CODEWITHSUNDEEP
c++network-programmingpacket
user3517454
user3517454

Reputation: 217

How to read/send packets correctly?

I am trying to send packets via UDP, and I am not allowed to use SOCK_RAW (school project). The packet I am sending has a header struct ip and a string data part. I put them into one char array (the packet itself is configured correctly).

Here is how I send: 

sendPacket(packet);

where packet is a char[] and

where sendPacket is defined as:

void IPNode::sendPacket(char* packet){
        //define socket, destSockAddr
        int success = sendto(socket, packet, sizeof(packet), 0,
                (struct sockaddr *) &destSockAddr, sizeof(destSockAddr));
    }
}

The packet seems to be correct. However, this is how I read it in. 

while (true) {
    struct sockaddr_in remoteAddr;
    socklen_t remoteAddrLen = sizeof(remoteAddr);
    char buffer[BUF_SIZE];
    int recvlen = recvfrom(myListenSocket, buffer, BUF_SIZE, 0, 0, 0);
    onReceive(buffer);
// other stuff

}

where onReceive is:

void onReceive(char* packet) {
    ip* ptr = (ip*)packet; //the struct ip is the beginning of the packet
    struct ip ipCpy = *ptr;
    struct in_addr inAddrCpy = ipCpy.ip_src;
    char* ipString = inet_ntoa(inAddrCpy);
    cout << ipString << endl;
    return;
}

However, the ipString that is printed is different from the ipString that was in the packet before being sent. Am I accessing the received packets wrongly?

Upvotes: 1

Views: 790

Answers (1)

ScottMcP-MVP
ScottMcP-MVP

Reputation: 10415

You are sending sizeof(packet) bytes. But sizeof(packet) is 4, because packet is a pointer. You need a better way to keep track of the actual size you want to send.

Upvotes: 1

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