FreeBSD-5.3/usr.sbin/tcpdump/tcpslice/search.c
/*
* Copyright (c) 1990, 1991, 1992, 1993
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that: (1) source code distributions
* retain the above copyright notice and this paragraph in its entirety, (2)
* distributions including binary code include the above copyright notice and
* this paragraph in its entirety in the documentation or other materials
* provided with the distribution, and (3) all advertising materials mentioning
* features or use of this software display the following acknowledgement:
* ``This product includes software developed by the University of California,
* Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
* the University nor the names of its contributors may be used to endorse
* or promote products derived from this software without specific prior
* written permission.
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
* WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*/
#if !defined(lint) && !defined(__GNUC__)
static char rcsid[] =
"@(#)$FreeBSD: src/usr.sbin/tcpdump/tcpslice/search.c,v 1.4 1999/08/28 05:11:32 peter Exp $ (LBL)";
#endif
/*
* search.c - supports fast searching through tcpdump files for timestamps
*/
#include "tcpslice.h"
/* Maximum number of seconds that we can conceive of a dump file spanning. */
#define MAX_REASONABLE_FILE_SPAN (3600*24*366) /* one year */
/* Maximum packet length we ever expect to see. */
#define MAX_REASONABLE_PACKET_LENGTH 65535
/* Size of a packet header in bytes; easier than typing the sizeof() all
* the time ...
*/
#define PACKET_HDR_LEN (sizeof( struct pcap_pkthdr ))
extern int snaplen;
/* The maximum size of a packet, including its header. */
#define MAX_PACKET_SIZE (PACKET_HDR_LEN + snaplen)
/* Number of contiguous bytes from a dumpfile in which there's guaranteed
* to be enough information to find a "definite" header if one exists
* therein. This takes 3 full packets - the first to be just misaligned
* (one byte short of a full packet), missing its timestamp; the second
* to have the legitimate timestamp; and the third to provide confirmation
* that the second is legit, making it a "definite" header. We could
* scrimp a bit here since not the entire third packet is required, but
* it doesn't seem worth it
*/
#define MAX_BYTES_FOR_DEFINITE_HEADER (3 * MAX_PACKET_SIZE)
/* Maximum number of seconds that might reasonably separate two headers. */
#define MAX_REASONABLE_HDR_SEPARATION (3600 * 24 * 7) /* one week */
/* When searching a file for a packet, if we think we're within this many
* bytes of the packet we just search linearly. Since linear searches are
* probably much faster than random ones (random ones require searching for
* the beginning of the packet, which may be unaligned in memory), we make
* this value pretty hefty.
*/
#define STRAIGHT_SCAN_THRESHOLD (100 * MAX_PACKET_SIZE)
/* Given a header and an acceptable first and last time stamp, returns non-zero
* if the header looks reasonable and zero otherwise.
*/
static int
reasonable_header( struct pcap_pkthdr *hdr, long first_time, long last_time )
{
if ( last_time == 0 )
last_time = first_time + MAX_REASONABLE_FILE_SPAN;
return hdr->ts.tv_sec >= first_time &&
hdr->ts.tv_sec <= last_time &&
hdr->len > 0 &&
hdr->len <= MAX_REASONABLE_PACKET_LENGTH &&
hdr->caplen > 0 &&
hdr->caplen <= MAX_REASONABLE_PACKET_LENGTH;
}
#define SWAPLONG(y) \
((((y)&0xff)<<24) | (((y)&0xff00)<<8) | (((y)&0xff0000)>>8) | (((y)>>24)&0xff))
#define SWAPSHORT(y) \
( (((y)&0xff)<<8) | (((y)&0xff00)>>8) )
/* Given a buffer, extracts a (properly aligned) packet header from it. */
static void
extract_header( pcap_t *p, u_char *buf, struct pcap_pkthdr *hdr )
{
bcopy((char *) buf, (char *) hdr, sizeof(struct pcap_pkthdr));
if ( pcap_is_swapped( p ) )
{
hdr->ts.tv_sec = SWAPLONG(hdr->ts.tv_sec);
hdr->ts.tv_usec = SWAPLONG(hdr->ts.tv_usec);
hdr->len = SWAPLONG(hdr->len);
hdr->caplen = SWAPLONG(hdr->caplen);
}
/*
* From bpf/libpcap/savefile.c:
*
* We interchanged the caplen and len fields at version 2.3,
* in order to match the bpf header layout. But unfortunately
* some files were written with version 2.3 in their headers
* but without the interchanged fields.
