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third_party_lib.cpp
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third_party_lib.cpp
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//
// third_party_lib.cpp
// ~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#include <array>
#include <asio.hpp>
#include <iostream>
#include <memory>
using asio::ip::tcp;
namespace third_party_lib {
// Simulation of a third party library that wants to perform read and write
// operations directly on a socket. It needs to be polled to determine whether
// it requires a read or write operation, and notified when the socket is ready
// for reading or writing.
class session
{
public:
session(tcp::socket &socket) : socket_(socket) {}
// Returns true if the third party library wants to be notified when the
// socket is ready for reading.
bool want_read() const { return state_ == reading; }
// Notify that third party library that it should perform its read
// operation.
void do_read(std::error_code &ec)
{
if (std::size_t len = socket_.read_some(asio::buffer(data_), ec)) {
write_buffer_ = asio::buffer(data_, len);
state_ = writing;
}
}
// Returns true if the third party library wants to be notified when the
// socket is ready for writing.
bool want_write() const { return state_ == writing; }
// Notify that third party library that it should perform its write
// operation.
void do_write(std::error_code &ec)
{
if (std::size_t len = socket_.write_some(asio::buffer(write_buffer_), ec)) {
write_buffer_ = write_buffer_ + len;
state_ = asio::buffer_size(write_buffer_) > 0 ? writing : reading;
}
}
private:
tcp::socket &socket_;
enum
{
reading,
writing
} state_ = reading;
std::array<char, 128> data_;
asio::const_buffer write_buffer_;
};
} // namespace third_party_lib
// The glue between asio's sockets and the third party library.
class connection : public std::enable_shared_from_this<connection>
{
public:
connection(tcp::socket socket) : socket_(std::move(socket)) {}
void start()
{
// Put the socket into non-blocking mode.
socket_.non_blocking(true);
do_operations();
}
private:
void do_operations()
{
auto self(shared_from_this());
// Start a read operation if the third party library wants one.
if (session_impl_.want_read() && !read_in_progress_) {
read_in_progress_ = true;
socket_.async_wait(tcp::socket::wait_read, [this, self](std::error_code ec) {
read_in_progress_ = false;
// Notify third party library that it can
// perform a read.
if (!ec)
session_impl_.do_read(ec);
// The third party library successfully
// performed a read on the socket. Start new
// read or write operations based on what it
// now wants.
if (!ec || ec == asio::error::would_block)
do_operations();
// Otherwise, an error occurred. Closing the
// socket cancels any outstanding
// asynchronous read or write operations. The
// connection object will be destroyed
// automatically once those outstanding
// operations complete.
else
socket_.close();
});
}
// Start a write operation if the third party library wants one.
if (session_impl_.want_write() && !write_in_progress_) {
write_in_progress_ = true;
socket_.async_wait(tcp::socket::wait_write, [this, self](std::error_code ec) {
write_in_progress_ = false;
// Notify third party library that it can
// perform a write.
if (!ec)
session_impl_.do_write(ec);
// The third party library successfully
// performed a write on the socket. Start new
// read or write operations based on what it
// now wants.
if (!ec || ec == asio::error::would_block)
do_operations();
// Otherwise, an error occurred. Closing the
// socket cancels any outstanding
// asynchronous read or write operations. The
// connection object will be destroyed
// automatically once those outstanding
// operations complete.
else
socket_.close();
});
}
}
private:
tcp::socket socket_;
third_party_lib::session session_impl_{socket_};
bool read_in_progress_ = false;
bool write_in_progress_ = false;
};
class server
{
public:
server(asio::io_context &io_context, unsigned short port) : acceptor_(io_context, {tcp::v4(), port}) { do_accept(); }
private:
void do_accept()
{
acceptor_.async_accept([this](std::error_code ec, tcp::socket socket) {
if (!ec) {
std::make_shared<connection>(std::move(socket))->start();
}
do_accept();
});
}
tcp::acceptor acceptor_;
};
int main(int argc, char *argv[])
{
try {
if (argc != 2) {
std::cerr << "Usage: third_party_lib <port>\n";
return 1;
}
asio::io_context io_context;
server s(io_context, std::atoi(argv[1]));
io_context.run();
} catch (std::exception &e) {
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}