NJS: variable access support

This commit introduces the 'vars' JavaScript object to NJS,
enabling direct access to native variables such as $uri and $arg_foo.
The syntax is `${vars.var_name}` or `${'vars[var_name]'}`.

For example:
    {
        "action": {
            "share": "`/www/html${vars.uri}`"
        }
    }

src/nxt_http_js.c

@@ -28,6 +28,8 @@ static njs_int_t nxt_http_js_ext_get_cookie(njs_vm_t *vm,
     njs_value_t *retval);
 static njs_int_t nxt_http_js_ext_keys_cookie(njs_vm_t *vm, njs_value_t *value,
     njs_value_t *keys);
+static njs_int_t nxt_http_js_ext_get_var(njs_vm_t *vm, njs_object_prop_t *prop,
+    njs_value_t *value, njs_value_t *setval, njs_value_t *retval);
 
 
 static njs_external_t  nxt_http_js_proto[] = {
@@ -88,6 +90,14 @@ static njs_external_t  nxt_http_js_proto[] = {
             .keys = nxt_http_js_ext_keys_cookie,
         }
     },
+
+    {
+        .flags = NJS_EXTERN_OBJECT,
+        .name.string = njs_str("vars"),
+        .u.object = {
+            .prop_handler = nxt_http_js_ext_get_var,
+        }
+    },
 };
 
 
@@ -338,3 +348,42 @@ nxt_http_js_ext_keys_cookie(njs_vm_t *vm, njs_value_t *value, njs_value_t *keys)
 
     return NJS_OK;
 }
+
+
+static njs_int_t
+nxt_http_js_ext_get_var(njs_vm_t *vm, njs_object_prop_t *prop,
+    njs_value_t *value, njs_value_t *setval, njs_value_t *retval)
+{
+    njs_int_t           rc;
+    njs_str_t           key;
+    nxt_str_t           name, *vv;
+    nxt_router_conf_t   *rtcf;
+    nxt_http_request_t  *r;
+
+    r = njs_vm_external(vm, nxt_js_proto_id, value);
+    if (r == NULL) {
+        njs_value_undefined_set(retval);
+        return NJS_DECLINED;
+    }
+
+    rc = njs_vm_prop_name(vm, prop, &key);
+    if (rc != NJS_OK) {
+        njs_value_undefined_set(retval);
+        return NJS_DECLINED;
+    }
+
+    rtcf = r->conf->socket_conf->router_conf;
+
+    name.start = key.start;
+    name.length = key.length;
+
+    vv = nxt_var_get(&r->task, rtcf->tstr_state, &r->tstr_cache.var, &name, r);
+
+    if (vv != NULL) {
+        return njs_vm_value_string_set(vm, retval, vv->start, vv->length);
+    }
+
+    njs_value_undefined_set(retval);
+
+    return NJS_DECLINED;
+}

src/nxt_js.c

@@ -240,7 +240,7 @@ nxt_js_add_tpl(nxt_js_conf_t *jcf, nxt_str_t *str, nxt_bool_t strz)
     nxt_str_t  *func;
 
     static nxt_str_t  func_str = nxt_string("function(uri, host, remoteAddr, "
-                                            "args, headers, cookies) {"
+                                            "args, headers, cookies, vars) {"
                                             "    return ");
 
     /*
@@ -391,7 +391,7 @@ nxt_js_call(nxt_task_t *task, nxt_js_conf_t *jcf, nxt_js_cache_t *cache,
     njs_uint_t          i, n;
     njs_value_t         *value;
     njs_function_t      *func;
-    njs_opaque_value_t  retval, opaque_value, arguments[6];
+    njs_opaque_value_t  retval, opaque_value, arguments[7];
 
     static const njs_str_t  js_args[] = {
         njs_str("uri"),
@@ -400,6 +400,7 @@ nxt_js_call(nxt_task_t *task, nxt_js_conf_t *jcf, nxt_js_cache_t *cache,
         njs_str("args"),
         njs_str("headers"),
         njs_str("cookies"),
+        njs_str("vars"),
     };
 
     vm = cache->vm;