wire.
You use a static buffer while the code may have different instances of the class. This is very false optimization. Instead, prevent all the allocations! Combining with the previous item:
char buffer[1000];
while (m_bContinueReading) {
size_t length = m_Socket.read_some(asio::buffer(&buffer, 1000), ec);
std::cout << "Received " << length << " (" << quoted(std::string(buffer, length)) << "), "
<< ec.message() << std::endl;
if (ec.failed())
break;
}
You start a new acceptor always, where there is no need: a single acceptor can accept as many connections as you wish. In fact, the method shown runs into the problems
that lingering connections can prevent the new acceptor from binding to the same port. You could also alleviate that with
m_Acceptor.set_option(tcp::acceptor::reuse_address(true));
the destroyed acceptor may have backlogged connections, which are discarded
Typically you want to support concurrent connection, so you can split of a "readSession" and immediately accept the next connection. Now, strangely your code seems to expect clients to be connected until the server is prompted to shutdown (from the console) but after that you somehow start listening to new connections (even though you know the service will be stopping, and m_bContinueReading will remain false).
In the grand scheme of things, you don't want to destroy the acceptor unless something invalidated it. In practice this is rare (e.g. on Linux the acceptor will happily survive disabling/re-enabling the network adaptor).
you have spurious explicit template arguments (bind<void>). This is an anti-pattern and may lead to subtle problems
similar with the buffer (just say asio::buffer(buffer) and no longer have correctness concerns. In fact, don't use C-style arrays:
std::array<char, 1000> buffer;
size_t n = m_Socket.read_some(asio::buffer(buffer), ec);
std::cout << "Received " << n << " " << quoted(std::string(buffer.data(), n))
<< " (" << ec.message() << ")" << std::endl;
Instead of running a manual run_one() loop (where you forget to handle exceptions), consider "just" letting the service run(). Then you can .cancel() the acceptor to let the service run out of work.
In fact, this subtlety isn't required in your code, since your code already forces "ungraceful" shutdown anyways:
m_IOService.stop(); // nuclear option
m_Thread.join();
More gentle would be e.g.
m_Acceptor.cancel();
m_Socket.cancel();
m_Thread.join();
In which case you can respond to the completion error_code == error::operation_aborted to stop the session/accept loop.
Technically, you may be able to do away with the boolean flag altogether.
I keep it because it allows us to handle multiple session-per-thread in
"fire-and-forget" manner.
In the client you have many of the same problems, and also a gotcha where
you only look at the first resolver result (assuming there was one),
ignoring the rest. You can use asio::connect instead of
m_Socket.connect to try all resolved entries
Addressing the majority of these issues, simplifying the code:
Live On Coliru
#include <boost/asio.hpp>
#include <boost/bind/bind.hpp>
#include <boost/optional.hpp>
#include <iomanip>
#include <iostream>
namespace asio = boost::asio;
using asio::ip::tcp;
using namespace std::chrono_literals;
using boost::system::error_code;
class TheServer {
public:
TheServer(int port) : m_port(port) {
m_Acceptor.set_option(tcp::acceptor::reuse_address(true));
do_accept();
}
~TheServer() {
m_shutdownRequested = true;
m_Work.reset(); // release the work-guard
m_Acceptor.cancel();
m_Thread.join();
}
private:
void do_accept() {
std::cout << "Starting async_accept" << std::endl;
m_Acceptor.async_accept( //
m_Socket, boost::bind(&TheServer::on_accept, this, asio::placeholders::error));
}
void on_accept(error_code ec) {
if (!ec) {
std::cout << "Connection established " << m_Socket.remote_endpoint() << std::endl;
// leave session running in the background:
std::thread(&TheServer::read_session_thread, this, std::move(m_Socket)).detach();
do_accept(); // and immediately accept new connection(s)
} else {
std::cout << "Connection error (" << ec.message() << ")" << std::endl;
std::cout << "Ending readSession" << std::endl;
}
}
