How to get Redis key values on Server side Dart with Angel - dart

Question

Having moved my mobile app development to Flutter I am now in the process of experimenting with using Dart as my main server side language. The productivity benefits in using a single coding language in both the app and on the server are considerable. To that end I have set up a server with an Nginx front end which proxies all dynamic web requests to an Angel/Dart server.
Angel is a remarkably well written package and I had a working server written up in no time at all. However, in order to have a fully functional backend I need to be able to use both Redis and PostgreSQL from within my server side Dart code. I am using the resp_client package to access Redis. The issue I have run into is with the fact that RespCommand.get is asynchronous. With my newbie knowledge of both Dart and Angel I am unable to find a way to acquire a Redis key value via RespCommand.get in an Angel route handler and then somehow use that value in the response it returns.
My entire Dart backend server code is shown below
import 'package:angel_framework/angel_framework.dart';
import 'package:angel_framework/http.dart';
import 'package:postgres/postgres.dart';
import 'package:resp_client/resp_client.dart';
import 'package:resp_client/resp_commands.dart';
class DartWeb
{
static Angel angel;
static AngelHttp http;
static RespCommands redis;
static PostgreSQLConnection db;
static init() async
{
angel = Angel();
http = AngelHttp(angel);
angel.get('/',rootRoute);
await prepareRedis();
await http.startServer('localhost',3000);
}
static prepareRedis() async
{
RespServerConnection rsc = await connectSocket('localhost');
RespClient client = RespClient(rsc);
redis = RespCommands(client);
}
static preparePostgres() async
{
db = new PostgreSQLConnection('serverurl',portNo,'database',username:'user',password:'password');
await db.open();
}
static void rootRoute(RequestContext req,ResponseContext res)
{
try
{
await redis.set('test','foobar',expire:Duration(seconds:10));
String testVal = await redis.get('test');
res.write('Done $testVal');
} catch(e) {res.write('++ $e ++');}
}
}
main() async {await DartWeb.init();}
If I start up this server and then access it through my web browser I end up with a 502 Bad Gateway message. Not surprising. dart2native main.dart -o mainCompiled returns the error await can only be used in async... message.
So I tried instead
try
{
res.write('Before');
redis.set('test','foobar',expire:Duration(seconds:10)).then((bool done)
{
res.write('DONE $done');
});
res.write('After');
} catch(e) {res.write('++ $e ++');}
which simply printed out BeforeAfter in my browser with the DONE bit never showing up although a quick test via redis-cli shows that the key test had in fact been created.
My knowledge of both Dart and Angel is still in its infancy so I guess I am doing something incorrectly here. Shorn of all the detail my questions are essentially these -
how do I call and get the result from async methods in an Angel route dispatcher?
given that I am editing my Dart code in VSCode on my local Windows machine which accesses the relevant dart files on my Ubuntu server I loose the benefits of error reporting provided by the VSCode Dart plugin. dart2native, as I have used here, helps out but it would be nicer if I could somehow get a running error report within VSCode as I do when building Flutter apps locally. How can I accomplish this - if at all possible?

Answer 1

It turns out that Dart/Angel does not impose excessively strict constraints on the signature of a route handler. So you can quite safely declare a route handler like this one
static Future<void> rootRoute(RequestContext req,ResponseContext res) async
{
try
{
res.write('!! Before ');
await redis.set('test','foobar',expire:Duration(seconds:10));
String test = await redis.get('test');
res.write('After $test !!');
} catch(e) {res.write('++ $e ++');}
}
With the route simply returning a Future we can now safely do anything we like there - including calling other asynchronous methods: in this instance to fetch a Redis key value.