Retrieving data from a socket client-server transaction - c

Question

I am emulating a client-server socket transaction. Suppose, the client sent some ip packet with
status = send(sock, packet, sizeof(struct iphdr) + sizeof(struct tcphdr),
0);
where sock is the socket, packet points to an ip packet (with ip header struct iphdr and tcp header struct tcphdr)
Now, on the server side, I want to use some function that retrieves the data in packet and displays it. The connection between client and server is correctly set up but when trying to use the recv function, I don't get any data. Is recv the right function
So on the client side I have
packet = malloc(sizeof(struct iphdr)+ sizeof(struct tcphdr));
and I use
send(sock, packet, sizeof(struct iphdr) + sizeof(struct tcphdr),
0);
on the server side, I declared some char packet[32]; and I used this
recv(sock, packet, 32, 0);
Edit 2 - here's the code
On the client side
Edit on the client side (to shorten, I didn't mention the included libraries, the struct iphdr, tcphdr, the in_chksum function, as well I didn't hydrate the tcp header, for now I just want to test)
struct tcphdr tcp_hdr;
struct ip ip_hdr;
#define PORT 23
int sendmeifyoucan(SOCKET sock, SOCKADDR_IN * sin , int size ){
struct ip * ip = (struct ip *)malloc(sizeof(struct ip));
struct tcphdr * tcp;
char * packet;
int sock_err;
int psize=0, status = 1;
packet = malloc(sizeof(struct ip)+ sizeof(struct tcphdr));
memset(packet, 0, sizeof(struct ip) + sizeof(struct tcphdr));
ip->ip_len = htons(sizeof(struct ip) + sizeof(struct tcphdr) + psize);
ip->ip_hl = 5;
ip->ip_v = 4;
ip->ip_ttl = 255;
ip->ip_tos = 0;
ip->ip_off = 0;
ip->ip_p = IPPROTO_ICMP;
ip->ip_src.s_addr = inet_addr("127.0.0.1");
ip->ip_dst.s_addr = inet_addr("127.0.0.1");
ip->ip_sum = in_chksum((u_short *)ip, sizeof(struct ip));
status = send(sock, packet, sizeof(struct iphdr) + sizeof(struct tcphdr),
0);
free(packet);
return 0;
}
int main(void)
{
int erreur = 0;
SOCKADDR_IN sin;
SOCKET sock;
SOCKADDR_IN csin;
SOCKET csock;
int sock_err;
if(!erreur)
{
sock = socket(AF_INET, SOCK_STREAM, 0);
if(sock != INVALID_SOCKET)
{
printf("La socket %d est maintenant ouverte en mode TCP/IP\n", sock);
int size = 0;
/* Configuration */
sin.sin_addr.s_addr = inet_addr("127.0.0.1");
sin.sin_family = AF_INET;
sin.sin_port = htons(PORT);
if(connect(sock, (SOCKADDR*)&sin, sizeof(sin)) != SOCKET_ERROR)
{
printf("Connection à %s sur le port %d\n", inet_ntoa(sin.sin_addr), htons(sin.sin_port));
sendmeifyoucan(sock, &sin,size);
/* Si l'on reçoit des informations : on les affiche à l'écran */
}
}
printf("Fermeture de la socket client\n");
closesocket(csock);
printf("Fermeture de la socket serveur\n");
closesocket(sock);
printf("Fermeture du serveur terminée\n");
}
else
perror("socket");
}
return EXIT_SUCCESS;
}
On the server side
#define PORT 23
int main(void)
{
int erreur = 0;
SOCKET sock;
SOCKADDR_IN sin;
socklen_t recsize = sizeof(sin);
SOCKADDR_IN csin;
char buffer[32] = "";
int sock_err;
if(!erreur)
{
sock = socket(AF_INET, SOCK_STREAM, 0);
if(sock != INVALID_SOCKET)
{
printf("La socket %d est maintenant ouverte en mode TCP/IP\n", sock);
/* Configuration */
csin.sin_addr.s_addr = inet_addr("127.0.0.1");
csin.sin_family = AF_INET;
csin.sin_port = htons(PORT);
sock_err = bind(sock, (SOCKADDR*) &csin, sizeof(csin));
if(sock_err != SOCKET_ERROR)
{
sock_err = listen(sock, 5);
printf("Listage du port %d...\n", PORT);
}
if(sock_err != SOCKET_ERROR)
{
/* Attente pendant laquelle le client se connecte */
printf("Patientez pendant que le client se connecte sur le port %d...\n", PORT);
sock = accept(sock, (SOCKADDR*)&sin, &recsize);
}
if(recv(sock, buffer, 32, 0) != SOCKET_ERROR)
{
printf("Recu : %s\n", buffer);
}
else
{
printf("Impossible de se connecter\n");
}
closesocket(sock);
}
else
perror("socket");
}
return EXIT_SUCCESS;
}
Edit 3 - the headers
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netinet/tcp.h>
#include <netinet/ip.h>
#include <unistd.h>
#define INVALID_SOCKET -1
#define SOCKET_ERROR -1
#define closesocket(s) close(s)
typedef int SOCKET;
typedef struct sockaddr_in SOCKADDR_IN;
typedef struct sockaddr SOCKADDR;
#include <stdio.h>
#include <stdlib.h>
#define PORT 23

Answer 1

Okay now I see your problems.
On client side:
First issue (big):
You are not CONNECTING at all.
where is your connect() call on the client side?
If you want to use SOCK_STREAM you need a connect(2) call
In the code snippet:
if(connect(sock, (SOCKADDR*)&sin, sizeof(sin)) != SOCKET_ERROR) {
printf("Connection à %s sur le port %d\n", inet_ntoa(sin.sin_addr), htons(sin.sin_port));
/* Si l'on reçoit des informations : on les affiche à l'écran */
}
your sendmeifyoucan() is OUTSIDE the if block { } ;
2nd issue
struct iphdr * ip = (struct iphdr *)malloc(sizeof(struct iphdr *));
should be
struct iphdr * ip = (struct iphdr *)malloc(sizeof(struct iphdr));
Otherwise you are in a stack overflow issue.
Third issue (not so big)
you are allocating char *packet but you are not copying anything on to it it's just memset to 0;
Debug accordingly and try again :)