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LQ Newbie
Registered: Jun 2008
Posts: 15
Rep: 
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libpcap equivalent for this winpcap program?
I have found this code that works in winpcap i want to convert it into libpcap can anybody help
Thanks in advance
/*
34 * This simple program implements a user-level bridge.
35 * It opens two adapters specified by the user and starts two threads.
36 * The first thread receives packets from adapter 1 and sends them down to
37 * adapter 2. The second thread does the same, but in the opposite
38 * direction.
39 */
#include <signal.h>
#include "pcap.h"
/* Storage data structure used to pass parameters to the threads */
typedef struct _in_out_adapters
{
unsigned int state; /* Some simple state information */
pcap_t *input_adapter;
pcap_t *output_adapter;
}in_out_adapters;
/* Prototypes */
DWORD WINAPI CaptureAndForwardThread(LPVOID lpParameter);
void ctrlc_handler(int sig);
/* This prevents the two threads to mess-up when they do printfs */
CRITICAL_SECTION print_cs;
/* Thread handlers. Global because we wait on the threads from the CTRL+C handler */
HANDLE threads[2];
/* This global variable tells the forwarder threads they must terminate */
volatile int kill_forwaders = 0;
/*******************************************************************/
int main()
{
pcap_if_t *alldevs;
pcap_if_t *d;
int inum1, inum2;
int i=0;
pcap_t *adhandle1, *adhandle2;
char errbuf[PCAP_ERRBUF_SIZE];
u_int netmask1, netmask2;
char packet_filter[256];
struct bpf_program fcode;
in_out_adapters couple0, couple1;
/*
* Retrieve the device list
*/
if (pcap_findalldevs_ex(PCAP_SRC_IF_STRING, NULL, &alldevs, errbuf) == -1)
{
fprintf(stderr,"Error in pcap_findalldevs: %s\n", errbuf);
exit(1);
}
/* Print the list */
for(d=alldevs; d; d=d->next)
{
printf("%d. ", ++i);
if (d->description)
printf("%s\n", d->description);
else
printf("<unknown adapter>\n");
}
if(i==0)
{
printf("\nNo interfaces found! Make sure WinPcap is installed.\n");
return -1;
}
/*
* Get input from the user
*/
/* Get the filter*/
printf("\nSpecify filter (hit return for no filter):");
gets(packet_filter);
if(strcmp(packet_filter, "") == 0)
{
sprintf(packet_filter, "");
}
/* Get the first interface number*/
printf("\nEnter the number of the first interface to use (1-%d):",i);
scanf("%d", &inum1);
if(inum1 < 1 || inum1 > i)
{
printf("\nInterface number out of range.\n");
/* Free the device list */
pcap_freealldevs(alldevs);
return -1;
}
/* Get the second interface number*/
printf("Enter the number of the first interface to use (1-%d):",i);
scanf("%d", &inum2);
if(inum2 < 1 || inum2 > i)
{
printf("\nInterface number out of range.\n");
/* Free the device list */
pcap_freealldevs(alldevs);
return -1;
}
if(inum1 == inum2 )
{
printf("\nCannot bridge packets on the same interface.\n");
/* Free the device list */
pcap_freealldevs(alldevs);
return -1;
}
/*
* Open the specified couple of adapters
*/
/* Jump to the first selected adapter */
for(d = alldevs, i = 0; i< inum1 - 1 ;d = d->next, i++);
/*
* Open the first adapter.
* *NOTICE* the flags we are using, they are important for the behavior of the prgram:
* - PCAP_OPENFLAG_PROMISCUOUS: tells the adapter to go in promiscuous mode.
* This means that we are capturing all the traffic, not only the one to or from
* this machine.
* - PCAP_OPENFLAG_NOCAPTURE_LOCAL: prevents the adapter from capturing again the packets
* transmitted by itself. This avoids annoying loops.
* - PCAP_OPENFLAG_MAX_RESPONSIVENESS: configures the adapter to provide minimum latency,
* at the cost of higher CPU usage.
