buffer: fix evbuffer_remove_buffer() with empty chain in front

In case we have empty chain (chain that do not have any data, i.e. ->off
== 0) at the beginning of the buffer, and no more full chains to move to
the dst, we will skip moving of this empty chain, and hence
last_with_datap will not be adjusted, and things will be broken after.

Fix this by not relying on ->off, just count if we have something to
move that's it.

Test case from:
  https://github.com/envoyproxy/envoy/pull/6062

Fixes: #774

1 files changed, 1 insertions, 1 deletions

diff --git a/buffer.c b/buffer.c
index f6ff8431..7a8c8b69 100644
--- a/buffer.c
+++ b/buffer.c
@@ -1299,7 +1299,7 @@ evbuffer_remove_buffer(struct evbuffer *src, struct evbuffer *dst,
 		chain = chain->next;
 	}
 
-	if (nread) {
+	if (chain != src->first) {
 		/* we can remove the chain */
 		struct evbuffer_chain **chp;
 		chp = evbuffer_free_trailing_empty_chains(dst);