ngx_conf_t args count

[Ruslan Ermilov]

On Sun, Dec 15, 2013 at 04:31:08PM -0500, Jeffrey Walton wrote:
> From Miller's http://www.evanmiller.org/nginx-modules-guide.html, section 5.2:
> 
> ngx_http_upstream_hash(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
>  {
>     ngx_http_upstream_srv_conf_t  *uscf;
>     ngx_http_script_compile_t      sc;
>     ngx_str_t                     *value;
>     ngx_array_t                   *vars_lengths, *vars_values;
> 
>     value = cf->args->elts;
> 
>     /* the following is necessary to evaluate the argument to "hash"
> as a $variable */
>     ngx_memzero(&sc, sizeof(ngx_http_script_compile_t));
> 
>     vars_lengths = NULL;
>     vars_values = NULL;
> 
>     sc.cf = cf;
>     sc.source = &value[1];
>     ...
> }
> 
> How does one know that value[1] is valid? Shouldn't cf->args->nelts be
> checked first? Or does ngx_conf_t always have at least two options?
> Related: why was value[0] not chosen?

value[0] is the directive name, "hash" in this case.  It's
like argv[] in main().

The "hash" directive can be specified in the "upstream" context
(NGX_HTTP_UPS_CONF) and it takes exactly one argument (NGX_CONF_TAKE1).
The generic configuration parser code ensures that the argument
exists.

http://www.evanmiller.org/nginx-modules-guide.html#directives