Fix function pointer type mismatches for GCC 15 compatibility

[DigitalCyberSoft]

Description

This PR fixes compilation errors when building nchan with GCC 15 (as used in Fedora 42+). GCC 15 has stricter type checking for function pointer assignments, which causes build failures with the current code.

Problem

When compiling with GCC 15.2.1, the following errors occur:

error: assignment to 'subscriber_callback_pt' from incompatible pointer type 'void (*)(void)'
error: assignment to 'ngx_http_cleanup_pt' from incompatible pointer type 'void (*)(void)' 
error: assignment to 'callback_pt' from incompatible pointer type 'ngx_int_t (*)(void)'

Solution

The fix involves ensuring all function pointers match their expected signatures:

1. longpoll.c & websocket.c: Split empty_handler() into two properly typed functions:

   • empty_subscriber_handler(subscriber_t *sub, void *data) for subscriber callbacks
   • empty_cleanup_handler(void *data) for cleanup callbacks

2. eventsource.c: Changed empty_handler(void) to empty_cleanup_handler(void *data)

3. memstore_ipc.c & memstore.c: Changed empty_callback() to empty_callback(ngx_int_t status, void *ptr1, void *ptr2) to match the callback_pt typedef

Testing

Compiles successfully with GCC 15.2.1 on Fedora 42, produces valid ngx_nchan_module.so (2.9MB shared object) with no compilation warnings or errors.

Important Note

This patch was developed with AI assistance. While it has been tested to compile successfully on the target system and the changes are straightforward type corrections, please review carefully for completeness, security implications, and compatibility with other GCC versions.

Files Changed

• src/subscribers/longpoll.c
• src/subscribers/websocket.c
• src/subscribers/eventsource.c
• src/subscribers/memstore_ipc.c
• src/store/memory/memstore.c

Related Issues

This addresses compilation failures on Fedora 42+ and other systems using GCC 15.