bspatch.c - chromiumos/third_party/bsdiff - Git at Google

 /*-
  * Copyright 2003-2005 Colin Percival
  * All rights reserved
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted providing that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
  * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.
  */

 #if 0
 __FBSDID("$FreeBSD: src/usr.bin/bsdiff/bspatch/bspatch.c,v 1.1 2005/08/06 01:59:06 cperciva Exp $");
 #endif

 #include <bzlib.h>
 #include <errno.h>
 #include <inttypes.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
 #include <err.h>
 #include <unistd.h>
 #include <fcntl.h>

 #define JOIN(a, b) __JOIN(a, b)
 #define __JOIN(a, b) a ## b
 #define COMPILE_ASSERT(expr, message) \
 	typedef char JOIN(message, JOIN(_, __LINE__)) [(expr) ? 1 : -1]

 COMPILE_ASSERT(sizeof(int64_t) == 8, int64_t_64_bit);

 #define MIN(a, b) \
 	((a) < (b) ? (a) : (b))

 // Reads next int from *ints. The int should be terminated with a comma
 // or NULL char. *ints will be updated to the space right after the comma
 // or set to NULL if this was the last number. This assumes the input is
 // a valid string, as validated with PositionsStringIsValid().
 // Returns 1 on success.
 int NextInt64(const char** ints, int64_t *out) {
 	if (!ints[0])
 		return 0;
 	int r = sscanf(*ints, "%" PRIi64, out);
 	if (r == 1) {
 		const char* next_comma = strchr(*ints, ',');
 		const char* next_colon = strchr(*ints, ':');
 		if (!next_comma && !next_colon)
 			*ints = NULL;
 		else if (!next_comma)
 			*ints = next_colon + 1;
 		else if (!next_colon)
 			*ints = next_comma + 1;
 		else
 			*ints = MIN(next_comma, next_colon) + 1;
 		return 1;
 	}
 	return 0;
 }

 COMPILE_ASSERT(sizeof(intmax_t) == 8, intmax_t_not_64_bit);

 // Returns 1 if str can be converted to int64_t without over/underflowing.
 // str is assumed to point to an optional negative sign followed by numbers,
 // optionally followed by non-numeric characters, followed by '\0'.
 int IsValidInt64(const char* str) {
 	const char* end_ptr;
 	errno = 0;
 	intmax_t result = strtoimax(str, &end_ptr, /* base: */ 10);
 	return errno == 0;
 }

 // Input validator. Make sure the positions string is well formatted.
 // All numerical values are checked to make sure they don't over/underflow
 // int64_t. Returns 1 if valid.
 int PositionsStringIsValid(const char* positions) {
 	if (positions == NULL)
 		errx(1, "bad string");

 	// Special case: empty string is valid
 	if (!positions[0])
 		return 1;

 	// Use a state machine to determine if the string is valid.
 	// Key: (s): state, ((s)) valid end state.
 	// n (negative_valid) is a boolean that starts out as true.
 	// If n is true, ':' is the delimiter, otherwise ','.
 	//
 	//         .--------------------------.
 	//         |                          | n ? ':' : ',' ; n = !n
 	//         V  '-'&&n           0-9    |
 	// start->(0)------------->(1)----->((2))---.
 	//           `--------------------->     <--' 0-9
 	//              0-9
 	int state = 0;
 	int negative_valid = 1;
 	const char* number_start = positions;
 	for (;; positions++) {
 		char c = *positions;
 		switch (state) {
 			case 0:
 				if (c == '-' && negative_valid) {
 					state = 1;
 					continue;
 				}
 				if (isdigit(c)) {
 					state = 2;
 					continue;
 				}
 				return 0;
 			case 1:
 				if (isdigit(c)) {
 					state = 2;
 					continue;
 				}
 				return 0;
 			case 2:
 				if (isdigit(c))
 					continue;
 				// number_start must point to a valid number
 				if (!IsValidInt64(number_start)) {
 					return 0;
 				}
 				if ((negative_valid && c == ':') ||
 				    (!negative_valid && c == ',')) {
 					state = 0;
 					number_start = positions + 1;
 					negative_valid = !negative_valid;
 					continue;
 				}
 				return (c == '\0');
 		}
 	}
 }

