Simple sniffer program in Linux

/***************************************
* Author: Li Yannan
* Time: 2006-02 2
* Function: detects the local network.
****************************************/

# Include <stdio. h>
# Include <stdlib. h>
# Include <string. h>
# Include <errno. h>
# Include <unistd. h>
# Include <sys/socket. h>
# Include <sys/types. h>
# Include <Linux/in. h>
# Include <Linux/if_ether.h>
# Include <net/If. h>
# Include <sys/IOCTL. h>
# Define interface "eth0"
Int set_promisc (char * interface, int sock );
Void write_file (File * FP, unsigned char * Buf, int Len );
Int main ()
{
Int sock, size, I, J;
File * FP;
Unsigned char buffer [2048];
Unsigned char * data;
Fp = fopen ("sniffer.txt", "W ");
If (! FP)
{
Printf ("can not open the file/N ");
Return;
}
If (sock = socket (pf_packet, sock_raw, htons (eth_p_ip) <0)
{
Printf ("socket init error/N ");
Return-1;
}

Set_promisc (interface, sock );
While (1)
{
Printf ("-------------------/N ");
Size = recvfrom (sock, buffer, 2048,0, null, null );
Printf ("% d bytes read/N", size );
If (size <14)
{
Printf ("Recv error/N ");
Close (sock );
Return-1;
}
Write_file (FP, buffer, size );
Printf ("the DST Mac is % 02x: % 02x: % 02x: % 02x: % 02x: % 02x/N", buffer [0], buffer [1], buffer [2],
Buffer [3], buffer [4], buffer [5]);
Printf ("the source MAC is % 02x: % 02x: % 02x: % 02x: % 02x: % 02x/N", buffer [6], buffer [7], buffer [8],
Buffer [9], buffer [10], buffer [11]);
Printf ("packet type is % 02x % 02x/N", buffer [12], buffer [13]);
Data = buffer + 14;
Size = size-14;
For (I = 0; I <size; I + = 16)
{
For (j = I; j <I + 16; j ++)
{
If (j <size)
Printf ("% 02x", data [J]);
Else
Break;
}
Printf ("/N ");
}
}
Fclose (FP );
Return 0;
}
// Set the NIC to the hybrid mode so that it can receive packets not sent to the Local Machine
Int set_promisc (char * interface, int sock)
{
Struct ifreq IFR;
Strncpy (IFR. ifr_name, interface, strnlen (Interface) + 1 );
If (IOCTL (sock, siocgifflags, & IFR) =-1 ))
{
Printf ("couldn't retrive flags for the interface/N ");
Exit (0 );
}
Printf ("the interface is: % s/n", interface );
Printf ("retrieved flags from the interface successly/N ");
IFR. ifr_flags | = iff_promisc;
If (IOCTL (sock, siocsifflags, & IFR) =-1)
{
Printf ("cocould not set the promisc flag/N ");
Exit (0 );
}
Printf ("setting interface: % s: To promisc/N", interface );
Return (0 );
}
// Write an object
Void write_file (File * FP, unsigned char * Buf, int Len)
{
Int I;
Int base;
/*
Fp = fopen ("sniffer.txt", "");
If (! FP)
{
Printf ("can not open the file/N ");
Return;
}
*/
Fprintf (FP, "% s: % d/N", "receive packet:", Len );
If (BUF [12] = 0x88 & Buf [13] = 0x63)
{
Fprintf (FP, "% s/n" "The pppoe discovery packet found ");
}
For (base = 0; base <Len; base + = 16)
{
For (I = base; I <base + 16; I ++)
{
If (I <Len)
{
Fprintf (FP, "% 02x", (unsigned) BUF [I]);
}
Else
{
Fprintf (FP ,"");
}
}
Fprintf (FP ,"");
For (I = base; I <base + 16; I ++)
{
If (I <Len)
{
If (isprint (BUF [I])
{
Fprintf (FP, "% C", Buf [I]);
}
Else
{
Fprintf (FP ,".");
}
}
Else {
Break;
}
}
Fprintf (FP, "/N ");
}
Fprintf (FP, "/N ");
// Fclose (FP );
}