(52) Empty reply from server

[Pankaj Chaudhary]

Hi,

thank you for your response.

>>You are writing into the headers_in structure. Normally, that is what
>>came from the client, so I guess you must have a plan for why you are
>>doing that.

I have tried to write in headers_out struture also but did not able to read
the my written value so tried with headers_in

>>The example code I see treats is as a ngx_http_header_t*.
i have tried to change return type to ngx_http_header_t but still same
result.

If i am writing in headers_out "Set-Cookie" value "somevalue" then same
value reflecting response header tab while viewing through developer option
in mozilla
and request header "cookie" value "somevalue".
So  what is the possible way to read this  "cookie" value that is
"somevalue".
i tried to read many way like using
ngx_http_parse_multi_header_lines(),ngx_hash_find() but still not able to
get correct value .
Below is snapshot of Response and Request header

[image: Inline image 1]


On Thu, Apr 28, 2016 at 12:39 PM, Francis Daly <francis at daoine.org> wrote:

> On Tue, Apr 26, 2016 at 04:52:22PM +0530, Pankaj Chaudhary wrote:
>
> Hi there,
>
> > I have requirement to create own cookie  based on input  and wirte the
> that
> > cookie in header.
> > whenever i need that i can read from header and use it.
>
> I confess that I do not understand what that requirement actually
> is. There are headers in the request from the client to nginx; there
> may be header-like things in whatever nginx does when communicating
> with an upstream; there may be header-like things in the response from
> that upstream; and there are headers in the response from nginx to the
> client. And it is not clear to me what your module architecture is.
>
> But that's ok; I don't have to understand it. You want to do some specific
> things in an nginx module.
>
> > for example:-
> >
> > I have created my own cookie "thissomevalue" worte in header and later
> the
> > same read from header.
> >
> > Please check my code and let me know why i am not able to read the value
> > from header.
> >
> > Below code snippet to set header value in request header:-
> >
> > ngx_table_elt_t *cookie;
> > cookie = ngx_list_push(&r->headers_in.headers);
>
> You are writing into the headers_in structure. Normally, that is what
> came from the client, so I guess you must have a plan for why you are
> doing that.
>
> (If I wanted to test "can I read from headers_in", I would probably add a
> "MyHeader" to my curl request, and look for that in my code.)
>
> > cookie->lowcase_key = (u_char*) "cookie";
> > ngx_str_set(&cookie->key, "Cookie");
> > ngx_str_set(&cookie->value, "somevalue");
> > cookie->hash = ngx_crc32_long(cookie->lowcase_key, cookie->key.len);
> >
> >
> > Below code snippet to read set value from header:-
> >
> > ngx_http_core_main_conf_t   *clcf;
> > ngx_str_t                   *type;
> > ngx_uint_t                   key;
> > ngx_str_t    val = ngx_string("cookie");
> > clcf = ngx_http_get_module_main_conf(r, ngx_http_core_module);
> > key= ngx_hash_key_lc(val.data, val.len);
> > type = ngx_hash_find(&clcf->headers_in_hash, key,  val.data, val.len);
>
> As mentioned elsewhere, you are not reading from the headers_in
> structure. So there's a reasonable chance that what you wrote into one
> structure will not be found in another one.
>
> Also, you are treating the output of ngx_hash_find() as a ngx_str_t*.
>
> The example code I see treats is as a ngx_http_header_t*.
>
> Is that an important difference?
>
> (As in: is that why you print the header name, but not the header
> value? Possibly not, if the original request did not have any Cookie
> header; but test rather than assume, if the documentation is not clear
> to you.)
>
> > if (type != NULL)
> > {
>
> The example code I see has separate handling for "header is unknown or
> is not hashed yet", and "header is hashed but not cached yet". You
> seem to skip testing for the second possibility here.
>
> > ngx_table_elt_t *test_val;
> > test_val= ngx_list_push(&r->headers_out.headers);
> > test_val->lowcase_key = (u_char*) "test_val";
> > ngx_str_set(&test_val->key, "Test_Val");
> > ngx_str_set(&test_val->value, type->data);
>
> I'd also suggest that if you are not sure what value your content has,
> use the simplest possible method to print it somewhere you can read
> it. Usually, that means logging, since that should not have a complex
> data structure.
>
> > test_val->hash = ngx_crc32_long(test_val->lowcase_key,
> test_val->key.len);
> > }
>
> Good luck with it,
>
>         f
> --
> Francis Daly        francis at daoine.org
>
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