Create beforeConnect and beforeSubscribe Cloud Triggers

[dblythy]

My first PR so feel free to make suggestions of course.

Creates two new cloud code triggers which affect LiveQuery: beforeConnect and beforeSubscribe.

beforeConnect allows validation prior to a LiveQuery opening connection. This is not class specific.

Parse.Cloud.beforeConnect(async request => {
      if (!request.user) {
          throw "Please login before you attempt to connect."
      }
  });

beforeSubscribe handles the .subscribe methods from LiveQuery. Can be used to validate users, or to mutate the request.query, enforcing fields, equalTo, or whatever required.

  Parse.Cloud.beforeSubscribe(Parse.User, async request => {
      if (!request.user) {
          throw "Please login before you attempt to connect."
      }
      let query = request.query; // the Parse.Query
      query.select("name","year")
      return query;
  });

I also created userForSessionToken on triggers.js, so that the sessionToken from LQ is only looked up if the trigger exists.

In relation to #6642.

[davimacedo]

Thanks for the PR. Can you please check the tests out? They are not passing.

[dblythy]

Will do!

[codecov]

Codecov Report

Merging #6649 into master will not change coverage.
The diff coverage is n/a.

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  Files         169      169           
  Lines       12059    12059           
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  Hits        11287    11287           
  Misses        772      772           

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[dblythy]

Sorry @davimacedo - not on my computer so had to edit through GitHub desktop which made it a bit difficult (and the commits a bit of a mess). I had to edit the LiveQuery spec so that it would await the result of the new beforeConnect / beforeSubscribe methods - is that okay?

[dplewis]

A few nits

[dplewis]

Adding await here is fine. Can you add additional tests for this feature? You might have to await in other places.

[dblythy]

@dplewis thank you!

[dplewis]

@dblythy Couldn't these trigger run in the background? (replace async with old fashion then / catch)

Edit:
beforeSubscribe doesn't need to return a query. You can mutate the query in the trigger and not enforce a return value.

beforeConnect in your example in the OP you assume its and async function returning

[dblythy]

@dplewis I can work on replacing the async with then / catch. The only reason I used async is because my JavaScript is not great, especially with promises 😝. I will reopen another PR at a later date with tests as well. Thank you for your time and advice!

[dplewis]

This is a great feature and a lot of progress was made. A lot of other data could be passed in too besides user and query. I look forward to your PR. If you don’t have time. Let me know and I can add this feature.