Ngx_http_send_special_response

Server NGINX
1

Hi

I am appreciate any help I can get on the following issues.

I am writing my own module.

  1. I can see in function ngx_http_send_special_response
    that it calculates the content length of the error page even if the
    request signed as header only (r->header_only = 1)
    and set the content length header with value, after sending the header
    it does not send the body ( because r->header_only = 1)
    so the response arrive with content length different than 0 but without
    body

Is it a BUG?

2.In the module I am trying to redirect the request with status code 302
(NGX_HTTP_MOVED_TEMPORARILY)
Trying to user->headers_out.location for the Alternate URL failed, I
looked in the code and saw the Location must start with “/” - why?

In the end I add it to r->headers_out.headers
using header = ngx_list_push(&r->headers_out.headers);
Is it the write way to do it?

  1. Can you explain please the different between
    a. r->headers_out.content_length_n
    b. r->headers_out.content_length

  2. Can you explain the usage of the hash field in ngx_table_elt_t

Thanks
Hagai A.

2

Hello!

On Mon, Apr 16, 2012 at 01:53:39AM -0700, hagai avrahami wrote:

and set the content length header with value, after sending the header it does
not send the body ( because r->header_only = 1)
so the response arrive with content length different than 0 but without body

Is it a BUG?

No. The r->header_only flag should is set when body isn’t
expected per protocol (HEAD requests, 304 responses). Having
Content-Length present in such responses is ok.

2.In the module I am trying to redirect the request with status code 302
(NGX_HTTP_MOVED_TEMPORARILY)
Trying to user->headers_out.location for the Alternate URL failed, I looked in
the code and saw the Location must start with “/” - why?

You have to set it correctly, i.e. add to r->headers_out.headers
and link to r->headers_out.location. If it starts with “/” it
works even if set incorrectly due to adding of a server_name,
that’s probably what confused you.

In the end I add it to r->headers_out.headers
using header = ngx_list_push(&r->headers_out.headers);
Is it the write way to do it?

  1. Can you explain please the different between
    a. r->headers_out.content_length_n
    b. r->headers_out.content_length

The content_length_n is a numeric length, this what you normaly
should set when generating response in nginx. The content_length
is a pointer to a headers array element, it might be present if
there is string representation of a Content-Length header
available for some reason (e.g. from a backend).

  1. Can you explain the usage of the hash field in ngx_table_elt_t

Normally the hash field is used for fast lookups in hash
structures. In case of r->headers_out it’s usually just set to 1
indicate the header is valid (or reset to 0 to indicate the
header should not be sent as it was superseeded by some other
header).

Maxim D.

3

WOW thanks for the quick and elaborate response

So what is the right way to send response with status code 302 on GET
request but
with content length 0 and no body (I want to redirect the request to
other Server)

Thanks

Hagai

4

Hello!

On Mon, Apr 16, 2012 at 04:29:18AM -0700, hagai avrahami wrote:

WOW thanks for the quick and elaborate response

So what is the right way to send response with status code 302 on GET request
but
with content length 0 and no body (I want to redirect the request to other
Server)

Easiest solution is to just write

return 302 $where;

in config. :slight_smile:

From the code point of view (assuming content handler context),
something like this should work:

ngx_table_elt_t  *h;

ngx_http_clear_location(r);

h = ngx_list_push(&r->headers_out.headers);
if (h == NULL) {
    return NGX_HTTP_INTERNAL_SERVER_ERROR;
}

h->hash = 1;
ngx_str_set(&h->key, "Location");

h->value.data = ...
h->value.len = ...

r->headers_out.location = h;

return NGX_HTTP_MOVED_TEMPORARILY;

Maxim D.

To: [email protected]

that’s probably what confused you.
should set when generating response in nginx. The content_length
header).

Maxim D.

nginx mailing list
[email protected]
nginx Info Page

5

Hi
Thanks

The redirect response is from content handler context.

Using the code you added

cause Nginx to send back the Error Page (302) with Content-Length and
Content-Type (“test/html”) (And I am trying avoid that) without Body

That’s why I assumed using r->header_only = 1 will solve my problem but
as you explained it is used for other cases.
please see that in ngx_http_send_special_response when this flag set to
1 the Header is set with this fields but no body in response (I think
this is not a good result)

if adding in the beginning of the function
(ngx_http_send_special_response) the following code it solves the
problem:

if (r->header_only == 1)
{
ngx_http_clear_accept_ranges®;
ngx_http_clear_last_modified®;

rc = ngx_http_send_header®;

return rc;
}

Is there any other way I can avoid content length and content-type in
302 response
Thanks
Hagai

6

Hello!

On Mon, Apr 16, 2012 at 08:14:25AM -0700, hagai avrahami wrote:

Hi
Thanks

The redirect response is from content handler context.

Using the code you added

cause Nginx to send back the Error Page (302) with
Content-Length and Content-Type (“test/html”) (And I am trying
avoid that) without Body

Ah, sorry, I missed you want to send 302 with an empty body, not
just 302. Then instead of

return NGX_HTTP_MOVED_TEMPORARY;

you have to send actual response youself, like this:

r->headers_out.status = NGX_HTTP_MOVED_TEMPORARY;
r->headers_out.content_length_n = 0;

rc = ngx_http_send_header(r);

if (rc == NGX_ERROR || rc > NGX_OK || r->header_only) {
    return rc;
}

return ngx_http_send_special(r, NGX_HTTP_LAST);

Maxim D.

7

Thanks!