void read_session_thread(tcp::socket sock) {
std::array<char, 1000> buffer;
for (error_code ec;;) {
size_t n = sock.read_some(asio::buffer(buffer), ec);
std::cout << "Received " << n << " " << quoted(std::string(buffer.data(), n)) << " ("
<< ec.message() << ")" << std::endl;
if (ec.failed() || m_shutdownRequested)
break;
}
std::cout << "Connection closed" << std::endl;
}
void thread_func() {
// http://www.boost.org/doc/libs/1_61_0/doc/html/boost_asio/reference/io_service.html#boost_asio.reference.io_service.effect_of_exceptions_thrown_from_handlers
for (;;) {
try {
m_IOService.run();
break; // exited normally
} catch (std::exception const& e) {
std::cerr << "[eventloop] error: " << e.what();
} catch (...) {
std::cerr << "[eventloop] unexpected error";
}
}
std::cout << "Exiting service thread" << std::endl;
}
std::atomic_bool m_shutdownRequested{false};
uint16_t m_port;
asio::io_service m_IOService;
boost::optional<asio::io_service::work> m_Work{m_IOService};
tcp::socket m_Socket{m_IOService};
tcp::acceptor m_Acceptor{m_IOService, tcp::endpoint{tcp::v4(), m_port}};
std::thread m_Thread{boost::bind(&TheServer::thread_func, this)};
};
constexpr uint16_t s_port = 1900;
void run_server() {
TheServer server(s_port);
std::cout << "Press Enter to quit" << std::endl;
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}
void run_client() {
std::cout << std::endl;
std::cout << "Starting client" << std::endl;
using asio::ip::tcp;
try {
asio::io_service m_IOService;
tcp::resolver resolver(m_IOService);
auto iterator = resolver.resolve("localhost", std::to_string(s_port));
tcp::socket m_Socket(m_IOService);
connect(m_Socket, iterator);
std::cout << "Client connected" << std::endl;
std::string hello = "Hello World";
write(m_Socket, asio::buffer(hello));
std::this_thread::sleep_for(100ms);
hello += "(2)";
write(m_Socket, asio::buffer(hello));
} catch (std::exception& e) {
std::cerr << "Exception: " << e.what() << "\n";
}
}
int main(int argc, char**) {
if (argc>1)
run_server();
else
run_client();
}
I'm new to C++ but so far most of the asio stuff has made sense. I am however stuggling to get my UDPServer working.
My question is possibly similar to: Trying to write UDP server class, io_context doesn't block
I think my UDPServer stops before work can be given to its io_context. However, I am issuing work to the context before calling io_context.run() so I don't understand why.
Of course, I am not entirely sure if I am even on the right track with the above statement and would appreciate some guidance. Here is my class:
template<typename message_T>
class UDPServer
{
public:
UDPServer(uint16_t port)
: m_socket(m_asioContext, asio::ip::udp::endpoint(asio::ip::udp::v4(), port))
{
m_port = port;
}
virtual ~UDPServer()
{
Stop();
}
public:
// Starts the server!
bool Start()
{
try
{
// Issue a task to the asio context
WaitForMessages();
m_threadContext = std::thread([this]() { m_asioContext.run(); });
}
catch (std::exception& e)
{
// Something prohibited the server from listening
std::cerr << "[SERVER # PORT " << m_port << "] Exception: " << e.what() << "\n";
return false;
}
std::cout << "[SERVER # PORT " << m_port << "] Started!\n";
return true;
}
// Stops the server!
void Stop()
{
// Request the context to close
m_asioContext.stop();
// Tidy up the context thread
if (m_threadContext.joinable()) m_threadContext.join();
// Inform someone, anybody, if they care...
std::cout << "[SERVER # PORT " << m_port << "] Stopped!\n";
}
void WaitForMessages()
{
m_socket.async_receive_from(asio::buffer(vBuffer.data(), vBuffer.size()), m_endpoint,
[this](std::error_code ec, std::size_t length)
{
if (!ec)
{
std::cout << "[SERVER # PORT " << m_port << "] Got " << length << " bytes \n Data: " << vBuffer.data() << "\n" << "Address: " << m_endpoint.address() << " Port: " << m_endpoint.port() << "\n" << "Data: " << m_endpoint.data() << "\n";
}
else
{
std::cerr << "[SERVER # PORT " << m_port << "] Exception: " << ec.message() << "\n";
return;
}
WaitForMessages();
}
);
}
void Send(message_T& msg, const asio::ip::udp::endpoint& ep)
{
asio::post(m_asioContext,
[this, msg, ep]()
{
// If the queue has a message in it, then we must
// assume that it is in the process of asynchronously being written.
