Empty headers_out in log phase

[Maxim Dounin]

Hello!

On Fri, Apr 13, 2012 at 09:58:14PM +0200, Samuel ROZE wrote:

> Hello,
> 
> I'm writing an nginx module but I've got a problem for getting
> response headers. It's using an NGX_HTTP_LOG_PHASE handler and I want
> to have access to response headers sent to client. (with or without
> proxy_pass)
> 
> And, in fact, the headers_out variable of request isn't really
> completed. When debugging module using gdb, in the log phase handler,
> the headers_out variable is always like that:
> 
>   headers_out = {
>     headers = {
>       last = 0x1ed5530,
>       part = {
>         elts = 0x1ec6250,
>         nelts = 1,
>         next = 0x0
>       },
>       size = 48,
>       nalloc = 20,
>       pool = 0x1ec6200
>     },
>     status = 304,
>     status_line = {
>       len = 0,
>       data = 0x0
>     },
>     server = 0x0,
>     date = 0x0,
>     content_length = 0x0,
>     content_encoding = 0x0,
>     location = 0x0,
>     refresh = 0x0,
>     last_modified = 0x0,
>     content_range = 0x0,
>     accept_ranges = 0x0,
>     www_authenticate = 0x0,
>     expires = 0x0,
>     etag = 0x0,
>     override_charset = 0x0,
>     content_type_len = 9,
>     content_type = {
>       len = 0,
>       data = 0x1ed1248 "text/html"
>     },
>     charset = {
>       len = 0,
>       data = 0x0
>     },
>     content_type_lowcase = 0x0,
>     content_type_hash = 0,
>     cache_control = {
>       elts = 0x0,
>       nelts = 0,
>       size = 0,
>       nalloc = 0,
>       pool = 0x0
>     },
>     content_length_n = -1,
>     date_time = 0,
>     last_modified_time = 1334219772
>   },
> 
> The headers_out array is containing the only request that I added
> using "add_header" in location, and the "server", "date", etc...
> variables are empty.
> 
> Do you know why there isn't any value in headers_out structure? And do
> you know how can I get these headers?

The "Server", "Date", "Content-Length", "Last-Modified" and other 
standard headers aren't normally exists in r->headers_out for 
nginx's own responses, they are instead constructed on the fly in 
ngx_http_header_filter.c.

The r->headers_out structure either hold needed data (as 
last_modified_time for the "Last-Modified" header) or just nothing 
(as for the "Date" header, as it just uses current time).

Maxim Dounin