Ipc buffers v4.x

[timkuijsten]

Checklist

• documentation is changed or added
• the commit message follows commit guidelines

Affected core subsystem(s)

doc/child_process

Description of change

If a socket is sent to a child, any data that is buffered in the
socket will not be sent to the child. The child will only receive
data from the socket that is sent after the child has the socket.

PoC:

From #6951:

$ node --version
v4.4.7

$ cat m.js
const fork = require('child_process').fork
const net = require('net')

const cp = fork('./child.js')

net.createServer(c => {
  setTimeout(() => {
    cp.send({}, c)
  }, 500) // send the connection after a delay
}).listen(1234, () => {
  net.createConnection(1234, function() {
    var i = 0
    setInterval(() => {
      this.write(`${i++} `)
    }, 100) // start sending data before the connection is sent to the child
  })
})

$ cat child.js 
process.on('message', (m, c) => {
  console.log('child: got connection')
  c.pipe(process.stdout)
})

$ node m.js
child: got connection
4 5 6 7 8 ^C

[addaleax]

You might want to use v4.x-staging as your base branch, not master. ;)

Closing this as this is basically not recoverable on Github without opening another PR.

[cjihrig]

I think you probably meant to target one of the v4 branches

[timkuijsten]

Sorry, this was against master but should have been against v4.x, see #7684.