同步读写

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同步写write_some

boost::asio提供了几种同步写的api，write_some可以每次向指定的空间写入固定的字节数，如果写缓冲区满了，就只写一部分，返回写入的字节数。

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void  wirte_to_socket(asio::ip::tcp::socket& sock) {
	std::string buf = "Hello World!";
	std::size_t  total_bytes_written = 0;
	//循环发送
	//write_some返回每次写入的字节数
	//total_bytes_written是已经发送的字节数。
	//每次发送buf.length()- total_bytes_written)字节数据
	
	while (total_bytes_written != buf.length()) {
		total_bytes_written += sock.write_some(
			asio::buffer(buf.c_str()+total_bytes_written, 
				buf.length()- total_bytes_written));
	}
}

同步写send

write_some使用起来比较麻烦，需要多次调用，asio提供了send函数。send函数会一次性将buffer中的内容发送给对端，如果有部分字节因为发送缓冲区满无法发送，则阻塞等待，直到发送缓冲区可用，则继续发送完成。

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int send_data_by_send(){
	std::string raw_ip_address = "127.0.0.1";
	unsigned short port_num = 3333;

	try {
		asio::ip::tcp::endpoint
			ep(asio::ip::address::from_string(raw_ip_address),
				port_num);

		asio::io_service ios;

		// Step 1. Allocating and opening the socket.
		asio::ip::tcp::socket sock(ios, ep.protocol());

		sock.connect(ep);
		std::string buf = "Hello World!";
		int send_length = sock.send(asio::buffer(buf.c_str(), buf.length()));
		if (send_length <= 0) {
			cout << "send failed" << endl;
			return 0;
		}
	}
	catch (system::system_error& e) {
		std::cout << "Error occured! Error code = " << e.code()
			<< ". Message: " << e.what();

		return e.code().value();
	}
	return 0;
}

同步写write

类似send方法，asio还提供了一个write函数，可以一次性将所有数据发送给对端，如果发送缓冲区满了则阻塞，直到发送缓冲区可用，将数据发送完成。

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int send_data_by_wirte() {
	std::string raw_ip_address = "127.0.0.1";
	unsigned short port_num = 3333;

	try {
		asio::ip::tcp::endpoint
			ep(asio::ip::address::from_string(raw_ip_address),
				port_num);

		asio::io_service ios;

		// Step 1. Allocating and opening the socket.
		asio::ip::tcp::socket sock(ios, ep.protocol());

		sock.connect(ep);
		std::string buf = "Hello World!";
		int send_length  = asio::write(sock, asio::buffer(buf.c_str(), buf.length()));
		if (send_length <= 0) {
			cout << "send failed" << endl;
			return 0;
		}
	}
	catch (system::system_error& e) {
		std::cout << "Error occured! Error code = " << e.code()
			<< ". Message: " << e.what();

		return e.code().value();
	}
	return 0;
 }

同步读read_some

同步读和同步写类似，提供了读取指定字节数的接口read_some

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std::string read_from_socket(asio::ip::tcp::socket& sock) {
	const unsigned char MESSAGE_SIZE = 7;
	char buf[MESSAGE_SIZE];
	std::size_t total_bytes_read = 0;

	while (total_bytes_read != MESSAGE_SIZE) {
		total_bytes_read += sock.read_some(
			asio::buffer(buf + total_bytes_read,
				MESSAGE_SIZE - total_bytes_read));
	}

	return std::string(buf, total_bytes_read);
}


int read_data_by_read_some() {
	std::string raw_ip_address = "127.0.0.1";
	unsigned short port_num = 3333;

	try {
		asio::ip::tcp::endpoint
			ep(asio::ip::address::from_string(raw_ip_address),
				port_num);

		asio::io_service ios;

		asio::ip::tcp::socket sock(ios, ep.protocol());

		sock.connect(ep);

		read_from_socket(sock);
	}
	catch (system::system_error& e) {
		std::cout << "Error occured! Error code = " << e.code()
			<< ". Message: " << e.what();

		return e.code().value();
	}

	return 0;
}

同步读receive

可以一次性同步接收对方发送的数据

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int read_data_by_receive() {
	std::string raw_ip_address = "127.0.0.1";
	unsigned short port_num = 3333;

	try {
		asio::ip::tcp::endpoint
			ep(asio::ip::address::from_string(raw_ip_address),
				port_num);

		asio::io_service ios;

		asio::ip::tcp::socket sock(ios, ep.protocol());

		sock.connect(ep);
		const unsigned char BUFF_SIZE = 7;
		 char buffer_receive[BUFF_SIZE];
		int receive_length =  sock.receive(asio::buffer(buffer_receive, BUFF_SIZE));
		if (receive_length <= 0) {
			cout << "receive failed" << endl;
		}
	}
	catch (system::system_error& e) {
		std::cout << "Error occured! Error code = " << e.code()
			<< ". Message: " << e.what();

		return e.code().value();
	}

	return 0;
}

同步读read

可以一次性同步读取对方发送的数据

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int read_data_by_read() {
	std::string raw_ip_address = "127.0.0.1";
	unsigned short port_num = 3333;

	try {
		asio::ip::tcp::endpoint
			ep(asio::ip::address::from_string(raw_ip_address),
				port_num);

		asio::io_service ios;

		asio::ip::tcp::socket sock(ios, ep.protocol());

		sock.connect(ep);
		const unsigned char BUFF_SIZE = 7;
		char buffer_receive[BUFF_SIZE];
		int receive_length = asio::read(sock, asio::buffer(buffer_receive, BUFF_SIZE));
		if (receive_length <= 0) {
			cout << "receive failed" << endl;
		}
	}
	catch (system::system_error& e) {
		std::cout << "Error occured! Error code = " << e.code()
			<< ". Message: " << e.what();

		return e.code().value();
	}

	return 0;
 }

读取直到指定字符

我们可以一直读取，直到读取指定字符结束

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std::string  read_data_by_until(asio::ip::tcp::socket& sock) {
	asio::streambuf buf;

	// Synchronously read data from the socket until
	// '\n' symbol is encountered.  
	asio::read_until(sock, buf, '\n');

	std::string message;

	// Because buffer 'buf' may contain some other data
	// after '\n' symbol, we have to parse the buffer and
	// extract only symbols before the delimiter. 

	std::istream input_stream(&buf);
	std::getline(input_stream, message);
	return message;
 }