https://src.fedoraproject.org/rpms/libserf/raw/rawhide/f/libserf-1.3.9-bio-ctrl.patch
https://bugs.gentoo.org/805161
https://issues.apache.org/jira/projects/SERF/issues/SERF-198
--- a/buckets/ssl_buckets.c
+++ b/buckets/ssl_buckets.c
@@ -407,7 +407,7 @@ static int bio_bucket_destroy(BIO *bio)
 
 static long bio_bucket_ctrl(BIO *bio, int cmd, long num, void *ptr)
 {
-    long ret = 1;
+    long ret = 0;
 
     switch (cmd) {
     default:
@@ -415,6 +415,7 @@ static long bio_bucket_ctrl(BIO *bio, int cmd, long num, void *ptr)
         break;
     case BIO_CTRL_FLUSH:
         /* At this point we can't force a flush. */
+        ret = 1;
         break;
     case BIO_CTRL_PUSH:
     case BIO_CTRL_POP: