Invalid LTI consumer response may result in empty error

[SidneyNemzer]

Code

const lti = require('ims-lti')

const outcome = new lti.OutcomeService({
  consumer_key: 'key',
  consumer_secret: 'secret',
  // Note: localhost:3000 is a server that simply responseds with a status 200, empty body, to any request
  service_url: 'http://localhost:3000',
  source_did: 'sourcedid'
})

outcome.send_replace_result(1.0, (error, result) => {
  if (error) {
    console.error('Encountered an error while sending result:')
    console.error(error)
  }
})

Actual outcome

$ node test.js
Encountered an error while sending result:
{ [Error] message: undefined }

Expected outcome

Maybe a more helpful error message?

Cause

After debugging the program, it looks like the XML parser does not throw an error. But the code from the response is undefined (since the XML is empty), so the library assumes there was a non-success code and tries to throw an error using the message in the XML. But, again, there is nothing in the XML. So msg === undefined

ims-lti/src/extensions/outcomes.coffee

Line 213 in 4df2936

callback new errors.OutcomeResponseError(msg), false

[lastmjs]

Funny, I think I just started running into this same problem. So are the grades sent back correctly? What does the error actually indicate?

[SidneyNemzer]

@lastmjs In my specific case, the LTI provider (which uses this library) sends the grades to the LTI consumer (which is another application that we control). The LTI consumer can extract the grade from the XML, but it doesn't bother with a valid LTI response (since both applications are only used internally). A valid response would be something like "got it, score recorded" (The actual response is detailed in the LTI specification of course).

But it's conceivable that you could get { [Error] message: undefined } by doing something else.

[lastmjs]

Looks like my error was coming from the server returning a 500 response. A more helpful error message would have been very valuable