Zephyr: Add wolfSSL DTLS backend support

- Add wolfSSL detection and configuration in zephyr/CMakeLists.txt
- Set wolfSSL to take priority over mbedTLS when both are available
- Bypass find_package() call and link wolfSSL library directly
- Prevent system wolfSSL library conflicts with ZEPHYR_BASE checks
- Fix compiler warnings in coap_wolfssl.c for unused functions

CMakeLists.txt

@@ -652,12 +652,17 @@ if(ENABLE_DTLS)
 endif()
 
 if(WITH_WOLFSSL)
-  find_library(WOLFSSL_LIBRARY wolfssl HINTS /usr/local/lib)
-  find_path(WOLFSSL_INCLUDE_DIR wolfssl/wolfcrypt/settings.h HINTS /usr/local/include)
-  if(WOLFSSL_LIBRARY AND WOLFSSL_INCLUDE_DIR)
-    message(STATUS "compiling with wolfssl support")
+  if(NOT ZEPHYR_BASE)
+    find_library(WOLFSSL_LIBRARY wolfssl HINTS /usr/local/lib)
+    find_path(WOLFSSL_INCLUDE_DIR wolfssl/wolfcrypt/settings.h HINTS /usr/local/include)
+    if(WOLFSSL_LIBRARY AND WOLFSSL_INCLUDE_DIR)
+      message(STATUS "compiling with wolfssl support")
+    else()
+      message(FATAL_ERROR "WolfSSL not found")
+    endif()
   else()
-    message(FATAL_ERROR "WolfSSL not found")
+    # Zephyr handles wolfSSL configuration via zephyr/CMakeLists.txt
+    message(STATUS "compiling with wolfssl support (Zephyr)")
   endif()
 endif()
 

src/coap_wolfssl.c

@@ -655,6 +655,7 @@ coap_dtls_psk_client_callback(WOLFSSL *ssl,
   return max_psk_len;
 }
 
+#if !COAP_DISABLE_TCP
 static unsigned int
 coap_dtls_psk_client_cs_callback(WOLFSSL *ssl, const char *hint,
                                  char *identity, unsigned int max_identity_len,
@@ -670,6 +671,7 @@ coap_dtls_psk_client_cs_callback(WOLFSSL *ssl, const char *hint,
   (void)ciphersuite;
   return key_len;
 }
+#endif /* !COAP_DISABLE_TCP */
 
 #endif /* COAP_CLIENT_SUPPORT */
 
@@ -807,6 +809,7 @@ coap_dtls_info_callback(const WOLFSSL *ssl, int where, int ret) {
   }
 }
 
+#if !COAP_DISABLE_TCP
 /*
  * strm
  * return +ve data amount
@@ -888,6 +891,7 @@ coap_sock_write(WOLFSSL *ssl, char *in, int inl, void *ctx) {
   }
   return ret;
 }
+#endif /* !COAP_DISABLE_TCP */
 
 static void
 coap_set_user_prefs(WOLFSSL_CTX *ctx) {
@@ -1877,6 +1881,7 @@ coap_dtls_context_load_pki_trust_store(coap_context_t *ctx) {
 #else /* LIBWOLFSSL_VERSION_HEX < 0x05005002 */
   coap_log_warn("coap_context_set_pki_trust_store: (D)TLS environment "
                 "not supported for wolfSSL < v5.5.2 or –enable-sys-ca-certs not defined\n");
+  return 0;
 #endif /* WOLFSSL_SYS_CA_CERTS */
 }
 

zephyr/CMakeLists.txt

@@ -12,14 +12,23 @@
 cmake_minimum_required(VERSION 3.20.0)
 
 if(CONFIG_LIBCOAP)
-  if(CONFIG_MBEDTLS)
+  if(CONFIG_MBEDTLS AND NOT CONFIG_WOLFSSL)
     set(ENABLE_DTLS ON)
     set(DTLS_BACKEND "zephyr" CACHE STRING "Zephyr build")
-    set_property(
-      CACHE DTLS_BACKEND
-      PROPERTY STRINGS
-             zephyr)
+    set_property(CACHE DTLS_BACKEND PROPERTY STRINGS zephyr wolfssl)
     set(COAP_WITH_LIBMBEDTLS 1)
+    message(STATUS "libcoap: Using mbedTLS for DTLS")
+  elseif(CONFIG_WOLFSSL)
+    set(ENABLE_DTLS ON)
+    set(DTLS_BACKEND "wolfssl" CACHE STRING "Zephyr build")
+    set_property(CACHE DTLS_BACKEND PROPERTY STRINGS zephyr wolfssl)
+    set(COAP_WITH_LIBWOLFSSL 1)
+    # Set wolfSSL variables to prevent find_package call
+    set(wolfSSL_FOUND TRUE CACHE BOOL "wolfSSL found via Zephyr module")
+    set(WOLFSSL_INCLUDE_DIR "${ZEPHYR_BASE}/../modules/crypto/wolfssl" CACHE PATH "wolfSSL include dir")
+    set(WOLFSSL_LIBRARIES "wolfSSL" CACHE STRING "wolfSSL library")
+    set(HAVE_LIBWOLFSSL 1 CACHE STRING "Have wolfSSL library")
+    message(STATUS "libcoap: Using wolfSSL for DTLS")
   else()
     set(ENABLE_DTLS OFF)
   endif()
@@ -112,6 +121,11 @@ if(CONFIG_LIBCOAP)
     target_link_libraries(coap-3 PUBLIC mbedTLS)
   endif()
 
+  if(CONFIG_WOLFSSL)
+    target_compile_definitions(coap-3 PRIVATE WOLFSSL_USER_SETTINGS)
+    target_link_libraries(coap-3 PUBLIC wolfSSL)
+  endif()
+
   set_property(GLOBAL APPEND PROPERTY ZEPHYR_INTERFACE_LIBS coap-3)
 
   target_link_libraries(app PUBLIC coap-3)