 // Reads into a buffer a series of byte ranges from filename.
 // Each range is a pair of comma-separated ints from positions.
 // -1 as an offset means a sparse-hole.
 // E.g. If positions were "1,5:23,4:-1,8:3,7", then we would return a buffer
 // consisting of 5 bytes from offset 1 of the file, followed by
 // 4 bytes from offset 23, then 8 bytes of all zeros, then 7 bytes from
 // offset 3 in the file.
 // Returns NULL on error.
 static char* PositionedRead(const char* filename,
                             const char* positions,
                             ssize_t* old_size) {
 	if (!PositionsStringIsValid(positions)) {
 		errx(1, "invalid positions string for read\n");
 	}

 	// Get length
 	const char* p = positions;
 	int64_t length = 0;
 	for (;;) {
 		int64_t value;
 		if (0 == NextInt64(&p, &value)) {
 			break;
 		}
 		int r = NextInt64(&p, &value);
 		if (r == 0) {
 			errx(1, "bad length parse\n");
 		}
 		if (value < 0) {
 			errx(1, "length can't be negative\n");
 		}
 		length += value;
 	}

 	// Malloc
 	if (length > 0x40000000) {  // 1 GiB; sanity check
 		errx(1, "Read length too long (exceeds 1 GiB)");
 	}
 	// Following bsdiff convention, allocate length + 1 to avoid malloc(0)
 	char* buf = malloc(length + 1);
 	if (buf == NULL) {
 		errx(1, "malloc failed\n");
 	}
 	char* buf_tail = buf;

 	int fd = open(filename, O_RDONLY);
 	if (fd < 0) {
 		errx(1, "open failed for read\n");
 	}

 	// Read bytes
 	p = positions;
 	for (;;) {
 		int64_t offset, read_length;
 		if (NextInt64(&p, &offset) == 0) {
 			break;
 		}
 		if (offset < 0) {
 			errx(1, "no support for sparse positions "
 			     "yet during read\n");
 		}
 		if (NextInt64(&p, &read_length) == 0) {
 			errx(1, "bad length parse (should never happen)\n");
 		}
 		if (read_length < 0) {
 			errx(1, "length can't be negative "
 			     "(should never happen)\n");
 		}
 		ssize_t rc = pread(fd, buf_tail, read_length, offset);
 		if (rc != read_length) {
 			errx(1, "read failed\n");
 		}
 		buf_tail += rc;
 	}
 	close(fd);
 	*old_size = length;
 	return buf;
 }

 static void PositionedWrite(const char* filename,
                             const char* positions,
                             const char* buf,
                             ssize_t new_size) {
 	if (!PositionsStringIsValid(positions)) {
 		errx(1, "invalid positions string for write\n");
 	}
 	int fd = open(filename, O_WRONLY | O_CREAT, 0666);
 	if (fd < 0) {
 		errx(1, "open failed for write\n");
 	}

 	for (;;) {
 		int64_t offset, length;
 		if (NextInt64(&positions, &offset) == 0) {
 			break;
 		}
 		if (NextInt64(&positions, &length) == 0) {
 			errx(1, "bad length parse for write\n");
 		}
 		if (length < 0) {
 			errx(1, "length can't be negative for write\n");
 		}

 		if (offset < 0) {
 			// Sparse hole. Skip.
 		} else {
 			ssize_t rc = pwrite(fd, buf, length, offset);
 			if (rc != length) {
 				errx(1, "write failed\n");
 			}
 		}
 		buf += length;
 		new_size -= length;
 	}
 	if (new_size != 0) {
 		errx(1, "output position length doesn't match new size\n");
 	}
 	close(fd);
 }

 static off_t offtin(u_char *buf)
 {
 	off_t y;

 	y=buf[7]&0x7F;
 	y=y*256;y+=buf[6];
 	y=y*256;y+=buf[5];
 	y=y*256;y+=buf[4];
 	y=y*256;y+=buf[3];
 	y=y*256;y+=buf[2];
 	y=y*256;y+=buf[1];
 	y=y*256;y+=buf[0];

 	if(buf[7]&0x80) y=-y;

 	return y;
 }

 int main(int argc,char * argv[])
 {
 	FILE * f, * cpf, * dpf, * epf;
 	BZFILE * cpfbz2, * dpfbz2, * epfbz2;
 	int cbz2err, dbz2err, ebz2err;
 	int fd;
 	ssize_t oldsize,newsize;
 	ssize_t bzctrllen,bzdatalen;
 	u_char header[32],buf[8];
 	u_char *old, *new;
 	off_t oldpos,newpos;
 	off_t ctrl[3];
 	off_t lenread;
 	off_t i;

 	if ((argc != 6) && (argc != 4)) {
 		errx(1,"usage: %s oldfile newfile patchfile \\\n"
 			"  [in_offset,in_length,in_offset,in_length,... \\\n"
 			"  out_offset,out_length,"
 			"out_offset,out_length,...]\n",argv[0]);
 	}
 	int using_positioning = (argc == 6);

