proxy_pass: keep trailer buffer on blocked client writes

When breaking early out of the upstream response body loop, we
must ensure we know we've hit the parser body EOF and preserve
the buffer for trailer parsing.  Otherwise, reentering
proxy_read_body will put us in a bad state and corrupt
responses.

This is a critical bugfix which only affects users of
the soon-to-be-released "proxy_buffering: false" feature
of proxy_pass.

1 files changed, 4 insertions, 1 deletions

diff --git a/lib/yahns/proxy_http_response.rb b/lib/yahns/proxy_http_response.rb
index 316c310..0ca2c34 100644
--- a/lib/yahns/proxy_http_response.rb
+++ b/lib/yahns/proxy_http_response.rb
@@ -167,7 +167,10 @@ module Yahns::HttpResponse # :nodoc:
       end
       wbuf = proxy_write(wbuf, tmp, req_res)
       chunk.clear if chunk
-      return proxy_unbuffer(wbuf) if Yahns::WbufLite === wbuf
+      if Yahns::WbufLite === wbuf
+        req_res.proxy_trailers = [ rbuf.dup, tip ] if chunk && kcar.body_eof?
+        return proxy_unbuffer(wbuf)
+      end
     when nil # EOF
       # HTTP/1.1 upstream, unexpected premature EOF:
       msg = "upstream EOF (#{len} bytes left)" if len