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From: davison@drivax.UUCP (Wayne Davison)
Newsgroups: comp.sys.amiga
Subject: Re: Late breaking fixes to VT100 R2.7
Message-ID: <2590@drivax.UUCP>
Date: Wed, 14-Oct-87 14:11:31 EDT
Article-I.D.: drivax.2590
Posted: Wed Oct 14 14:11:31 1987
Date-Received: Sat, 17-Oct-87 19:39:43 EDT
References: <15638@amdahl.amdahl.com>
Reply-To: davison@drivax.UUCP (Wayne Davison)
Organization: Digital Research, Inc.
Lines: 103

Here's a few fixes for VT100 R2.7:

Firstly, the file-chopping code for XMODEM downloads is a little over-zealous.
The current code (which has been around for quite some time) will chop off ANY
pattern of nulls AND Ctrl-Z's.  This is particularly bad for .arc files, since
the last two characters before the padding are always a Ctrl-Z/null.  There is
also a problem with the xmodem send-padding.  It always uses nulls for padding
even when the last character of the file was a null.  This makes it impossible
to chop the file upon receipt, because there is no distinction between padding
and data.  While fixing these bugs, I noticed that the number of bytes to send
was decremented inside the retry loop, which will trash your file if you don't
have a perfectly clean send.  I also found that the chop algorithm will always
write at least 1 byte, when sometimes it shouldn't write any.

The following context diff fixes these problems.  The chopping algorithm chops
contiguous strings of nulls OR Ctrl-Zs (not a mixture), and will avoid writing
anything if we chopped them all (e.g. 128-bytes worth).  The sending algorithm
is optimized a bit and fixes the subtraction and padding bugs.  Enjoy!
--
 Wayne Davison					      ...amdahl!drivax!davison
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
	   Ziol soft ol of egrt.  Stz'l ltt oy ngx eqf rteohitk oz.
	       Oy ngx rg, hstqlt rkgh dt q fgzt zg stz dt afgv.


*** xmodem.c.orig	Wed Oct  7 17:11:05 1987
--- xmodem.c	Wed Oct  7 18:26:57 1987
***************
*** 287,295 ****
      if ((firstchar == EOT) && (errors < ERRORMAX))
  	{
  	sendchar(ACK);
! 	while (bufptr > 0 && (bufr[--bufptr] == 0x00 ||
! 			      bufr[bufptr]   == 0x1A)) ;
! 	write(fd, bufr, ++bufptr);
  	close(fd);
  	Do_XON();
  	ScrollInfoMsg(1);
--- 287,300 ----
      if ((firstchar == EOT) && (errors < ERRORMAX))
  	{
  	sendchar(ACK);
! 		/* use firstchar to remember the last char for chopping */
! 	if (bufptr && ((firstchar = bufr[--bufptr]) == 0 || firstchar == 0x1A))
! 	    {
! 	    while (bufptr && bufr[--bufptr] == firstchar)
! 		;
! 	    if (bufptr || bufr[0] != firstchar)	 /* check for null buffer */
! 		write(fd, bufr, ++bufptr);
! 	    }
  	close(fd);
  	Do_XON();
  	ScrollInfoMsg(1);
***************
*** 343,362 ****
  	    {
  	    attempts = 0;
  	    sprintf(scrstr2,"Sending block %4d",sectnum);
  	    do {
  		InfoMsgNoScroll(scrstr2);
  		sendchar(SOH);
  		sendchar(sectnum);
  		sendchar(~sectnum);
  		checksum = 0;
! 		size = SECSIZ <= bytes_to_send ? SECSIZ : bytes_to_send;
! 		bytes_to_send -= size;
! 		for (j = bufptr; j < (bufptr + SECSIZ); j++)
! 		if (j < (bufptr + size)) {
! 		    sendchar(bufr[j]);
  		    checksum += bufr[j];
  		    }
! 		else sendchar(0);
  		sendchar(checksum);
  		attempts++;
  		c = readchar();
--- 348,374 ----
  	    {
  	    attempts = 0;
  	    sprintf(scrstr2,"Sending block %4d",sectnum);
+ 	    size = SECSIZ <= bytes_to_send ? SECSIZ : bytes_to_send;
+ 	    bytes_to_send -= size;
  	    do {
  		InfoMsgNoScroll(scrstr2);
  		sendchar(SOH);
  		sendchar(sectnum);
  		sendchar(~sectnum);
  		checksum = 0;
! 		for (j = bufptr; j < bufptr + size; j++)
! 		    {
! 		    sendchar(bufr[j]);		/* send buffer data */
  		    checksum += bufr[j];
  		    }
! 		if( size < SECSIZ )		/* check if we need to pad */
! 		    {
! 		    c = bufr[j-1] ? 0 : 0x1A;	/* choose correct padding */
! 		    j = SECSIZ - size;
! 		    checksum += j * c;
! 		    while ( j-- )
! 			sendchar(c);		/* send padding */
! 		    }
  		sendchar(checksum);
  		attempts++;
  		c = readchar();