submit_event() always returns False on Windows (MSVC) — IS_ENABLED() macro mismatch

[Jeffeke]

Hi, I had an issue trying to make a test cardreader PD in python on Windows with submit_event(). After bashing my head into a wall with Claude for a while I managed to fix the issue.

Full transparency: I'm very much out of my depth here, so here is Claude's synopsis on what went wrong and how to fix it. Apologies for the AI slop.

Summary

osdp_pd_submit_event() silently fails on Windows builds because the IS_ENABLED() macro evaluates incorrectly under MSVC's legacy preprocessor, creating a code path mismatch between the Python C extension and the core library.

Root Cause

libosdp uses a Linux kernel-style IS_ENABLED() macro (from c-utils/include/utils/utils.h):

#define __IS_ENABLED1(x)             __IS_ENABLED2(__XXXX ## x)
#define __XXXX1                      __YYYY,
#define __IS_ENABLED2(y)             __IS_ENABLED3(y 1, 0)
#define __IS_ENABLED3(_i, val, ...)  val
#define IS_ENABLED(x)                __IS_ENABLED1(x)

This relies on token-pasting:

When OPT_OSDP_APP_OWNED_QUEUE_DATA=1, __XXXX ## 1 → __XXXX1 → expands to __YYYY, which injects a comma and makes __IS_ENABLED3 return 1.

MSVC's legacy preprocessor does not expand macro arguments before ## token pasting like GCC/Clang do.
Result:
IS_ENABLED(OPT_OSDP_APP_OWNED_QUEUE_DATA) evaluates to 0 on MSVC even when the flag is defined.

This creates a mismatch:

File | Guard | Evaluates to | Behavior -- | -- | -- | -- python/osdp_sys/pd.c | #ifdef OPT_OSDP_APP_OWNED_QUEUE_DATA | true | Allocates event with calloc, calls osdp_pd_submit_event() src/osdp_pd.c | IS_ENABLED(OPT_OSDP_APP_OWNED_QUEUE_DATA) | false | Takes !IS_ENABLED branch → calls pd_event_alloc() src/osdp_pd.c | #ifndef OPT_OSDP_APP_OWNED_QUEUE_DATA | false | pd_event_alloc() compiled as no-op returning NULL

So:

osdp_pd_submit_event()
  -> pd_event_alloc()
     -> returns NULL
  -> return -1

Python wrapper converts this to:

PeripheralDevice.submit_event(...) -> False

No events are queued or sent.

Impact

On Windows:

• PeripheralDevice.submit_event() always returns False
• No card reads / keypad / manufacturer events sent
• PD replies to POLL with ACK (0x40) instead of REPLY_RAW (0x50)
• Appears as if event submission is broken

Affected Versions

• libosdp 3.2.0 (PyPI Windows wheel)
• Any build using IS_ENABLED() with MSVC legacy preprocessor

Fix Options

Option A — Compiler flag (workaround)

Enable conformant MSVC preprocessor:

set CL=/Zc:preprocessor
pip install --no-binary :all: --no-cache-dir libosdp==3.2.0

This fixes IS_ENABLED() evaluation.

---

Option B — Code fix (preferred)

Make both files use identical guards.

In src/osdp_pd.c:

// Before
if (IS_ENABLED(OPT_OSDP_APP_OWNED_QUEUE_DATA)) {

// After
#ifdef OPT_OSDP_APP_OWNED_QUEUE_DATA

This matches python/osdp_sys/pd.c and avoids macro dependence.

---

Option C — Disable flag (alternate path)

Requires full Git source (PyPI tarball missing slab.c):

set OPT_OSDP_APP_OWNED_QUEUE_DATA=off
pip install "git+https://github.com/goToMain/libosdp@v3.2.0#egg=libosdp&subdirectory=python"

Additional Issue

PyPI source tarball for v3.2.0 is missing:

vendor/utils/src/slab.c

When building with:

OPT_OSDP_APP_OWNED_QUEUE_DATA=off

Build fails:

RuntimeError: Path 'vendor\utils/src/slab.c' does not exist

Full Git clone (with submodules) is required.

Suggested Resolution

Either:

1. Replace IS_ENABLED() with #ifdef in src/osdp_pd.c
2. Or force /Zc:preprocessor in Windows build flags
3. Or remove mixed guard usage across compilation units

This restores correct event submission on Windows.

[sidcha]

@kanaan2027, yes please. A PR would be the best option. A patch posted here would also work.

[sidcha]

@kanaan2027, no offense, but for obvious reasons I can't (won't) run such binaries. A text file with a patch or a comment with the approach you took would be the next best thing.

If not, I will take a stab at this when time permits (as none of the methods suggested by claude above is acceptable to me).