MSVC build is broken (undeclared DTLS_DEBUG_BUF_SIZE) #283

The MSVC-Build is currently (develop: d9738c3) broken. It looks like a 4-year-old regression (see below).

Observation

Building with basic cmake commands under Win11 with VS2026:

$ rm -rf build/; cmake -B build && cmake --build build
-- Building for: Visual Studio 18 2026
-- Selecting Windows SDK version 10.0.26100.0 to target Windows 10.0.22631.
-- The C compiler identification is MSVC 19.51.36256.0
-- The CXX compiler identification is MSVC 19.51.36256.0
[...]
D:\github\eclipse-tinydtls\tinydtls\dtls_debug.c(402,16): error C2065: 'DTLS_DEBUG_BUF_SIZE': undeclared identifier [D:\github\eclipse-tinydtls\tinydtls\build\tinydtls.vcxproj]
D:\github\eclipse-tinydtls\tinydtls\dtls_debug.c(402,16): error C2057: expected constant expression [D:\github\eclipse-tinydtls\tinydtls\build\tinydtls.vcxproj]
D:\github\eclipse-tinydtls\tinydtls\dtls_debug.c(402,16): error C2466: cannot allocate an array of constant size 0 [D:\github\eclipse-tinydtls\tinydtls\build\tinydtls.vcxproj]
D:\github\eclipse-tinydtls\tinydtls\dtls_debug.c(402,8): error C2133: 'message': unknown size [D:\github\eclipse-tinydtls\tinydtls\build\tinydtls.vcxproj]

Build fails because of error C2065: 'DTLS_DEBUG_BUF_SIZE': undeclared identifier.

Analysis

The indentifier DTLS_DEBUG_BUF_SIZE is undeclared in this constellation because

1. It gets declared inside a preprocessor condition #if !defined(WITH_CONTIKI) && !defined(_MSC_VER):
   

   tinydtls/dtls_debug.c

   Lines 250 to 279 in d9738c3

   	#if !defined(WITH_CONTIKI) && !defined(_MSC_VER)
   	static void
   	dtls_logging_handler(log_t level, const char *message) {
   	static char timebuf[32];
   	FILE* log_fd = level <= DTLS_LOG_CRIT ? stderr : stdout;
   	if (print_timestamp(timebuf,sizeof(timebuf), time(NULL)))
   	fprintf(log_fd, "%s ", timebuf);
   	if (level <= DTLS_LOG_DEBUG)
   	fprintf(log_fd, "%s ", loglevels[level]);
   	fwrite(message, strlen(message), 1, log_fd);
   	fflush(log_fd);
   	}
   	static dtls_log_handler_t log_handler = dtls_logging_handler;
   	void
   	dtls_set_log_handler(dtls_log_handler_t app_handler) {
   	if (app_handler == NULL)
   	log_handler = dtls_logging_handler;
   	else
   	log_handler = app_handler;
   	}
   	#ifndef DTLS_DEBUG_BUF_SIZE
   	#define DTLS_DEBUG_BUF_SIZE 128
   	#endif

2. It gets used inside a different preprocessor condition #ifndef WITH_CONTIKI
   

   tinydtls/dtls_debug.c

   Lines 397 to 403 in d9738c3

   	#ifndef WITH_CONTIKI
   	void
   	dtls_dsrv_hexdump_log(log_t level, const char *name, const unsigned char *buf, size_t length, int extend) {
   	int n = 0;
   	#ifndef DTLS_CONSTRAINED_STACK
   	char message[DTLS_DEBUG_BUF_SIZE];
   	#endif /* ! DTLS_CONSTRAINED_STACK */

This means that the identifier is undeclared when building without contiki with the MSVC compiler.

It has probably been this way since the introduction of DTLS_DEBUG_BUF_SIZE in 2022: 70a2b39 (unconfirmed).

Conclusion

I'm not sure what the correct fix would be, but changing the latter condition to equal the former at least builds without errors again.