nowritecb error thrown

[scottcorgan]

Any reason why I would be getting the following error:

uncaughtException no writecb in Transform class
Error: no writecb in Transform class
    at afterTransform (/Users/scott/www/particle/node_modules/through2/node_modules/readable-stream/lib/_stream_transform.js:92:33)
    at TransformState.afterTransform (/Users/scott/www/particle/node_modules/through2/node_modules/readable-stream/lib/_stream_transform.js:76:1

Code worked using map-stream module. Converterted to try this module and getting this error now.

Thanks.

[rvagg]

it's possible this is due to not having a more consistent streams2 stack; one of the reasons I wrote this and also csv2 is because mixing and matching streams2 with other style streams can be a bit hit-and-miss.

Can you show me more of your code? What's piping in to your through2 stream? Also, your transformFrunction can't be bound to anything else, it must be passed in as a plain function that can participate as a member of the stream.Transform class.

[scottcorgan]

Ya, I made sure the functions weren't bound to anything. It might by a mixture somewhere of the streams2 and streams somewhere in the pipe.

Would that cause it?

JSONStream does start it all off at the beginning of the pipes.

[rvagg]

JSONStream is based on through which I've had some streams2 compat issues with, but it seems to work ok with through2 with basic use:

var hyperquest = require('hyperquest')
  , JSONStream = require('JSONStream')
  , through2 = require('through2')

  hyperquest('http://isaacs.couchone.com/registry/_all_docs')
    .pipe(JSONStream.parse('rows.*'))
    .pipe(through2({ objectMode: true }, function (chunk, enc, callback) {
       this.push({ name: chunk.key })
       callback()
    }))
    .on('data', console.log)

->

{ name: '' }
{ name: '0' }
{ name: '007' }
{ name: '06_byvoidmodule' }
{ name: '0815' }
{ name: '0x21' }
{ name: '0x23' }
{ name: '1' }
{ name: '10tcl' }
{ name: '11zgit-fs' }
...

What else do you have in your stream stack? And is this error happening before you get any output, in the middle somewhere or at the end of a stream?

[scottcorgan]

would an error be called if using the callback with

callback(null, cunk);

[rvagg]

I don't think it would cause an error. You can see the implementation of that callback here: https://github.com/joyent/node/blob/9e1eb361e8deb3f296a3c9d01de8fcc10361443f/lib/_stream_transform.js#L73-L106 - note there's a this.push(chunk) if you've passed a chunk. But that function is also where your original error is coming from, I'm not sure that's related thouh.

[rvagg]

    .pipe(through2({ objectMode: true }, function (chunk, enc, callback) {
       callback(null, { name: chunk.key })
    }))

does the same thing as the example above. There's no chance your callback is being re-bound to something else? it's just a plain callback(null, chunk)?

[brycebaril]

It looks like the way you get that error is by calling the callback twice, e.g.:

var spigot = require("stream-spigot")
var through = require("through2")

var tx = through(function (chunk, encoding, callback) {
  callback(null)
  callback(null, chunk)
})

spigot(["a", "b", "c", "d"])
  .pipe(tx)
  .pipe(process.stdout)

events.js:72
        throw er; // Unhandled 'error' event
              ^
Error: no writecb in Transform class
    at afterTransform (_stream_transform.js:90:33)
    at TransformState.afterTransform (_stream_transform.js:74:12)
    at Through2._transform (/tmp/t.js:6:9)
    at Through2.Transform._read (_stream_transform.js:179:10)
    at Through2.Transform._write (_stream_transform.js:167:12)
    at doWrite (_stream_writable.js:219:10)
    at writeOrBuffer (_stream_writable.js:209:5)
    at Through2.Writable.write (_stream_writable.js:180:11)
    at write (_stream_readable.js:573:24)
    at flow (_stream_readable.js:582:7)

[scottcorgan]

@brycebaril I think it might not be about calling the callback twice as much as it is about calling the callback with a null value. But yo calling it twice produces the error as well.

Thanks for the heads up. Sent me in the right direction.

[scottcorgan]

After updating to 0.0.5 and using the default streams class, I'm still getting the error. I'm going to assume it's my code and close the issue. I'll re open if I find otherwise.

Thanks for all the insight.

[rvagg]

Very interesting, but also very weird! Glad you fixed it though.

[towry]

I had this error today and the reason is I called the callback more than once.

[dcousens]

Thanks @towry 👍