Use s2n_cleanup_thread() and path (#682)

Co-authored-by: Michael Graeb <graebm@amazon.com>

Author: TingDaoK

CMakeLists.txt

@@ -152,10 +152,21 @@ if (BYO_CRYPTO)
 endif()
 
 if (USE_S2N)
-    file(GLOB AWS_IO_TLS_SRC
-            "source/s2n/*.c"
-            )
-    aws_use_package(s2n)
+        file(GLOB AWS_IO_TLS_SRC
+                "source/s2n/*.c"
+                )
+        # Prefer find_package() because it's the normal CMake way to do dependencies.
+        # But fall back on aws_use_package() because some projects still need to do an IN_SOURCE_BUILD of S2N.
+        # (e.g. aws-crt-java until this is resolved: https://github.com/awslabs/aws-crt-java/pull/817)
+        find_package(s2n QUIET)
+
+        if (s2n_FOUND)
+            list(APPEND DEP_AWS_LIBS AWS::s2n)
+        else()
+            # Set flag to use in-source path to  <s2n/unstable/*.h> headers if we do an IN_SOURCE_BUILD.
+            aws_use_package(s2n)
+            add_definitions(-DAWS_S2N_INSOURCE_PATH)
+        endif()
 endif()
 
 file(GLOB IO_HEADERS

source/s2n/s2n_tls_channel_handler.c

@@ -20,10 +20,16 @@
 #include <aws/common/task_scheduler.h>
 #include <aws/common/thread.h>
 
+#include <s2n.h>
+#ifdef AWS_S2N_INSOURCE_PATH
+#    include <api/unstable/cleanup.h>
+#else
+#    include <s2n/unstable/cleanup.h>
+#endif
+
 #include <errno.h>
 #include <inttypes.h>
 #include <math.h>
-#include <s2n.h>
 #include <stdio.h>
 #include <stdlib.h>
 
@@ -1247,7 +1253,7 @@ static struct aws_event_loop_local_object s_tl_cleanup_object = {
 static void s_aws_cleanup_s2n_thread_local_state(void *user_data) {
     (void)user_data;
 
-    s2n_cleanup();
+    s2n_cleanup_thread();
 }
 
 /* s2n allocates thread-local data structures. We need to clean these up when the event loop's thread exits. */