bool bWritingMessage = !m_messagesOut.empty();
m_messagesOut.push_back(msg);
if (!bWritingMessage)
{
WriteMessage(ep);
}
}
);
}
private:
void WriteMessage(const asio::ip::udp::endpoint& ep)
{
m_socket.async_send_to(asio::buffer(&m_messagesOut.front(), sizeof(message_T)), ep,
[this, ep](std::error_code ec, std::size_t length)
{
if (!ec)
{
m_messagesOut.pop_front();
// If the queue is not empty, there are more messages to send, so
// make this happen by issuing the task to send the next header.
if (!m_messagesOut.empty())
{
WriteMessage(ep);
}
}
else
{
std::cout << "[SERVER # PORT " << m_port << "] Write Header Fail.\n";
m_socket.close();
}
});
}
void ReadMessage()
{
}
private:
uint16_t m_port = 0;
asio::ip::udp::endpoint m_endpoint;
std::vector<char> vBuffer = std::vector<char>(21);
protected:
TSQueue<message_T> m_messagesIn;
TSQueue<message_T> m_messagesOut;
Message<message_T> m_tempMessageBuf;
asio::io_context m_asioContext;
std::thread m_threadContext;
asio::ip::udp::socket m_socket;
};
}
Code is invoked in the main function for now:
enum class TestMsg {
Ping,
Join,
Leave
};
int main() {
Message<TestMsg> msg; // Message is a pretty basic struct that I'm not using yet. When I was, I was only receiving the first 4 bytes - which led me down this path of investigation
msg.id = TestMsg::Join;
msg << "hello";
UDPServer<Message<TestMsg>> server(60000);
}
When invoked the Server immediately exits before it gets chance to print "[SERVER] Started"
I'll try adding the work guard as the link post describes but I would still like to understand why the io_context is not being primed with work quick enough.
Update (Now I also read the question not just the code)
While in WaitForMessages you do start listening by calling the m_socket.async_receive_from function, as it is async, that function will return/unblock as soon as it has setup the listening. So as long as you don't actually have a client sending you something, you server has nothing do to. Only when it has received something the callback will be called, by a thread calling io_context::run. So you need the work guard so that your thread running run won't unblock right after start, but will block as long as the work guard is there.
Usually it is also combined with a try/while pattern if an exception gets thrown in a handler and you still want to move on with your server.
Also in the code you posted, you never actually call UDPServer::Start!
This was my first idea of an answer:
This is normal behavior of ASIO. The io_context::run function will return as soon as it has no work to do.
So to change the behaviour of the run function to block you have to use a boost::asio::executor_work_guard<boost::asio::io_context::executor_type> i.e. a so called work guard. Construct that object with a reference to your io_context and hold it i.e. don't let it destruct as long as you want to let the server run, i.e. do not want to let io_context::run return when there is not work.
So given
boost::asio::io_context io_context_;
boost::asio::executor_work_guard<boost::asio::io_context::executor_type> work_guard_;
you then could call
work_guard_{boost::asio::make_work_guard(io_context_)},
const auto thread_count{std::max<unsigned>(std::thread::hardware_concurrency(), 1)};
std::generate_n(std::back_inserter(this->io_run_threads_),
thread_count,
[this]() {
return std::thread{io_run_loop,
std::ref(this->io_context_), std::ref(this->error_handler_)};
});
void io_run_loop(boost::asio::io_context &context,
const std::function<void(std::exception &)> &error_handler) {
while (true) {
try {
context.run();
break;
} catch (std::exception &e) {
error_handler(e);
}
}
}
And then for server shutdown:
work_guard_.reset();
io_context_.stop();
std::for_each(this->io_run_threads_.begin(), this->io_run_threads_.end(), [](auto &thread) {
if (thread.joinable()) thread.join();
});
For a more graceful shutdown you can omit the stop call and rather close all sockets before.
Looks like you forgot to call server.Start();. Moreover, you will want to make the main thread wait for some amount of time, otherwise the destructor of Server will immediately cause Stop() to be called:
int main()
{
Message<TestMsg> msg;
msg.id = TestMsg::Join;
msg << "hello";
UDPServer<Message<TestMsg>> server(60000);
server.Start();
std::this_thread::sleep_for(30s);
}
Issues
There is a conceptual problem with the Send API.
