event-protocol: Extract lib, executable npm package

[aslakhellesoy]

Summary

• Extract a library so the validator can be used from other JavaScript programs.
• Create a CLI so it can be used standalone after installing the npm package

Details

The lib is just a single function:

function validateEvent(event) {
  // throws an error if the event is invalid
}

Motivation and Context

Library: Some programs (such as cucumber-gui) may want to validate incoming events before they are processed.

CLI: Being able to use the validator as a CLI is easier when it can just be npm installed. This makes it easier for developers of event producers to test that they are producing valid events.

The CLI reads events from STDIN and writes them to STDOUT, which makes it possible to use it just like cat in between two programs (a producer and a consumer).

If the CLI fails to parse or validate an event, a detailed error message is written to STDERR in red and stops processing further events.

How Has This Been Tested?

As before - just run make. Change an event (or a schema) and run make again to see it fail.

Types of changes

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).

Checklist:

• I've added tests for my code.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[lock]

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