I have an scenario where I need to be both client and server and we can receive/send data in any possible direction.
This is pretty standard for a networked application.
The chat server seems a good example to start with (since it does send/receive in all directions): https://www.boost.org/doc/libs/1_75_0/doc/html/boost_asio/examples/cpp11_examples.html#boost_asio.examples.cpp11_examples.chat
Now, as barebones example of a server that also initiates outgoing connections:
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Let's create a server that spawns an async session for each accepted
connection. Each session is a "reverse echo" service.
// echo server, multi-client
spawn(io, [&io](ba::yield_context yc) {
tcp::acceptor acc(io, {{}, 6868});
acc.set_option(tcp::acceptor::reuse_address(true));
while (true) {
tcp::socket s(io);
acc.async_accept(s, yc);
spawn(yc, [s = std::move(s)]
(ba::yield_context yc) mutable {
log("Connection from ", s.remote_endpoint());
std::string msg;
while (auto n = async_read_until(s, ba::dynamic_buffer(msg), "
", yc)) {
std::string_view vw(msg.data(), n);
vw.remove_suffix(1); // leave '
'
log("Responding to ", std::quoted(vw));
std::reverse(msg.data(), msg.data() + vw.size());
async_write(s, ba::buffer(msg, n), yc);
msg = msg.substr(n);
}
});
}
});
Simultaneously, let's run 5 clients. For want of an external server, we'll just make them connect to our own server.
That allows us to have a self-contained demo, and will prove that the single-threading is not leading to any blocking.
// a random client, let's make it connect to our own server, just for this demo
for (auto client_id = 0; client_id<5; ++client_id) {
spawn(io,
[&io, delay, client_id, log=logger("client #" + std::to_string(client_id))]
(ba::yield_context yc) {
tcp::resolver r(io);
tcp::socket s(io);
async_connect(s, r.async_resolve("127.0.0.1", "6868", yc), yc);
while (true) {
delay(yc);
ba::streambuf buf;
std::ostream(&buf)
<< "Hello from client #" << client_id << "
";
async_write(s, buf, yc);
std::string response;
async_read_until(s, ba::dynamic_buffer(response), "
", yc);
if (!response.empty())
response.pop_back();
log("Received response ", std::quoted(response));
}
});
}
Where delay is a random delay (500..1500ms):
auto delay = [&io](ba::yield_context yc) {
ba::steady_timer(io, 500ms + (prng() % 1000) * 1ms)
.async_wait(yc);
};
We run the whole program for 3 seconds, and quit:
io.run_for(3s);
logger("main")("Bye");
Prints
at 0ms session #0 Connection from 127.0.0.1:51024
at 1ms session #1 Connection from 127.0.0.1:51026
at 1ms session #2 Connection from 127.0.0.1:51028
at 1ms session #3 Connection from 127.0.0.1:51030
at 1ms session #4 Connection from 127.0.0.1:51032
at 831ms session #3 Responding to "Hello from client #3"
at 831ms client #3 Received response "3# tneilc morf olleH"
at 1148ms session #4 Responding to "Hello from client #4"
at 1148ms client #4 Received response "4# tneilc morf olleH"
at 1196ms session #1 Responding to "Hello from client #1"
at 1196ms client #1 Received response "1# tneilc morf olleH"
at 1327ms session #0 Responding to "Hello from client #0"
at 1327ms client #0 Received response "0# tneilc morf olleH"
at 1401ms session #2 Responding to "Hello from client #2"
at 1401ms client #2 Received response "2# tneilc morf olleH"
at 1446ms session #3 Responding to "Hello from client #3"
at 1446ms client #3 Received response "3# tneilc morf olleH"
at 1836ms session #4 Responding to "Hello from client #4"
at 1836ms client #4 Received response "4# tneilc morf olleH"
at 2163ms session #0 Responding to "Hello from client #0"
at 2163ms client #0 Received response "0# tneilc morf olleH"
at 2382ms session #2 Responding to "Hello from client #2"
at 2383ms client #2 Received response "2# tneilc morf olleH"
at 2426ms session #3 Responding to "Hello from client #3"
at 2426ms client #3 Received response "3# tneilc morf olleH"
at 2444ms session #4 Responding to "Hello from client #4"
at 2444ms client #4 Received response "4# tneilc morf olleH"
at 2579ms session #1 Responding to "Hello from client #1"
at 2580ms client #1 Received response "1# tneilc morf olleH"
at 3002ms main Bye
Full Listing
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#include <boost/asio/detail/handler_alloc_helpers.hpp>
#include <boost/system/system_error.hpp>
#define BOOST_BIND_NO_PLACEHOLDERS
#include <boost/asio.hpp>
#include <boost/asio/spawn.hpp>
#include <iostream>
#include <iomanip>
#include <thread>
#include <chrono>
#include <random>
namespace ba = boost::asio;
using ba::ip::tcp;
using namespace std::literals;
static auto const now = &std::chrono::steady_clock::now;
static auto const start = now();
auto logger(std::string name) {
return [name](auto const&... args) {
((std::cout << "at" << std::setw(6) << (now() - start)/1ms << "ms"
<< name << "")
<< ... << args) << std::endl;
};
}
int main() {
ba::io_context io;
static std::mt19937 prng { std::random_device{}() };
// insert random async delays
auto delay = [&io](auto yc) {
ba::steady_timer(io, 500ms + (prng() % 1000) * 1ms)
.async_wait(yc);
};
// echo server, multi-client
spawn(io, [&io, log=logger("accept")](ba::yield_context yc) {
tcp::acceptor acc(io, {{}, 6868});
acc.set_option(tcp::acceptor::reuse_address(true));
auto num_clients = 0;
while (true) {
tcp::socket s(io);
acc.async_accept(s, yc);
spawn(yc, [s = std::move(s), log=logger("session #" + std::to_string(num_clients++))]
(ba::yield_context yc) mutable {
log("Connection from ", s.remote_endpoint());
std::string msg;
while (auto n = async_read_until(s, ba::dynamic_buffer(msg), "
", yc)) {
std::string_view vw(msg.data(), n);
vw.remove_suffix(1); // leave '
'
log("Responding to ", std::quoted(vw));
std::reverse(msg.data(), msg.data() + vw.size());
async_write(s, ba::buffer(msg, n), yc);
msg = msg.substr(n);
}
});
}
});
// a random client, let's make it connect to our own server, just for this demo
for (auto client_id = 0; client_id<5; ++client_id) {
spawn(io,
[&io, delay, client_id, log=logger("client #" + std::to_string(client_id))]
(ba::yield_context yc) {
tcp::resolver r(io);
tcp::socket s(io);
async_connect(s, r.async_resolve("127.0.0.1", "6868", yc), yc);
while (true) {
delay(yc);
ba::streambuf buf;
std::ostream(&buf)
<< "Hello from client #" << client_id << "
";
async_write(s, buf, yc);
std::string response;
async_read_until(s, ba::dynamic_buffer(response), "
", yc);
if (!response.empty())
response.pop_back();
log("Received response ", std::quoted(response));
}
});
}
io.run_for(3s);
logger("main")("Bye");
}
