source: lib/trace.c @ 74c7660

/*
 * This file is part of libtrace
 *
 * Copyright (c) 2004 The University of Waikato, Hamilton, New Zealand.
 * Authors: Daniel Lawson 
 *          Perry Lorier 
 *          
 * All rights reserved.
 *
 * This code has been developed by the University of Waikato WAND 
 * research group. For further information please see http://www.wand.net.nz/
 *
 * libtrace is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * libtrace is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with libtrace; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * $Id$
 *
 */


/** @file 
 *
 * @brief Trace file processing library
 *
 * @author Daniel Lawson
 * @author Perry Lorier
 *
 * @internal
 */
#define _GNU_SOURCE
#include "common.h"
#include "config.h"
#include "format.h"
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>

#ifdef HAVE_LIMITS_H
#  include <limits.h>
#endif

#ifdef HAVE_SYS_LIMITS_H
#  include <sys/limits.h>
#endif

#include <sys/socket.h>
#include <sys/un.h>
#include <sys/mman.h>
#include <unistd.h>

#ifdef HAVE_NET_IF_ARP_H
#  include <net/if_arp.h>
#endif

#ifdef HAVE_NET_IF_H
#  include <net/if.h>
#endif

#ifdef HAVE_NETINET_IN_H
#  include <netinet/in.h>
#endif

#ifdef HAVE_NET_ETHERNET_H
#  include <net/ethernet.h>
#endif

#ifdef HAVE_NETINET_IF_ETHER_H
#  include <netinet/if_ether.h>
#endif

#include <time.h>
#include <sys/ioctl.h>

#ifdef HAVE_INTTYPES_H
#  include <inttypes.h>
#else
#  error "Can't find inttypes.h - this needs to be fixed"
#endif 

#ifdef HAVE_STDDEF_H
#  include <stddef.h>
#else
# error "Can't find stddef.h - do you define ptrdiff_t elsewhere?"
#endif

#include "libtrace.h"
#include "fifo.h"

#if HAVE_PCAP_BPF_H
#  include <pcap-bpf.h>
#else
#  ifdef HAVE_NET_BPF_H
#    include <net/bpf.h>
#  endif
#endif

#if HAVE_PCAP_H
#  include <pcap.h>
#  ifdef HAVE_PCAP_INT_H
#    include <pcap-int.h>
#  endif
#endif 

#ifdef HAVE_ZLIB_H
#  include <zlib.h>
#endif


#include "wag.h"

#ifdef HAVE_DAG_API
#  include "dagnew.h"
#  include "dagapi.h"
#else
#  include "dagformat.h"
#endif

#include "format.h"
//#include "format/format_list.h"
#include <err.h>

//typedef enum {SOCKET, TRACE, STDIN, DEVICE, INTERFACE, RT } source_t;

//typedef enum {ERF, PCAP, PCAPINT, DAG, RTCLIENT, WAG, WAGINT } format_e_t;

typedef enum {RTSERVER, GZERF } output_t;
#if HAVE_BPF
/** A type encapsulating a bpf filter
 * This type covers the compiled bpf filter, as well as the original filter
 * string
 *
 */
struct libtrace_filter_t {
        struct bpf_insn *filter;
        char * filterstring;
};
#endif

struct libtrace_out_t {
        output_t outputformat;

        union {
                struct {
                        char *hostname;
                        short port;
                } rt;
                char *path;
                char *interface;
        } conn_info;

        union {
                int fd;
#if HAVE_ZLIB
                gzFile *file;
#else
                FILE *file;
#endif
#if HAVE_PCAP
                pcap_t *pcap;
#endif
        } output;

        struct fifo_t *fifo;
};



struct format_t **format_list = 0;
int format_size = 0;
int nformats = 0;

void register_format(struct format_t *f) {
        fprintf(stderr,"Registering input format %s\n",f->name);
        if (format_list == 0) {
                format_size = 10;
                format_list = malloc(sizeof(struct format_t *) * format_size);
        } else if (format_size == nformats) {
                format_size = format_size + 10;
                format_list = realloc(format_list,
                                sizeof(struct format_t *) * format_size);
        }
        format_list[nformats] = f;
        nformats++;
}


#define RP_BUFSIZE 65536

#define URI_PROTO_LINE 16
static int init_trace(struct libtrace_t **libtrace, char *uri) {
        char *scan = calloc(sizeof(char),URI_PROTO_LINE);
        char *uridata = 0;                  
        int i = 0;
        struct stat buf;
        
        // parse the URI to determine what sort of event we are dealing with
       
        // want snippet before the : to get the uri base type.

        if((uridata = strchr(uri,':')) == NULL) {
                // badly formed URI - needs a :
                return 0;
        }

        if ((*uridata - *uri) > URI_PROTO_LINE) {
                // badly formed URI - uri type is too long
                return 0;
        }
        strncpy(scan,uri, (uridata - uri));

        (*libtrace)->tdelta = 0.0;


        (*libtrace)->format = 0;
        for (i = 0; i < nformats; i++) {
                if (strlen(scan) == strlen(format_list[i]->name) &&
                                !strncasecmp(scan,
                                        format_list[i]->name,
                                        strlen(scan))) {
                                (*libtrace)->format=format_list[i];
                                break;
                                }
        }
        if ((*libtrace)->format == 0) {
                fprintf(stderr,
                        "libtrace has no support for this format (%s)\n",scan);
                return 0;
        }

        // push uridata past the delimiter
        uridata++;
        (*libtrace)->conn_info.path = strdup(uridata);

        // libtrace->format now contains the type of uri
        // libtrace->uridata contains the appropriate data for this
        
        if ((*libtrace)->format->init_input) {
                (*libtrace)->format->init_input( (*libtrace));
        } else {
                fprintf(stderr,
                        "No init function for format %s\n",scan);
                return 0;
        }
        

        (*libtrace)->fifo = create_fifo(1048576);
        assert( (*libtrace)->fifo);
        //(*libtrace)->packet.buffer = 0;
        //(*libtrace)->packet.size = 0;

        return 1;
}

/** Initialises the data contained within the libtrace_out_t structure, based on the provided uri.
 *
 * @param libtrace      the libtrace_out_t structure to initialise
 * @param uri           the uri defining the output type and destination
 * @returns             1 if initialised successfully, 0 otherwise
 *
 * @author Shane Alcock
 * */
static int init_output(struct libtrace_out_t **libtrace, char *uri) {
        char *scan = calloc(sizeof(char),URI_PROTO_LINE);
        char *uridata = 0;

