Amostra 1: Capturando Dados do Packet e Imprimindo-o em Formulário Binário para a Tela

/*
 * 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 Sample 3, 
 * for formatting and readability.
 */

#include <stdio.h>
#include <pcap.h>
#include <netinet/in.h>
#include <sys/socket.h>

#include <string.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, you 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 can be piped into
         * another application for further processing or formatting before
         * reading.
         */
        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 the 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);
}