错误接收UDP：连接被拒绝 [英] Error receiving in UDP: Connection refused

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：

  

错误接收UDP：连接被拒绝。

可能是什么这方面的原因？服务器是不是我的控制之下，但我知道它的工作的罚款。

我已经加入了code

  INT sockfdudp;
烧焦bu​​fudp [MAXDATASIZE]，口岸[6];
结构addrinfo中的提示，* servinfo，* P;
结构sockaddr_storage地址;
INT RV;
个char [INET6_ADDRSTRLEN]
INT bytes_recv，bytes_sent;
socklen_t的LEN;scanf函数（％S，口）;
的printf（UDP端口：％S \\ n，口）;//开始连接报服务器
memset的（安培;提示，0，sizeof的提示）;
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_DGRAM;如果（（RV =的getaddrinfo（SERVER_NAME，端口＆放大器;提示，＆放大器;！servinfo））= 0）{
    fprintf中（标准错误的getaddrinfo：％S \\ n，gai_strerror（RV））;
    返回1;
}//通过所有的结果循环，使插座
为（P = servinfo; P！= NULL; P = P-＆GT; ai_next）{
    如果（（sockfdudp =插座（对GT; ai_family，P-＆GT; ai_socktype，
            P-＆GT; ai_protocol））== -1）{
        PERROR（创建数据报套接字）;
        继续;
    }如果（连接（sockfdudp，P-＆GT; ai_addr，P-＆GT; ai_addrlen）== -1）{
        关闭（sockfdudp）;
        PERROR（连接流套接字）;
        继续;
    }
    打破;
}如果（P == NULL）{
    fprintf中（标准错误，ClientUDP：无法绑定套接字\\ n）;
    返回2;
}
freeaddrinfo（servinfo）;如果（（bytes_sent = SENDTO（sockfdudp，UDP_MSG，strlen的（UDP_MSG），0，p型＆GT; ai_addr，P-＆GT; ai_addrlen））== -1）{
    PERROR（ClientUDP：错误发送数据）;
    出口（1）;
}
的printf（数据％S发出\\ n，UDP_MSG）;LEN = sizeof的（结构sockaddr_storage）;如果（（bytes_recv = recvfrom的（sockfdudp，bufudp，MAXDATASIZE-1，0，（结构sockaddr *）及地址，和放大器; LEN））== -1）{
    PERROR（错误接收UDP）;
    出口（1）;
}的printf（字节的recv％d个\\ N，bytes_recv）;bufudp [bytes_recv] ='\\ 0';的printf（ClientUDP：收到\\ n％S \\ n，bufudp）;关闭（sockfdudp）;返回0;
 

解决方案

机会是your're送点东西给谁不特定端口上侦听的服务器。
这将导致发送一个ICMP消息回来了，你的下一个recvfrom的将在你连接插座的情况下返回一个错误。

检查使用tcpdump或者Wireshark的正在发生的事情在电线上。

I am trying to send a string HI to a server over UDP in a particular port and then to receive a response. However, after I try to get the response using recvfrom() I was stuck in blocking state. I tried using connected UDP but I got:

Error receiving in UDP: Connection refused

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.

这篇关于错误接收UDP：连接被拒绝的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！