Error receiving in UDP: Connection refused

c, sockets, udp, udpclient

Solution

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.

Problem

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; ```

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