(52) Empty reply from server

Francis Daly francis at daoine.org
Thu Apr 14 16:55:41 UTC 2016

On Thu, Apr 14, 2016 at 03:34:40PM +0530, Pankaj Chaudhary wrote:

Hi there,

> i am trying to set value in header with the help of below code snippet .

Web searches for how to write nginx modules tend to point towards
"Emiller's Guide" or the "Nginx Development Kit".

You may find good background reading there (allowing for any changes
to the nginx internals since they were written) to help you create a
"hello world" module.

After that, you'll have a skeleton into which you can add your specific
pieces, knowing that the basic starting point does work for you.

> ngx_table_elt_t *h1;
>   h1 = ngx_list_push(&r->headers_out.headers);
>   h1->hash = 1;
>   ngx_str_set(&h1->key, "http_user_agent");
>   ngx_str_set(&h1->value, "user_agent_value");
> if i try to retrieve the same value then getting response "(52) Empty reply
> from server"

There, it looks like you wrote something to a "headers_out.headers"
data structure.

> ngx_http_core_loc_conf_t          *clcf;
> ngx_str_t                         *type;
> ngx_uint_t                   hash;
> ngx_str_t    name = ngx_string("http_user_agent");
> clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
> hash = ngx_hash_key_lc(name.data, name.len);
> type = ngx_hash_find(&clcf->types_hash, hash, name.data, name.len);

And there it looks like you tried to read something from a "types_hash"
data structure. So the "type" variable is probably NULL, and your code
should do something sensible with that value.

Good luck with it,

Francis Daly        francis at daoine.org

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