*/
if((adhandle1 = pcap_open(d->name, // name of the device
65536, // portion of the packet to capture.
// 65536 grants that the whole packet will be captured on every link layer.
PCAP_OPENFLAG_PROMISCUOUS | // flags. We specify that we don't want to capture loopback packets, and that the driver should deliver us the packets as fast as possible
PCAP_OPENFLAG_NOCAPTURE_LOCAL |
PCAP_OPENFLAG_MAX_RESPONSIVENESS,
500, // read timeout
NULL, // remote authentication
errbuf // error buffer
)) == NULL)
{
fprintf(stderr,"\nUnable to open the adapter. %s is not supported by WinPcap\n", d->description);
/* Free the device list */
pcap_freealldevs(alldevs);
return -1;
}
if(d->addresses != NULL)
{
/* Retrieve the mask of the first address of the interface */
netmask1 = ((struct sockaddr_in *)(d->addresses->netmask))->sin_addr.S_un.S_addr;
}
else
{
/* If the interface is without addresses we suppose to be in a C class network */
netmask1 = 0xffffff;
}
/* Jump to the second selected adapter */
for(d = alldevs, i = 0; i< inum2 - 1 ;d = d->next, i++);
/* Open the second adapter */
if((adhandle2 = pcap_open(d->name, // name of the device
65536, // portion of the packet to capture.
// 65536 grants that the whole packet will be captured on every link layer.
PCAP_OPENFLAG_PROMISCUOUS | // flags. We specify that we don't want to capture loopback packets, and that the driver should deliver us the packets as fast as possible
PCAP_OPENFLAG_NOCAPTURE_LOCAL |
PCAP_OPENFLAG_MAX_RESPONSIVENESS,
500, // read timeout
NULL, // remote authentication
errbuf // error buffer
)) == NULL)
{
fprintf(stderr,"\nUnable to open the adapter. %s is not supported by WinPcap\n", d->description);
/* Free the device list */
pcap_freealldevs(alldevs);
return -1;
}
if(d->addresses != NULL)
{
/* Retrieve the mask of the first address of the interface */
netmask2 = ((struct sockaddr_in *)(d->addresses->netmask))->sin_addr.S_un.S_addr;
}
else
{
/* If the interface is without addresses we suppose to be in a C class network */
netmask2 = 0xffffff;
}
/*
234 * Compile and set the filters
235 */
/* compile the filter for the first adapter */
if (pcap_compile(adhandle1, &fcode, packet_filter, 1, netmask1) <0 )
{
fprintf(stderr,"\nUnable to compile the packet filter. Check the syntax.\n");
/* Close the adapters */
pcap_close(adhandle1);
pcap_close(adhandle2);
/* Free the device list */
pcap_freealldevs(alldevs);
return -1;
}
/* set the filter for the first adapter*/
if (pcap_setfilter(adhandle1, &fcode)<0)
{
fprintf(stderr,"\nError setting the filter.\n");
/* Close the adapters */
pcap_close(adhandle1);
pcap_close(adhandle2);
/* Free the device list */
pcap_freealldevs(alldevs);
return -1;
}
/* compile the filter for the second adapter */
if (pcap_compile(adhandle2, &fcode, packet_filter, 1, netmask2) <0 )
{
fprintf(stderr,"\nUnable to compile the packet filter. Check the syntax.\n");
/* Close the adapters */
pcap_close(adhandle1);
pcap_close(adhandle2);
/* Free the device list */
pcap_freealldevs(alldevs);
return -1;
}
/* set the filter for the second adapter*/
if (pcap_setfilter(adhandle2, &fcode)<0)
{
fprintf(stderr,"\nError setting the filter.\n");
/* Close the adapters */
pcap_close(adhandle1);
pcap_close(adhandle2);
/* Free the device list */
pcap_freealldevs(alldevs);
return -1;
}
/* At this point, we don't need the device list any more. Free it */
pcap_freealldevs(alldevs);
/*
297 * Start the threads that will forward the packets
298 */
/* Initialize the critical section that will be used by the threads for console output */
InitializeCriticalSection(&print_cs);
