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c++ asio beast http networking

cpp: c++ network silice

Created on Oct 9, 2024

cpp boost::asio, boost::beast networking silice

c++ boost::asio, boost::beast networking silice

boost::asio, boost::beast, async

boost::asio::ip::tcp::resolver

The tcp resolver type. 

resolver.async_resolve(...

Asynchronous perform forward or reverse resolution of a query or an endpoint to entries.

Commonly used on client side.

boost::asio::ip::tcp::acceptor

The tcp acceptor type. 

acceptor.async_accept(...

Asynchronous start an accept.

Commonly used on server side.

boost::beast::tcp_stream

A TCP/IP stream socket with timeouts and a polymorphic executor.

Commonly used on both server side and client side.

__tcp_stream.async_connect 

__tcp_stream.async_connect(ep_or_ep_sequence_or_ep_iterators, ...

Connect the stream to the specified endpoint asynchronously.

Commonly used on client side.

http::async_write 

http::async_write(...

Write a complete message to a stream asynchronously.

Commonly used on both server side and client side.

http::async_read 

http::async_read(...

Read a complete message from a stream asynchronously.

Commonly used on both server side and client side.

Async Server Side Http (silice)

Server side code can be divided into two stages:

  1. acceptor looper
    • boost::asio::ip::tcp::acceptor
  2. session
    • tcp::socket to boost::beast::tcp_stream, and commuicates with the client side.

cpp example

c++ example 

#include <boost/asio.hpp>
#include <boost/beast.hpp>
#include <iostream>

using std::string_literals::operator""s;

namespace asio = boost::asio;
namespace beast = boost::beast;
namespace http = beast::http;
using asio::ip::tcp;

namespace space
{

class http_session:
	virtual public std::enable_shared_from_this<
		space::http_session
	>
{
protected:
	beast::tcp_stream __tcp_stream;
	http::request<http::string_body> __request;
	http::response<http::string_body> __response;
	beast::flat_buffer __buffer;
public:
	virtual ~http_session()
	{
		__tcp_stream.close();
		std::clog << "Session is ended.\n";
	}
public:
	http_session(tcp::socket && socket__):
		__tcp_stream{std::move(socket__)}
	{
		std::clog << "Session is started.\n";
	}
public:
	void run()
	{
		std::cout << "Session is running ...\n";
		this->read_write();
	}
protected:
	void read_write()
	{
		this->read();
	}
	void read()
	{
		http::async_read(
			__tcp_stream,
			__buffer,
			__request,
			[self=this->shared_from_this()] (std::error_code ec, unsigned long bytes)
			{
				if (ec)
					throw std::system_error{ec, "http::asyn_read error."};
				std::clog << "Request read: " << bytes << " bytes.\n";
				self->write();
			}
		);
	}
	void write()
	{
		__response.body() = "<html><body>Hello, c++ http server!</body></html>";
		__response.keep_alive(__request.keep_alive());
		http::async_write(
			__tcp_stream,
			__response,
			[self=this->shared_from_this()] (std::error_code ec, unsigned long bytes)
			{
				if (ec)
					throw std::system_error{ec, "http::async write error."};
				std::clog << "Response written: " << bytes << " bytes.\n";
			}
		);
	}
};

class http_server:
	virtual public std::enable_shared_from_this<
		space::http_server
	>
{
protected:
	asio::io_context __io_ctx;
	const std::string __address;
	const unsigned short __port;
	tcp::acceptor __acceptor;
	http::request<http::string_body> __request;
	http::response<http::string_body> __response;
public:
	virtual ~http_server()
	{
	}
public:
	http_server(
		const std::string_view address__,
		const unsigned short port__
	):
		__io_ctx{},
		__address{address__},
		__port{port__},
		__acceptor{
			__io_ctx,
			tcp::endpoint{
				asio::ip::make_address(__address),
				__port
			}
		}
	{
	}
public:
	void run()
	{
		this->start();
		__io_ctx.run();
	}
protected:
	void start()
	{
		this->accept();
	}
	void accept()
	{
		__acceptor.async_accept(
			[self=this->shared_from_this()] (std::error_code ec, tcp::socket socket)
			{
				if (ec)
					throw std::system_error{ec, "Accept Error."};
				std::clog << "Accept OK.\n";
				std::make_shared<space::http_session>(std::move(socket))->run();
				self->accept();
			}
		);
	}
};

