/* Un-TAR a Tape ARchive file */
/* By Andrew Church           */
/* 95ACHURCH@vax.mbhs.edu     */

#include "stdio.h"
#include "stdlib.h"

struct FileHeader {
  int  type;
  long size;
  char name[100];
};

FILE *tar,*f;
long pos;
struct FileHeader hdr;

void AbsSeek(f,pos)
FILE *f;
long pos;
{
  fsetpos(f,&pos);
}

void RelSeek(f,pos)
FILE *f;
long pos;
{
  long a;

  fgetpos(f,&a); a+=pos;
  fsetpos(f,&a);
}

void CopyData(f1,f2,size)
FILE *f1,*f2;
long size;
{
  char buf[512];

  while(size>512) {
    fread(buf,512,1,f1);
    fwrite(buf,512,1,f2);
    size-=512;
  }
  fread(buf,size,1,f1);
  fwrite(buf,size,1,f2);
}

long OctalToDec(s)
char *s;
{
  int i;
  long n=0;

  for(i=0;i<strlen(s);i++)
    if(s[i]!=' ') {
      n<<=3; n+=s[i]-'0';
    }
  return n;
}

void ReadHeader(hdr)
struct FileHeader *hdr;
{
  char s[16];

  fread(hdr->name,1,100,tar);
  fread(s,1,8,tar); s[8]=0; hdr->type=OctalToDec(s);
  RelSeek(tar,16);
  fread(s,1,12,tar); s[12]=0; hdr->size=OctalToDec(s);
  RelSeek(tar,376);
  pos+=512;
}

int main(argc,argv)
int argc;
char **argv;
{
  if(argc==1) {
    puts("Required argument missing");
    exit(20);
  }
  if(tar=fopen(argv[1],"r")) {
    printf("Extracting files from archive: %s\n",argv[1]);
    pos=0;
    ReadHeader(&hdr);
    while(ftell(tar)!=EOF && hdr.name[0]) {
      if(hdr.name[strlen(hdr.name)-1]=='/') {
        hdr.name[strlen(hdr.name)-1]=0;  /* remove trailing '/' */
        printf("Creating directory %s\n",hdr.name);
        mkdir(hdr.name,0);
      } else {
        if(f=fopen(hdr.name,"w")) {
          printf("Extracting (%8d bytes) %s\n",hdr.size,hdr.name);
          CopyData(tar,f,hdr.size);
          fclose(f);
        }
        pos+=(hdr.size+511) & -512;
        AbsSeek(tar,pos);
      }
      ReadHeader(&hdr);
    }
    fclose(tar);
    exit(0);
  }
  printf("File not found: %s\n",argv[1]);
  exit(20);
}