SSL: avoid calling SSL_write() with zero data size.
According to documentation, calling SSL_write() with num=0 bytes to be sent
results in undefined behavior.
We don't currently call ngx_ssl_send_chain() with empty chain and buffer.
This check handles the case of a chain with total data size that is
a multiple of NGX_SSL_BUFSIZE, and with the special buffer at the end.
In practice such cases resulted in premature connection close and critical
error "SSL_write() failed (SSL:)" in the error log.
diff --git a/src/event/ngx_event_openssl.c b/src/event/ngx_event_openssl.c
index c27dba9..d288bc8 100644
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -1213,6 +1213,12 @@
size = buf->last - buf->pos;
+ if (size == 0) {
+ buf->flush = 0;
+ c->buffered &= ~NGX_SSL_BUFFERED;
+ return in;
+ }
+
n = ngx_ssl_write(c, buf->pos, size);
if (n == NGX_ERROR) {
