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。

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。

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。

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

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

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

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

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;
 }