CODEWITHSUNDEEP
socketswinapiudpc++-cli
user5588850
user5588850

Reputation:

UDP socket with "winsock"

I send a UDP request to a server, although it returns me the right answer on wireshark but in my code with " recvfrom " I get what I sent.

Code : 

char* udp_recv;
udp_recv = (char*)malloc(256);
s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
for (i; i < 1; i++)
{

    String^ delimStr = ":";
    array<Char>^ delimiter = delimStr->ToCharArray();

    array<String^>^ addrPort = addr[i]->Split(delimiter);

    char *cAddr, *cPort, *cPartAddr;

    cAddr = (char*)malloc(16);
    cPort = (char*)malloc(16);
    cPartAddr = (char*)malloc(16);

    ConvertStringToChar(addrPort[0], cAddr, 16);
    ConvertStringToChar(addrPort[1], cPort, 16);

    SOCKADDR_IN udpbind;

    udpbind.sin_family = AF_INET;
    udpbind.sin_addr.s_addr = INADDR_ANY;
    udpbind.sin_port = htons((u_short)atoi(cPort));

    if (bind(s, (struct sockaddr*)&udpbind, sizeof(udpbind)) < 0) std::cout << "Erreur" << std::endl;

    delimStr = ".";
    delimiter = delimStr->ToCharArray();

    array<String^>^ partAddr = addrPort[0]->Split(delimiter);

    std::string send("SAMP");

    int j = 0;
    for (j; j < 4; j++)
    {
        ConvertStringToChar(partAddr[j], cPartAddr, 16);
        send += (char)atoi(cPartAddr);
    }
    send += (char)(atoi(cPort) & 0xFF);
    send += (char)(atoi(cPort) >> 8 & 0xFF);
    send += "i";

    server.sin_addr.s_addr = inet_addr(cAddr);
    server.sin_family = AF_INET;
    server.sin_port = htons((u_short)atoi(cPort));

    sendto(s, (char*)send.c_str(), strlen((char*)send.c_str()), 0, (struct sockaddr *)&server, sizeof(server));

    struct sockaddr_in recv;
    int client_len = sizeof(recv);
    recv_size = recvfrom(s, udp_recv, 256, 0, NULL, NULL);

    udp_recv[recv_size] = '\0';

    std::cout << udp_recv << std::endl;

    free(cPartAddr);
    free(cAddr);
    free(cPort);

}
closesocket(s);

Thanks !

Upvotes: 0

Views: 334

Answers (1)

selbie
selbie

Reputation: 104569

This may not be the answer, but this looks suspicious:

udp_recv = (char*)malloc(256);

...

recv_size = recvfrom(s, udp_recv, 256, 0, NULL, NULL);

udp_recv[recv_size] = '\0';

Two immediate problems:

  1. If the number of bytes received is actually 256, then you'll be assigning udp_recv[256]=0.

  2. If the result is an error recvfrom returns -1 (SOCKET_ERROR). You'll be assigning udp_recv[-1]=0;

In both cases, the valid index ranges of udp_recv is [0..255]. -1 and 256 are invalid index ranges. Thus, undefined behavior.

Check for socket error and allocate the buffer to be 1 more byte larger than what you declare the buffer size to be.

Upvotes: 1

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