}	// namespace space

int main(int argc, char * argv[])
try
{
	if (argc != 3)
		throw std::runtime_error{""s + argv[0] + " <bind address> <bind port>"};

	std::make_shared<space::http_server>(argv[1], std::stoi(argv[2]))->run();
}
catch (const std::exception & e)
{
	std::cerr << "ERROR:\n" << e.what() << std::endl;
}

Async Client Side Http (silice)

Client side code can be divided into some stages:

  1. Resolve
    • resolver.resolve
  2. Connect
    • tcp_stream.async_connect
  3. Write Request
  4. Read Response

cpp example

c++ example 

#include <boost/beast.hpp>
#include <boost/asio.hpp>
#include <iostream>

namespace asio = boost::asio;
namespace beast = boost::beast;
namespace http = beast::http;
using asio::ip::tcp;

using std::string_literals::operator""s;

namespace space
{

class http_client_session:
	virtual public std::enable_shared_from_this<
		space::http_client_session
	>
{
protected:
	asio::io_context __io_ctx;
	const std::string __target;
	const std::string __protocol;
	tcp::resolver __resolver;
	beast::tcp_stream __tcp_stream;
	http::request<http::string_body> __request;
	http::response<http::string_body> __response;
	beast::flat_buffer __buffer;
public:
	virtual ~http_client_session()
	{
	}
public:
	http_client_session(const std::string_view target__, const std::string_view protocol__):
		__io_ctx{},
		__target{target__},
		__protocol{protocol__},
		__resolver{__io_ctx},
		__tcp_stream{__io_ctx}
	{
	}
public:
	void run()
	{
		this->start();
		__io_ctx.run();
	}
protected:
	void start()
	{
		this->resolve();
	}
	void resolve()
	{
		__resolver.async_resolve(
			__target,
			__protocol,
			[self=this->shared_from_this()] (
				std::error_code ec,
				tcp::resolver::results_type results
			)
			{
				if (ec)
					throw std::system_error{ec, "__resolver.async_resolve Error."};
				std::clog << "Resolve OK.\n";
				self->connect(std::move(results));
			}
		);
	}
	void connect(tcp::resolver::results_type && results__)
	{
		__tcp_stream.expires_after(std::chrono::seconds(3));
		__tcp_stream.async_connect(
			results__,
			[self=this->shared_from_this()] (
				std::error_code ec,
				tcp::endpoint ep
			)
			{
				if (ec)
					throw std::system_error{ec, "__tcp_stream.async_connect error."};
				std::clog << "Connect OK.\n";
				self->write_read();
			}
		);
	}
protected:
	void write_read()
	{
		this->write();
	}
	void write()
	{
		__request.method(http::verb::get);
		__request.set(http::field::host, __target);
		__request.target("/");
		__tcp_stream.expires_after(std::chrono::seconds(3));
		http::async_write(
			__tcp_stream,
			__request,
			[self=this->shared_from_this()] (
				std::error_code ec,
				unsigned long bytes
			)
			{
				if (ec)
					throw std::system_error{ec, "http::async_write error."};
				self->read();
			}
		);
	}
	void read()
	{
		__tcp_stream.expires_after(std::chrono::seconds(3));
		http::async_read(
			__tcp_stream,
			__buffer,
			__response,
			[self=this->shared_from_this()] (
				std::error_code ec,
				unsigned long bytes
			)
			{
				if (ec)
					throw std::system_error{ec, "http::async_read error."};
				std::cout << self->__response.body() << std::endl;
			}
		);
	}
};	// class http_client_session

}	// namespace space

int main(int argc, char * argv[])
try
{
	if (argc != 3)
		throw std::runtime_error{""s + argv[0] + " <remote host> <protocol (a port number)>"};
	std::make_shared<space::http_client_session>(argv[1], argv[2])->run();
}
catch (const std::exception & e)
{
	std::cerr << "ERROR:\n" << e.what() << std::endl;
}

c++ boost::asio Coroutines

cpp coroutines

c++ coroutines

asio::co_spawn

boost::asio::co_spawn

Spawn a new coroutine-based thread of execution. 

asio::co_spawn(x__, awaitable__, token__ = DEFAULT, constraint__ = 0);

asio::awaitable<value_type, executor_type>

The return type of a coroutine

asio::use_awaitable

A completion token object that reprensents the currently executing coroutine.

asio::this_coro::executor

As the name described, asio::this_coro::executor is an awaitable object that returns the executor of the current coroutine.

co_await asio::this_coro::executor; gets the executor that the awaitable object returns.

