Uncompress Zyxel WAP3205 etc. LZSS compressed config files ( <Config_Information_File_8671> )

lzss.c

// Uncompress Zyxel WAP3205 etc. LZSS compressed config files
// These are in format <Config_Information_File_8671> 
// Format description: https://qhimm-modding.fandom.com/wiki/FF7/LZS_format
// Author: leecher@dose.0wnz.at  05/2023
//
// gcc -o lzss lzss.c
//
#include <arpa/inet.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <limits.h>
#include <errno.h>
#include <stdint.h>

int lzssDecompress(const uint8_t *src, uint8_t *dst, uint32_t size) {
  uint8_t flags = 0, mask = 0;
  uint32_t  len, disp, os=0, od=0, i;

  while(os < size) {
    if(mask == 0) {
      // read in the flags data
      // from bit 7 to bit 0:
      //     1: raw byte
      //     0: compressed block
      flags = ~src[os++];
      mask  = 0x01;
    }

    if(flags & mask) { // compressed block
      // disp: displacement
      // len:  length
      disp = (src[os] | (((src[os+1]) & 0xF0) << 4)); os++;
      len  = ((src[os++])&0x0F)+3;

      disp=od - ((od - 18 - disp) % 4096);
      // printf ("Offset: %04X, len: %d\n", disp, len);


      // for len, copy data from the displacement
      // to the current buffer position
      if (dst)
      {
          // NB: memcpy implementations are different and decompression
          // relies on memcpy bein REBE MOVSB, so roll manually
          // memcpy(&dst[od], &dst[disp], len);
          for (i=0; i<len; i++) dst[od+i]=dst[disp+i];
      }
      od += len;
    }
    else { // uncompressed block
      // copy a raw byte from the input to the output
      if (dst) dst[od]=src[os];
      od++; os++;
    }

    mask <<= 1;
  }
  return od;
}

int main(int argc, char **argv)
{
	char destfile[PATH_MAX];
	FILE *fp;
	uint32_t size, sizeout, unk;
	int ret=0;
	uint8_t *memIn, *memOut;

	if (argc<2)
	{
		printf ("Usage: %s <source file> [dest file]\n", argv[0]);
		return -1;
	}
	if (argc<3) sprintf(destfile, "%s.xml", argv[1]);
	else strcpy(destfile, argv[2]);

	if (!(fp = fopen(argv[1], "rb")))
	{
		perror("Cannot open source file");
		return -1;
	}
	if (fread(&size, 4, 1, fp) != 1 || fread(&unk, 4, 1, fp) != 1)
	{
		perror("Cannot read header");
		fclose(fp);
		return -1;
	}
	size = htonl(size);
	if (!(memIn = malloc(size)))
	{
		fprintf(stderr, "Cannot allocate memory buffer of %d bytes\n", size);
		fclose(fp);
		return -1;
	}
	if (fread(memIn, size, 1, fp) != 1)
	{
		fprintf(stderr, "Cannot read %d bytes from file: %s\n", size, strerror(errno));
		fclose(fp);
		return -1;
	}
	fclose(fp);
	sizeout = lzssDecompress(memIn, NULL, size);
	if (!(memOut = malloc(sizeout)))
	{
		fprintf(stderr, "Cannot allocate output memory buffer of %d bytes\n", sizeout);
		fclose(fp);
		return -1;
	}
	size = lzssDecompress(memIn, memOut, size);
	printf ("Decompressed file to %d bytes.\n", size);
	if (!(fp = fopen(destfile, "w")))
	{
		perror("Cannot open destination file");
		return -1;
	}
	if (fwrite(memOut, size, 1, fp) != 1)
	{
		fprintf(stderr, "Cannot write %d bytes to destination file: %s\n", size, strerror(errno));
		ret = -1;
	}
	fclose(fp);
	return ret;
}