Support writing the logs to stderr when i/o is redirected

[mcollina]

Fixes #85.

Please review, cc @krazylek

[mcollina]

@jsumners can you have a look here?

[jsumners]

@mcollina I don't think this is affected by the extreme mode buffer flushing. _writableState doesn't track whether or not the backing file descriptor is blockable. Indeed, I pulled this patch into my feature branch and ran the tests. Everything is checking out just fine.

[mcollina]

@jsumners the problem is that stderr do not have a _writableState, because it inherits directly from Stream.

[jsumners]

It looks to have one to me:

> process.stderr
WriteStream {
  // *snip*
  _writableState:
   WritableState {
     objectMode: false,
     highWaterMark: 16384,
     needDrain: false,
     ending: false,
     ended: false,
     finished: false,
     decodeStrings: false,
     defaultEncoding: 'utf8',
     length: 0,
     writing: false,
     corked: 0,
     sync: true,
     bufferProcessing: false,
     onwrite: [Function],
     writecb: null,
     writelen: 0,
     bufferedRequest: null,
     lastBufferedRequest: null,
     pendingcb: 0,
     prefinished: false,
     errorEmitted: false,
     bufferedRequestCount: 0,
     corkedRequestsFree: CorkedRequest { next: null, entry: null, finish: [Function] } },
  writable: true,
  allowHalfOpen: false,
  destroyed: false,
  _bytesDispatched: 0,
  _sockname: null,
  _writev: null,
  _pendingData: null,
  _pendingEncoding: '',
  server: null,
  _server: null,
  columns: 130,
  rows: 50,
  _type: 'tty',
  fd: 2,
  _isStdio: true,
  destroySoon: [Function],
  destroy: [Function] }

I'm not clear what you want me to investigate here.

[mcollina]

The original issue:

$ node a.js 2> out
SyncWriteStream {
  domain: null,
  _events: {},
  _eventsCount: 0,
  _maxListeners: undefined,
  fd: 2,
  writable: true,
  readable: false,
  autoClose: false,
  _type: 'fs',
  _isStdio: true,
  destroySoon: [Function],
  destroy: [Function] }

The content of a.js:

console.log(process.stderr)

As you see, it's our old friend SyncWriteStream.

[jsumners]

I see. I'll dig into it soon and see what I can figure out.

[mcollina]

@jsumners this is already passing, just check if it's ok for you.

[jsumners]

Yep. The tests pass and the following does what you'd expect:

var pino = require('./')
var log = pino(process.stderr)
log.info(process.stderr)

[github-actions]

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