关于socket组播和ssdp

Posted 2021-07-15 qianbo_insist

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1、说明

在制作的过程中，实际上ssdp发现协议特别简单，只是加入组播后，发送搜索的字符串，然后再在单播上接收，如果是发送，则要发送到多播地址，而且，发送的字符串不能出错，这里说明作者的一个错误，开始时，“MAN: “ssdp:discover”\\r\\n”，一直写成了"MAN: ssdp:discover\\r\\n"，所以在单播上没有收到数据，值得注意！

2、show me the code，以下用boost库来做组播的接收和发送

socket.bind(
udp::endpoint(boost::asio::ip::address_v4::any(),
receiver ? port /* same as multicast port /
: 6200 / any */));
以上这句话比较重要，在使用发送的时候，使用组播端口，接收的时候，使用本地的一个端口，切记！

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
// 3rd party includes.
#include <boost/asio.hpp>
#include <boost/thread.hpp>
#include <string>


static const char msearchmsgfmt[] = "M-SEARCH * HTTP/1.1\\r\\n"
"Connection: close"
"HOST: 239.255.255.250:1900\\r\\n"
"ST: %s\\r\\n"
"MAN: \\"ssdp:discover\\"\\r\\n"
"USER-AGENT: qbupnp 1.0"
"MX: 3\\r\\n\\r\\n";



void read(boost::asio::ip::udp::socket& socket)
    {
        boost::asio::ip::udp::endpoint sender;
        std::vector<char> buffer;
        std::size_t bytes_readable = 0;
        for (;;)
        {
            // Poll until data is available.
            while (!bytes_readable)
            {
                // Issue command to socket to get number of bytes readable.
                boost::asio::socket_base::bytes_readable num_of_bytes_readable(true);
                socket.io_control(num_of_bytes_readable);

                // Get the value from the command.
                bytes_readable = num_of_bytes_readable.get();

                // If there is no data available, then sleep.
                if (!bytes_readable)
                {
                    boost::this_thread::sleep(boost::posix_time::seconds(1));
                }
            }

            // Resize the buffer to store all available data.
            buffer.resize(bytes_readable);

            // Read available data.
            socket.receive_from(
                boost::asio::buffer(buffer, bytes_readable),
                sender);

            // Extract data from the buffer.
            std::string message(buffer.begin(), buffer.end());

            // Output data.
            std::cout << "Received message: ";
            std::cout << message << std::endl;
        }
    }

void write(boost::asio::ip::udp::socket& socket,
	boost::asio::ip::udp::endpoint& destination)
{
	std::string message;

	char buffer[256];
	sprintf(buffer, msearchmsgfmt, "upnp:rootdevice");
	/*socket.async_send_to(
		boost::asio::buffer(buffer, strlen(buffer)), endpoint_,
		boost::bind(handle_send_to, this,
			boost::asio::placeholders::error));*/

	for (unsigned int i = 0; i < 3; ++i)
	{
		//std::ostringstream stream;
		//stream << i;
		//message = stream.str();
		socket.send_to(boost::asio::buffer(msearchmsgfmt, strlen(msearchmsgfmt)), destination);
		std::cout << "Sent message: " << message << std::endl;
	}
}


int main(int argc, char* argv[])
{
    // Extract command-line arguments.
    bool receiver = false;// std::string(argv[1]) == "receive";
    boost::asio::ip::address address =
        boost::asio::ip::address::from_string("239.255.255.250");
    unsigned short port = 1900;  

    // Create socket.
    using boost::asio::ip::udp;
    boost::asio::io_service service;
    udp::socket socket(service);
    socket.open(boost::asio::ip::udp::v4());

    // Allow other processes to reuse the address, permitting other processes on
    // the same machine to use the multicast address.
    socket.set_option(udp::socket::reuse_address(true));

    
    socket.set_option(boost::asio::ip::multicast::enable_loopback(true));
    socket.bind(
        udp::endpoint(boost::asio::ip::address_v4::any(),
            receiver ? port /* same as multicast port */
            : 6200 /* any */));
    udp::endpoint destination(address, port);

    // Join group.
    namespace ip = boost::asio::ip;
    socket.set_option(ip::multicast::join_group(address));

    // Start read or write loops based on command line options.
    if (receiver) 
    	read(socket);
    else
        write(socket, destination);
    return 0;
}

3、有关于wireshark 抓包

注意使用port 1900 的包在局域网里面应该是有很多的，包含网关的，chrome 发送的ssdp，等等，读者可以适当自己过滤加上not host 192.168.0.1 诸如此类的网关过滤
在这里插入图片描述

4 、接下来使用http去接收和发送数据

建议
1 使用boost asio库直接接收发送，甚至直接使用asio
2 使用httplib接收发送
3 使用nlohmann 解析json
4 xml 库可以使用ixml，或者直接手动解析：
如何手动解析xml
以上为什么推荐使用httplib，和 nlohmann，这两个只要加入头文件即可，不用编译。为什么使用asio，可以直接使用头文件，简化加载库，以及asio封装得非常方便。