How

Get it step by step

-)

First of all, all coroutines can not be used directly in main:

A coroutine execution thread must be spawned as the start point of all other coroutines, which is done by boost::asio::co_spawn.

main calls asio::co_spawn, asio::co_spawn calls coroutines. 

boost::asio::co_spawn(io_context, yyzz, asio::detached);
io_context.run();

boost::asio::co_spawn(io_context, yyzz(), asio::detached);
io_context.run();

Both work.

Both yyzz and yyzz() are not actual value. Their relationships are:

lambda returns awaitable object,

awaitable object returns actual value .

-)

The return type of a coroutine is boost::asio::awaitable, and can not be auto-deduced.

EX.: 

class server
{
public:
	asio::awaitable<void> run()
	{
		co_return;
	}
};

-)

completion-token: boost::asio::use_awaitable

In most cases, boost::asio::use_awaitable takes the handler place, as a completion token. And then the calling returns an awaitable object.

EX.: 

auto awaitable_object = http::async_write(
	tcp_stream,
	request,
	boost::asio::use_awaitable
);

co_await awaitable_object;

In most cases, we do not want the awaitable object, we want the actual object, then: 

unsigned long bytes = co_await http::async_write(tcp_stream, request, asio::use_awaitable);

Further on, we don't need both, we only need the write action: 

co_await http::async_write(tcp_stream, request, asio::use_awaitable);

The boost::asio::use_awaitable takes pace of the async handler, the async handler: 

http::async_write(
	tcp_stream,
	request,
	[] (std::error_code ec, unsigned long byte)	// This lambda is the so-called handler.
	{
		if (! ec)	// if no error
			...
	}
);

-)

asio::this_coro::executor

As the name described, get the executor from this-coro, it returns an awaitable object, we need to get the executor from the awaitable object further on: 

auto executor = co_await asio::this_coro::executor;

But be careful, co_await can not be used as the constructor parameter.

-) Compare them, do not be confused:

Async Server Side Http (silice: if coroutines)

Server side code can be divided into two stages:

  1. acceptor looper
    • boost::asio::ip::tcp::acceptor
  2. session
    • tcp::socket to boost::beast::tcp_stream, and commuicates with the client side.

Server side example

Server side c++ example code. 

#include <boost/asio.hpp>
#include <boost/asio/detached.hpp>
#include <iostream>
#include <memory>
#include <boost/beast.hpp>

using std::string_literals::operator""s;

namespace space
{

class http_session:
	virtual public std::enable_shared_from_this<space::http_session>
{
protected:
	boost::beast::tcp_stream __stream;
protected:
	boost::beast::http::request<boost::beast::http::string_body> __request;
	boost::beast::http::response<boost::beast::http::string_body> __response;
	boost::beast::flat_buffer __buffer;
public:
	virtual ~http_session()
	{
		__stream.close();
		std::cout << "Session is ended.\n";
	}
public:
	http_session(boost::asio::ip::tcp::socket && socket__):
		__stream{std::move(socket__)}
	{
		std::cout << "Session is created.\n";
	}
public:
	boost::asio::awaitable<void> run()
	{
		co_await this->read_write();
	}
	boost::asio::awaitable<void> read_write()
	{
		co_await boost::beast::http::async_read(__stream, __buffer, __request, boost::asio::use_awaitable);
		
		__response.body() = R"(
			<html>
			<head>
				<title>Hello, c++!</title>
			</head>
			<body>
				<h1>Hello, c++ !!</h1>
			</body>
			</html>
		)";
		co_await boost::beast::http::async_write(__stream, __response, boost::asio::use_awaitable);
	}
};	// class http_session

class http_server:
	virtual public std::enable_shared_from_this<
		space::http_server
	>
{
protected:
	const std::string __address;
	const unsigned short __port;
	boost::asio::ip::tcp::acceptor __acceptor;
public:
	virtual ~http_server()
	{
	}
public:
	http_server(
		auto executor,
		const std::string_view address__,
		const unsigned short port__
	):
		__address{address__},
		__port{port__},
		__acceptor{
			executor,
			boost::asio::ip::tcp::endpoint{
				boost::asio::ip::make_address(__address),
				__port
			}
		}
	{
	}
public:
	boost::asio::awaitable<void> operator()()
	{
		co_return;
	}
public:
	boost::asio::awaitable<void> run()
	{
		co_await this->accept();
	}
	boost::asio::awaitable<void> accept()
	{
		boost::asio::ip::tcp::socket socket = co_await __acceptor.async_accept(boost::asio::use_awaitable);
		co_await std::make_shared<space::http_session>(std::move(socket))->run();
		co_await this->accept();
	}
};	// class http_server