It takes an endpoint on each call, but it only uses the one that starts the write call chain! This means that if you do
srv.Send(msg1, {mymachine, 60001});
srv.Send(msg1, {otherserver, 5517});
It is likely they both get sent to mymachine:60001.
How you treat the buffer received. Just using .data() blindly assumes that the data is NUL-terminated. Don't do that:
std::string const data(vBuffer.data(), length);
Also, you seem to have at some time been confused about data and printed m_endpoint.data() - your princess is in another castle.
In reality you probably want ways to extract the typed data. I'm leaving that as beyond the scope of this question for today.
Regardless you should clear the buffer before reuse, because you might be seeing old data in subsequent reads.
vBuffer.assign(vBuffer.size(), '\0');
This is most likely undefined behaviour:
asio::buffer(&m_messagesOut.front(), sizeof(message_T)), ep,
This is only valid if message_T is trivial and standard-layout ("POD" - Plain Old Data). The presence of operator<< strongly suggests that is not the case.
Instead, build a (sequence of) buffer(s) hat represents the message as raw bytes, e.g.
auto& msg = m_messagesOut.front();
msg.length = msg.body.size();
m_socket.async_send_to(
std::vector<asio::const_buffer>{
asio::buffer(&msg.id, sizeof(msg.id)),
asio::buffer(&msg.length, sizeof(msg.length)),
asio::buffer(msg.body),
},
// ...
Thread safe queues seem to be overkill since you have a single service thread; that is an implicit "strand" so you can post to it to have single-threaded semantics.
Here's a few adaptations to make it work so far (except the exercise-for-the-reader pointed out):
Live On Coliru
#include <boost/asio.hpp>
#include <iostream>
#include <deque>
#include <sstream>
// Library facilities
namespace asio = boost::asio;
using asio::ip::udp;
using boost::system::error_code;
using namespace std::chrono_literals;
/////////////////////////////////
// mock ups:
template <typename message_T> struct Message {
message_T id;
uint16_t length; // automatically filled on send, UDP packets are < 64k
std::string body;
template <typename T> friend Message& operator<<(Message& m, T const& v)
{
std::ostringstream oss;
oss << v;
m.body += oss.str();
//m.body += '\0'; // suggestion for easier message extraction
return m;
}
};
// Thread-safety can be replaced with the implicit strand of a single service
// thread
template <typename T> using TSQueue = std::deque<T>;
// end mock ups
/////////////////////////////////
template <typename message_T> class UDPServer {
public:
UDPServer(uint16_t port)
: m_socket(m_asioContext, udp::endpoint(udp::v4(), port))
{
m_port = port;
}
virtual ~UDPServer() { Stop(); }
public:
// Starts the server!
bool Start()
{
if (m_threadContext.joinable() && !m_asioContext.stopped())
return false;
try {
// Issue a task to the asio context
WaitForMessages();
m_threadContext = std::thread([this]() { m_asioContext.run(); });
} catch (std::exception const& e) {
// Something prohibited the server from listening
std::cerr << "[SERVER # PORT " << m_port
<< "] Exception: " << e.what() << "\n";
return false;
}
std::cout << "[SERVER # PORT " << m_port << "] Started!\n";
return true;
}
// Stops the server!
void Stop()
{
// Tell the context to stop processing
m_asioContext.stop();
// Tidy up the context thread
if (m_threadContext.joinable())
m_threadContext.join();
// Inform someone, anybody, if they care...
std::cout << "[SERVER # PORT " << m_port << "] Stopped!\n";
m_asioContext
.reset(); // required in case you want to reuse this Server object
}
void Send(message_T& msg, const udp::endpoint& ep)
{
asio::post(m_asioContext, [this, msg, ep]() {
// If the queue has a message in it, then we must
// assume that it is in the process of asynchronously being written.
