Add nghttp2_session_set_user_data() public API function

doc/Makefile.am

@@ -143,6 +143,7 @@ APIDOCS= \
 	nghttp2_session_set_local_window_size.rst \
 	nghttp2_session_set_next_stream_id.rst \
 	nghttp2_session_set_stream_user_data.rst \
+	nghttp2_session_set_user_data.rst \
 	nghttp2_session_terminate_session.rst \
 	nghttp2_session_terminate_session2.rst \
 	nghttp2_session_upgrade.rst \

lib/includes/nghttp2/nghttp2.h

@@ -3081,6 +3081,16 @@ NGHTTP2_EXTERN int
 nghttp2_session_set_stream_user_data(nghttp2_session *session,
                                      int32_t stream_id, void *stream_user_data);
 
+/**
+ * @function
+ *
+ * Sets |user_data| to |session|, overwriting the existing user data
+ * specified in `nghttp2_session_client_new()`, or
+ * `nghttp2_session_server_new()`.
+ */
+NGHTTP2_EXTERN void nghttp2_session_set_user_data(nghttp2_session *session,
+                                                  void *user_data);
+
 /**
  * @function
  *

lib/nghttp2_session.c

@@ -7521,3 +7521,7 @@ size_t
 nghttp2_session_get_hd_deflate_dynamic_table_size(nghttp2_session *session) {
   return nghttp2_hd_deflate_get_dynamic_table_size(&session->hd_deflater);
 }
+
+void nghttp2_session_set_user_data(nghttp2_session *session, void *user_data) {
+  session->user_data = user_data;
+}