*/
if ( pcap_minor_version( p ) < 3 ||
(pcap_minor_version( p ) == 3 && hdr->caplen > hdr->len) )
{
int t = hdr->caplen;
hdr->caplen = hdr->len;
hdr->len = t;
}
}
/* Search a buffer to locate the first header within it. Return values
* are HEADER_NONE, HEADER_CLASH, HEADER_PERHAPS, and HEADER_DEFINITELY.
* The first indicates that no evidence of a header was found; the second
* that two or more possible headers were found, neither more convincing
* than the other(s); the third that exactly one "possible" header was
* found; and the fourth that exactly one "definite" header was found.
*
* Headers are detected by looking for positions in the buffer which have
* reasonable timestamps and lengths. If there is enough room in the buffer
* for another header to follow a candidate header, a check is made for
* that following header. If it is present then the header is *definite*
* (unless another "perhaps" or "definite" header is found); if not, then
* the header is discarded. If there is not enough room in the buffer for
* another header then the candidate is *perhaps* (unless another header
* is subsequently found). A "tie" between a "definite" header and a
* "perhaps" header is resolved in favor of the definite header. Any
* other tie leads to HEADER_CLASH.
*
* The buffer position of the header is returned in hdrpos_addr and
* for convenience the corresponding header in return_hdr.
*
* first_time is the earliest possible acceptable timestamp in the
* header. last_time, if non-zero, is the last such timestamp. If
* zero, then up to MAX_REASONABLE_FILE_SPAN seconds after first_time
* is acceptable.
*/
#define HEADER_NONE 0
#define HEADER_CLASH 1
#define HEADER_PERHAPS 2
#define HEADER_DEFINITELY 3
static int
find_header( pcap_t *p, u_char *buf, int buf_len,
long first_time, long last_time,
u_char **hdrpos_addr, struct pcap_pkthdr *return_hdr )
{
u_char *bufptr, *bufend, *last_pos_to_try;
struct pcap_pkthdr hdr, hdr2;
int status = HEADER_NONE;
int saw_PERHAPS_clash = 0;
/* Initially, try each buffer position to see whether it looks like
* a valid packet header. We may later restrict the positions we look
* at to avoid seeing a sequence of legitimate headers as conflicting
* with one another.
*/
bufend = buf + buf_len;
last_pos_to_try = bufend - PACKET_HDR_LEN;
for ( bufptr = buf; bufptr < last_pos_to_try; ++bufptr )
{
extract_header( p, bufptr, &hdr );
if ( reasonable_header( &hdr, first_time, last_time ) )
{
u_char *next_header = bufptr + PACKET_HDR_LEN + hdr.caplen;
if ( next_header + PACKET_HDR_LEN < bufend )
{ /* check for another good header */
extract_header( p, next_header, &hdr2 );
if ( reasonable_header( &hdr2, hdr.ts.tv_sec,
hdr.ts.tv_sec + MAX_REASONABLE_HDR_SEPARATION ) )
{ /* a confirmed header */
switch ( status )
{
case HEADER_NONE:
case HEADER_PERHAPS:
status = HEADER_DEFINITELY;
*hdrpos_addr = bufptr;
*return_hdr = hdr;
/* Make sure we don't demote this "definite"
* to a "clash" if we stumble across its
* successor.
*/
last_pos_to_try = next_header - PACKET_HDR_LEN;
break;
case HEADER_DEFINITELY:
return HEADER_CLASH;
default:
error( "bad status in find_header()" );
}
}
/* ... else the header is bogus - we've verified that it's
* not followed by a reasonable header.
*/
}
else
{ /* can't check for another good header */
switch ( status )
{
case HEADER_NONE:
status = HEADER_PERHAPS;
*hdrpos_addr = bufptr;
*return_hdr = hdr;
break;
case HEADER_PERHAPS:
/* We don't immediately turn this into a
* clash because perhaps we'll later see a
* "definite" which will save us ...
*/
saw_PERHAPS_clash = 1;
break;
case HEADER_DEFINITELY:
/* Keep the definite in preference to this one. */
break;
default:
error( "bad status in find_header()" );
}
}
}
}
if ( status == HEADER_PERHAPS && saw_PERHAPS_clash )
status = HEADER_CLASH;
return status;
}
/* Positions the sf_readfile stream such that the next sf_read() will
* read the final full packet in the file. Returns non-zero if
* successful, zero if unsuccessful. If successful, returns the
* timestamp of the last packet in last_timestamp.
