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/* tcpip720 src/tcpip/usr/samples/tcpip/libpcap/pcap_exI.c 1.1 */
/* */
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/* COPYRIGHT International Business Machines Corp. 2000 */
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/*
* NOTICE TO USERS OF THE SOURCE CODE EXAMPLES
*
* INTERNATIONAL BUSINESS MACHINES CORPORATION PROVIDES THE SOURCE CODE
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* Corporation.
*/
/*
* Use pcap_open_live() to open a packet capture device and use pcap_dump()
* to output the packet capture data in binary format to standard out. The
* output can be piped to another program, such as the one in example III,
* for formatting and readablility.
*/
#include <stdio.h>
#include <pcap.h>
#include <netinet/in.h>
#include <sys/socket.h>
#define FLTRSZ 120
#define MAXHOSTSZ 256
#define ADDR_STRSZ 16
extern char *inet_ntoa();
int
main(int argc, char **argv)
{
pcap_t *p; /* packet capture descriptor */
pcap_dumper_t *pd; /* pointer to the dump file */
char *ifname; /* interface name (such as "en0") */
char errbuf[PCAP_ERRBUF_SIZE]; /* buffer to hold error text */
char lhost[MAXHOSTSZ]; /* local host name */
char fltstr[FLTRSZ]; /* bpf filter string */
char prestr[80]; /* prefix string for errors from pcap_perror */
struct bpf_program prog; /* compiled bpf filter program */
int optimize = 1; /* passed to pcap_compile to do optimization */
int snaplen = 80; /* amount of data per packet */
int promisc = 0; /* do not change mode; if in promiscuous */
/* mode, stay in it, otherwise, do not */
int to_ms = 1000; /* timeout, in milliseconds */
int count = 20; /* number of packets to capture */
u_int32 net = 0; /* network IP address */
u_int32 mask = 0; /* network address mask */
char netstr[INET_ADDRSTRLEN]; /* dotted decimal form of address */
char maskstr[INET_ADDRSTRLEN]; /* dotted decimal form of net mask */
/*
* Find a network device on the system.
*/
if (!(ifname = pcap_lookupdev(errbuf))) {
fprintf(stderr, "Error getting device on system: %s\n", errbuf);
exit(1);
}
/*
* Open the network device for packet capture. This must be called
* before any packets can be captured on the network device.
*/
if (!(p = pcap_open_live(ifname, snaplen, promisc, to_ms, errbuf))) {
fprintf(stderr,
"Error opening interface %s: %s\n", ifname, errbuf);
exit(2);
}
/*
* Look up the network address and subnet mask for the network device
* returned by pcap_lookupdev(). The network mask will be used later
* in the call to pcap_compile().
*/
if (pcap_lookupnet(ifname, &net, &mask, errbuf) < 0) {
fprintf(stderr, "Error looking up network: %s\n", errbuf);
exit(3);
}
/*
* Create the filter and store it in the string called 'fltstr.'
* Here, we want only incoming packets (destined for this host),
* which use port 23 (telnet), and originate from a host on the
* local network.
*/
/* First, get the hostname of the local system */
if (gethostname(lhost,sizeof(lhost)) < 0) {
fprintf(stderr, "Error getting hostname.\n");
exit(4);
}
/*
* Second, get the dotted decimal representation of the network address
* and netmask. These will be used as part of the filter string.
*/
inet_ntop(AF_INET, (char*) &net, netstr, sizeof netstr);
inet_ntop(AF_INET, (char*) &mask, maskstr, sizeof maskstr);
/* Next, put the filter expression into the fltstr string. */
sprintf(fltstr,"dst host %s and src net %s mask %s and tcp port 23",
lhost, netstr, maskstr);
/*
* Compile the filter. The filter will be converted from a text
* string to a bpf program that can be used by the Berkely Packet
* Filtering mechanism. The fourth argument, optimize, is set to 1 so
* the resulting bpf program, prog, is compiled for better performance.
*/
if (pcap_compile(p,&prog,fltstr,optimize,mask) < 0) {
/*
* Print out appropriate text, followed by the error message
* generated by the packet capture library.
*/
fprintf(stderr, "Error compiling bpf filter on %s: %s\n",
ifname, pcap_geterr(p));
exit(5);
}
/*
* Load the compiled filter program into the packet capture device.
* This causes the capture of the packets defined by the filter
* program, prog, to begin.
*/
if (pcap_setfilter(p, &prog) < 0) {
/* Copy appropriate error text to prefix string, prestr */
sprintf(prestr, "Error installing bpf filter on interface %s",
ifname);
/*
* Print out error. The format will be the prefix string,
* created above, followed by the error message that the packet
* capture library generates.
*/
pcap_perror(p,prestr);
exit(6);
}
/*
* Open dump device for writing packet capture data. Passing in "-"
* indicates that packets are to be written to standard output.
* pcap_dump() will be called to write the packet capture data in
* binary format, so the output from this program may be piped into
* another application for further processing or formatting before
* reading. For an example of an application that reads and processes
* binary packet data, see the Packet Capture Chapter of the
* Communications Programming Concepts Book.
*/
if ((pd = pcap_dump_open(p,"-")) == NULL) {
/*
* Print out error message if pcap_dump_open failed. This will
* be the below message followed by the pcap library error text,
* obtained by pcap_geterr().
*/
fprintf(stderr, "Error opening dump device stdout: %s\n",
pcap_geterr(p));
exit(7);
}
/*
* Call pcap_loop() to read and process a maximum of count (20)
* packets. For each captured packet (a packet that matches the filter
* specified to pcap_compile()), pcap_dump() will be called to write
* the packet capture data (in binary format) to the savefile specified
* to pcap_dump_open(). NOTE that packet in this case may not be a
* complete packet. The amount of data captured per packet is
* determined by the snaplen variable which is passed to
* pcap_open_live().
*/
if (pcap_loop(p, count, &pcap_dump, (char *)pd) < 0) {
/*
* Print out appropriate text, followed by the error message
* generated by the packet capture library.
*/
sprintf(prestr,"Error reading packets from interface %s",
ifname);
pcap_perror(p,prestr);
exit(8);
}
/*
* Close the packet capture device and free the memory used by the
* packet capture descriptor.
*/
pcap_close(p);
}