        // parse the URI to determine what sort of event we are dealing with

        // want snippet before the : to get the uri base type.

        if((uridata = strchr(uri,':')) == NULL) {
                // badly formed URI - needs a :
                return 0;
        }

        if ((*uridata - *uri) > URI_PROTO_LINE) {
                // badly formed URI - uri type is too long
                return 0;
        }
        strncpy(scan,uri, (uridata - uri));

        if (!strncasecmp(scan,"gzerf",5)) {
                (*libtrace)->outputformat = GZERF;
        } else if (!strncasecmp(scan, "rt", 2)) {
                (*libtrace)->outputformat = RTSERVER;
        } else {
                return 0;
        }

        uridata ++;
        switch((*libtrace)->outputformat) {
                case GZERF:
                        /* 
                         * Acceptable uridata takes the form:
                         * /path/to/file.gz
                         */
                        (*libtrace)->conn_info.path = strdup(uridata);
                        break;
                case RTSERVER:
                        /* 
                         * Possible uridata formats:
                         * hostname
                         * hostname:port
                         */
                        if (strlen(uridata) == 0) {
                                (*libtrace)->conn_info.rt.hostname =
                                        strdup("localhost");
                                (*libtrace)->conn_info.rt.port =
                                        COLLECTOR_PORT;
                                break;
                        }
                        if ((scan = strchr(uridata,':')) == NULL) {
                                (*libtrace)->conn_info.rt.hostname =
                                        strdup(uridata);
                                (*libtrace)->conn_info.rt.port =
                                        COLLECTOR_PORT;
                        } else {
                                (*libtrace)->conn_info.rt.hostname =
                                        (char *)strndup(uridata,(scan - uridata));

                                (*libtrace)->conn_info.rt.port =
                                        atoi(++scan);
                        }
                        break;
                default:
                        fprintf(stderr, "How did you get here??\n");
        }
        (*libtrace)->fifo = create_fifo(1048576);
        assert( (*libtrace)->fifo);
        return 1;
} 

/** Create a trace file from a URI
 * 
 * @returns opaque pointer to a libtrace_t
 *
 * Valid URI's are:
 *  erf:/path/to/erf/file
 *  erf:/path/to/erf/file.gz
 *  erf:/path/to/rtclient/socket
 *  erf:-                       (stdin)
 *  pcapint:pcapinterface               (eg: pcapint:eth0)
 *  pcap:/path/to/pcap/file
 *  pcap:-
 *  rtclient:hostname
 *  rtclient:hostname:port
 *  wag:-
 *  wag:/path/to/wag/file
 *  wag:/path/to/wag/file.gz
 *  wag:/path/to/wag/socket
 *  wagint:/dev/device
 *
 * URIs which have yet to be implemented are:
 * dag:/dev/dagcard
 * pcap:/path/to/pcap/socket
 *
 * If an error occured when attempting to open a trace, NULL is returned
 * and an error is output to stdout.
 */
struct libtrace_t *trace_create(char *uri) {
        struct libtrace_t *libtrace = malloc(sizeof(struct libtrace_t));
        struct hostent *he;
        struct sockaddr_in remote;
        struct sockaddr_un unix_sock;
#if HAVE_PCAP
        char errbuf[PCAP_ERRBUF_SIZE];
#endif

        if(init_trace(&libtrace,uri) == 0) {
                return 0;
        }
       
        return libtrace;
}

/** Creates a libtrace_out_t structure and the socket / file through which output will be directed.
 *
 * @param uri   the uri string describing the output format and the destination
 * @returns the newly created libtrace_out_t structure
 * 
 * @author Shane Alcock
 * */
struct libtrace_out_t *trace_output_create(char *uri) {
        struct libtrace_out_t *libtrace = malloc(sizeof(struct libtrace_out_t));
        struct sockaddr_in remote, client;
        int client_fd, clilen;
        struct hostent *he;
        
        if (init_output(&libtrace, uri) == 0)
                return 0;

        switch(libtrace->outputformat) {
                case RTSERVER:
                        if ((he=gethostbyname(libtrace->conn_info.rt.hostname)) == NULL) {
                                perror("gethostbyname");
                                return 0;
                        }
                        if ((libtrace->output.fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
                                perror("socket");
                                return 0;
                        }
                        // Need to set up a listening server here
                        bzero((char *) &remote, sizeof(remote)); 
                        remote.sin_family = AF_INET;
                        remote.sin_addr.s_addr = INADDR_ANY;
                        remote.sin_port = htons(libtrace->conn_info.rt.port);

                        if (bind(libtrace->output.fd, (struct sockaddr *) &remote, sizeof(remote)) < 0) {
                                perror("bind");
                                return 0;
                        }
                        fprintf(stderr, "Waiting for client to connect\n");

                        listen(libtrace->output.fd, 5);
                        clilen = sizeof(client);
                        if ((client_fd = accept(libtrace->output.fd, (struct sockaddr *) &client, &clilen)) < 0) {
                                perror("accept");
                                return 0;
                        }
                        libtrace->output.fd = client_fd;
                        fprintf(stderr, "Client connected\n");                       
                        break;


                case GZERF:
/* Catch undefined O_LARGEFILE on *BSD etc */
#ifndef O_LARGEFILE
#  define O_LARGEFILE 0
#endif

#if HAVE_ZLIB
                        // using gzdopen means we can set O_LARGEFILE
                        // ourselves. However, this way is messy and
                        // we lose any error checking on "open"
                        libtrace->output.file = gzdopen(open(libtrace->conn_info.path, O_CREAT | O_LARGEFILE | O_WRONLY, S_IRUSR | S_IWUSR), "w");
#else
                        libtrace->output.file = fdopen(open(libtrace->conn_info.path,O_CREAT | O_LARGEFILE | O_WRONLY, S_IRUSR | S_IWUSR), "w");
#endif                  
                        if (!libtrace->output.file) {
                                perror("gzdopen (or fdopen)");
                                return 0;
                        }
                        break;
                default:
                        fprintf(stderr, "Unrecognised output type - failure to create output instance \n");
                        exit(0);
        }
        return libtrace;
}

