原則上說，打洞伺服器應該是可以返回多個節點的，這裡為了簡化，只返回一個節點。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>

#include <list>
#include <ostream>
 

#include <algorithm>

#include "p2pServer.hpp"
namespace ShaCoin
{
    static std::list<Node> g_lstNode;

    static Node &GetQualityNode(std::list<Node> &lstNode, Node &node)
    {
        std::list<Node>::iterator it, next;
        for (it = lstNode.begin(); it != lstNode.end(); ++it)
        {
            if
 
 (*it == node)
                continue;

            return *it;
        }

        return node;
    }
}

using namespace ShaCoin;

int main(int argc, char **argv)
{
    NodeInfo nodeInfo;
    const unsigned long long nodeSize = sizeof(NodeInfo);
    memset(&nodeInfo, 0, nodeSize);

    char client_ip[16
 
] = { 0 };

    int sock = socket(AF_INET, SOCK_DGRAM, 0);
    if (sock < 0)
    {
        perror("socket");
        exit(1);
    }

    int val = 1;
    if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val)) < 0)
    {
        perror("setsockopt");
    }

    struct sockaddr_in local;
    local.sin_family = AF_INET;
    local.sin_port = htons(SERVERPORT);
    local.sin_addr.s_addr = htonl(INADDR_ANY);
    if (bind(sock, (struct sockaddr*)&local, sizeof(local)) < 0)
    {
        perror("bind");
        exit(2);
    }

    struct sockaddr_in client;
    socklen_t len = sizeof(client);
    while (1)
    {
        //讀取資料
        memset(&nodeInfo, 0, nodeSize);
        int r = recvfrom(sock, &nodeInfo, nodeSize, 0, (struct sockaddr*)&client, &len);
        if (r < 0)
        {
            perror("recvfrom");
            exit(3);
        }

        memset(client_ip, 0, sizeof(client_ip));
        inet_ntop(AF_INET, &client.sin_addr, client_ip, sizeof(client_ip));

        switch (nodeInfo.cmd)
        {
        case cmd_register:
            nodeInfo.node.count = 0;
            strcpy(nodeInfo.node.queryIp, client_ip);
            nodeInfo.node.queryPort = ntohs(client.sin_port);
            printf("query:%s:%d\n", nodeInfo.node.queryIp, nodeInfo.node.queryPort);
            printf("recv:%s:%d\n", nodeInfo.node.recvIp, nodeInfo.node.recvPort);
            if (g_lstNode.end() == std::find(g_lstNode.begin(), g_lstNode.end(), nodeInfo.node))
                g_lstNode.push_back(nodeInfo.node);
            if (sendto(sock, &nodeInfo, nodeSize, 0, (struct sockaddr*)&client, len) < 0)
            {
                perror("sendto");
                exit(4);
            }
            break;
        case cmd_unregister:
            g_lstNode.remove(nodeInfo.node);
            break;
        case cmd_getnode:
            if (g_lstNode.size() > 1)
            {
                Node recvNode = nodeInfo.node;
                memset(&nodeInfo, 0, nodeSize);
                nodeInfo.cmd = cmd_getnode;
                nodeInfo.node = GetQualityNode(g_lstNode, recvNode);
                ++nodeInfo.node.count;
                if (sendto(sock, &nodeInfo, nodeSize, 0, (struct sockaddr*)&client, len) < 0)
                {
                    perror("sendto");
                    exit(4);
                }
            }
            break;
        default:
            break;
        }
    }
    return 0;
}