Unsafe call to JSON.parse in CsvError class

[loriamichele]

Hi there 👋
First, thank you guys for the awesome work on this library!

I might have found a bug in the implementation of the CsvError class: if a malformed CSV file is being parsed, and by malformed I mean one of the rows have less values than expected, a proper error is thrown from the __onRow internal handler, but when the CsvError constructor is reached, an unsafe call to JSON.parse is made.

Here's the stack trace of that error with the latest version (4.6.3) of the library:

SyntaxError: Unexpected token u in JSON at position 0
        at JSON.parse (<anonymous>)

      at new CsvError (/*****/node_modules/csv-parse/lib/index.js:960:26)
      at Parser.__onRow (/*****/node_modules/csv-parse/lib/index.js:636:15)
      at Parser.__parse (/*****/node_modules/csv-parse/lib/index.js:527:40)
      at Parser._transform (/*****/node_modules/csv-parse/lib/index.js:341:22)

This error comes from an anonymous function and is not catchable by the stream error event handler because it's not emitted at all, which makes it impossible to handle it properly.

Just for reference, here's the stack trace for the expected error (got by replacing the JSON.parse(JSON.stringify(value)); with JSON.parse(JSON.stringify(value || ''));):

Error: Invalid Record Length: header length is 24, got 23 on line 3
      at Parser.__onRow (/*****/node_modules/csv-parse/lib/index.js:636:15)
      at Parser.__parse (/*****/node_modules/csv-parse/lib/index.js:527:40)
      at Parser._transform (/*****/node_modules/csv-parse/lib/index.js:341:22)
      at Parser.Transform._read (_stream_transform.js:190:10)
      at Parser.Transform._write (_stream_transform.js:178:12)
      at doWrite (_stream_writable.js:415:12)
      at writeOrBuffer (_stream_writable.js:399:5)
      at Parser.Writable.write (_stream_writable.js:299:11)
      at ReadStream.ondata (_stream_readable.js:709:20)
      at ReadStream.emit (events.js:198:13)

If you are fine with the proposed quick fix, I can also open a pull request.
Otherwise, just let me know what you think and/or how can this be fixed in a better way.

Cheers!

[wdavidw]

Could you write us a simple example reproducing the issue?

[loriamichele]

Right, sorry, I completely forgot to provide a way to reproduce this 😅

Basically, you need to have a CSV file that looks like this:

col_a,col_b,col_c
foo,bar
foo,bar,baz

If you use the parser without any options, you get the expected behavior.

However, the bug comes in only if you happen to use the feature from the columns configuration option that allows you to skip entire columns in the parsed objects by passing an array and setting a certain value to undefined, null or false.

So, here's the code to reproduce it (having input.csv in the same folder as the following NodeJS script, with both csv-parse and csv-stringify installed as NPM deps):

const {resolve} = require('path');
const {createReadStream} = require('fs');
const parse = require('csv-parse');
const stringify = require('csv-stringify');

const parser = parse({columns: ['a', 'b', null]});
const stringifier = stringify();

createReadStream(resolve(__dirname, './input.csv'))
  .pipe(parser)
  .pipe(stringifier)
  .pipe(process.stdout);

I also tried passing undefined or false as values of the columns array, but they all throw the same way.

Let me know if I can provide additional information or anything else. And as I mentioned before, I'll be glad to help solving it ✌️