 	/* Open patch file */
 	if ((f = fopen(argv[3], "r")) == NULL)
 		err(1, "fopen(%s)", argv[3]);

 	/*
 	File format:
 		0	8	"BSDIFF40"
 		8	8	X
 		16	8	Y
 		24	8	sizeof(newfile)
 		32	X	bzip2(control block)
 		32+X	Y	bzip2(diff block)
 		32+X+Y	???	bzip2(extra block)
 	with control block a set of triples (x,y,z) meaning "add x bytes
 	from oldfile to x bytes from the diff block; copy y bytes from the
 	extra block; seek forwards in oldfile by z bytes".
 	*/

 	/* Read header */
 	if (fread(header, 1, 32, f) < 32) {
 		if (feof(f))
 			errx(1, "Corrupt patch\n");
 		err(1, "fread(%s)", argv[3]);
 	}

 	/* Check for appropriate magic */
 	if (memcmp(header, "BSDIFF40", 8) != 0)
 		errx(1, "Corrupt patch\n");

 	/* Read lengths from header */
 	bzctrllen=offtin(header+8);
 	bzdatalen=offtin(header+16);
 	newsize=offtin(header+24);
 	if((bzctrllen<0) || (bzdatalen<0) || (newsize<0))
 		errx(1,"Corrupt patch\n");

 	/* Close patch file and re-open it via libbzip2 at the right places */
 	if (fclose(f))
 		err(1, "fclose(%s)", argv[3]);
 	if ((cpf = fopen(argv[3], "r")) == NULL)
 		err(1, "fopen(%s)", argv[3]);
 	if (fseeko(cpf, 32, SEEK_SET))
 		err(1, "fseeko(%s, %lld)", argv[3],
 		    (long long)32);
 	if ((cpfbz2 = BZ2_bzReadOpen(&cbz2err, cpf, 0, 0, NULL, 0)) == NULL)
 		errx(1, "BZ2_bzReadOpen, bz2err = %d", cbz2err);
 	if ((dpf = fopen(argv[3], "r")) == NULL)
 		err(1, "fopen(%s)", argv[3]);
 	if (fseeko(dpf, 32 + bzctrllen, SEEK_SET))
 		err(1, "fseeko(%s, %lld)", argv[3],
 		    (long long)(32 + bzctrllen));
 	if ((dpfbz2 = BZ2_bzReadOpen(&dbz2err, dpf, 0, 0, NULL, 0)) == NULL)
 		errx(1, "BZ2_bzReadOpen, bz2err = %d", dbz2err);
 	if ((epf = fopen(argv[3], "r")) == NULL)
 		err(1, "fopen(%s)", argv[3]);
 	if (fseeko(epf, 32 + bzctrllen + bzdatalen, SEEK_SET))
 		err(1, "fseeko(%s, %lld)", argv[3],
 		    (long long)(32 + bzctrllen + bzdatalen));
 	if ((epfbz2 = BZ2_bzReadOpen(&ebz2err, epf, 0, 0, NULL, 0)) == NULL)
 		errx(1, "BZ2_bzReadOpen, bz2err = %d", ebz2err);

 	// Read

 	if (!using_positioning) {
 		if(((fd=open(argv[1],O_RDONLY,0))<0) ||
 			((oldsize=lseek(fd,0,SEEK_END))==-1) ||
 			((old=malloc(oldsize+1))==NULL) ||
 			(lseek(fd,0,SEEK_SET)!=0) ||
 			(read(fd,old,oldsize)!=oldsize) ||
 			(close(fd)==-1)) err(1,"%s",argv[1]);
 	} else {
 		old = PositionedRead(argv[1], argv[4], &oldsize);
 	}
 	if((new=malloc(newsize+1))==NULL) err(1,NULL);

 	oldpos=0;newpos=0;
 	while(newpos<newsize) {
 		/* Read control data */
 		for(i=0;i<=2;i++) {
 			lenread = BZ2_bzRead(&cbz2err, cpfbz2, buf, 8);
 			if ((lenread < 8) || ((cbz2err != BZ_OK) &&
 			    (cbz2err != BZ_STREAM_END)))
 				errx(1, "Corrupt patch\n");
 			ctrl[i]=offtin(buf);
 		};