bool bWritingMessage = !m_messagesOut.empty();
m_messagesOut.push_back(msg);
if (!bWritingMessage) {
WriteMessage(ep);
}
});
}
private:
void WaitForMessages() // assumed to be on-strand
{
vBuffer.assign(vBuffer.size(), '\0');
m_socket.async_receive_from(
asio::buffer(vBuffer.data(), vBuffer.size()), m_endpoint,
[this](std::error_code ec, std::size_t length) {
if (!ec) {
std::string const data(vBuffer.data(), length);
std::cout << "[SERVER # PORT " << m_port << "] Got "
<< length << " bytes \n Data: " << data << "\n"
<< "Address: " << m_endpoint.address()
<< " Port: " << m_endpoint.port() << "\n"
<< std::endl;
} else {
std::cerr << "[SERVER # PORT " << m_port
<< "] Exception: " << ec.message() << "\n";
return;
}
WaitForMessages();
});
}
void WriteMessage(const udp::endpoint& ep)
{
auto& msg = m_messagesOut.front();
msg.length = msg.body.size();
m_socket.async_send_to(
std::vector<asio::const_buffer>{
asio::buffer(&msg.id, sizeof(msg.id)),
asio::buffer(&msg.length, sizeof(msg.length)),
asio::buffer(msg.body),
},
ep, [this, ep](std::error_code ec, std::size_t length) {
if (!ec) {
m_messagesOut.pop_front();
// If the queue is not empty, there are more messages to
// send, so make this happen by issuing the task to send the
// next header.
if (!m_messagesOut.empty()) {
WriteMessage(ep);
}
} else {
std::cout << "[SERVER # PORT " << m_port
<< "] Write Header Fail.\n";
m_socket.close();
}
});
}
private:
uint16_t m_port = 0;
udp::endpoint m_endpoint;
std::vector<char> vBuffer = std::vector<char>(21);
protected:
TSQueue<message_T> m_messagesIn;
TSQueue<message_T> m_messagesOut;
Message<message_T> m_tempMessageBuf;
asio::io_context m_asioContext;
std::thread m_threadContext;
udp::socket m_socket;
};
enum class TestMsg {
Ping,
Join,
Leave
};
int main()
{
UDPServer<Message<TestMsg>> server(60'000);
if (server.Start()) {
std::this_thread::sleep_for(3s);
{
Message<TestMsg> msg;
msg.id = TestMsg::Join;
msg << "hello PI equals " << M_PI << " in this world";
server.Send(msg, {{}, 60'001});
}
std::this_thread::sleep_for(27s);
}
}
For some reason netcat doesn't work with UDP on Coliru, so here's a "live" demo:
You can see our netcat client messages arriving. You can see the message Sent to 60001 arriving in the tcpdump output.
I'm trying to learn how Boost.asio works. I've written a basic server and client example as such:
server.cpp
#include <iostream>
#include <string>
#include <boost/asio.hpp>
#define PORT 27015
using namespace boost::asio;
using ip::tcp;
std::string read(tcp::socket& socket) {
boost::system::error_code error;
boost::asio::streambuf buffer;
boost::asio::read(socket, buffer, boost::asio::transfer_all(), error);
if (error) {
std::cerr << "read error: " << error.message() << "\n";
return "ERROR";
}
else {
std::string data = boost::asio::buffer_cast<const char*>(buffer.data());
return data;
}
}
void send(tcp::socket& socket, const std::string& message) {
boost::system::error_code error;
boost::asio::write(socket, boost::asio::buffer(message), error);
if (error)
std::cerr << "send error: " << error.message() << "\n";
else
std::cout << "sent \"" << message << "\" to the client" << "\n";
}
int main() {
boost::asio::io_service io_service;
tcp::acceptor acceptor(io_service, tcp::endpoint(tcp::v4(), PORT)); // create listener for new connection(s)
tcp::socket socket(io_service); // socket creation
std::cout << "awaiting connection..." << "\n";
acceptor.accept(socket); // direct connection(s) to the socket we created
std::cout << "accepted connection!" << "\n";
std::string received = read(socket); // receive data
std::cout << "received message: " << received << "\n";
send(socket, "hello from server!"); // send data
}
client.cpp
#include <iostream>
#include <string>
#include <boost/asio.hpp>
#define PORT 27015
using namespace boost::asio;
using ip::tcp;
int main(int argc, char *argv[])
{
boost::asio::io_service io_service;
tcp::socket socket(io_service); // socket creation
std::string server_ipv4_address = "192.168.1.2";
std::cout << "connecting to server at " << server_ipv4_address << "\n";
try {
socket.connect(tcp::endpoint(boost::asio::ip::address::from_string(server_ipv4_address), PORT)); // connection
std::cout << "connected!" << "\n";
}
catch (const boost::system::system_error& e) {
std::cerr << "error while connecting: " << e.what() << "\n";
return -1;
}
boost::system::error_code error; // error holder
std::string message = "hello from client!!\n";
boost::asio::write(socket, boost::asio::buffer(message), error); // send message to server
if (error)
std::cerr << "send failed: " << error.message() << "\n";
else
std::cout << "sent \"" << message << "\" to the server" << "\n";
boost::asio::streambuf receive_buffer;
boost::asio::read(socket, receive_buffer, boost::asio::transfer_all(), error); // receive from server
if (error && error != boost::asio::error::eof)
std::cerr << "receive failed: " << error.message() << "\n";
else {
std::string data = boost::asio::buffer_cast<const char*>(receive_buffer.data());
std::cout << "received data: " << data << "\n";
}
}
The connection gets established properly, but the read() function from the server blocks the program as either it does not receive data from the client, or there is a problem with the way I'm calling it. What seems to be the issue with the boost::asio::read() here?