/** Close a trace file, freeing up any resources it may have been using
 *
 */
void trace_destroy(struct libtrace_t *libtrace) {
        assert(libtrace);
        libtrace->format->fin_input(libtrace);
        // need to free things!
        destroy_fifo(libtrace->fifo);
        free(libtrace);
}

/** Close an output trace file, freeing up any resources it may have been using
 *
 * @param libtrace      the output trace file to be destroyed
 *
 * @author Shane Alcock
 * */
void trace_output_destroy(struct libtrace_out_t *libtrace) {
        assert(libtrace);

        if (libtrace->outputformat == RTSERVER) {
                close(libtrace->output.fd);
        }
        else {
#if HAVE_ZLIB
                gzclose(libtrace->output.file);
#else
                fclose(libtrace->output.file);
#endif
        }
        destroy_fifo(libtrace->fifo);
        free(libtrace);
}

static int trace_read(struct libtrace_t *libtrace, void *buffer, size_t len) {
        int numbytes;
        static short lctr = 0;
        struct dag_record_t *recptr = 0;
        int rlen;
        assert(libtrace);
        assert(len >= 0);

        if (buffer == 0)
                buffer = malloc(len);

        while(1) {
                switch(libtrace->sourcetype) {
                        case SOCKET:
                        case RT:

#ifndef MSG_NOSIGNAL
#define MSG_NOSIGNAL 0
#endif
                                // read from the network
                                if ((numbytes=recv(libtrace->input.fd, 
                                                                buffer, 
                                                                len, 
                                                                MSG_NOSIGNAL)) == -1) {
                                        if (errno == EINTR) {
                                                // ignore EINTR in case 
                                                // a caller is using signals
                                                continue;
                                        }
                                        perror("recv");
                                        return -1;
                                }
                                break;
                        case DEVICE:
                                if (libtrace->format->read) {
                                        libtrace->format->read(libtrace,buffer,len);
                                } else {
                                        if ((numbytes=read(libtrace->input.fd, 
                                                                buffer, 
                                                                len)) == -1) {
                                                perror("read");
                                                return -1;
                                        }
                                }
                                break;
                        default:
#if HAVE_ZLIB
                                if ((numbytes=gzread(libtrace->input.file,
                                                                buffer,
                                                                len)) == -1) {
                                        perror("gzread");
                                        return -1;
                                }
#else
                                if ((numbytes=fread(buffer,len,1,libtrace->input.file)) == 0 ) {
                                        if(feof(libtrace->input.file)) {
                                                return 0;
                                        }
                                        if(ferror(libtrace->input.file)) {
                                                perror("fread");
                                                return -1;
                                        }
                                        return 0;
                                }
#endif
                }
                break;
        }
        return numbytes;

}

#if HAVE_PCAP
void trace_pcap_handler(u_char *user, const struct pcap_pkthdr *pcaphdr, const u_char *pcappkt) {
        struct libtrace_packet_t *packet = (struct libtrace_packet_t *)user;    
        void *buffer = packet->buffer;
        int numbytes = 0;
        
        memcpy(buffer,pcaphdr,sizeof(struct pcap_pkthdr));
        numbytes = pcaphdr->len;
        memcpy(buffer + sizeof(struct pcap_pkthdr),pcappkt,numbytes);

        packet->size = numbytes + sizeof(struct pcap_pkthdr);

}
#endif
/** Read one packet from the trace into buffer
 *
 * @param libtrace      the libtrace opaque pointer
 * @param packet        the packet opaque pointer
 * @returns false if it failed to read a packet
 *
 */
int trace_read_packet(struct libtrace_t *libtrace, struct libtrace_packet_t *packet) {

        if (!libtrace) {
                fprintf(stderr,"Oi! You called trace_read_packet() with a NULL libtrace parameter!\n");
        }
        assert(libtrace);
        assert(packet);
      
        /* Store the trace we are reading from into the packet opaque 
         * structure */
        packet->trace = libtrace;

        if (libtrace->format->read_packet) {
                return libtrace->format->read_packet(libtrace,packet);
        }
}

static int trace_write(struct libtrace_out_t *libtrace, void *buffer, size_t len) {
        int numbytes = 0;

        assert(libtrace);
        assert(len >= 0);

        if (buffer == NULL) {
                return 0;
        }

        while (1) {
                switch(libtrace->outputformat) {
                        case RTSERVER:
#ifndef MSG_NOSIGNAL
#define MSG_NOSIGNAL 0
#endif
                                // Write to the network
                                if ((numbytes = send(libtrace->output.fd, 
                                                        buffer,
                                                        len,
                                                        MSG_NOSIGNAL)) == -1) {
                                        if (errno == EINTR) {
                                                continue;
                                        }
                                        perror("send");
                                        return -1;
                                }
                                break;
                        case GZERF:                     
#if HAVE_ZLIB
                                if ((numbytes = gzwrite(libtrace->output.file,
                                                        buffer,
                                                        len)) == -1) {
                                        perror("gzwrite");
                                        return -1;
                                }
                                break;
#else
                                // Do binary write instead
                                if ((numbytes = fwrite(buffer, len, 1, libtrace->output.file)) == 0) {
                                        perror("fwrite");
                                        return -1;
                                }
                                break;
#endif
                        default:
                                fprintf(stderr, "Bad output type\n");
                                break;
                }
                break;
        }       
        return numbytes;
}               

/** Writes a packet to the specified output
 *
 * @param libtrace      describes the output format, destination, etc.
 * @param packet        the packet to be written out
 * @returns the number of bytes written, -1 if write failed
 *
 * @author Shane Alcock
 * */
int trace_write_packet(struct libtrace_out_t *libtrace, struct libtrace_packet_t *packet) {
        // initialise stuff
        int numbytes, size;
        char buf[RP_BUFSIZE];
        int intsize = sizeof(int);
        void *buffer = &buf[intsize];
        int write_required = 0;

        assert(libtrace);
        assert(packet); 

        if (libtrace->outputformat == GZERF) {
                // do gzwrite
                if ((numbytes = gzwrite(libtrace->output.file, packet->buffer, packet->size)) == 0) {
                        perror("gzwrite");
                        return -1;
                }
                return numbytes;
        }
        
        // do fifo stuff for RT output instead
        if (libtrace->outputformat == RTSERVER) {
                do {
                        assert(libtrace->fifo);