 		/* Sanity-check */
 		if(newpos+ctrl[0]>newsize)
 			errx(1,"Corrupt patch\n");

 		/* Read diff string */
 		lenread = BZ2_bzRead(&dbz2err, dpfbz2, new + newpos, ctrl[0]);
 		if ((lenread < ctrl[0]) ||
 		    ((dbz2err != BZ_OK) && (dbz2err != BZ_STREAM_END)))
 			errx(1, "Corrupt patch\n");

 		/* Add old data to diff string */
 		for(i=0;i<ctrl[0];i++)
 			if((oldpos+i>=0) && (oldpos+i<oldsize))
 				new[newpos+i]+=old[oldpos+i];

 		/* Adjust pointers */
 		newpos+=ctrl[0];
 		oldpos+=ctrl[0];

 		/* Sanity-check */
 		if(newpos+ctrl[1]>newsize)
 			errx(1,"Corrupt patch\n");

 		/* Read extra string */
 		lenread = BZ2_bzRead(&ebz2err, epfbz2, new + newpos, ctrl[1]);
 		if ((lenread < ctrl[1]) ||
 		    ((ebz2err != BZ_OK) && (ebz2err != BZ_STREAM_END)))
 			errx(1, "Corrupt patch\n");

 		/* Adjust pointers */
 		newpos+=ctrl[1];
 		oldpos+=ctrl[2];
 	};

 	/* Clean up the bzip2 reads */
 	BZ2_bzReadClose(&cbz2err, cpfbz2);
 	BZ2_bzReadClose(&dbz2err, dpfbz2);
 	BZ2_bzReadClose(&ebz2err, epfbz2);
 	if (fclose(cpf) || fclose(dpf) || fclose(epf))
 		err(1, "fclose(%s)", argv[3]);

 	/* Write the new file */
 	if (!using_positioning) {
 		if(((fd=open(argv[2],O_CREAT|O_TRUNC|O_WRONLY,0666))<0) ||
 			(write(fd,new,newsize)!=newsize) || (close(fd)==-1))
 			err(1,"%s",argv[2]);
 	} else {
 		PositionedWrite(argv[2], argv[5], new, newsize);
 	}

 	free(new);
 	free(old);

 	return 0;
 }
	/*-
	* Copyright 2003-2005 Colin Percival
	* All rights reserved
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted providing that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	*
	* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
	* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
	* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
	* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
	* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
	* IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
	* POSSIBILITY OF SUCH DAMAGE.
	*/

	#if 0
	__FBSDID("$FreeBSD: src/usr.bin/bsdiff/bspatch/bspatch.c,v 1.1 2005/08/06 01:59:06 cperciva Exp $");
	#endif

	#include <bzlib.h>
	#include <errno.h>
	#include <inttypes.h>
	#include <stdint.h>
	#include <stdlib.h>
	#include <stdio.h>
	#include <string.h>
	#include <err.h>
	#include <unistd.h>
	#include <fcntl.h>

	#define JOIN(a, b) __JOIN(a, b)
	#define __JOIN(a, b) a ## b
	#define COMPILE_ASSERT(expr, message) \
	typedef char JOIN(message, JOIN(_, __LINE__)) [(expr) ? 1 : -1]

	COMPILE_ASSERT(sizeof(int64_t) == 8, int64_t_64_bit);

	#define MIN(a, b) \
	((a) < (b) ? (a) : (b))

	// Reads next int from *ints. The int should be terminated with a comma
	// or NULL char. *ints will be updated to the space right after the comma
	// or set to NULL if this was the last number. This assumes the input is
	// a valid string, as validated with PositionsStringIsValid().
	// Returns 1 on success.
	int NextInt64(const char** ints, int64_t *out) {
	if (!ints[0])
	return 0;
	int r = sscanf(*ints, "%" PRIi64, out);
	if (r == 1) {
	const char* next_comma = strchr(*ints, ',');
	const char* next_colon = strchr(*ints, ':');
	if (!next_comma && !next_colon)
	*ints = NULL;
	else if (!next_comma)
	*ints = next_colon + 1;
	else if (!next_colon)
	*ints = next_comma + 1;
	else
	*ints = MIN(next_comma, next_colon) + 1;
	return 1;
	}
	return 0;
	}

