Windows 中的 SO_REUSEADDR 和 UDP 行为 [英] SO_REUSEADDR and UDP behavior in Windows

问题描述

我知道在 *NIX 环境中将 SO_REUSEADDR 与 UDP 一起使用，其行为类似于多播，其中绑定到同一端口的多个客户端可以同时侦听和接收广播数据报.这也是 Windows 上的行为吗?

I'm aware that using SO_REUSEADDR with UDP in a *NIX environment, behaves like a multicast, where multiple clients bound to the same port can listen and receive broadcast datagrams simultaneously. Is this the behavior on Windows as well?

推荐答案

Windows 上绑定到同一端口的多个 UDP 套接字将一起接收广播数据包.

Multiple UDP sockets on Windows bound to the same port will all receive broadcast packets together.

这是一个演示程序，您可以使用 GCC 为 Windows 和 Linux 构建，并如上所述使用 Netcat 进行测试.在这两种系统中，当使用单播地址作为目标时，只有一个套接字(A 或 B)接收每个数据报.如果使用广播地址，则两个套接字都会收到消息.

Here's a demo program you can build for windows and Linux with GCC and test with Netcat as mentioned. In both systems, only one socket (either A or B) receives each datagram when a unicast address is used as the target. If a broadcast address is used then both sockets will receive the message.

/* Tested on linux and windows 7.
 * On windows use mingw-gcc:
 *    gcc -Wall -g -o udplisten udplisten.c -lws2_32
 * Test with:
 *    echo hello | netcat -u machinename 9898 (unicast)
 *    echo hello | netcat -u 172.16.255.255 9898 (broadcast)
 */
#ifdef WIN32
#include <winsock2.h>
#include <ws2tcpip.h>
#else
#include <sys/select.h>
#include <sys/socket.h>
#include <netinet/in.h>
#define SOCKET int
#define INVALID_SOCKET -1
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#undef max
#define max(x,y) ((x) > (y) ? (x) : (y))

static void
die(const char *str)
{
    perror(str);
    exit(1);
}

static SOCKET
mksocket(struct sockaddr_in *addr)
{
    SOCKET sock = INVALID_SOCKET;
    int opt = 1;
    if ((sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0)
        die("socket");
    if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (const char *)&opt, sizeof(opt)) < 0)
        die("setsockopt");
    if (bind(sock, (struct sockaddr *)addr, sizeof(struct sockaddr_in)) < 0)
        die("bind");
    return sock;
}

static void
process(SOCKET sock, const char *label)
{
    char buffer[8192];
    struct sockaddr_in caddr;
    socklen_t caddr_size = sizeof(caddr);
    memset(&caddr, 0, caddr_size);
    int count = recvfrom(sock, buffer, sizeof(buffer), 0,
                         (struct sockaddr *)&caddr, &caddr_size);
    if (count < 0) die(label);
    printf("%s %d '", label, count);
    fwrite(buffer, 1, count, stdout);
    printf("'\n");
}

int
main(int argc, char *argv[])
{
    struct sockaddr_in addr;
    SOCKET socka = INVALID_SOCKET, sockb = INVALID_SOCKET;
    fd_set read_set;
#ifdef WIN32
    WSADATA wsaData;
    if (WSAStartup(MAKEWORD(2,2), &wsaData))
        return -1;
#endif
    addr.sin_family = AF_INET;
    addr.sin_port = htons(9898);
    addr.sin_addr.s_addr = INADDR_ANY;

    socka = mksocket(&addr);
    sockb = mksocket(&addr);

    for (;;) {
        FD_ZERO(&read_set);
        FD_SET(socka, &read_set);
        FD_SET(sockb, &read_set);
        if (select(max(socka,sockb)+1, &read_set, NULL, NULL, NULL) < 0)
            die("select");
        if (FD_ISSET(socka, &read_set))
            process(socka, "A");
        if (FD_ISSET(sockb, &read_set))
            process(sockb, "B");
    }
    return 0;
}

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