                        if (fifo_out_available(libtrace->fifo) == 0 || write_required) {
                                // Packet added to fifo
                                if ((numbytes = fifo_write(libtrace->fifo, packet->buffer, packet->size)) == 0) {
                                        // some error with the fifo
                                        perror("fifo_write");
                                        return -1;
                                }
                                write_required = 0;
                        }
                        
                        // Read from fifo and add protocol header
                        if ((numbytes = fifo_out_read(libtrace->fifo, buffer, sizeof(dag_record_t))) == 0) {
                                // failure reading in from fifo
                                fifo_out_reset(libtrace->fifo);
                                write_required = 1;
                                continue;
                        }
                        size = ntohs(((dag_record_t *)buffer)->rlen);           
                        assert(size < LIBTRACE_PACKET_BUFSIZE);
        
                        if ((numbytes = fifo_out_read(libtrace->fifo, buffer, size)) == 0) {
                                // failure reading in from fifo
                                fifo_out_reset(libtrace->fifo);
                                write_required = 1;
                                continue;
                        }
                        fifo_out_update(libtrace->fifo, size);  
                        // Sort out the protocol header
                        memcpy(buf, &packet->status, intsize);
                                                

                        // Send the buffer out on the wire
                        if ((numbytes = trace_write(libtrace, buf, size + sizeof(int))) <=0 ) {
                                return numbytes;
                        }

                        // Need an ack to come back
                        // TODO: Obviously this is a little unfinished
                        if ("ACK_ARRIVES") {
                                fifo_ack_update(libtrace->fifo, size);
                                return numbytes;
                        } else {
                                fifo_out_reset(libtrace->fifo);
                        }
                } while(1);
        }

        // Unacceptable output format
        fprintf(stderr, "Unknown Output format \n");
        assert(0);
}

/** get a pointer to the link layer
 * @param packet        a pointer to a libtrace_packet structure
 *
 * @returns a pointer to the link layer, or NULL if there is no link layer
 * you should call trace_get_link_type() to find out what type of link layer this is
 */
void *trace_get_link(const struct libtrace_packet_t *packet) {
        const void *ethptr = 0;
        
        if (packet->trace->format->get_link) {
                ethptr = packet->trace->format->get_link(packet);
        }
        return (void *)ethptr;
}

/** get a pointer to the IP header (if any)
 * @param packet        a pointer to a libtrace_packet structure
 *
 * @returns a pointer to the IP header, or NULL if there is not an IP packet
 */
struct libtrace_ip *trace_get_ip(const struct libtrace_packet_t *packet) {
        struct libtrace_ip *ipptr = 0;

        switch(trace_get_link_type(packet)) {
                case TRACE_TYPE_80211:
                        { 
                                
                                struct ieee_802_11_header *wifi = trace_get_link(packet);       
                                if (!wifi) {
                                        ipptr = NULL;
                                        break;
                                }

                                // Data packet?
                                if (wifi->type != 2) {
                                        ipptr = NULL;
                                }
                                else {
                                        struct ieee_802_11_payload *eth = (void*)wifi->data;
                                        if (eth->type != 0x0008) {
                                                ipptr=NULL;
                                        } else {
                                                ipptr=(void*)eth->data;
                                        }
                                }
                        }
                        break;
                case TRACE_TYPE_ETH:
                        {
                                struct ether_header *eth = 
                                        trace_get_link(packet);
                                if (!eth) {
                                        ipptr = NULL;
                                        break;
                                }
                                if (ntohs(eth->ether_type)!=0x0800) {
                                        ipptr = NULL;
                                }
                                else {
                                        ipptr = ((void *)eth) + 14;
                                }
                                break;
                        }
                case TRACE_TYPE_NONE:
                        ipptr = trace_get_link(packet);
                        break;
                case TRACE_TYPE_LINUX_SLL:
                        {
                                struct trace_sll_header_t *sll;

                                sll = trace_get_link(packet);
                                if (!sll) {
                                        ipptr = NULL;
                                        break;
                                }
                                if (ntohs(sll->protocol)!=0x0800) {
                                        ipptr = NULL;
                                }
                                else {
                                        ipptr = ((void*)sll)+sizeof(*sll);
                                }
                        }
                        break;
                case TRACE_TYPE_PFLOG:
                        {
                                struct trace_pflog_header_t *pflog;
                                pflog = trace_get_link(packet);
                                if (!pflog) {
                                        ipptr = NULL;
                                        break;
                                }
                                if (pflog->af != AF_INET) {
                                        ipptr = NULL;
                                } else {
                                        ipptr = ((void*)pflog)+sizeof(*pflog);
                                }
                        }
                        break;
                case TRACE_TYPE_ATM:
                        {
                                struct atm_rec *atm = 
                                        trace_get_link(packet);
                                // TODO: Find out what ATM does, and return
                                //       NULL for non IP data
                                //       Presumably it uses the normal stuff
                                if (!atm) {
                                        ipptr = NULL;
                                        break;
                                }
                                ipptr =  (void*)&atm->pload;
                                break;
                        }
                default:
                        fprintf(stderr,"Don't understand link layer type %i in trace_get_ip()\n",
                                trace_get_link_type(packet));
                        ipptr=NULL;
                        break;
        }

        return ipptr;
}

#define SW_IP_OFFMASK 0xff1f

/** get a pointer to the TCP header (if any)
 * @param packet        a pointer to a libtrace_packet structure
 *
 * @returns a pointer to the TCP header, or NULL if there is not a TCP packet
 */
struct libtrace_tcp *trace_get_tcp(const struct libtrace_packet_t *packet) {
        struct libtrace_tcp *tcpptr = 0;
        struct libtrace_ip *ipptr = 0;

        if(!(ipptr = trace_get_ip(packet))) {
                return 0;
        }
        if ((ipptr->ip_p == 6) && ((ipptr->ip_off & SW_IP_OFFMASK) == 0))  {
                tcpptr = (struct libtrace_tcp *)((ptrdiff_t)ipptr + (ipptr->ip_hl * 4));
        }
        return tcpptr;
}