	COMPILE_ASSERT(sizeof(intmax_t) == 8, intmax_t_not_64_bit);

	// Returns 1 if str can be converted to int64_t without over/underflowing.
	// str is assumed to point to an optional negative sign followed by numbers,
	// optionally followed by non-numeric characters, followed by '\0'.
	int IsValidInt64(const char* str) {
	const char* end_ptr;
	errno = 0;
	intmax_t result = strtoimax(str, &end_ptr, /* base: */ 10);
	return errno == 0;
	}

	// Input validator. Make sure the positions string is well formatted.
	// All numerical values are checked to make sure they don't over/underflow
	// int64_t. Returns 1 if valid.
	int PositionsStringIsValid(const char* positions) {
	if (positions == NULL)
	errx(1, "bad string");

	// Special case: empty string is valid
	if (!positions[0])
	return 1;

	// Use a state machine to determine if the string is valid.
	// Key: (s): state, ((s)) valid end state.
	// n (negative_valid) is a boolean that starts out as true.
	// If n is true, ':' is the delimiter, otherwise ','.
	//
	// .--------------------------.
	// \| \| n ? ':' : ',' ; n = !n
	// V '-'&&n 0-9 \|
	// start->(0)------------->(1)----->((2))---.
	// `---------------------> <--' 0-9
	// 0-9
	int state = 0;
	int negative_valid = 1;
	const char* number_start = positions;
	for (;; positions++) {
	char c = *positions;
	switch (state) {
	case 0:
	if (c == '-' && negative_valid) {
	state = 1;
	continue;
	}
	if (isdigit(c)) {
	state = 2;
	continue;
	}
	return 0;
	case 1:
	if (isdigit(c)) {
	state = 2;
	continue;
	}
	return 0;
	case 2:
	if (isdigit(c))
	continue;
	// number_start must point to a valid number
	if (!IsValidInt64(number_start)) {
	return 0;
	}
	if ((negative_valid && c == ':') \|\|
	(!negative_valid && c == ',')) {
	state = 0;
	number_start = positions + 1;
	negative_valid = !negative_valid;
	continue;
	}
	return (c == '\0');
	}
	}
	}

	// Reads into a buffer a series of byte ranges from filename.
	// Each range is a pair of comma-separated ints from positions.
	// -1 as an offset means a sparse-hole.
	// E.g. If positions were "1,5:23,4:-1,8:3,7", then we would return a buffer
	// consisting of 5 bytes from offset 1 of the file, followed by
	// 4 bytes from offset 23, then 8 bytes of all zeros, then 7 bytes from
	// offset 3 in the file.
	// Returns NULL on error.
	static char* PositionedRead(const char* filename,
	const char* positions,
	ssize_t* old_size) {
	if (!PositionsStringIsValid(positions)) {
	errx(1, "invalid positions string for read\n");
	}

	// Get length
	const char* p = positions;
	int64_t length = 0;
	for (;;) {
	int64_t value;
	if (0 == NextInt64(&p, &value)) {
	break;
	}
	int r = NextInt64(&p, &value);
	if (r == 0) {
	errx(1, "bad length parse\n");
	}
	if (value < 0) {
	errx(1, "length can't be negative\n");
	}
	length += value;
	}

	// Malloc
	if (length > 0x40000000) { // 1 GiB; sanity check
	errx(1, "Read length too long (exceeds 1 GiB)");
	}
	// Following bsdiff convention, allocate length + 1 to avoid malloc(0)
	char* buf = malloc(length + 1);
	if (buf == NULL) {
	errx(1, "malloc failed\n");
	}
	char* buf_tail = buf;

	int fd = open(filename, O_RDONLY);
	if (fd < 0) {
	errx(1, "open failed for read\n");
	}