*
* Note that this routine is a special case of sf_find_packet(). In
* order to use sf_find_packet(), one first must use this routine in
* order to give sf_find_packet() an upper bound on the timestamps
* present in the dump file.
*/
int
sf_find_end( pcap_t *p, struct timeval *first_timestamp,
struct timeval *last_timestamp )
{
long first_time = first_timestamp->tv_sec;
u_int num_bytes;
u_char *buf, *bufpos, *bufend;
u_char *hdrpos;
struct pcap_pkthdr hdr, successor_hdr;
int status;
/* Allow enough room for at least two full (untruncated) packets,
* perhaps followed by a truncated packet, so we have a shot at
* finding a "definite" header and following its chain to the
* end of the file.
*/
num_bytes = MAX_BYTES_FOR_DEFINITE_HEADER;
if ( fseek( pcap_file( p ), (long) -num_bytes, 2 ) < 0 )
return 0;
buf = (u_char *)malloc((u_int) num_bytes);
if ( ! buf )
return 0;
status = 0;
bufpos = buf;
bufend = buf + num_bytes;
if ( fread( (char *) bufpos, num_bytes, 1, pcap_file( p ) ) != 1 )
goto done;
if ( find_header( p, bufpos, num_bytes,
first_time, 0L, &hdrpos, &hdr ) != HEADER_DEFINITELY )
goto done;
/* Okay, we have a definite header in our hands. Follow its
* chain till we find the last valid packet in the file ...
*/
for ( ; ; )
{
/* move to the next header position */
bufpos = hdrpos + PACKET_HDR_LEN + hdr.caplen;
/* bufpos now points to a candidate packet, which if valid
* should replace the current packet pointed to by hdrpos as
* the last valid packet ...
*/
if ( bufpos >= bufend - PACKET_HDR_LEN )
/* not enough room for another header */
break;
extract_header( p, bufpos, &successor_hdr );
first_time = hdr.ts.tv_sec;
if ( ! reasonable_header( &successor_hdr, first_time, 0L ) )
/* this bodes ill - it means bufpos is perhaps a
* bogus packet header after all ...
*/
break;
/* Note that the following test is for whether the next
* packet starts at a position > bufend, *not* for a
* position >= bufend. If this is the last packet in the
* file and there isn't a subsequent partial packet, then
* we expect the first buffer position beyond this packet
* to be just beyond the end of the buffer, i.e., at bufend
* itself.
*/
if ( bufpos + PACKET_HDR_LEN + successor_hdr.caplen > bufend )
/* the packet is truncated */
break;
/* Accept this packet as fully legit. */
hdrpos = bufpos;
hdr = successor_hdr;
}
/* Success! Last valid packet is at hdrpos. */
*last_timestamp = hdr.ts;
status = 1;
/* Seek so that the next read will start at last valid packet. */
if ( fseek( pcap_file( p ), (long) -(bufend - hdrpos), 2 ) < 0 )
error( "final fseek() failed in sf_find_end()" );
done:
free( (char *) buf );
return status;
}
/* Takes two timeval's and returns the difference, tv2 - tv1, as a double. */
static double
timeval_diff( struct timeval *tv1, struct timeval *tv2 )
{
double result = (tv2->tv_sec - tv1->tv_sec);
result += (tv2->tv_usec - tv1->tv_usec) / 1000000.0;
return result;
}
/* Returns true if timestamp t1 is chronologically less than timestamp t2. */
int
sf_timestamp_less_than( struct timeval *t1, struct timeval *t2 )
{
return t1->tv_sec < t2->tv_sec ||
(t1->tv_sec == t2->tv_sec &&
t1->tv_usec < t2->tv_usec);
}
/* Given two timestamps on either side of desired_time and their positions,
* returns the interpolated position of the desired_time packet. Returns a
* negative value if the desired_time is outside the given range.
*/
static long
interpolated_position( struct timeval *min_time, long min_pos,
struct timeval *max_time, long max_pos,
struct timeval *desired_time )
{
double full_span = timeval_diff( max_time, min_time );
double desired_span = timeval_diff( desired_time, min_time );
long full_span_pos = max_pos - min_pos;
double fractional_offset = desired_span / full_span;
if ( fractional_offset < 0.0 || fractional_offset > 1.0 )
return -1;
return min_pos + (long) (fractional_offset * (double) full_span_pos);
}
/* Reads packets linearly until one with a time >= the given desired time
* is found; positions the dump file so that the next read will start
* at the given packet. Returns non-zero on success, 0 if an EOF was
* first encountered.
