rgw: make sending Content-Length in 204 and 304 controllable

This commit introduces a new configurable "rgw print prohibited
content length" to let operator decide whether RadosGW complies
to RFC 7230 (a part of the HTTP specification) or violates it
but follows the Swift's behavior.

Fixes: http://tracker.ceph.com/issues/16602
Signed-off-by: Radoslaw Zarzynski <rzarzynski@mirantis.com>

src/common/config_opts.h

@@ -1486,6 +1486,7 @@ OPTION(rgw_admin_entry, OPT_STR, "admin")  // entry point for which a url is con
 OPTION(rgw_enforce_swift_acls, OPT_BOOL, true)
 OPTION(rgw_swift_token_expiration, OPT_INT, 24 * 3600) // time in seconds for swift token expiration
 OPTION(rgw_print_continue, OPT_BOOL, true)  // enable if 100-Continue works
+OPTION(rgw_print_prohibited_content_length, OPT_BOOL, false) // violate RFC 7230 and send Content-Length in 204 and 304
 OPTION(rgw_remote_addr_param, OPT_STR, "REMOTE_ADDR")  // e.g. X-Forwarded-For, if you have a reverse proxy
 OPTION(rgw_op_thread_timeout, OPT_INT, 10*60)
 OPTION(rgw_op_thread_suicide_timeout, OPT_INT, 0)

src/rgw/rgw_client_io_filters.h

@@ -291,7 +291,8 @@ class ConLenControllingFilter : public DecoratedRestfulClient<T> {
 
   size_t send_status(const int status,
                      const char* const status_name) override {
-    if (204 == status || 304 == status) {
+    if ((204 == status || 304 == status) &&
+        ! g_conf->rgw_print_prohibited_content_length) {
       action = ContentLengthAction::INHIBIT;
     } else {
       action = ContentLengthAction::FORWARD;