	// Read bytes
	p = positions;
	for (;;) {
	int64_t offset, read_length;
	if (NextInt64(&p, &offset) == 0) {
	break;
	}
	if (offset < 0) {
	errx(1, "no support for sparse positions "
	"yet during read\n");
	}
	if (NextInt64(&p, &read_length) == 0) {
	errx(1, "bad length parse (should never happen)\n");
	}
	if (read_length < 0) {
	errx(1, "length can't be negative "
	"(should never happen)\n");
	}
	ssize_t rc = pread(fd, buf_tail, read_length, offset);
	if (rc != read_length) {
	errx(1, "read failed\n");
	}
	buf_tail += rc;
	}
	close(fd);
	*old_size = length;
	return buf;
	}

	static void PositionedWrite(const char* filename,
	const char* positions,
	const char* buf,
	ssize_t new_size) {
	if (!PositionsStringIsValid(positions)) {
	errx(1, "invalid positions string for write\n");
	}
	int fd = open(filename, O_WRONLY \| O_CREAT, 0666);
	if (fd < 0) {
	errx(1, "open failed for write\n");
	}

	for (;;) {
	int64_t offset, length;
	if (NextInt64(&positions, &offset) == 0) {
	break;
	}
	if (NextInt64(&positions, &length) == 0) {
	errx(1, "bad length parse for write\n");
	}
	if (length < 0) {
	errx(1, "length can't be negative for write\n");
	}

	if (offset < 0) {
	// Sparse hole. Skip.
	} else {
	ssize_t rc = pwrite(fd, buf, length, offset);
	if (rc != length) {
	errx(1, "write failed\n");
	}
	}
	buf += length;
	new_size -= length;
	}
	if (new_size != 0) {
	errx(1, "output position length doesn't match new size\n");
	}
	close(fd);
	}

	static off_t offtin(u_char *buf)
	{
	off_t y;

	y=buf[7]&0x7F;
	y=y*256;y+=buf[6];
	y=y*256;y+=buf[5];
	y=y*256;y+=buf[4];
	y=y*256;y+=buf[3];
	y=y*256;y+=buf[2];
	y=y*256;y+=buf[1];
	y=y*256;y+=buf[0];

	if(buf[7]&0x80) y=-y;

	return y;
	}

	int main(int argc,char * argv[])
	{
	FILE * f, * cpf, * dpf, * epf;
	BZFILE * cpfbz2, * dpfbz2, * epfbz2;
	int cbz2err, dbz2err, ebz2err;
	int fd;
	ssize_t oldsize,newsize;
	ssize_t bzctrllen,bzdatalen;
	u_char header[32],buf[8];
	u_char old, new;
	off_t oldpos,newpos;
	off_t ctrl[3];
	off_t lenread;
	off_t i;

	if ((argc != 6) && (argc != 4)) {
	errx(1,"usage: %s oldfile newfile patchfile \\\n"
	" [in_offset,in_length,in_offset,in_length,... \\\n"
	" out_offset,out_length,"
	"out_offset,out_length,...]\n",argv[0]);
	}
	int using_positioning = (argc == 6);

	/* Open patch file */
	if ((f = fopen(argv[3], "r")) == NULL)
	err(1, "fopen(%s)", argv[3]);

	/*
	File format:
	0 8 "BSDIFF40"
	8 8 X
	16 8 Y
	24 8 sizeof(newfile)
	32 X bzip2(control block)
	32+X Y bzip2(diff block)
	32+X+Y ??? bzip2(extra block)
	with control block a set of triples (x,y,z) meaning "add x bytes
	from oldfile to x bytes from the diff block; copy y bytes from the
	extra block; seek forwards in oldfile by z bytes".
	*/

	/* Read header */
	if (fread(header, 1, 32, f) < 32) {
	if (feof(f))
	errx(1, "Corrupt patch\n");
	err(1, "fread(%s)", argv[3]);
	}

	/* Check for appropriate magic */
	if (memcmp(header, "BSDIFF40", 8) != 0)
	errx(1, "Corrupt patch\n");

	/* Read lengths from header */
	bzctrllen=offtin(header+8);
	bzdatalen=offtin(header+16);
	newsize=offtin(header+24);
	if((bzctrllen<0) \|\| (bzdatalen<0) \|\| (newsize<0))
	errx(1,"Corrupt patch\n");

