Handle JSON parse errors to prevent watch from crashing if a non-JSON request body is received.

[brianpursley]

The problem

When using lambda-local in --watch mode, if you post and empty body or body containing invalid JSON, the lambda-local process crashes.

Example output when posting empty body:

info: Lambda handler listening on http://localhost:8008
undefined:1


SyntaxError: Unexpected end of JSON input
    at JSON.parse (<anonymous>)
    at IncomingMessage.<anonymous> (C:\Users\lc1211766\Projects\eVault\src\api\node_modules\lambda-local\build\lambdalocal.js:159:28)
    at IncomingMessage.emit (events.js:412:35)
    at endReadableNT (internal/streams/readable.js:1317:12)
    at processTicksAndRejections (internal/process/task_queues.js:82:21)

(lambda-local process crashes after this error occurs)

Example output when posting body that is not valid JSON:

info: Lambda handler listening on http://localhost:8008
undefined:1
x
^

SyntaxError: Unexpected token x in JSON at position 0
    at JSON.parse (<anonymous>)
    at IncomingMessage.<anonymous> (C:\Users\lc1211766\Projects\eVault\src\api\node_modules\lambda-local\build\lambdalocal.js:159:28)
    at IncomingMessage.emit (events.js:412:35)
    at endReadableNT (internal/streams/readable.js:1317:12)
    at processTicksAndRejections (internal/process/task_queues.js:82:21)

(lambda-local process crashes after this error occurs)

How this PR fixes the problem

This PR adds a try/catch around the JSON.parse(body) call to handle exceptions that can occur while parsing the body and returning them through the callback.

(It also adds a return after the callback for missing payload.event so that it doesn't trigger multiple callbacks in that case)

[jamesliupenn]

@brianpursley do you recall why was this closed?

[brianpursley]

@brianpursley do you recall why was this closed?

Not sure. We stopped using lambda-local (we switched to serverless). I probably just closed it because it sat open for months without any comment and I figured it wasn't something that would ever get merged.

I think it is probably a good change if they want to accept it though.

[gpotter2]

Yeah the change is fine, sorry about that. I think I missed this PR :/