HTTP mocks in simulation

[Chriscbr]

Inspired by https://twitter.com/mattpocockuk/status/1841074839446003927

When a Wing app runs in the simulator, all user-authored inflight code is executed in child Node processes (see sandbox.ts). If the compiler injected HTTP mocking code in each child process, then it's possible to simulate the behavior of uniformly mocking an HTTP endpoint across all inflight functions.

Perhaps these mocks could be configured through a preflight API of some kind (just a sketch):

bring cloud;
bring http;

// methods that can only be called in preflight
let mock = http.mockUrl("http://localhost:3000");
mock.response(status: 201, body: "success");

new cloud.Function(inflight () => {
  let res = http.get("http://localhost:3000");
  assert(req.status == 201);
});

Internally, code would be inserted at the beginning of each child process's bundled code that initializes the appropriate mock(s).

The only downside of this approach is that the mocking effect would only apply to code using Node.js's fetch function, like Wing's built-in http module. For example, if an inflight function ran util.shell("curl http://localhost:3000"), the response would not be mocked. But this may be a reasonable tradeoff.