/** get a pointer to the TCP header (if any) given a pointer to the IP header
 * @param ip            The IP header
 * @param[out] skipped  An output variable of the number of bytes skipped
 *
 * @returns a pointer to the TCP header, or NULL if this is not a TCP packet
 *
 * Skipped can be NULL, in which case it will be ignored by the program.
 */
struct libtrace_tcp *get_tcp_from_ip(const struct libtrace_ip *ip, int *skipped)
{
#define SW_IP_OFFMASK 0xff1f
        struct libtrace_tcp *tcpptr = 0;

        if ((ip->ip_p == 6) && ((ip->ip_off & SW_IP_OFFMASK) == 0))  {
                tcpptr = (struct libtrace_tcp *)((ptrdiff_t)ip+ (ip->ip_hl * 4));
        }

        if (skipped)
                *skipped=(ip->ip_hl*4);

        return tcpptr;
}

/** get a pointer to the UDP header (if any)
 * @param packet        a pointer to a libtrace_packet structure
 *
 * @returns a pointer to the UDP header, or NULL if this is not a UDP packet
 */
struct libtrace_udp *trace_get_udp(const struct libtrace_packet_t *packet) {
        struct libtrace_udp *udpptr = 0;
        struct libtrace_ip *ipptr = 0;
        
        if(!(ipptr = trace_get_ip(packet))) {
                return 0;
        }
        if ((ipptr->ip_p == 17) && ((ipptr->ip_off & SW_IP_OFFMASK) == 0)) {
                udpptr = (struct libtrace_udp *)((ptrdiff_t)ipptr + (ipptr->ip_hl * 4));
        }

        return udpptr;
}

/** get a pointer to the UDP header (if any) given a pointer to the IP header
 * @param ip            The IP header
 * @param[out] skipped  An output variable of the number of bytes skipped
 *
 * @returns a pointer to the UDP header, or NULL if this is not a UDP packet
 *
 * Skipped can be NULL, in which case it will be ignored by the program.
 */
struct libtrace_udp *get_udp_from_ip(const struct libtrace_ip *ip, int *skipped)
{
        struct libtrace_udp *udpptr = 0;

        if ((ip->ip_p == 6) && ((ip->ip_off & SW_IP_OFFMASK) == 0))  {
                udpptr = (struct libtrace_udp *)((ptrdiff_t)ip+ (ip->ip_hl * 4));
        }

        if (skipped)
                *skipped=(ip->ip_hl*4);

        return udpptr;
}


/** get a pointer to the ICMP header (if any)
 * @param packet        a pointer to a libtrace_packet structure
 *
 * @returns a pointer to the ICMP header, or NULL if this is not a ICMP packet
 */
struct libtrace_icmp *trace_get_icmp(const struct libtrace_packet_t *packet) {
        struct libtrace_icmp *icmpptr = 0;
        struct libtrace_ip *ipptr = 0;
        
        if(!(ipptr = trace_get_ip(packet))) {
                return 0;
        }
        if ((ipptr->ip_p == 1)&& ((ipptr->ip_off & SW_IP_OFFMASK) == 0 )){
                icmpptr = (struct libtrace_icmp *)((ptrdiff_t)ipptr + (ipptr->ip_hl * 4));
        }
        return icmpptr;
}

/** get a pointer to the ICMP header (if any) given a pointer to the IP header
 * @param ip            The IP header
 * @param[out] skipped  An output variable of the number of bytes skipped
 *
 * @returns a pointer to the ICMP header, or NULL if this is not a ICMP packet
 *
 * Skipped can be NULL, in which case it will be ignored by the program.
 */
struct libtrace_icmp *get_icmp_from_ip(struct libtrace_ip *ip, int *skipped)
{
        struct libtrace_icmp *icmpptr = 0;

        if ((ip->ip_p == 6) && ((ip->ip_off & SW_IP_OFFMASK) == 0))  {
                icmpptr = (struct libtrace_icmp *)((ptrdiff_t)ip+ (ip->ip_hl * 4));
        }

        if (skipped)
                *skipped=(ip->ip_hl*4);

        return icmpptr;
}
/** parse an ip or tcp option
 * @param[in,out] ptr   the pointer to the current option
 * @param[in,out] len   the length of the remaining buffer
 * @param[out] type     the type of the option
 * @param[out] optlen   the length of the option
 * @param[out] data     the data of the option
 *
 * @returns bool true if there is another option (and the fields are filled in)
 *               or false if this was the last option.
 *
 * This updates ptr to point to the next option after this one, and updates
 * len to be the number of bytes remaining in the options area.  Type is updated
 * to be the code of this option, and data points to the data of this option,
 * with optlen saying how many bytes there are.
 *
 * @note Beware of fragmented packets.
 * @author Perry Lorier
 */
int trace_get_next_option(unsigned char **ptr,int *len,
                        unsigned char *type,
                        unsigned char *optlen,
                        unsigned char **data)
{
        if (*len<=0)
                return 0;
        *type=**ptr;
        switch(*type) {
                case 0: /* End of options */
                        return 0;
                case 1: /* Pad */
                        (*ptr)++;
                        (*len)--;
                        return 1;
                default:
                        *optlen = *(*ptr+1);
                        if (*optlen<2)
                                return 0; // I have no idea wtf is going on
                                          // with these packets
                        (*len)-=*optlen;
                        (*data)=(*ptr+2);
                        (*ptr)+=*optlen;
                        if (*len<0)
                                return 0;
                        return 1;
        }
        assert(0);
}


/** Get the current time in DAG time format 
 * @param packet        a pointer to a libtrace_packet structure
 * @returns a 64 bit timestamp in DAG ERF format (upper 32 bits are the seconds
 * past 1970-01-01, the lower 32bits are partial seconds)
 * @author Daniel Lawson
 */ 
uint64_t trace_get_erf_timestamp(const struct libtrace_packet_t *packet) {
        uint64_t timestamp = 0;
        struct timeval ts;

        if (packet->trace->format->get_erf_timestamp) {
                timestamp = packet->trace->format->get_erf_timestamp(packet);
        } else if (packet->trace->format->get_timeval) {
                ts = packet->trace->format->get_timeval(packet);
                timestamp = ((((uint64_t)ts.tv_sec) << 32) + \
                                (((uint64_t)ts.tv_usec * UINT_MAX)/1000000));
        }
        return timestamp;
}

