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

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