Everything works properly if I swap boost::asio::read with boost::asio::read_until as shown below. Why does the function work properly in the client but not in the server?
std::string read(tcp::socket& socket) {
boost::system::error_code error;
boost::asio::streambuf buffer;
boost::asio::read_until(socket, buffer, "\n");
std::string data = boost::asio::buffer_cast<const char*>(buffer.data());
return data;
}
Read with the completion condition transfer_all means it will just keep reading until the buffer is full or the connection becomes invalid.
The buffer will "never" be full (since it's a DynamicBuffer).
So that leaves the cause that the client never hangs up.
Everything works properly if I swap boost::asio::read with boost::asio::read_until as shown below.
Exactly. Because then you have another reason to stop reading. Mind you, it could still block forever (when a '\n' never arrives).
Why does the function work properly in the client but not in the server?
It doesn't. It appears to because the server, apparently, does shutdown the connection (signalling EOF). [You would notice this because a subsequent read would return error_code boost::asio::error::eof.]
I have tried following the tutorial from boost, however the API is not identical so I have had to guess some parts.
My attempt so far is shown bellow:
#include <iostream>
#include <experimental/internet>
#include <experimental/socket>
#include <thread>
#include <chrono>
using namespace std::experimental;
int main(int argc, char* argv[])
{
std::thread server = std::thread([]()
{
std::cout << "Starting server" << std::endl;
net::io_context context;
net::ip::tcp::endpoint endpoint{net::ip::tcp::v4(), 1234};
net::ip::tcp::acceptor acceptor{context, endpoint};
acceptor.non_blocking(true);
std::cout << "opened server on " << endpoint << std::endl;
std::error_code error;
net::ip::tcp::socket socket(context);
while (true)
{
socket = acceptor.accept(error); //accept connections
if (!error) //if connected with a client
{
std::cout << "Connected to client!" << std::endl;
std::this_thread::sleep_for(std::chrono::seconds(2));
std::string data = "Hello World!";
net::const_buffer buf(&data, sizeof(data));
socket.send(buf);
std::cout << "Sent data!" << std::endl;
while(true) {}
}
}
});
std::thread client = std::thread([]()
{
net::io_context context;
net::ip::tcp::socket socket(context);
net::ip::tcp::endpoint server{net::ip::tcp::v4(), 1234};
std::error_code error;
while(true)
{
socket.connect(server, error); //attempt to connect
if (!error) //if connected
{
std::cout << "Connected to server!" << std::endl;
net::mutable_buffer buf;
while(buf.size() == 0)
{
socket.receive(buf);
}
std::cout << "Received data!" << std::endl;
std::cout << buf.data() << std::endl;
while(true) {}
}
}
});
server.join();
return 0;
}
The sever and client connect, but the message is not received by the client. The output from the program above is:
Starting server
opened server on 0.0.0.0:1234
Connected to server!
Connected to client!
Sent data!
And then it waits forever.
How do I get the socket to correctly receive the data?
This
std::string data = "Hello World!";
net::const_buffer buf(&data, sizeof(data));
is wrong. You want to send content of data string, not its internal bytes. &data gives you a pointer to underlying data of string instance, not its content. If you want to create buffer which represents content of data you can do:
const std::string data = "Hello World!";
net::const_buffer buf = net::buffer(data);
This
net::mutable_buffer buf;
while(buf.size() == 0)
{
socket.receive(buf);
}
gives you infinite loop because initial size of buf is 0, so receive reads 0 bytes and returns. Then while condition is checked, buf's size is still 0, and the loop goes on.
