[PATCH 1 of 2] HTTP: add support for trailers in HTTP responses

[Maxim Dounin]

Hello!

On Sun, Jun 26, 2016 at 04:13:15PM -0700, Piotr Sikora wrote:

> # HG changeset patch
> # User Piotr Sikora <piotrsikora at google.com>
> # Date 1466735480 25200
> #      Thu Jun 23 19:31:20 2016 -0700
> # Node ID a96187a9806536ab2a8bf3fa7f7b659cf5d3ff13
> # Parent  6f69e3c0f780e29bca752fc1f938f4a459a1ec59
> HTTP: add support for trailers in HTTP responses.
> 
> Example:
> 
>    ngx_table_elt_t  *h;
> 
>    h = ngx_list_push(&r->headers_out.trailers);
>    if (h == NULL) {
>        return NGX_ERROR;
>    }
> 
>    ngx_str_set(&h->key, "Fun");
>    ngx_str_set(&h->value, "with trailers");
>    h->hash = ngx_hash_key_lc(h->key.data, h->key.len);
> 
> The code above adds "Fun: with trailers" trailer to the response to
> the request with "TE: trailers" header (which indicates support for
> trailers).
> 
> Note that trailers MUST be added before last buffer of the response
> (last_buf = 1) reaches chunked or v2 output filters, otherwise they
> are going to be ignored.
> 
> Signed-off-by: Piotr Sikora <piotrsikora at google.com>

What's the goal?  Any real-world use for this?

> 
> diff -r 6f69e3c0f780 -r a96187a98065 src/http/modules/ngx_http_chunked_filter_module.c
> --- a/src/http/modules/ngx_http_chunked_filter_module.c
> +++ b/src/http/modules/ngx_http_chunked_filter_module.c
> @@ -17,6 +17,7 @@ typedef struct {
>  
>  
>  static ngx_int_t ngx_http_chunked_filter_init(ngx_conf_t *cf);
> +static ngx_chain_t *ngx_http_chunked_get_trailers(ngx_http_request_t *r);
>  
>  
>  static ngx_http_module_t  ngx_http_chunked_filter_module_ctx = {
> @@ -69,28 +70,31 @@ ngx_http_chunked_header_filter(ngx_http_
>          return ngx_http_next_header_filter(r);
>      }
>  
> -    if (r->headers_out.content_length_n == -1) {
> +    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
> +
> +    if (clcf->chunked_transfer_encoding && r->trailers_ok) {
> +        ngx_http_clear_content_length(r);
> +        r->chunked = 1;

As far as I understand the patch, this will cause chunked encoding 
to be used for all responses to a client which supports trailers.  
This certainly looks like a bad idea.

[...]

-- 
Maxim Dounin
http://nginx.org/