*/
static int
read_up_to( pcap_t *p, struct timeval *desired_time )
{
struct pcap_pkthdr hdr;
const u_char *buf;
long pos;
int status;
for ( ; ; )
{
struct timeval *timestamp;
pos = ftell( pcap_file( p ) );
buf = pcap_next( p, &hdr );
if ( buf == 0 )
{
if ( feof( pcap_file( p ) ) )
{
status = 0;
clearerr( pcap_file( p ) );
break;
}
error( "bad status in read_up_to()" );
}
timestamp = &hdr.ts;
if ( ! sf_timestamp_less_than( timestamp, desired_time ) )
{
status = 1;
break;
}
}
if ( fseek( pcap_file( p ), pos, 0 ) < 0 )
error( "fseek() failed in read_up_to()" );
return (status);
}
/* Positions the sf_readfile stream so that the next sf_read() will
* return the first packet with a time greater than or equal to
* desired_time. desired_time must be greater than min_time and less
* than max_time, which should correspond to actual packets in the
* file. min_pos is the file position (byte offset) corresponding to
* the min_time packet and max_pos is the same for the max_time packet.
*
* Returns non-zero on success, 0 if the given position is beyond max_pos.
*
* NOTE: when calling this routine, the sf_readfile stream *must* be
* already aligned so that the next call to sf_next_packet() will yield
* a valid packet.
*/
int
sf_find_packet( pcap_t *p,
struct timeval *min_time, long min_pos,
struct timeval *max_time, long max_pos,
struct timeval *desired_time )
{
int status = 1;
struct timeval min_time_copy, max_time_copy;
u_int num_bytes = MAX_BYTES_FOR_DEFINITE_HEADER;
int num_bytes_read;
long desired_pos, present_pos;
u_char *buf, *hdrpos;
struct pcap_pkthdr hdr;
buf = (u_char *) malloc( num_bytes );
if ( ! buf )
error( "malloc() failured in sf_find_packet()" );
min_time_copy = *min_time;
min_time = &min_time_copy;
max_time_copy = *max_time;
max_time = &max_time_copy;
for ( ; ; ) /* loop until positioned correctly */
{
desired_pos =
interpolated_position( min_time, min_pos,
max_time, max_pos,
desired_time );
if ( desired_pos < 0 )
{
status = 0;
break;
}
present_pos = ftell( pcap_file( p ) );
if ( present_pos <= desired_pos &&
desired_pos - present_pos < STRAIGHT_SCAN_THRESHOLD )
{ /* we're close enough to just blindly read ahead */
status = read_up_to( p, desired_time );
break;
}
/* Undershoot the target a little bit - it's much easier to
* then scan straight forward than to try to read backwards ...
*/
desired_pos -= STRAIGHT_SCAN_THRESHOLD / 2;
if ( desired_pos < min_pos )
desired_pos = min_pos;
if ( fseek( pcap_file( p ), desired_pos, 0 ) < 0 )
error( "fseek() failed in sf_find_packet()" );
num_bytes_read =
fread( (char *) buf, 1, num_bytes, pcap_file( p ) );
if ( num_bytes_read == 0 )
/* This shouldn't ever happen because we try to
* undershoot, unless the dump file has only a
* couple packets in it ...
*/
error( "fread() failed in sf_find_packet()" );
if ( find_header( p, buf, num_bytes, min_time->tv_sec,
max_time->tv_sec, &hdrpos, &hdr ) !=
HEADER_DEFINITELY )
error( "can't find header at position %ld in dump file",
desired_pos );
/* Correct desired_pos to reflect beginning of packet. */
desired_pos += (hdrpos - buf);
/* Seek to the beginning of the header. */
if ( fseek( pcap_file( p ), desired_pos, 0 ) < 0 )
error( "fseek() failed in sf_find_packet()" );
if ( sf_timestamp_less_than( &hdr.ts, desired_time ) )
{ /* too early in the file */
*min_time = hdr.ts;
min_pos = desired_pos;
}
else if ( sf_timestamp_less_than( desired_time, &hdr.ts ) )
{ /* too late in the file */
*max_time = hdr.ts;
max_pos = desired_pos;
}
else
/* got it! */
break;
}
free( (char *) buf );
return status;
}