Before calling receive you need to specify the size of buffer - it indicates how many bytes must be read. You are sending Hello World! so
std::string msg;
msg.resize(12); // prepare space for incoming data
net::mutable_buffer buf = net::buffer(msg);
socket.receive(buf);
std::cout << "I got: " << msg << std::endl;
I'm connecting to a WebSocket whom always replies in JSON. I see there is an extract_string method for websocket_incoming_message however after trying numerous things with json:value it seems as though you can only construct JSON arrays on-the-fly by inserting key-value pairs one-by-one. Am I missing something here or is there a way to take the output from websocket_incoming_message and directly convert it into a json:value array?
websocket_client client;
//start socket connection to server
try {
std::cout << "s
----------
client.connect(U("wss://XZXXXZZy.com/ws?account_id=4de3f308f2f8d3247As70228f94e0d2aAea&ws_key=reception")).wait();
}
catch (const std::exception&e)
{
std::cout << e.what() << std::endl;
}
//send messages to the server
//websocket_outgoing_message msg;
//msg.set_pong_message();
//std::cout << "\n...........2nd.........;";
//std::string data = "hii";
//client.send(msg).then([]() {
//
//
//
//
// /* Successfully sent the message. */ });
//std::cout << " Successfully sent the message.";
//std::cout << "\n...........3rd.........;";
//receive messages from the server
client.receive().then([](websocket_incoming_message msg) {
std::cout << "receiving data from socket";
return msg.extract_string();
}).then([](std::string body) {
//FETCHING THE DATA FROM BODY. "TEXT/JSON"
std::cout << "displaying the data";
std::cout << body << std::endl;
const json::value& v1 = body.substr;
utility::string_t jsonval = v1.serialize();
auto array = v1.at(U("rows")).as_array();
for (int i = 0; i<array.size(); ++i)
{
auto id = array[i].at(U("id")).as_string();
std::wcout << "\n" << id;
auto key = array[i].at(U("key")).as_string();
std::wcout << "\n" << key;
auto array2 = array[i].at(U("value")).as_array();
std::wcout << array2[0];
std::wcout << array2[1];
}
}
);
//close the connection
client.close().then([]() {
std::cout << "successfully close socket connction";
/* Successfully closed the connection. */
});
I have json response in my string body.but i dont know how to parse json data from websocket responses event. i want to display contacts from api responses.please help me..
MY JSON RESPONSES
--------------------------------------
.{"action":"refresh_dashboard","data":{"users_list":[{"user_id":"901e6076ff351cfc2195fb86f8438a26","extensions":["1002"],"name":"Karthik M"},{"user_id":"cc3f94ecc14ee9c55670dcde9adc1887","extensions":["1006"],"name":"Rounak S Kiran"},{"user_id":"6c29ebdb34e1761fdf9423c573087979","extensions":["1003"],"name":"Amar Nath"},{"user_id":"74d5b5a9aca1faa4c2f217ce87b621d8","extensions":["1008"],"name":"Robin Raju"},{"user_id":"a7ad7e73bf93ea83c8efdc1723cba198","extensions":["1007"],"name":"Arshad Arif"},{"user_id":"b55146df593ec8d09e5fe12a8a4c1108","extensions":["1001"],"name":"Rahib Rasheed"},{"user_id":"3258f7ae4ae1db60435cbcf583f64a89","extensions":["1009"],"name":"Test User"},{"user_id":"90bc84e5e8a3427fe35e99bd4386de95","extensions":["1010"],"name":"Prince T"},{"user_id":"b501ef5b270a196afc0eed557ca74237","extensions":["1005","+17325951060"],"name":"Jineed AJ"},{"user_id":"1422af351e06adeab2de92f5a633a444","extensions":["1004"],"name":"Ashok PA"}],"busy_users":[],"reg_users":[{"user_id":"cc3f94ecc14ee9c55670dcde9adc1887","status":"registered"},{"user_id":"901e6076ff351cfc2195fb86f8438a26","status":"registered"},{"user_id":"1422af351e06adeab2de92f5a633a444","status":"registered"},{"user_id":"3258f7ae4ae1db60435cbcf583f64a89","status":"registered"},{"user_id":"b55146df593ec8d09e5fe12a8a4c1108","status":"registered"},{"user_id":"6c29ebdb34e1761fdf9423c573087979","status":"registered"}],"contacts":[{"owner_id":"cc3f94ecc14ee9c55670dcde9adc1887","status":"ready"},{"owner_id":"901e6076ff351cfc2195fb86f8438a26","status":"ready"},{"owner_id":"1422af351e06adeab2de92f5a633a444","status":"ready"},{"owner_id":"3258f7ae4ae1db60435cbcf583f64a89","status":"ready"},{"owner_id":"b55146df593ec8d09e5fe12a8a4c1108","status":"ready"},{"owner_id":"6c29ebdb34e1761fdf9423c573087979","status":"ready"}]}}
I got the complete solution .please try to use boost pacakges from nuget. The documentation will help you to parse the json data from string. I think jsoncpp is not an updated packages available in the nuget.so please try boost packages available in the nuget.
