CODEWITHSUNDEEP
csocketswiresharkrecvfrom
zidanow
zidanow

Reputation: 700

Recvfrom and Wireshark

I communicate with a server, i send a message with a socket (sock_raw..), it's works fine, the client (me), send the message, the server receive the right message, but when the server need to send it to me (the client), the client don't retrieve the right information with the recv from.

I retrieve this on two calls server->client :

buffer = [E] | len_buffer = [2]
buffer = [E] | len_buffer = [2]

But my buffer need to be equal to this data and have this size :

First call (Data in hexadecimal with 10 bytes) enter image description here

And Second call (Data in hexadecimal with 2 bytes) enter image description here

This is how i use the recvfrom function (t->sock is the socket fd of the server, t->msg_recv is the buffer created to receive the msg from the servern and t->_recv is the sockaddr* struct for the receive):

if (recvfrom(t->sock, t->msg_recv, sizeof(t->msg_recv), 0, \
    (struct sockaddr *)&t->_recv, \
    (socklen_t[1]){sizeof(struct sockaddr_in)}) < 0) {
        perror("recvto()");
        exit(84);
    }

Barmar here is the output of the Wireshark message send :

enter image description here

Here is the code of send and recvfrom on the same function :

int len = 0;
    if (sendto(t->sock, t->buffer, t->ip->tot_len, 0,
               (struct sockaddr *)&t->_sin, sizeof(t->_sin)) < 0) {
      perror("sendto()");
      exit(84);
    }
    if ((len = recvfrom(t->sock, t->msg_recv, sizeof(t->msg_recv), 0, \
    (struct sockaddr *)&t->_recv, \
    (socklen_t[1]){sizeof(struct sockaddr_in)})) < 0) {
        perror("recvto()");
        exit(84);
    }

Upvotes: 1

Views: 523

Answers (1)

Barmar
Barmar

Reputation: 780663

The buffer is not a string, it's binary data, so you shouldn't print it with %s.

You need to get the length of the buffer when you call recvfrom. Then use a loop that prints each byte with %02X format.

len = recvfrom(t->sock, t->msg_recv, sizeof(t->msg_recv), 0, \
    (struct sockaddr *)&t->_recv, \
    (socklen_t[1]){sizeof(struct sockaddr_in)});
if (len < 0) {
        perror("recvto()");
        exit(84);
}
for (int i = 0; i < len; i ++) {
    printf("%02X ", t->msg_recv[i]);
    if (i % 16 == 15) {
        printf("\n");
    } else if (i % 16 == 7) {
        printf(" ");
    }
}
printf("\n");

Upvotes: 0

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