/** Get the current time in struct timeval
 * @param packet        a pointer to a libtrace_packet structure
 *
 * @returns time that this packet was seen in a struct timeval
 * @author Daniel Lawson
 * @author Perry Lorier
 */ 
struct timeval trace_get_timeval(const struct libtrace_packet_t *packet) {
        struct timeval tv;
        uint64_t ts = 0;

        if (packet->trace->format->get_timeval) {
                tv = packet->trace->format->get_timeval(packet);
        } else if (packet->trace->format->get_erf_timestamp) {
                ts = packet->trace->format->get_erf_timestamp(packet);
#if __BYTE_ORDER == __BIG_ENDIAN
                tv.tv_sec = ts & 0xFFFFFFFF;
#elif __BYTE_ORDER == __LITTLE_ENDIAN
                tv.tv_sec = ts >> 32;
#else
#error "What on earth are you running this on?"
#endif
                ts = (1000000 * (ts & 0xffffffffULL));
                ts += (ts & 0x80000000ULL) << 1;
                tv.tv_usec = ts >> 32;
                if (tv.tv_usec >= 1000000) {
                        tv.tv_usec -= 1000000;
                        tv.tv_sec += 1;
                }
        }

        return tv;
}

/** Get the current time in floating point seconds
 * @param packet        a pointer to a libtrace_packet structure
 * @returns time that this packet was seen in 64bit floating point seconds
 * @author Perry Lorier
 */ 
double trace_get_seconds(const struct libtrace_packet_t *packet) {
        double seconds;
        uint64_t ts;
        
        if (packet->trace->format->get_seconds) {
                seconds = packet->trace->format->get_seconds(packet);
        } else if (packet->trace->format->get_erf_timestamp) {
                ts = packet->trace->format->get_erf_timestamp(packet);
                seconds =  (ts>>32) + ((ts & UINT_MAX)*1.0 / UINT_MAX);
        } 
        return seconds;
}

/** Get the size of the packet in the trace
 * @param packet the packet opaque pointer
 * @returns the size of the packet in the trace
 * @author Perry Lorier
 * @note Due to this being a header capture, or anonymisation, this may not
 * be the same size as the original packet.  See trace_get_wire_length() for the 
 * original size of the packet.
 * @note This can (and often is) different for different packets in a trace!
 * @par 
 *  This is sometimes called the "snaplen".
 */ 
int trace_get_capture_length(const struct libtrace_packet_t *packet) {

        if (packet->trace->format->get_capture_length) {
                return packet->trace->format->get_capture_length(packet);
        }
        return -1;
}
        
/** Get the size of the packet as it was seen on the wire.
 * @param packet        a pointer to a libtrace_packet structure
 *
 * @returns the size of the packet as it was on the wire.
 * @author Perry Lorier
 * @author Daniel Lawson
 * @note Due to the trace being a header capture, or anonymisation this may
 * not be the same as the Capture Len.
 */ 
int trace_get_wire_length(const struct libtrace_packet_t *packet){
        if (packet->trace->format->get_wire_length) {
                return packet->trace->format->get_wire_length(packet);
        }
        return -1;

}

/** Get the type of the link layer
 * @param packet        a pointer to a libtrace_packet structure
 * @returns libtrace_linktype_t
 * @author Perry Lorier
 * @author Daniel Lawson
 */
libtrace_linktype_t trace_get_link_type(const struct libtrace_packet_t *packet ) {
        if (packet->trace->format->get_link_type) {
                return packet->trace->format->get_link_type(packet);
        }
        return -1;
}

/** Get the source MAC addres
 * @param packet        a pointer to a libtrace_packet structure
 * @returns a pointer to the source mac, (or NULL if there is no source MAC)
 * @author Perry Lorier
 */
uint8_t *trace_get_source_mac(const struct libtrace_packet_t *packet) {
        void *link = trace_get_link(packet);
        struct ieee_802_11_header *wifi = link;
        struct ether_header *ethptr = link;
        if (!link)
                return NULL;
        switch (trace_get_link_type(packet)) {
                case TRACE_TYPE_80211:
                        return (uint8_t*)&wifi->mac2;
                case TRACE_TYPE_ETH:
                        return (uint8_t*)&ethptr->ether_shost;
                default:
                        fprintf(stderr,"Not implemented\n");
                        assert(0);
        }
}

/** Get the destination MAC addres
 * @param packet a libtrace_packet pointer
 * @returns a pointer to the destination mac, (or NULL if there is no 
 * destination MAC)
 * @author Perry Lorier
 */
uint8_t *trace_get_destination_mac(const struct libtrace_packet_t *packet) {
        void *link = trace_get_link(packet);
        struct ieee_802_11_header *wifi = link;
        struct ether_header *ethptr = link;
        if (!link)
                return NULL;
        switch (trace_get_link_type(packet)) {
                case TRACE_TYPE_80211:
                        return (uint8_t*)&wifi->mac1;
                case TRACE_TYPE_ETH:
                        return (uint8_t*)&ethptr->ether_dhost;
                default:
                        fprintf(stderr,"Not implemented\n");
                        assert(0);
        }
}


/** process a libtrace event
 * @param trace the libtrace opaque pointer
 * @param packet the libtrace_packet opaque pointer
 * @returns
 *  TRACE_EVENT_IOWAIT  Waiting on I/O on fd
 *  TRACE_EVENT_SLEEP   Next event in seconds
 *  TRACE_EVENT_PACKET  Packet arrived in buffer with size size
 *  TRACE_EVENT_TERMINATE Trace terminated (perhaps with an error condition)
 * FIXME currently keeps a copy of the packet inside the trace pointer,
 * which in turn is stored inside the new packet object...
 * @author Perry Lorier
 */
struct libtrace_eventobj_t trace_event(struct libtrace_t *trace, 
                struct libtrace_packet_t *packet) {
        struct libtrace_eventobj_t event;

        if (!trace) {
                fprintf(stderr,"You called trace_event() with a NULL trace object!\n");
        }
        assert(trace);
        assert(packet);

        /* Store the trace we are reading from into the packet opaque
         * structure */
        packet->trace = trace;

