ngx.var.arg_xx与ngx.req.get_uri_args["xx"]两者都是为了获取请求uri中的参数，例如
http://pureage.info?strider=1 为了获取输入参数strider，以下两种方法都可以：
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local strider = ngx.var.arg_strider
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local strider = ngx.req.get_uri_args["strider"]
差别在于，当请求uri中有多个同名参数时,ngx.var.arg_xx的做法是取第一个出现的值,ngx.req_get_uri_args["xx"]的做法是返回一个table，该table里存放了该参数的所有值，例如,当请求uri为：
http://pureage.info?strider=1&strider=2&strider=3&strider=4 时，ngx.var.arg_strider的值为"1",而ngx.req.get_uri_args["strider"]的值为table ["1", "2", "3", "4"]。因此，ngx.req.get_uri_args属于ngx.var.arg_的增强。
ngx.var.arg_的实现是直接使用nginx原生的变量支持，nginx相关代码为：
ngx_http_variable_value_t * ngx_http_get_variable(ngx_http_request_t *r, ngx_str_t *name, ngx_uint_t key) { ....(略）.... if (ngx_strncmp(name->data, "arg_", 4) == 0) { if (ngx_http_variable_argument(r, vv, (uintptr_t) name) == NGX_OK) { return vv; } return NULL; } vv->not_found = 1; return vv; } static ngx_int_t ngx_http_variable_argument(ngx_http_request_t *r, ngx_http_variable_value_t *v, uintptr_t data) { ngx_str_t *name = (ngx_str_t *) data; u_char *arg; size_t len; ngx_str_t value; len = name->len - (sizeof("arg_") - 1); arg = name->data + sizeof("arg_") - 1; if (ngx_http_arg(r, arg, len, &value) != NGX_OK) { v->not_found = 1; return NGX_OK; } v->data = value.data; v->len = value.len; v->valid = 1; v->no_cacheable = 0; v->not_found = 0; return NGX_OK; } ngx_int_t ngx_http_arg(ngx_http_request_t *r, u_char *name, size_t len, ngx_str_t *value) { u_char *p, *last; if (r->args.len == 0) { return NGX_DECLINED; } p = r->args.data; last = p + r->args.len; for ( /* void */ ; p < last; p++) { /* we need '=' after name, so drop one char from last */ p = ngx_strlcasestrn(p, last - 1, name, len - 1); if (p == NULL) { return NGX_DECLINED; } if ((p == r->args.data || *(p - 1) == '&') && *(p + len) == '=') { value->data = p + len + 1; p = ngx_strlchr(p, last, '&'); if (p == NULL) { p = r->args.data + r->args.len; } value->len = p - value->data; return NGX_OK; } } return NGX_DECLINED; }