Potential NULL dereference issue in the function ngx_stream_lua_sema_handler (ngx_stream_lua_semaphore.c)

Issue
Fix potential null pointer dereference in ngx_stream_lua_sema_handler.

Description
The current implementation of ngx_stream_lua_sema_handler function lacks verification of the return value from ngx_stream_lua_get_req. It can potentially lead to a NULL pointer dereference, causing unexpected crashes:

494: r = ngx_stream_lua_get_req(wait_co_ctx->co);
495:
496: ctx = ngx_stream_lua_get_module_ctx(r, ngx_stream_lua_module);
497: ngx_stream_lua_assert(ctx != NULL);

r is dereferenced in 496 without verifying that it is not NULL.

Patch

--- ngx_stream_lua_semaphore.c
+++ ngx_stream_lua_semaphore_patch.c
@@ -492,6 +492,10 @@
         }
 
         r = ngx_stream_lua_get_req(wait_co_ctx->co);
+        
+        if (r == NULL) {
+            return luaL_error(L, "no request found");
+        }
 
         ctx = ngx_stream_lua_get_module_ctx(r, ngx_stream_lua_module);
         ngx_stream_lua_assert(ctx != NULL);

Expected Result
After applying this patch, the function properly handles the case when the request object (r) is NULL and gracefully returns an error to Lua instead of crashing.

Start in ngx_stream_lua_semaphore.c at ngx_stream_lua_sema_handler, especially the ngx_stream_lua_get_req call around lines 494-496. Check the NULL case and the surrounding error-handling conventions; done means a missing request no longer reaches ngx_stream_lua_get_module_ctx or causes a crash, and Lua receives an error.