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@djarek
Created Dec 6, 2018
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send_fd.cpp
#include <boost/asio/coroutine.hpp>
#include <boost/asio/local/connect_pair.hpp>
#include <boost/asio/local/stream_protocol.hpp>
#include <iostream>
#include <sys/wait.h>
std::size_t
send_fd(boost::asio::local::stream_protocol::socket& socket,
int fd,
boost::system::error_code& ec)
{
::msghdr msg{};
union {
::cmsghdr cmsghdr;
char control[CMSG_SPACE(sizeof(int))];
} cmsgu;
::iovec io = {.iov_base = (void*)"ABC", .iov_len = 3};
msg.msg_iov = &io;
msg.msg_iovlen = 1;
msg.msg_control = cmsgu.control;
msg.msg_controllen = sizeof(cmsgu.control);
::cmsghdr* cmsg = CMSG_FIRSTHDR(&msg);
cmsg->cmsg_len = CMSG_LEN(sizeof(int));
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
std::memcpy(CMSG_DATA(cmsg), &fd, sizeof(fd));
if (auto size = ::sendmsg(socket.native_handle(), &msg, 0); size < 0)
{
ec = {errno, boost::system::system_category()};
return 0;
}
else
{
return size;
}
}
std::size_t
read_fd(boost::asio::local::stream_protocol::socket& socket,
int& fd,
boost::system::error_code& ec)
{
::msghdr msg = {0};
char m_buffer[256];
::iovec io = {.iov_base = m_buffer, .iov_len = sizeof(m_buffer)};
msg.msg_iov = &io;
msg.msg_iovlen = 1;
union {
::cmsghdr cmsghdr;
char control[CMSG_SPACE(sizeof(int))];
} cmsgu;
msg.msg_control = &cmsgu;
msg.msg_controllen = sizeof(cmsgu.control);
if (auto size = ::recvmsg(socket.native_handle(), &msg, 0); size < 0)
{
ec = {errno, boost::system::system_category()};
return 0;
}
else
{
::cmsghdr* cmsg = CMSG_FIRSTHDR(&msg);
unsigned char* data = CMSG_DATA(cmsg);
std::memcpy(&fd, data, sizeof(fd));
return size;
}
}
struct child_op
{
std::unique_ptr<boost::asio::local::stream_protocol::socket> socket;
boost::asio::coroutine coro{};
void operator()(boost::system::error_code ec)
{
int fd;
BOOST_ASIO_CORO_REENTER(coro)
{
BOOST_ASIO_CORO_YIELD socket->async_wait(
boost::asio::socket_base::wait_read, std::move(*this));
if (ec)
{
std::cerr << "Child wait error: " << ec.message() << '\n';
return;
}
read_fd(*socket, fd, ec);
::write(fd, "hello", strlen("hello"));
::close(fd);
if (ec)
{
std::cerr << "Child read error: " << ec.message() << '\n';
return;
}
std::cout << "Child finished \n";
}
}
};
int
open_file(boost::system::error_code& ec)
{
auto fd = ::open("test.txt", O_APPEND | O_WRONLY | O_CREAT);
if (fd < 0)
ec = {errno, boost::system::system_category()};
else
ec = {};
return fd;
}
struct parent_op
{
std::unique_ptr<boost::asio::local::stream_protocol::socket> socket;
boost::asio::coroutine coro{};
void operator()(boost::system::error_code ec)
{
int fd;
BOOST_ASIO_CORO_REENTER(coro)
{
BOOST_ASIO_CORO_YIELD socket->async_wait(
boost::asio::socket_base::wait_write, std::move(*this));
if (ec)
{
std::cerr << "Parent wait_write error: " << ec.message()
<< '\n';
return;
}
fd = open_file(ec);
if (ec)
{
std::cerr << "Parent open_file error: " << ec.message() << '\n';
return;
}
send_fd(*socket, fd, ec);
if (ec)
{
std::cerr << "Parent send_fd error: " << ec.message() << '\n';
return;
}
::close(fd);
BOOST_ASIO_CORO_YIELD socket->async_wait(
boost::asio::socket_base::wait_read, std::move(*this));
if (ec)
{
std::cerr << "Parent wait_read error: " << ec.message() << '\n';
return;
}
}
}
};
void
do_fork(boost::asio::io_context& ctx, boost::system::error_code ec)
{
auto parent =
std::make_unique<boost::asio::local::stream_protocol::socket>(ctx);
auto child =
std::make_unique<boost::asio::local::stream_protocol::socket>(ctx);
boost::asio::local::connect_pair(*parent, *child);
ctx.notify_fork(boost::asio::execution_context::fork_prepare);
if (::pid_t pid = ::fork(); pid == 0)
{
ctx.notify_fork(boost::asio::execution_context::fork_child);
child_op{std::move(child)}(boost::system::error_code{});
}
else if (pid > 0)
{
ctx.notify_fork(boost::asio::execution_context::fork_parent);
parent_op{std::move(parent)}(boost::system::error_code{});
}
else
{
ec = {errno, boost::system::system_category()};
}
}
void
wait_for_children(boost::system::error_code& ec)
{
int status = 0;
for (;;)
{
if (::pid_t pid = ::wait(&status); pid < 0 && errno == ECHILD)
{
ec = {};
return;
}
else if (pid < 0)
{
ec = {errno, boost::system::system_category()};
return;
}
}
}
int
main()
{
boost::asio::io_context ctx;
boost::system::error_code ec;
do_fork(ctx, ec);
if (ec)
{
std::cerr << "Error, fork failed: " << ec.message() << '\n';
return 1;
}
ctx.run();
wait_for_children(ec);
if (ec)
{
std::cerr << "Error, waiting for children failed: " << ec.message()
<< '\n';
return 1;
}
}
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