Hi Yann, 2016-12-05 13:54 GMT+01:00 Yann Ylavic <[email protected]>:
> Hi Luca, > > sorry for the delay (overwhelmed these times)... > thanks a lot for the help! > > On Mon, Dec 5, 2016 at 1:21 PM, Luca Toscano <[email protected]> > wrote: > > > > > > 2016-11-30 18:46 GMT+01:00 Luca Toscano <[email protected]>: > >> > >> Hi everybody, > >> > >> while working on https://bz.apache.org/bugzilla/show_bug.cgi?id=51350 a > >> user asked why httpd send the "Content-Length: 0" header for HTTP 204 > >> responses given the following statement in the RFC: > >> > >> https://tools.ietf.org/html/rfc7230#page-30 > >> "A server MUST NOT send a Content-Length header field in any response > with > >> a status code of 1xx (Informational) or 204 (No Content)." > >> > >> I tried with a simple PHP script returning an HTTP 204 header (via > >> mod_proxy_fcgi) and indeed I can see the Content-Length: 0. After a bit > of > >> digging it seems that ap_content_length_filter in protocol.c adds the > header > >> when it evaluates: > >> > >> if (!(r->header_only > >> && !r->bytes_sent > >> && (r->sent_bodyct > >> || conf->http_cl_head_zero != > >> AP_HTTP_CL_HEAD_ZERO_ENABLE > >> || apr_table_get(r->headers_out, "Content-Length")))) > { > >> ap_set_content_length(r, r->bytes_sent); > >> } > > How about adding (yet) another condition to the above: > > Index: server/protocol.c > =================================================================== > --- server/protocol.c (revision 1772657) > +++ server/protocol.c (working copy) > @@ -1766,7 +1766,9 @@ AP_CORE_DECLARE_NONSTD(apr_status_t) ap_content_le > * such filters update or remove the C-L header, and just use it > * if present. > */ > - if (!(r->header_only > + if (!((r->header_only > + || r->status == HTTP_NO_CONTENT > + || r->status == HTTP_NOT_MODIFIED) > && !r->bytes_sent > && (r->sent_bodyct > || conf->http_cl_head_zero != > AP_HTTP_CL_HEAD_ZERO_ENABLE > ? This was the other solution that I had in mind (fixing the issue at its origin rather than patching it afterwards) but I wasn't confident to make changes to the already crowded if (that seems to be related to a specific use case). One caveat that I realized only now: if the backend sets a C-L header (for a 204 response) it will not be handled by the above if, so if we want to patch this use case too we'd probably want to add a stricter condition in ap_http_header_filter. Follow up: I got tricked by the "r->header_only" condition in the beginning, I thought that it would have been applied to all the responses requiring headers and no body, but it applies only to HEAD requests. I didn't find any trace in the code about how to prevent a HTTP 204 response body to be sent, except for mod_proxy_http that explicitly handle this case. I tested the presence of a body in a simple 204 response from a Perl/PHP cgi/fcgi script with telnet and I confirmed my suspicion. So this might help: Index: modules/http/http_filters.c =================================================================== --- modules/http/http_filters.c (revision 1772510) +++ modules/http/http_filters.c (working copy) @@ -1297,6 +1297,10 @@ apr_table_unset(r->headers_out, "Content-Length"); } + if (r->status == HTTP_NO_CONTENT || ap_is_HTTP_INFO(r->status)){ + apr_table_unset(r->headers_out, "Content-Length"); + } + ctype = ap_make_content_type(r, r->content_type); if (ctype) { apr_table_setn(r->headers_out, "Content-Type", ctype); @@ -1368,7 +1372,7 @@ ap_pass_brigade(f->next, b2); - if (r->header_only) { + if (r->header_only || r->status == HTTP_NO_CONTENT) { apr_brigade_cleanup(b); ctx->headers_sent = 1; return OK; Does it make any sense? Thanks, Luca