MYJSON STRING
{"action":"refresh_dashboard","data":{"users_list":[{"user_id":"901e6076ff351cfc2195fb86f8438a26","extensions":["1002"],"name":"Karthik M"},{"user_id":"7d617ef5b2390d081d901b0d5cd108eb","extensions":["1015"],"name":"Synway User2"},{"user_id":"c8f667f7d663e81f6e7fa34b9296f067","extensions":["1012"],"name":"Rahib Video"},{"user_id":"cc3f94ecc14ee9c55670dcde9adc1887","extensions":["1006"],"name":"Rounak S Kiran"},{"user_id":"6c29ebdb34e1761fdf9423c573087979","extensions":["1003"],"name":"Amar Nath"},{"user_id":"8e15c2d95d4325cb07f0750846966be8","extensions":["1011"],"name":"TLS User"},{"user_id":"2fc4142bdacf83c1957bda0ad9d50e3d","extensions":["1014"],"name":"Synway User1"},{"user_id":"74d5b5a9aca1faa4c2f217ce87b621d8","extensions":["1008"],"name":"Robin Raju"},{"user_id":"a7ad7e73bf93ea83c8efdc1723cba198","extensions":["1007"],"name":"Arshad Arif"},{"user_id":"b55146df593ec8d09e5fe12a8a4c1108","extensions":["1001"],"name":"Rahib Rasheed"},{"user_id":"391391de005a8f5403c7b5591f462ea1","extensions":["1013"],"name":"Sangeeth J"},{"user_id":"3258f7ae4ae1db60435cbcf583f64a89","extensions":["1009"],"name":"Aby TL"},{"user_id":"90bc84e5e8a3427fe35e99bd4386de95","extensions":["1010"],"name":"Prince T"},{"user_id":"b501ef5b270a196afc0eed557ca74237","extensions":["1005"],"name":"Jineed AJ"},{"user_id":"1422af351e06adeab2de92f5a633a444","extensions":["1004"],"name":"Ashok PA"}],"busy_users":[],"reg_users":[{"user_id":"901e6076ff351cfc2195fb86f8438a26","status":"registered"},{"user_id":"6c29ebdb34e1761fdf9423c573087979","status":"registered"}],"contacts":[{"owner_id":"901e6076ff351cfc2195fb86f8438a26","status":"ready"},{"owner_id":"6c29ebdb34e1761fdf9423c573087979","status":"ready"}]}}
CODES
client.receive().then([](websocket_incoming_message msg) {
std::cout << "receiving data from socket";
// msg.message_type();
return msg.extract_string();
//1..i have one string
//cout<<"\n///////////test"<< msg.extract_string().get().c_str();
// // 2.convert to json array
//json::value::parse( ::to_string_t(msg.extract_string().get()))
//
}).then([](std::string body) {
//std::cout << "displaying the data";
std::cout << body << std::endl;
std::string ss = body;
ptree pt;
std::istringstream is(ss);
read_json(is, pt);
std::cout <<"\n 1st"<< "action: " << pt.get<std::string>("action") << "\n";
std::cout <<"\n 2nd"<< "data: " << pt.get<std::string>("data") << "\n";
std::cout << "--------------------------------------------------------------";
for (auto& e : pt.get_child("data.users_list")) {
std::cout << "\n" << "users id " << e.second.get<std::string>("user_id") << "\n";
}
});
useful resources
Parse JSON array as std::string with Boost ptree
C++ boost parse dynamically generated json string (not a file)