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//
// throttling_proxy.cpp
// ~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2023 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 <boost/asio.hpp>
#include <boost/asio/experimental/awaitable_operators.hpp>
#include <boost/asio/experimental/channel.hpp>
#include <iostream>
using boost::asio::as_tuple;
using boost::asio::awaitable;
using boost::asio::buffer;
using boost::asio::co_spawn;
using boost::asio::detached;
using boost::asio::experimental::channel;
using boost::asio::io_context;
using boost::asio::ip::tcp;
using boost::asio::steady_timer;
using boost::asio::use_awaitable;
namespace this_coro = boost::asio::this_coro;
using namespace boost::asio::experimental::awaitable_operators;
using namespace std::literals::chrono_literals;
using token_channel = channel<void(boost::system::error_code, std::size_t)>;
awaitable<void> produce_tokens(std::size_t bytes_per_token,
steady_timer::duration token_interval, token_channel& tokens)
{
steady_timer timer(co_await this_coro::executor);
for (;;)
{
co_await tokens.async_send(
boost::system::error_code{}, bytes_per_token,
use_awaitable);
timer.expires_after(token_interval);
co_await timer.async_wait(use_awaitable);
}
}
awaitable<void> transfer(tcp::socket& from,
tcp::socket& to, token_channel& tokens)
{
std::array<unsigned char, 4096> data;
for (;;)
{
std::size_t bytes_available = co_await tokens.async_receive(use_awaitable);
while (bytes_available > 0)
{
std::size_t n = co_await from.async_read_some(
buffer(data, bytes_available), use_awaitable);
co_await async_write(to, buffer(data, n), use_awaitable);
bytes_available -= n;
}
}
}
awaitable<void> proxy(tcp::socket client, tcp::endpoint target)
{
constexpr std::size_t number_of_tokens = 100;
constexpr size_t bytes_per_token = 20 * 1024;
constexpr steady_timer::duration token_interval = 100ms;
auto ex = client.get_executor();
tcp::socket server(ex);
token_channel client_tokens(ex, number_of_tokens);
token_channel server_tokens(ex, number_of_tokens);
co_await server.async_connect(target, use_awaitable);
co_await (
produce_tokens(bytes_per_token, token_interval, client_tokens) &&
transfer(client, server, client_tokens) &&
produce_tokens(bytes_per_token, token_interval, server_tokens) &&
transfer(server, client, server_tokens)
);
}
awaitable<void> listen(tcp::acceptor& acceptor, tcp::endpoint target)
{
for (;;)
{
auto [e, client] = co_await acceptor.async_accept(as_tuple(use_awaitable));
if (!e)
{
auto ex = client.get_executor();
co_spawn(ex, proxy(std::move(client), target), detached);
}
else
{
std::cerr << "Accept failed: " << e.message() << "\n";
steady_timer timer(co_await this_coro::executor);
timer.expires_after(100ms);
co_await timer.async_wait(use_awaitable);
}
}
}
int main(int argc, char* argv[])
{
try
{
if (argc != 5)
{
std::cerr << "Usage: throttling_proxy";
std::cerr << " <listen_address> <listen_port>";
std::cerr << " <target_address> <target_port>\n";
return 1;
}
io_context ctx;
auto listen_endpoint =
*tcp::resolver(ctx).resolve(argv[1], argv[2],
tcp::resolver::passive).begin();
auto target_endpoint =
*tcp::resolver(ctx).resolve(argv[3], argv[4]).begin();
tcp::acceptor acceptor(ctx, listen_endpoint);
co_spawn(ctx, listen(acceptor, target_endpoint), detached);
ctx.run();
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
}
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