process.stdout cannot be JSON.stringify()ed because of circular dependency

[nazarhussain]

• Version: v12.14.1
• Platform: Darwin Kernel Version 19.2.0
• Subsystem: Streams

There are some change introduced in 12.14.1 in process.stdout which created a circular dependency. This behaviour is not detected in 12.14.0, and can't find any reference for changes
in published change log.

Here is the simple code to reproduce the issue in 12.14.1

➜  nvm use 12.14.1
➜  node -i
Welcome to Node.js v12.14.1.
Type ".help" for more information.
> JSON.stringify(process.stdout)
Thrown:
TypeError: Converting circular structure to JSON
    --> starting at object with constructor 'WriteStream'
    |     property '_writableState' -> object with constructor 'WritableState'
    |     property 'afterWriteTickInfo' -> object with constructor 'Object'
    --- property 'stream' closes the circle
    at JSON.stringify (<anonymous>)
>

It works well with 12.14.0

➜  nvm use 12.14.0
➜  node -i
Welcome to Node.js v12.14.0.
Type ".help" for more information.
> JSON.stringify(process.stdout)
'{"connecting":false,"_hadError":false,"_parent":null,"_host":null,"_readableState":{"objectMode":false,"highWaterMark":16384,"buffer":{"head":null,"tail":null,"length":0},"length":0,"pipes":null,"pipesCount":0,"flowing":null,"ended":false,"endEmitted":false,"reading":false,"sync":true,"needReadable":false,"emittedReadable":false,"readableListening":false,"resumeScheduled":false,"paused":true,"emitClose":false,"autoDestroy":false,"destroyed":false,"defaultEncoding":"utf8","awaitDrain":0,"readingMore":false,"decoder":null,"encoding":null},"readable":false,"_events":{},"_eventsCount":3,"_writableState":{"objectMode":false,"highWaterMark":16384,"finalCalled":false,"needDrain":false,"ending":false,"ended":false,"finished":false,"destroyed":false,"decodeStrings":false,"defaultEncoding":"utf8","length":0,"writing":false,"corked":0,"sync":false,"bufferProcessing":false,"writecb":null,"writelen":0,"bufferedRequest":null,"lastBufferedRequest":null,"pendingcb":1,"prefinished":false,"errorEmitted":false,"emitClose":false,"autoDestroy":false,"bufferedRequestCount":0,"corkedRequestsFree":{"next":null,"entry":null}},"writable":true,"allowHalfOpen":false,"_sockname":null,"_pendingData":null,"_pendingEncoding":"","server":null,"_server":null,"columns":210,"rows":80,"_type":"tty","fd":1,"_isStdio":true}'
>

I don't know if it's a bug or an explicit change made in interface. If its known change, then must be reported to the change log.

[addaleax]

@nazarhussain Since nobody has replied here … there is an open PR that would fix this for the time being, but stringifying Node.js streams using JSON.stringify is generally not supported, and it would be best if this is avoided either way.

[nazarhussain]

I agree stringifying a stream should be avoided. But we should consider it a breaking change and introduce properly with change long. Many packages may be using this change will be breaking for them. As what happens in my case, I found it because it was used in our product.

[avivkeller]

This appears to be no-longer reproducible:

console.log(JSON.stringify(process.stdout))

{"connecting":false,"_hadError":false,"_parent":null,"_host":null,"_closeAfterHandlingError":false,"_events":{},"_readableState":{"highWaterMark":0,"buffer":[],"bufferIndex":0,"length":0,"pipes":[],"awaitDrainWriters":null},"_writableState":{"highWaterMark":65536,"length":0,"corked":0,"writelen":0,"bufferedIndex":0,"pendingcb":0},"allowHalfOpen":false,"_eventsCount":1,"_sockname":null,"_pendingData":null,"_pendingEncoding":"","server":null,"_server":null,"columns":200,"rows":16,"_type":"tty","fd":1,"_isStdio":true}