/* Init input parameters of the threads */
couple0.state = 0;
couple0.input_adapter = adhandle1;
couple0.output_adapter = adhandle2;
couple1.state = 1;
couple1.input_adapter = adhandle2;
couple1.output_adapter = adhandle1;
/* Start first thread */
if((threads[0] = CreateThread(
NULL,
0,
CaptureAndForwardThread,
&couple0,
0,
NULL)) == NULL)
{
fprintf(stderr, "error creating the first forward thread");
/* Close the adapters */
pcap_close(adhandle1);
pcap_close(adhandle2);
/* Free the device list */
pcap_freealldevs(alldevs);
return -1;
}
/* Start second thread */
if((threads[1] = CreateThread(
NULL,
0,
CaptureAndForwardThread,
&couple1,
0,
NULL)) == NULL)
{
fprintf(stderr, "error creating the second forward thread");
/* Kill the first thread. Not very gentle at all...*/
TerminateThread(threads[0], 0);
/* Close the adapters */
pcap_close(adhandle1);
pcap_close(adhandle2);
/* Free the device list */
pcap_freealldevs(alldevs);
return -1;
}
/*
355 * Install a CTRL+C handler that will do the cleanups on exit
356 */
signal(SIGINT, ctrlc_handler);
/*
360 * Done!
361 * Wait for the Greek calends...
362 */
printf("\nStart bridging the two adapters...\n", d->description);
Sleep(INFINITE);
return 0;
}
/*******************************************************************
369 * Forwarding thread.
370 * Gets the packets from the input adapter and sends them to the output one.
371 *******************************************************************/
DWORD WINAPI CaptureAndForwardThread(LPVOID lpParameter)
{
struct pcap_pkthdr *header;
const u_char *pkt_data;
int res;
in_out_adapters* ad_couple = lpParameter;
unsigned int n_fwd = 0;
/*
* Loop receiving packets from the first input adapter
*/
while((!kill_forwaders) && (res = pcap_next_ex(ad_couple->input_adapter, &header, &pkt_data)) >= 0)
{
if(res != 0) /* Note: res=0 means "read timeout elapsed"*/
{
/*
* Print something, just to show when we have activity.
* BEWARE: acquiring a critical section and printing strings with printf
* is something inefficient that you seriously want to avoid in your packet loop!
* However, since this is a *sample program*, we privilege visual output to efficiency.
*/
EnterCriticalSection(&print_cs);
if(ad_couple->state == 0)
printf(">> Len: %u\n", header->caplen);
else
printf("<< Len: %u\n", header->caplen);
LeaveCriticalSection(&print_cs);
/*
* Send the just received packet to the output adaper
*/
if(pcap_sendpacket(ad_couple->output_adapter, pkt_data, header->caplen) != 0)
{
EnterCriticalSection(&print_cs);
printf("Error sending a %u bytes packets on interface %u: %s\n",
header->caplen,
ad_couple->state,
pcap_geterr(ad_couple->output_adapter));
LeaveCriticalSection(&print_cs);
}
else
{
n_fwd++;
}
}
}
/*
* We're out of the main loop. Check the reason.
*/
if(res < 0)
{
EnterCriticalSection(&print_cs);
printf("Error capturing the packets: %s\n", pcap_geterr(ad_couple->input_adapter));
fflush(stdout);
LeaveCriticalSection(&print_cs);
}
else
{
EnterCriticalSection(&print_cs);
printf("End of bridging on interface %u. Forwarded packets:%u\n",
ad_couple->state,
n_fwd);
fflush(stdout);
LeaveCriticalSection(&print_cs);
}
return 0;
}
/*******************************************************************
* CTRL+C hanlder.
* We order the threads to die and then we patiently wait for their
* suicide.
*******************************************************************/
void ctrlc_handler(int sig)
{
kill_forwaders = 1;
WaitForMultipleObjects(2,
threads,
TRUE, /* Wait for all the handles */
5000); /* Timeout */
exit(0);
}
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