	/* Close patch file and re-open it via libbzip2 at the right places */
	if (fclose(f))
	err(1, "fclose(%s)", argv[3]);
	if ((cpf = fopen(argv[3], "r")) == NULL)
	err(1, "fopen(%s)", argv[3]);
	if (fseeko(cpf, 32, SEEK_SET))
	err(1, "fseeko(%s, %lld)", argv[3],
	(long long)32);
	if ((cpfbz2 = BZ2_bzReadOpen(&cbz2err, cpf, 0, 0, NULL, 0)) == NULL)
	errx(1, "BZ2_bzReadOpen, bz2err = %d", cbz2err);
	if ((dpf = fopen(argv[3], "r")) == NULL)
	err(1, "fopen(%s)", argv[3]);
	if (fseeko(dpf, 32 + bzctrllen, SEEK_SET))
	err(1, "fseeko(%s, %lld)", argv[3],
	(long long)(32 + bzctrllen));
	if ((dpfbz2 = BZ2_bzReadOpen(&dbz2err, dpf, 0, 0, NULL, 0)) == NULL)
	errx(1, "BZ2_bzReadOpen, bz2err = %d", dbz2err);
	if ((epf = fopen(argv[3], "r")) == NULL)
	err(1, "fopen(%s)", argv[3]);
	if (fseeko(epf, 32 + bzctrllen + bzdatalen, SEEK_SET))
	err(1, "fseeko(%s, %lld)", argv[3],
	(long long)(32 + bzctrllen + bzdatalen));
	if ((epfbz2 = BZ2_bzReadOpen(&ebz2err, epf, 0, 0, NULL, 0)) == NULL)
	errx(1, "BZ2_bzReadOpen, bz2err = %d", ebz2err);

	// Read

	if (!using_positioning) {
	if(((fd=open(argv[1],O_RDONLY,0))<0) \|\|
	((oldsize=lseek(fd,0,SEEK_END))==-1) \|\|
	((old=malloc(oldsize+1))==NULL) \|\|
	(lseek(fd,0,SEEK_SET)!=0) \|\|
	(read(fd,old,oldsize)!=oldsize) \|\|
	(close(fd)==-1)) err(1,"%s",argv[1]);
	} else {
	old = PositionedRead(argv[1], argv[4], &oldsize);
	}
	if((new=malloc(newsize+1))==NULL) err(1,NULL);

	oldpos=0;newpos=0;
	while(newpos<newsize) {
	/* Read control data */
	for(i=0;i<=2;i++) {
	lenread = BZ2_bzRead(&cbz2err, cpfbz2, buf, 8);
	if ((lenread < 8) \|\| ((cbz2err != BZ_OK) &&
	(cbz2err != BZ_STREAM_END)))
	errx(1, "Corrupt patch\n");
	ctrl[i]=offtin(buf);
	};

	/* Sanity-check */
	if(newpos+ctrl[0]>newsize)
	errx(1,"Corrupt patch\n");

	/* Read diff string */
	lenread = BZ2_bzRead(&dbz2err, dpfbz2, new + newpos, ctrl[0]);
	if ((lenread < ctrl[0]) \|\|
	((dbz2err != BZ_OK) && (dbz2err != BZ_STREAM_END)))
	errx(1, "Corrupt patch\n");

	/* Add old data to diff string */
	for(i=0;i<ctrl[0];i++)
	if((oldpos+i>=0) && (oldpos+i<oldsize))
	new[newpos+i]+=old[oldpos+i];

	/* Adjust pointers */
	newpos+=ctrl[0];
	oldpos+=ctrl[0];

	/* Sanity-check */
	if(newpos+ctrl[1]>newsize)
	errx(1,"Corrupt patch\n");

	/* Read extra string */
	lenread = BZ2_bzRead(&ebz2err, epfbz2, new + newpos, ctrl[1]);
	if ((lenread < ctrl[1]) \|\|
	((ebz2err != BZ_OK) && (ebz2err != BZ_STREAM_END)))
	errx(1, "Corrupt patch\n");

	/* Adjust pointers */
	newpos+=ctrl[1];
	oldpos+=ctrl[2];
	};

	/* Clean up the bzip2 reads */
	BZ2_bzReadClose(&cbz2err, cpfbz2);
	BZ2_bzReadClose(&dbz2err, dpfbz2);
	BZ2_bzReadClose(&ebz2err, epfbz2);
	if (fclose(cpf) \|\| fclose(dpf) \|\| fclose(epf))
	err(1, "fclose(%s)", argv[3]);

	/* Write the new file */
	if (!using_positioning) {
	if(((fd=open(argv[2],O_CREAT\|O_TRUNC\|O_WRONLY,0666))<0) \|\|
	(write(fd,new,newsize)!=newsize) \|\| (close(fd)==-1))
	err(1,"%s",argv[2]);
	} else {
	PositionedWrite(argv[2], argv[5], new, newsize);
	}

	free(new);
	free(old);

	return 0;
	}