错误接收UDP：连接被拒绝

问题描述

我试图通过UDP在特定端口的字符串HI发送到服务器，然后接收响应。然而，当我试图让响应使用recvfrom的（）我被卡在阻塞状态。我尝试使用UDP连接，但我得到了：

What could be the reasons for this? The server is not under my control, but I do know its working fine.

I have added the code

int sockfdudp;
char bufudp[MAXDATASIZE], port[6];
struct addrinfo hints, *servinfo, *p;
struct sockaddr_storage addr;
int rv;
char s[INET6_ADDRSTRLEN];
int bytes_recv, bytes_sent;
socklen_t len;

scanf("%s",port);
printf("UDP Port: %s \n", port);

// Start connecting to datagram server
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_DGRAM;

if ((rv = getaddrinfo(SERVER_NAME, port, &hints, &servinfo)) != 0) {
    fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
    return 1;
}

// loop through all the results and make a socket
for(p = servinfo; p != NULL; p = p->ai_next) {
    if ((sockfdudp = socket(p->ai_family, p->ai_socktype,
            p->ai_protocol)) == -1) {
        perror("Creating datagram socket");
        continue;
    }

if (connect(sockfdudp, p->ai_addr, p->ai_addrlen) == -1) {
        close(sockfdudp);
        perror("Connecting stream socket");
        continue;
    }
    break;
}

if (p == NULL) {
    fprintf(stderr, "ClientUDP: failed to bind socket\n");
    return 2;
}


freeaddrinfo(servinfo);

if ((bytes_sent = sendto(sockfdudp, UDP_MSG, strlen(UDP_MSG), 0, p->ai_addr, p->ai_addrlen)) == -1) {
    perror("ClientUDP: Error sending data");
    exit(1);
}
printf("Data %s sent\n", UDP_MSG );

len = sizeof(struct sockaddr_storage);

if ((bytes_recv = recvfrom(sockfdudp, bufudp, MAXDATASIZE-1, 0,(struct sockaddr*)&addr, &len)) == -1) {
    perror("Error receiving in UDP");
    exit(1);
}

printf("Bytes recv %d\n", bytes_recv);

bufudp[bytes_recv] = '\0';

printf("ClientUDP: Received\n %s \n",bufudp );

close(sockfdudp);

return 0;

解决方案

Chances are your're sending something to a server who does not listen on that particular port.That would cause an icmp message to be sent back , and your next recvfrom will return an error in the case where you connect the socket.

Check with tcpdump or wireshark what's going on on the wire.

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