How to catch parsing errors

[ishandutta2007]

How do I catch in such scenarios:
str is rightly printed but when it enters parser.feed, it gets stuck and never returns; nor does it throw any errors.
And hence it never reaches console.log("event", event) even

import { createParser } from 'eventsource-parser'
  const parser = createParser((event) => {
    console.log("event", event)
    if (event.type === 'event') {
      onMessage(event.data)
    }
  })
  for await (const chunk of streamAsyncIterable(resp.body!)) {
    const str = new TextDecoder().decode(chunk)
    console.log("str", str)
    parser.feed(str)
  }

resp is the respose object and onMessage is just a function

[ishandutta2007]

On debugging I found it encounters the break on this line and since it breaks out of while loop it never processes parseEventStreamLine.
What I understand event was supposed to be returned by feed but since it reaches the end of the function the callback passed to createParser never gets called.

[rexxars]

Could you provide some example data?

Using string chunks is usually the easiest in order to debug:

import {createParser} from 'eventsource-parser'

const parser = createParser((event) => {
  console.log('event', event)
})

const chunks = [
  'data: hello\n\n',
  'data: world\n\n',
  'event: custom\n',
  'id: abc123\n',
  'data: event\n\n',
]

for (const str of chunks) {
  console.log('chunk', JSON.stringify(str))
  parser.feed(str)
}

Output:

chunk "data: hello\n\n"
event { type: 'event', id: undefined, event: undefined, data: 'hello' }
chunk "data: world\n\n"
event { type: 'event', id: undefined, event: undefined, data: 'world' }
chunk "event: custom\n"
chunk "id: abc123\n"
chunk "data: event\n\n"
event { type: 'event', id: 'abc123', event: 'custom', data: 'event' }

[ishandutta2007]

@rexxars As I said my example data isn't valid format starting with data: .
It's some json, like something like this {key1:data1,key2:data2} but not what this library parses out of the box.
I didn't expect the API server to return it suddenly, which is why I had to suffer code freeze on production.
Now I handle it like this but Ideally eventsource-parser library should have thrown some error while parsing instead of silently suppressing it.

    if (str.includes('some_keyword')) {
      console.log("non parsable str")
      onMessage(str)
    } else {
      parser.feed(str)
    }

[rexxars]

I don't see you mentioning anything about invalid data, but fair enough - thanks for clarifying.

[ishandutta2007]

I guess I meant it by explaining the debugging steps especially break-ing etc that it was not a format which eventsource-parser expects. Sorry for not being explicit which cased miscommunication.

Anyways lets keep it as a priority issue for next release. Throwing all invalid cases as exception in loud and clear manner is a must have for any library in today's world where projects depend on hundreds of libraries. I kept hunting for hours to figure out which library is making it go in infinite loop .

By the way this is a very nice lib, it eased my parsing headache, we should always thank people of npm community for their free of cost volunteering before any communication❤️

[Peek-A-Booo]

Could you provide some example data?

This is my code, console.log(event) will not run when I receive a value in this format which not starting with data:

const textDecoder = new TextDecoder()
let eventSourceParser: EventSourceParser

return new TransformStream({
  async start(controller) {
    eventSourceParser = createParser(
      (event: ParsedEvent | ReconnectInterval) => {
        console.log(event)
      },
    )
  },
  transform(chunk) {
    const value = textDecoder.decode(chunk)
    // the value is a string like:
    // {
    //   "error": {
    //     "message": "An assistant message with 'tool_calls' must be followed by tool messages responding to each 'tool_call_id'. The following tool_call_ids did not have response messages: call_FwpczVWzU3oIb0tSLiCHOt2z",
    //     "type": "invalid_request_error",
    //     "param": "messages",
    //     "code": null
    //   }
    // }
    eventSourceParser.feed(value)
  },
})

[rexxars]

Just released v3.0.0 with support for onError callback.