fix: prevent print crash on bad deviceName

docs/api/web-contents.md

@@ -1259,7 +1259,7 @@ Returns [`PrinterInfo[]`](structures/printer-info.md)
   * `silent` Boolean (optional) - Don't ask user for print settings. Default is `false`.
   * `printBackground` Boolean (optional) - Prints the background color and image of
     the web page. Default is `false`.
-  * `deviceName` String (optional) - Set the printer device name to use. Default is `''`.
+  * `deviceName` String (optional) - Set the printer device name to use. Must be the system-defined name and not the 'friendly' name, e.g 'Brother_QL_820NWB' and not 'Brother QL-820NWB'.
   * `color` Boolean (optional) - Set whether the printed web page will be in color or grayscale. Default is `true`.
   * `margins` Object (optional)
     * `marginType` String (optional) - Can be `default`, `none`, `printableArea`, or `custom`. If `custom` is chosen, you will also need to specify `top`, `bottom`, `left`, and `right`.

shell/browser/api/atom_api_web_contents.cc

@@ -121,6 +121,10 @@
 #if BUILDFLAG(ENABLE_PRINTING)
 #include "chrome/browser/printing/print_view_manager_basic.h"
 #include "components/printing/common/print_messages.h"
+
+#if defined(OS_WIN)
+#include "printing/backend/win_helper.h"
+#endif
 #endif
 
 #if BUILDFLAG(ENABLE_ELECTRON_EXTENSIONS)
@@ -350,6 +354,26 @@ base::Optional<base::TimeDelta> GetCursorBlinkInterval() {
   return base::nullopt;
 }
 
+#if BUILDFLAG(ENABLE_PRINTING)
+// This will return false if no printer with the provided device_name can be
+// found on the network. We need to check this because Chromium does not do
+// sanity checking of device_name validity and so will crash on invalid names.
+bool IsDeviceNameValid(const base::string16& device_name) {
+#if defined(OS_MACOSX)
+  base::ScopedCFTypeRef<CFStringRef> new_printer_id(
+      base::SysUTF16ToCFStringRef(device_name));
+  PMPrinter new_printer = PMPrinterCreateFromPrinterID(new_printer_id.get());
+  bool printer_exists = new_printer != nullptr;
+  PMRelease(new_printer);
+  return printer_exists;
+#elif defined(OS_WIN)
+  printing::ScopedPrinterHandle printer;
+  return printer.OpenPrinterWithName(device_name.c_str());
+#endif
+  return true;
+}
+#endif
+
 }  // namespace
 
 WebContents::WebContents(v8::Isolate* isolate,
@@ -1772,6 +1796,10 @@ void WebContents::Print(mate::Arguments* args) {
   // Printer device name as opened by the OS.
   base::string16 device_name;
   options.Get("deviceName", &device_name);
+  if (!device_name.empty() && !IsDeviceNameValid(device_name)) {
+    args->ThrowError("webContents.print(): Invalid deviceName provided.");
+    return;
+  }
   settings.SetStringKey(printing::kSettingDeviceName, device_name);
 
   int scale_factor = 100;

spec-main/api-web-contents-spec.ts

@@ -104,22 +104,35 @@ describe('webContents module', () => {
   })
 
   ifdescribe(features.isPrintingEnabled())('webContents.print()', () => {
+    let w: BrowserWindow
+
+    beforeEach(() => {
+      w = new BrowserWindow({ show: false })
+    })
+
     afterEach(closeAllWindows)
+
     it('throws when invalid settings are passed', () => {
-      const w = new BrowserWindow({ show: false })
       expect(() => {
         // @ts-ignore this line is intentionally incorrect
         w.webContents.print(true)
       }).to.throw('webContents.print(): Invalid print settings specified.')
+    })
 
+    it('throws when an invalid callback is passed', () => {
       expect(() => {
         // @ts-ignore this line is intentionally incorrect
         w.webContents.print({}, true)
       }).to.throw('webContents.print(): Invalid optional callback provided.')
     })
 
+    ifit(process.platform !== 'linux')('throws when an invalid deviceName is passed', () => {
+      expect(() => {
+        w.webContents.print({ deviceName: 'i-am-a-nonexistent-printer' }, () => {})
+      }).to.throw('webContents.print(): Invalid deviceName provided.')
+    })
+
     it('does not crash', () => {
-      const w = new BrowserWindow({ show: false })
       expect(() => {
         w.webContents.print({ silent: true })
       }).to.not.throw()