webContents.print() doesn't work under Windows

[gozzoo]

• Electron Version 4.0.4
• Operating System Windows 10 32 bit
• Last known working Electron version 3.1.3

Expected Behavior

webContents.print() shold send print job to a printer

Actual behavior

Nothing happens. Callback doesn't gets called.

printToPDF works though.

To Reproduce

let deviceName = 'HP LaserJet 1020'
let options = {deviceName, silent: true}
win.webContents.print({}, (err) => {
    if (!err)
      console.error('printing failed')
})

[gozzoo]

Here is the code for my testing app:

const { app, shell, BrowserWindow, Menu } = require('electron')
var path = require('path');
var fs = require('fs');

let win 

function createWindow () {
  win = new BrowserWindow({ width: 800, height: 600 })
  win.loadFile('note.html')
  win.webContents.openDevTools({mode: 'undocked'})
}

app.on('ready', createWindow)

const template = [
{ label: 'Print', submenu: [
    { label: 'Print PDF A4', click() { printToPDF('A4') } },
    { label: 'Print PDF A5', click() { printToPDF('A5') } },
    { label: 'Print to printer', click() { printToPrinter() } }
  ]
}
]
var menu = Menu.buildFromTemplate(template)
Menu.setApplicationMenu(menu); 

function printToPrinter() {
  win.webContents.print({}, (err) => {
    if (!err)
      console.error('printing failed')
  })
}

function printToPDF(pageSize) {
  let options = {marginsType:2, pageSize, landscape: pageSize == 'A5'}
  win.webContents.printToPDF(options, printToPdfCallBack)
}

function printToPdfCallBack(error, data)  {
  if (error)
    return console.error(error)
  let userDataDir = app.getPath('userData')
  let pdf = path.join(userDataDir, 'note.pdf')
  fs.writeFile(pdf, data, (err) => {
    if (err)
      return console.error(err)
    shell.openExternal('file://' + pdf )
  })
}  

[Thomas101]

We've also seen this on macOS.

There are two issues here...

1. Silent is not initialized properly, meaning it's normally true
2. When the arguments are sent from JavaScript to C, they're not serialized properly, meaning the C side has an array, rather two optional arguments of object and callback.

This has the side effect of it calling print with silent=true and no printer set which makes it fail silently. I've opened a PR to address both of these

[sofianguy]

fixed: #17052