QWK is a common protocol for offline message readers and BBS software. This is a quick synopsis on how to implement support into your product (reader, processor, or BBS).

Even though the files are zipped, the file extension is renamed to .QWK for the download from the BBS software, and .REP for the zip uploading messages to the BBS.

1. CONTROL.DAT (a string list file)
2. MESSAGES.DAT (a 128 block ASCII file)
3. *.NDX (an array of binary bytes)

Each line is CRLF 0x0D 0x0A (#13#10) (\r\n) delimited.

Some BBS systems will have additional lines after those above:

Messages file starts with a 128 byte product information. Like:

• Produced by Qmail…Copyright © 1987 by Sparkware. All Rights Reserved. (padded with spaces)
• QWK Packet Produced by PCBoard v15.0 (padded with spaces)

That block is followed by messages using PCBoard 12.0 format.

In Pascal:

    type
       MsgHeaderRec=Packed Record
          TypeID:String[1];
          MsgID:String[7];
          DateStr:String[8];
          TimeStr:String[5];
          MsgTo:String[25];
          MsgFrom:String[25];
          MsgSubj:String[25];
          Reserved:String[12];
          MsgRefer:String[8];
          Chunks:Longint;
          Attributes:String[6];
       End;

In C:

    struct QwkHeader {
	unsigned char Msgstat;     /* Message status       */
	unsigned char Msgnum[7];   /* Message number       */
	unsigned char Msgdate[8];  /* Message date MM-DD-YY*/
	unsigned char Msgtime[5];  /* Message time HH:MM   */
	unsigned char MsgTo[25];   /* Message To:          */
	unsigned char MsgFrom[25]; /* Message From:        */
	unsigned char MsgSubj[25]; /* Message Subject:     */
	unsigned char Msgpass[12]; /* Message password     */
	unsigned char Msgrply[8];  /* Message reply to     */
	unsigned char Msgrecs[6];  /* Length in records    */
	unsigned char Msglive;     /* Message active status*/
	unsigned char Msgarealo;   /* Lo-byte message area */
	unsigned char Msgareahi;   /* Hi-byte message area */
	unsigned char Msgofflo;
	unsigned char Msgoffhi;
	unsigned char Msgtagp;
    } __attribute__((packed));

Of course to populate that structure you will BlockRead 128 bytes, them move from offset to length to each field.

Instead of carriage return and line feed combination, each line in the message end with an ASCII 227 (pi character) symbol. If a message does not completely occupy the 128-bytes block, the remainder of the block is padded with space or null.

The index files contain a list of pointers pointing to the beginning of messages in the MESSAGES.DAT file. The pointer is in terms of the 128-bytes block logical record that the MESSAGES.DAT file is in. Each conference has its own xxx.NDX file, where xxx is the conference number left padded with zeroes. Some mail programs offer the user the option to not generate index files. So the mail readers need to create the index files if they are missing.

[1] = This number is in the Microsoft MKS$ BASIC format.

In Pascal:

  Type
     BSingle:Array[0..3] of Byte;
  
  Procedure LONG2MSB(Index:LongInt;Var MS:BSingle);
  Var
     Exp : Byte;
  Begin
     If Index <> 0 Then Begin
        Exp := 0;
        While Index And $800000 = 0 Do Begin
           Inc (Exp);
           Index := Index SHL 1;
        End;
  
        Index := Index And $7FFFFF;
     End
     Else Exp := 152;
     MS[0] := Index AND $FF;
     MS[1] := (Index SHR 8) AND $FF;
     MS[2] := (Index SHR 16) AND $FF;
     MS[3] := 152 - Exp;
  End;

In C:

  int ieee_to_msbin(float *src4, float *dest4) {
unsigned char *ieee = (unsigned char *)src4;
unsigned char *msbin = (unsigned char *)dest4;
unsigned char sign = 0x00;
unsigned char msbin_exp = 0x00;
int i;
/* See _fmsbintoieee() for details of formats   */
sign = ieee[3] & 0x80;
msbin_exp |= ieee[3] << 1;
msbin_exp |= ieee[2] >> 7;
/* An ieee exponent of 0xfe overflows in MBF    */
if (msbin_exp == 0xfe) return 1;
msbin_exp += 2; /* actually, -127 + 128 + 1 */
for (i = 0; i < 4; i++) msbin[i] = 0;
msbin[3] = msbin_exp;
msbin[2] |= sign;
msbin[2] |= ieee[2] & 0x7f;
msbin[1] = ieee[1];
msbin[0] = ieee[0];
return 0;
  }

There is a special index file named PERSONAL.NDX. This file contains pointers to messages which are addressed to the user, i.e. personal messages. Some mail door and utility programs also allow the selection of other messages to be flagged as personal messages.

NOTE I have found that not all BBS software generate this file, for example PCBoard 15.x