NULL mag Issue 07 25 Read .dir files

eZine lover (@eZine)

Published in 

null magazine

 · 26 Dec 2020

  

 
    this time lets read a .DIR file, that contains general info for files  
    inside a filebase and after, read the description (file_id.diz) of  
    that file, from a .DES file, of mystic. 
     
    the readdirfile() function is 99% the same as the readfilebase()  
    function, also included in this issue. so i am not going to explain  
    that. but i will explain how to get the description from the .DES  
    file. 
     
    first of all we need three parameters. the offset of the description  
    inside the .DES file, the length of the text (in lines, not  
    bytes/chars) and the filename we need to read. 
     
    def getfiledesc(ofs,length,filename): 
     
    always check if the file exists, otherwise we exit, with some error  
    num. 
     
      if os.path.exists(filename) == False: 
        return -1 
     
    open the file in byte mode, only for reading 
     
      f = open(filename, 'rb') 
     
    initialize some variables. cnt is how many lines we read until now, x  
    is the offset while we read the file and finally, desc[] is a list,  
    containing the description. 
     
      cnt = 1 
      x = 0 
      desc = [] 
       
    set the pointer of the file to the desired position. this position we  
    know it, from the readdirfile() function. 
     
      f.seek(ofs,0) 
       
    now, until we read all lines of the description, read line by line. 
    because the .DES file is saved as a Pascal record file, as i have said  
    countless times, pascal, always saves the length of a string in the  
    beginning of that string. so if we read it first, we know, how many  
    characters we need to read next and that's what we do here. 
     
    read the length of the string, then read the whole string and append  
    it to the list 
     
      while cnt <=length: 
        x = f.tell() 
        c = f.read(1) 
        f.seek(f.tell()-1) 
        desc.append((f.read(ord(c)+1)).decode("CP437")[1:]) 
        cnt +=1 
         
      close the file and exit the function with the desc[] list as our  
      result. 
       
      f.close() 
      return desc 
     
    done...  
     
     
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  full script here 
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#!/usr/bin/python3 

import os 
import struct 
import sys 

# RecFileList = Record   // .DIR 
    # FileName  : String[70]; 
    # Size      : Cardinal; 
    # DateTime  : LongInt; 
    # Uploader  : String[30]; 
    # Flags     : Byte; 
    # Downloads : LongInt; 
    # Rating    : Byte; 
    # DescPtr   : Cardinal; 
    # DescLines : Byte; 
  # End; 

def readdirfile(i,filename): 
   
  def byte2str(v): 
    s=''.join(str(v)) 
    return s[2:-1] 
     
  if os.path.exists(filename) == False: 
    return -1 
  size = os.path.getsize(filename) 
  fdirrec = "<x70sLIx30sBIBLB" 
  sf = struct.calcsize(fdirrec) 
  items = size // sf 
  if i > items: 
    return -3 
  f = open(filename, 'rb') 
  try: 
    f.seek((i-1)*sf,1) 
  except: 
    return -2 
  fdirb = f.read(sf) 
  s = struct.unpack(fdirrec,fdirb) 
  f.close() 
  res = {} 
   
  res['filename'] = byte2str(s[0]).replace('\\x00','') 
  res['size'] = s[1] 
  res['datetime'] = s[2] 
  res['uploader'] = byte2str(s[3]).replace('\\x00','') 
  res['flags'] = s[4] 
  res['downloads'] = s[5] 
  res['rating'] = s[6] 
  res['descptr'] = s[7] 
  res['desclines'] = s[8] 
  return res 
   
def getfiledesc(ofs,length,filename): 
  if os.path.exists(filename) == False: 
    return -1 
  f = open(filename, 'rb') 
  cnt = 1 
  x = 0 
  desc = [] 
  f.seek(ofs,0) 
  while cnt <=length: 
    x = f.tell() 
    c = f.read(1) 
    f.seek(f.tell()-1) 
    desc.append((f.read(ord(c)+1)).decode("CP437")[1:]) 
    cnt +=1 
  f.close() 
  return desc 

#change the filenames to yours or else it will fail. 
   
z=readdirfile(1,'fsx_mutl.dir') 
desc = getfiledesc(z['descptr'],z['desclines'],'fsx_mutl.des') 

for i in range(len(desc)): 
  print(desc[i]) 

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  end of script 
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