ssl ecdh adapt if missing ecdh.h include

https://github.com/warmcat/libwebsockets/issues/457

CMakeLists.txt

@@ -695,6 +695,15 @@ if (LWS_WITH_SSL)
 		include_directories("${OPENSSL_INCLUDE_DIRS}")
 		list(APPEND LIB_LIST ${OPENSSL_LIBRARIES})
 	endif()
+
+	# older (0.98) Openssl lacks this
+	set(CMAKE_REQUIRED_INCLUDES ${OPENSSL_INCLUDE_DIRS})
+	check_include_file(openssl/ecdh.h LWS_HAVE_OPENSSL_ECDH_H)
+
+	if (LWS_SSL_SERVER_WITH_ECDH_CERT AND NOT LWS_HAVE_OPENSSL_ECDH_H)
+		message(FATAL_ERROR "Missing openssl/ecdh.h, so cannot use LWS_SSL_SERVER_WITH_ECDH_CERT")
+	endif()
+
 endif(LWS_WITH_SSL)
 
 if (LWS_WITH_LIBEV)
@@ -1208,6 +1217,7 @@ message(" LWS_WITH_HTTP2 = ${LWS_WITH_HTTP2}")
 message(" LWS_MBED3 = ${LWS_MBED3}")
 message(" LWS_SSL_SERVER_WITH_ECDH_CERT = ${LWS_SSL_SERVER_WITH_ECDH_CERT}")
 message(" LWS_MAX_SMP = ${LWS_MAX_SMP}")
+message(" LWS_HAVE_OPENSSL_ECDH_H = ${LWS_HAVE_OPENSSL_ECDH_H}")
 message("---------------------------------------------------------------------")
 
 # These will be available to parent projects including libwebsockets using add_subdirectory()

lib/ssl.c

@@ -24,7 +24,7 @@
  #include <openssl/err.h>
 #endif
 
-#if OPENSSL_VERSION_NUMBER >= 0x0090800fL
+#ifdef LWS_HAVE_OPENSSL_ECDH_H
 #include <openssl/ecdh.h>
 #endif
 
@@ -139,7 +139,7 @@ static int
 lws_context_ssl_init_ecdh_curve(struct lws_context_creation_info *info,
 				struct lws_context *context)
 {
-#if OPENSSL_VERSION_NUMBER >= 0x0090800fL
+#ifdef LWS_HAVE_OPENSSL_ECDH_H
 	EC_KEY *ecdh;
 	int ecdh_nid;
 	const char *ecdh_curve = "prime256v1";

lws_config.h.in

@@ -74,6 +74,9 @@
 /* SSL server using ECDH certificate */
 #cmakedefine LWS_SSL_SERVER_WITH_ECDH_CERT
 
+/* whether the Openssl is recent enough, and / or built with, ecdh */
+#cmakedefine LWS_HAVE_OPENSSL_ECDH_H
+
 /* Maximum supported service threads */
 #define LWS_MAX_SMP ${LWS_MAX_SMP}