        /* Is there a packet ready? */
        switch (trace->sourcetype) {
#if HAVE_PCAP
                case INTERFACE:
                        {
                                int data;
                                event.fd = pcap_fileno(trace->input.pcap);
                                if(ioctl(event.fd,FIONREAD,&data)==-1){
                                        perror("ioctl(FIONREAD)");
                                }
                                if (data>0) {
                                        event.size = trace_read_packet(trace,packet);
                                        event.type = TRACE_EVENT_PACKET;
                                        return event;
                                }
                                event.type = TRACE_EVENT_IOWAIT;
                                return event;
                        }
#endif
                case SOCKET:
                case DEVICE:
                case RT:
                        {
                                int data;
                                event.fd = trace->input.fd;
                                if(ioctl(event.fd,FIONREAD,&data)==-1){
                                        perror("ioctl(FIONREAD)");
                                }
                                if (data>0) {
                                        event.size = trace_read_packet(trace,packet);
                                        event.type = TRACE_EVENT_PACKET;
                                        return event;
                                }
                                event.type = TRACE_EVENT_IOWAIT;
                                return event;
                        }
                case STDIN:
                case TRACE:
                        {
                                double ts;
                                double now;
                                struct timeval stv;
                                /* "Prime" the pump */
                                if (!trace->packet.buffer) {
                                        trace->packet.buffer = malloc(4096);
                                        trace->packet.size=
                                                trace_read_packet(trace,packet);
                                        event.size = trace->packet.size;
                                        if (trace->packet.size > 0 ) {
                                                memcpy(trace->packet.buffer,packet->buffer,trace->packet.size);
                                        } else {
                                                // return here, the test for event.size will sort out the error
                                                event.type = TRACE_EVENT_PACKET;
                                                return event;
                                        }
                                }

                                ts=trace_get_seconds(packet);
                                if (trace->tdelta!=0) {
                                        // Get the adjusted current time
                                        gettimeofday(&stv, NULL);
                                        now = stv.tv_sec + ((double)stv.tv_usec / 1000000.0);
                                        now -= trace->tdelta; // adjust for trace delta
                                        
                                        
                                        // if the trace timestamp is still in the future, 
                                        // return a SLEEP event, otherwise fire the packet
                                        if (ts > now) {
                                                event.seconds = ts - trace->trace_last_ts;
                                                event.type = TRACE_EVENT_SLEEP;
                                                return event;
                                        }
                                } else {
                                        gettimeofday(&stv, NULL);
                                        // work out the difference between the start of trace replay,
                                        // and the first packet in the trace
                                        trace->tdelta = stv.tv_sec + ((double)stv.tv_usec / 1000000.0);
                                        trace->tdelta -= ts;

                                }
                                
                                        // This is the first packet, so just fire away.
                                packet->size = trace->packet.size;
                                memcpy(packet->buffer,trace->packet.buffer,trace->packet.size);

                                free(trace->packet.buffer);
                                trace->packet.buffer = 0;
                                event.type = TRACE_EVENT_PACKET;
                                
                                trace->trace_last_ts = ts;

                                return event;
                        }
                default:
                        assert(0);
        }
        assert(0);
}

/** setup a BPF filter
 * @param filterstring a char * containing the bpf filter string
 * @returns opaque pointer pointer to a libtrace_filter_t object
 * @author Daniel Lawson
 */
struct libtrace_filter_t *trace_bpf_setfilter(const char *filterstring) {
#if HAVE_BPF
        struct libtrace_filter_t *filter = malloc(sizeof(struct libtrace_filter_t));
        filter->filterstring = strdup(filterstring);
        filter->filter = 0;
        return filter;
#else
        fprintf(stderr,"This version of libtrace does not have bpf filter support\n");
        return 0;
#endif
}

/** apply a BPF filter
 * @param filter the filter opaque pointer
 * @param packet the packet opaque pointer
 * @returns 0 if the filter fails, 1 if it succeeds
 * @author Daniel Lawson
 */
int trace_bpf_filter(struct libtrace_filter_t *filter,
                        const struct libtrace_packet_t *packet) {
#if HAVE_BPF
        void *linkptr = 0;
        int clen = 0;
        assert(filter);
        assert(packet);
        linkptr = trace_get_link(packet);
        if (!linkptr) {
                return 0;
        }
        
        clen = trace_get_capture_length(packet);
        

        if (filter->filterstring && ! filter->filter) {
                pcap_t *pcap;
                struct bpf_program bpfprog;

                switch (trace_get_link_type(packet)) {
                        case TRACE_TYPE_ETH:
                                pcap = (pcap_t *)pcap_open_dead(DLT_EN10MB, 1500);
                                break;
#ifdef DLT_LINUX_SLL
                        case TRACE_TYPE_LINUX_SLL:
                                pcap = (pcap_t *)pcap_open_dead(DLT_LINUX_SLL, 1500);
                                break;
#endif
#ifdef DLT_PFLOG
                        case TRACE_TYPE_PFLOG:
                                pcap = (pcap_t *)pcap_open_dead(DLT_PFLOG, 1500);
                                break;
#endif
                        default:
                                printf("only works for ETH and LINUX_SLL (ppp) at the moment\n");
                                assert(0);
                }               

                // build filter
                if (pcap_compile( pcap, &bpfprog, filter->filterstring, 1, 0)) {
                        printf("bpf compilation error: %s: %s\n", 
                                pcap_geterr(pcap),filter->filterstring);
                        assert(0);
                }
                pcap_close(pcap);
                filter->filter = bpfprog.bf_insns;      
        }

        assert(filter->filter);
        return bpf_filter(filter->filter, linkptr, clen, clen);
#else
        fprintf(stderr,"This version of libtrace does not have bpf filter support\n");
        return 0;
#endif
}

/** Set the direction flag, if it has one
 * @param packet the packet opaque pointer
 * @param direction the new direction (0,1,2,3)
 * @returns a signed value containing the direction flag, or -1 if this is not supported
 * @author Daniel Lawson
 */
int8_t trace_set_direction(struct libtrace_packet_t *packet, int8_t direction) {


        if (packet->trace->format->set_direction) {
                return packet->trace->format->set_direction(packet,direction);
        }
        return -1;
}

/** Get the direction flag, if it has one
 * @param packet a pointer to a libtrace_packet structure
 * @returns a signed value containing the direction flag, or -1 if this is not supported
 * The direction is defined as 0 for packets originating locally (ie, outbound)
 * and 1 for packets originating remotely (ie, inbound).
 * Other values are possible, which might be overloaded to mean special things
 * for a special trace.
 * @author Daniel Lawson
 */
int8_t trace_get_direction(const struct libtrace_packet_t *packet) {
        
        assert(packet);

        if (packet->trace->format->get_direction) {
                return packet->trace->format->get_direction(packet);
        }
        return -1;
        
