Boost.Asio: Segmentation fault when sending too big message - c++

Question

My program saves some internal logs to a .txt file.
If you connect to it via TCP (SSL encrypted), the program will send the contents of the log file.
This is the code that is sending the data:
void NIUserSession::write(std::string message)
{
std::cout << "Writing message" << std::endl;
message.append("<EOF>");
boost::system::error_code ec;
boost::asio::async_write(this->socket_, boost::asio::buffer(message),
boost::asio::transfer_all(), boost::bind(&NIUserSession::writeHandler,
this, boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred()));
}
void NIUserSession::writeHandler(const boost::system::error_code &error, std::size_t bytes_transferred)
{
std::cout << "Write Handler" << std::endl;
if(error)
{
std::cout << "Write handler error: " << error.message() << std::endl;
this->disconnect();
}
}
So NIUserSession::write gets passed the logfile contents as string.
If the program is not running for a very long time the logfile is short and everything works fine. However, if it runs for a while and the log file gets longer and longer, the program will receive a SIGSEGV when it tries to send the data. This is the gdb log:
Writing message
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff4fe1700 (LWP 21047)]
__memcpy_sse2_unaligned () at ../sysdeps/x86_64/multiarch/memcpy-sse2-unaligned.S:33
33 ../sysdeps/x86_64/multiarch/memcpy-sse2-unaligned.S: No such file or directory.
(gdb) where
#0 __memcpy_sse2_unaligned () at ../sysdeps/x86_64/multiarch/memcpy-sse2-unaligned.S:33
#1 0x00007ffff7998454 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#2 0x00007ffff79985c3 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#3 0x00000000004b7eca in boost::asio::ssl::detail::io_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> >, boost::asio::ssl::detail::write_op<boost::asio::const_buffers_1>, boost::asio::detail::write_op<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> > >, boost::asio::const_buffers_1, boost::asio::detail::transfer_all_t, boost::_bi::bind_t<void, boost::_mfi::mf2<void, NIUserSession, boost::system::error_code const&, unsigned long>, boost::_bi::list3<boost::_bi::value<NIUserSession*>, boost::arg<1> (*)(), boost::arg<2> > > > >::operator()(boost::system::error_code, unsigned long, int) ()
#4 0x00000000004b8bf8 in boost::asio::detail::write_op<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> > >, boost::asio::const_buffers_1, boost::asio::detail::transfer_all_t, boost::_bi::bind_t<void, boost::_mfi::mf2<void, NIUserSession, boost::system::error_code const&, unsigned long>, boost::_bi::list3<boost::_bi::value<NIUserSession*>, boost::arg<1> (*)(), boost::arg<2> > > >::operator()(boost::system::error_code const&, unsigned long, int) ()
#5 0x00000000004b7e6c in boost::asio::ssl::detail::io_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> >, boost::asio::ssl::detail::write_op<boost::asio::const_buffers_1>, boost::asio::detail::write_op<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> > >, boost::asio::const_buffers_1, boost::asio::detail::transfer_all_t, boost::_bi::bind_t<void, boost::_mfi::mf2<void, NIUserSession, boost::system::error_code const&, unsigned long>, boost::_bi::list3<boost::_bi::value<NIUserSession*>, boost::arg<1> (*)(), boost::arg<2> > > > >::operator()(boost::system::error_code, unsigned long, int) ()
#6 0x00000000004b965c in boost::asio::detail::reactive_socket_send_op<boost::asio::mutable_buffers_1, boost::asio::detail::write_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> >, boost::asio::mutable_buffers_1, boost::asio::detail::transfer_all_t, boost::asio::ssl::detail::io_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> >, boost::asio::ssl::detail::write_op<boost::asio::const_buffers_1>, boost::asio::detail::write_op<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> > >, boost::asio::const_buffers_1, boost::asio::detail::transfer_all_t, boost::_bi::bind_t<void, boost::_mfi::mf2<void, NIUserSession, boost::system::error_code const&, unsigned long>, boost::_bi::list3<boost::_bi::value<NIUserSession*>, boost::arg<1> (*)(), boost::arg<2> > > > > > >::do_complete(boost::asio::detail::task_io_service*, boost::asio::detail::task_io_service_operation*, boost::system::error_code const&, unsigned long) ()
#7 0x00000000004add59 in boost::asio::detail::epoll_reactor::descriptor_state::do_complete(boost::asio::detail::task_io_service*, boost::asio::detail::task_io_service_operation*, boost::system::error_code const&, unsigned long) ()
#8 0x00000000004ad911 in boost::asio::detail::task_io_service::run(boost::system::error_code&) ()
#9 0x00000000004a9c1f in NetInterface::init() ()
#10 0x00007ffff641aa60 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#11 0x00007ffff566e184 in start_thread (arg=0x7ffff4fe1700) at pthread_create.c:312
#12 0x00007ffff5b8237d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
I don't understand why it is happening. Do I maybe have to give a size to boost::asio::buffer?
Also, io_service::run() is running in its own detached thread. Could this be a problem?

Answer 1

This is the common issue with asio usage. You are sending buffer using boost::asio::buffer(message), which does not copy the data. It just creating a reference for the data and you are responsible for this object (your message) lifetime until operation ends. But when you exit function NIUserSession::write all stack variables are destroyed, including your message.
To fix this you should place your data into a object with longer lifetime, for example into shared_ptr. Valid example can be something like this:
void NIUserSession::write(std::string &message_orig)
{
std::cout << "Writing message" << std::endl;
std::shared_ptr message = std::make_shared<std::string>( message_orig );
message->append("<EOF>");
boost::system::error_code ec;
boost::asio::async_write(this->socket_, boost::asio::buffer(*message),
boost::asio::transfer_all(), boost::bind(&NIUserSession::writeHandler,
this, boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred(),
message /* <- capture it into callback to guarantee lifetime */
));
}