Subj : 31-line DOOR.SYS: blank-line padding makes OpenDoors misdetect it as t
To   : GitLab note in main/sbbs
From : Rob Swindell
Date : Sat Aug 08 2026 21:11:27

https://gitlab.synchro.net/main/sbbs/-/issues/1217#note_10107

The padding was not speculative -- it was tested. The history is in `syncprog`, 15-16 Oct 2024, replying to the commit announcement for b2601ca82c (stack-3-build, 2024-10-15):

* **#50075, Nightfox:** Thunder Cat v3.30 runs fine with the 52-line DOOR.SYS, but after switching to the new 31-line option "Thunder Cat didn't run." (dosemu2 on Linux.)
* **#50076, Digital Man:** "The problem that Rixter reported was with line 42 (Time credit, in minutes)." and "I wonder if adding 21 blank lines would resolve that problem."
* **#50083, Nightfox:** "the door was giving an error value of 62 with the 31-line door.sys. I tried adding 21 blank lines to that door.sys and manually running the door, and it didn't report that error anymore."

ba8fdb5a7f (cups-37-soap, 2024-10-16) landed the same day.

So Thunder Cat v3.30 genuinely requires 52 lines to be present, and the padding is confirmed to fix it. Error 62 is the QuickBASIC "Input past end of file" code, which fits a door that reads a fixed 52 lines regardless of the format it was told to expect, though I have not confirmed what Thunder Cat is written in.

That rules out option 1 in the description above. Dropping the padding would restore the OpenDoors behavior at the cost of re-breaking the door the 31-line option was added for.

Option 2 is the one the evidence actually supports, and can be narrowed further. Rixter's complaint was specifically **line 42** (time credits). Blanking all of lines 32-52 was broader than that report required, and lines 32-36 -- birthday, main and gen directory, sysop name, alias -- are precisely the ones OpenDoors reads once it has decided the file is the extended variant.

So: keep writing 52 lines, populate lines 32-36 as we do for the 52-line type, and leave line 42 (plus whatever else has no known-good value) blank. Thunder Cat still finds its 52 lines, OpenDoors gets a sysop name and a handle instead of empty strings, and the field that caused the original report stays empty.

Worth confirming with a Thunder Cat v3.30 run before committing to it, since the only thing we know for certain is that the door counts lines and that line 42 upset it.

I could not find the original Rixter report in the local message bases or in this tracker; the summary in #50076 appears to be the only record of it.

— *Authored by Claude (Claude Code), on behalf of @rswindell*
--- SBBSecho 3.37-Linux
 * Origin: Vertrauen - [vert/cvs/bbs].synchro.net (1:103/705)

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