}	// namespace space

int main(int argc, char * argv[])
try
{
	if (argc != 3)
		throw std::runtime_error{""s + argv[0] + " <bind address> <bind port>"};
	auto io_context = boost::asio::io_context{};
	boost::asio::co_spawn(
		io_context,
		[] (const std::string_view host, const unsigned short port) -> boost::asio::awaitable<void>
		{
			co_await
			std::make_shared<space::http_server>(
				co_await boost::asio::this_coro::executor,
				host,
				port
			)
			->run();
		}
		(argv[1], static_cast<unsigned short>(std::stoi(argv[2]))),
		boost::asio::detached
	);
	io_context.run();
}
catch (const std::exception & e)
{
	std::cerr << "ERROR:\n" << e.what() << std::endl;
}

Async Client Side Http (silice: if coroutines)

Client side code can be divided into some stages:

  1. Resolve
    • resolver.resolve
  2. Connect
    • tcp_stream.async_connect
  3. Write Request
  4. Read Response

Client side example

Client side c++ example code.

(exceptions or error codes might not work) 

#include <boost/beast.hpp>
#include <boost/asio.hpp>
#include <boost/asio/detached.hpp>
#include <boost/asio/co_spawn.hpp>
#include <iostream>

namespace asio = boost::asio;
namespace beast = boost::beast;
namespace http = beast::http;
using asio::ip::tcp;

using std::string_literals::operator""s;

namespace space
{

class http_session:
	virtual public std::enable_shared_from_this<
		space::http_session
	>
{
protected:
	const std::string __target;
	const std::string __protocol;
	asio::ip::tcp::resolver __resolver;
	beast::tcp_stream __stream;
protected:
	http::request<http::string_body> __request;
	http::response<http::string_body> __response;
	beast::flat_buffer __buffer;
public:
	virtual ~http_session()
	{
		__stream.close();
	}
public:
	http_session(auto executor__, const std::string_view target__, const std::string_view protocol__):
		__target{target__},
		__protocol{protocol__},
		__resolver{executor__},
		__stream{executor__}
	{
	}
public:
	asio::awaitable<void> run()
	{
		co_await this->Run();
	}
protected:
	asio::awaitable<void> Run()
	{
		tcp::resolver::results_type results = co_await this->resolve();
		[[maybe_unused]] tcp::endpoint ep = co_await this->connect(std::move(results));
		co_await this->write_read();
	}
protected:
	asio::awaitable<tcp::resolver::results_type> resolve()
	{
		co_return co_await __resolver.async_resolve(
			__target,
			__protocol,
			asio::use_awaitable
		);
	}
	asio::awaitable<tcp::endpoint> connect(tcp::resolver::results_type && results)
	{
		__stream.expires_after(std::chrono::seconds(3));
		co_return co_await __stream.async_connect(results, asio::use_awaitable);
	}
	asio::awaitable<void> write_read()
	{
		__request.method(http::verb::get);
		__request.version(11);
		__request.target("/");
		__request.set(http::field::host, __target);

		__stream.expires_after(std::chrono::seconds(3));
		co_await http::async_write(__stream,  __request, asio::use_awaitable);
		__stream.expires_after(std::chrono::seconds(3));
		co_await http::async_read(__stream, __buffer, __response, asio::use_awaitable);

		if (true)
		{
			std::cout << __response.body() << std::endl;
		}
		else
		{
			std::cout << __response << std::endl;	// works too.
			std::cout << __response.body().data() << std::endl;	// works too.
		}
	}
};

}	// namespace space

int main(int argc, char * argv[])
try
{
	if (argc != 3)
		throw std::runtime_error{""s + argv[0] + " <remote host> <remote port>"};

	auto io_context = asio::io_context{};

	asio::co_spawn(
		io_context,
		[&] -> asio::awaitable<void>
		{
			co_await
			std::make_shared<space::http_session>(co_await asio::this_coro::executor, argv[1], argv[2])->run();
		},
		asio::detached
	);

	io_context.run();
}
catch (const std::exception & e)
{
	std::cerr << "ERROR:\n" << e.what() << std::endl;
}

See Also

boost::asio

boost::beast

cpp/c++

c++ std::exception:

std::cout.write(err.data(), err.size());

std::cout << std::endl;

caught: 

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