}

struct ports_t {
        uint16_t src;
        uint16_t dst;
};

/* Return the client port
 */
uint16_t trace_get_source_port(const struct libtrace_packet_t *packet)
{
        struct libtrace_ip *ip = trace_get_ip(packet);
        struct ports_t *port;
        if (6 != ip->ip_p
          && 17 != ip->ip_p)
                return 0;
        if (0 != (ip->ip_off & SW_IP_OFFMASK))
                return 0;

        port = (struct ports_t *)((ptrdiff_t)ip + (ip->ip_hl * 4));

        return htons(port->src);
}

/* Same as get_source_port except use the destination port */
uint16_t trace_get_destination_port(const struct libtrace_packet_t *packet)
{
        struct libtrace_ip *ip = trace_get_ip(packet);
        struct ports_t *port;

        if (6 != ip->ip_p
          && 17 != ip->ip_p)
                return 0;

        if (0 != (ip->ip_off & SW_IP_OFFMASK))
                return 0;

        port = (struct ports_t *)((ptrdiff_t)ip + (ip->ip_hl * 4));

        return htons(port->dst);
}

#define ROOT_SERVER(x) ((x) < 512)
#define ROOT_CLIENT(x) ((512 <= (x)) && ((x) < 1024))
#define NONROOT_SERVER(x) ((x) >= 5000)
#define NONROOT_CLIENT(x) ((1024 <= (x)) && ((x) < 5000))
#define DYNAMIC(x) ((49152 < (x)) && ((x) < 65535))
#define SERVER(x) ROOT_SERVER(x) || NONROOT_SERVER(x)
#define CLIENT(x) ROOT_CLIENT(x) || NONROOT_CLIENT(x) 

/* Attempt to deduce the 'server' port
 * @param protocol the IP protocol (eg, 6 or 17 for TCP or UDP)
 * @param source the TCP or UDP source port
 * @param dest the TCP or UDP destination port
 * @returns a hint as to which port is the server port
 * @author Daniel Lawson
 */
int8_t trace_get_server_port(uint8_t protocol, uint16_t source, uint16_t dest) {
        /*
         * * If the ports are equal, return DEST
         * * Check for well-known ports in the given protocol
         * * Root server ports: 0 - 511
         * * Root client ports: 512 - 1023
         * * non-root client ports: 1024 - 4999
         * * non-root server ports: 5000+
         * * Check for static ranges: 1024 - 49151
         * * Check for dynamic ranges: 49152 - 65535
         * * flip a coin.
         */

        uint16_t server, client;

        /* equal */
        if (source == client)
                return USE_DEST;

        /* root server port, 0 - 511 */
        if (ROOT_SERVER(source) && ROOT_SERVER(dest)) {
                if (source < dest)
                        return USE_SOURCE;
                return USE_DEST;
        }

        if (ROOT_SERVER(source) && !ROOT_SERVER(dest))
                return USE_SOURCE;
        if (!ROOT_SERVER(source) && ROOT_SERVER(dest))
                return USE_DEST;

        /* non-root server */
        if (NONROOT_SERVER(source) && NONROOT_SERVER(dest)) {
                if (source < dest)
                        return USE_SOURCE;
                return USE_DEST;
        }
        if (NONROOT_SERVER(source) && !NONROOT_SERVER(dest))
                return USE_SOURCE;
        if (!NONROOT_SERVER(source) && NONROOT_SERVER(dest))
                return USE_DEST;

        /* root client */
        if (ROOT_CLIENT(source) && ROOT_CLIENT(dest)) {
                if (source < dest)
                        return USE_SOURCE;
                return USE_DEST;
        }
        if (ROOT_CLIENT(source) && !ROOT_CLIENT(dest)) {
                /* prefer root-client over nonroot-client */
                if (NONROOT_CLIENT(dest))
                        return USE_SOURCE;
                return USE_DEST;
        }
        if (!ROOT_CLIENT(source) && ROOT_CLIENT(dest)) {
                /* prefer root-client over nonroot-client */
                if (NONROOT_CLIENT(source))
                        return USE_DEST;
                return USE_SOURCE;
        }
        
        /* nonroot client */
        if (NONROOT_CLIENT(source) && NONROOT_CLIENT(dest)) {
                if (source < dest) 
                        return USE_SOURCE;
                return USE_DEST;
        }
        if (NONROOT_CLIENT(source) && !NONROOT_CLIENT(dest))
                return USE_DEST;
        if (!NONROOT_CLIENT(source) && NONROOT_CLIENT(dest))
                return USE_SOURCE;

        /* dynamic range */
        if (DYNAMIC(source) && DYNAMIC(dest))
                if (source < dest)
                        return USE_SOURCE;
                return USE_DEST;
        if (DYNAMIC(source) && !DYNAMIC(dest))
                return USE_DEST;
        if (!DYNAMIC(source) && DYNAMIC(dest))
                return USE_SOURCE;
        /*
        if (SERVER(source) && CLIENT(dest)) 
                return USE_SOURCE;
        
        if (SERVER(dest) && CLIENT(source)) 
                return USE_DEST;
        if (ROOT_SERVER(source) && !ROOT_SERVER(dest)) 
                return USE_SOURCE;
        if (ROOT_SERVER(dest) && !ROOT_SERVER(source)) 
                return USE_DEST;
        */
        // failing that test...
        if (source < dest) {
                return USE_SOURCE;
        } 
        return USE_DEST;
        
}

/** Truncate the packet at the suggested length
 * @param packet        the packet opaque pointer
 * @param size          the new length of the packet
 * @returns the new length of the packet, or the original length of the 
 * packet if unchanged
 * NOTE: len refers to the network-level payload of the packet, and not
 * any capture headers included as well. For example, to truncate a packet
 * after the IP header, set scan to sizeof(ethernet_header) + sizeof(ip_header)
 * @author Daniel Lawson
 */
size_t trace_set_capture_length(struct libtrace_packet_t *packet, size_t size) {
        dag_record_t *erfptr;
#if HAVE_PCAP
        struct pcap_pkthdr *pcaphdr;
#endif

        assert(packet);

        if (size > packet->size) {
                // can't make a packet larger
                return packet->size;
        }
        if (packet->trace->format->truncate_packet) {
                return packet->trace->format->truncate_packet(packet,size);
        }
        return -1;
}