feat: add webContents.getPrintersAsync()

This deprecates the synchronous and blocking webContents.getPrinters() function and introduces webContents.getPrintersAsync(), which is asynchronous and non-blocking. Signed-off-by: Darshan Sen <darshan.sen@postman.com>
electron · Sep 20, 2021 · 77dd7ce · 77dd7ce
1 parent aa9da78
commit 77dd7ce
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Showing 5 changed files with 64 additions and 4 deletions.
diff --git a/docs/api/web-contents.md b/docs/api/web-contents.md
@@ -1366,12 +1366,20 @@ Decrease the capturer count by one. The page will be set to hidden or occluded s
 browser window is hidden or occluded and the capturer count reaches zero. If you want to
 decrease the hidden capturer count instead you should set `stayHidden` to true.
 
-#### `contents.getPrinters()`
+#### `contents.getPrinters()` _Deprecated_
 
 Get the system printer list.
 
 Returns [`PrinterInfo[]`](structures/printer-info.md)
 
+**Deprecated:** Should use the new [`contents.getPrintersAsync`](web-contents.md#contentsgetprintersasync) API.
+
+#### `contents.getPrintersAsync()`
+
+Get the system printer list.
+
+Returns `Promise<PrinterInfo[]>` - Resolves with a [`PrinterInfo[]`](structures/printer-info.md)
+
 #### `contents.print([options], [callback])`
 
 * `options` Object (optional)

diff --git a/lib/browser/api/web-contents.ts b/lib/browser/api/web-contents.ts
@@ -390,6 +390,17 @@ WebContents.prototype.getPrinters = function () {
   }
 };
 
+WebContents.prototype.getPrintersAsync = async function () {
+  // TODO(nornagon): this API has nothing to do with WebContents and should be
+  // moved.
+  if (printing.getPrinterListAsync) {
+    return printing.getPrinterListAsync();
+  } else {
+    console.error('Error: Printing feature is disabled.');
+    return [];
+  }
+};
+
 WebContents.prototype.loadFile = function (filePath, options = {}) {
   if (typeof filePath !== 'string') {
     throw new Error('Must pass filePath as a string');

diff --git a/shell/browser/api/electron_api_printing.cc b/shell/browser/api/electron_api_printing.cc
@@ -11,6 +11,8 @@
 
 #if BUILDFLAG(ENABLE_PRINTING)
 #include "printing/backend/print_backend.h"
+#include "shell/common/gin_helper/promise.h"
+#include "shell/common/process_util.h"
 #endif
 
 namespace gin {
@@ -39,18 +41,43 @@ namespace electron {
 namespace api {
 
 #if BUILDFLAG(ENABLE_PRINTING)
-printing::PrinterList GetPrinterList() {
+printing::PrinterList GetPrinterList(v8::Isolate* isolate) {
+  EmitWarning(node::Environment::GetCurrent(isolate),
+              "Deprecation Warning: getPrinterList() is deprecated. "
+              "Use the asynchronous and non-blocking version, "
+              "getPrinterListAsync(), instead.",
+              "electron");
   printing::PrinterList printers;
   auto print_backend = printing::PrintBackend::CreateInstance(
       g_browser_process->GetApplicationLocale());
   {
-    // TODO(deepak1556): Deprecate this api in favor of an
-    // async version and post a non blocing task call.
     base::ThreadRestrictions::ScopedAllowIO allow_io;
     print_backend->EnumeratePrinters(&printers);
   }
   return printers;
 }
+
+v8::Local<v8::Promise> GetPrinterListAsync(v8::Isolate* isolate) {
+  gin_helper::Promise<printing::PrinterList> promise(isolate);
+  const v8::Local<v8::Promise> handle = promise.GetHandle();
+
+  base::PostTask(FROM_HERE, {content::BrowserThread::UI},
+                 base::BindOnce(
+                     [](gin_helper::Promise<printing::PrinterList>&& promise) {
+                       printing::PrinterList printers;
+                       auto print_backend =
+                           printing::PrintBackend::CreateInstance(
+                               g_browser_process->GetApplicationLocale());
+                       {
+                         base::ThreadRestrictions::ScopedAllowIO allow_io;
+                         print_backend->EnumeratePrinters(&printers);
+                       }
+                       promise.Resolve(printers);
+                     },
+                     std::move(promise)));
+
+  return handle;
+}
 #endif
 
 }  // namespace api
@@ -61,6 +88,7 @@ namespace {
 
 #if BUILDFLAG(ENABLE_PRINTING)
 using electron::api::GetPrinterList;
+using electron::api::GetPrinterListAsync;
 #endif
 
 void Initialize(v8::Local<v8::Object> exports,
@@ -71,6 +99,8 @@ void Initialize(v8::Local<v8::Object> exports,
   gin_helper::Dictionary dict(isolate, exports);
 #if BUILDFLAG(ENABLE_PRINTING)
   dict.SetMethod("getPrinterList", base::BindRepeating(&GetPrinterList));
+  dict.SetMethod("getPrinterListAsync",
+                 base::BindRepeating(&GetPrinterListAsync));
 #endif
 }
 

diff --git a/spec-main/api-web-contents-spec.ts b/spec-main/api-web-contents-spec.ts
@@ -1728,6 +1728,16 @@ describe('webContents module', () => {
     });
   });
 
+  ifdescribe(features.isPrintingEnabled())('getPrintersAsync()', async () => {
+    afterEach(closeAllWindows);
+    it('can get printer list', async () => {
+      const w = new BrowserWindow({ show: false, webPreferences: { sandbox: true } });
+      await w.loadURL('about:blank');
+      const printers = await w.webContents.getPrintersAsync();
+      expect(printers).to.be.an('array');
+    });
+  });
+
   ifdescribe(features.isPrintingEnabled())('printToPDF()', () => {
     let w: BrowserWindow;
 

diff --git a/typings/internal-electron.d.ts b/typings/internal-electron.d.ts
@@ -70,6 +70,7 @@ declare namespace Electron {
     _printToPDF(options: any): Promise<Buffer>;
     _print(options: any, callback?: (success: boolean, failureReason: string) => void): void;
     _getPrinters(): Electron.PrinterInfo[];
+    _getPrintersAsync(): Promise<Electron.PrinterInfo[]>;
     _init(): void;
     canGoToIndex(index: number): boolean;
     getActiveIndex(): number;