tree 61cdd4823536103fd17e617bfe42b128fb3c742c
parent a001fe286ce205ae829e9d1a5ff1fee48e6d2db4
author Maxim Dounin <mdounin@mdounin.ru> 1515696229 +0300
committer Maxim Dounin <mdounin@mdounin.ru> 1515696229 +0300

Upstream: fixed "header already sent" alerts on backend errors.

Following ad3f342f14ba046c (1.9.13), it is possible that a request where
header was already sent will be finalized with NGX_HTTP_BAD_GATEWAY,
triggering an attempt to return additional error response and the
"header already sent" alert as a result.

In particular, it is trivial to reproduce the problem with a HEAD request
and caching enabled.  With caching enabled nginx will change HEAD to GET
and will set u->pipe->downstream_error to suppress sending the response
body to the client.  When a backend-related error occurs (for example,
proxy_read_timeout expires), ngx_http_finalize_upstream_request() will
be called with NGX_HTTP_BAD_GATEWAY.  After ad3f342f14ba046c this will
result in ngx_http_finalize_request(NGX_HTTP_BAD_GATEWAY).

Fix is to move u->pipe->downstream_error handling to a later point,
where all special response codes are changed to NGX_ERROR.

Reported by Jan Prachar,
http://mailman.nginx.org/pipermail/nginx-devel/2018-January/010737.html.