Proposal: Abortable and timeouts

[aliendrew]

• tests and linter show no problems (npm t)
• tests are added/updated for bug fixes and new features
• code is properly formatted (npm run fmt)
• description of changes is added in CHANGELOG.md
• update .d.ts typings

This is a proposal to use the Abortable class proposed in metarhia/metautil#198 to manage any kind of abortable tasks.

Currently:

1. There's only one way to abort user defined APIs by optionally setting timeout for method;
2. There's no way to check if user API is aborted by timeout in the middle of user code execution;
3. There's a request timeout in application/config/server.js that can be used for transport-level timeouts:

...
  timeouts: {
    ...
    request: 5000,
    ...
  },
...

Abortable can:

1. Perform a manual task abortion by explicitly calling abort() method;
2. Perform task abortion on timeout;
3. The resetTimeout() method can reset the scheduled timeout to a different value when the task is already running.
   We can also check if the task is aborted by calling aborted getter and throw by throwIfAborted()

This implementation utilizes timeouts.request from application/config/server.js to create transport-level timeouts (currently only HttpTransport) and also timeout that is optionally defined on user API endpoint. Abortable is created on user request and injected into Client as private member. The aborted and throwIfAborted() are public in Client so they can be used on endpoint to check if the task is aborted and stop execution. Additionally, onAborted handler can be implemented by the user.

Here's an example:

({
  access: 'public',

  parameters: {
    a: 'number',
    b: 'number',
  },

  timeout: 150,

  method: async ({ a, b }) => {
    const result = a + b;
    await node.timers.promises.setTimeout(200);
    console.log(context.client.aborted); // true
    context.client.throwIfAborted();
    /* this line will never be reached,
    the execution will be aborted with request timeout (408)
    */
    console.log(context.client.aborted);
    await node.timers.promises.setTimeout(6000);
    console.log(context.client.aborted);
    context.client.throwIfAborted();
    return result;
  },

  onAborted: (reason) => {
    console.log(`Aborted! ${reason}`);
  },

  returns: 'number',
});

This will be aborted as well by Server.rpc() (timeouts.request = 5000):

({
  access: 'public',

  parameters: {
    a: 'number',
    b: 'number',
  },

  method: async ({ a, b }) => {
    const result = a + b;
    await node.timers.promises.setTimeout(6000);
    console.log(context.client.aborted);
    return result;
  },

  onAborted: (reason) => {
    console.log(`Aborted! ${reason}`);
  },

  returns: 'number',
});

[tshemsedinov]

Closed in favour of metarhia/impress#1958