From f4f4ec30f46d7bc7fc586056aaf7b532d1bb3d17 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emilio=20Cobos=20=C3=81lvarez?= <emilio@crisal.io>
Date: Wed, 2 Sep 2020 11:38:10 +0200
Subject: [PATCH] print: Make the firefox printing code able to fail and be
 re-invoked.

This fixes a set of issues described in Mozilla bug 1662426[1].

In particular, once the print callback fails once (because the printing
operation has been canceled in Gecko / replaced by a newer one, for example) it
can't be re-invoked.

This patch fixes it by properly cancelling the render task if it throws, or if
the print callback is called again while ongoing.

[1]: https://bugzilla.mozilla.org/show_bug.cgi?id=1662426
---
 web/firefox_print_service.js | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/web/firefox_print_service.js b/web/firefox_print_service.js
index 98b8d0d88..9f748985f 100644
--- a/web/firefox_print_service.js
+++ b/web/firefox_print_service.js
@@ -41,6 +41,14 @@ function composePage(
   canvasWrapper.appendChild(canvas);
   printContainer.appendChild(canvasWrapper);
 
+  // A callback for a given page may be executed multiple times for different
+  // print operations (think of changing the print settings in the browser).
+  //
+  // Since we don't support queueing multiple render tasks for the same page
+  // (and it'd be racy anyways if painting the page is not done in one go) we
+  // keep track of the last scheduled task in order to properly cancel it before
+  // starting the next one.
+  let currentRenderTask = null;
   canvas.mozPrintCallback = function (obj) {
     // Printing/rendering the page.
     const ctx = obj.context;
@@ -50,9 +58,14 @@ function composePage(
     ctx.fillRect(0, 0, canvas.width, canvas.height);
     ctx.restore();
 
+    let thisRenderTask = null;
     pdfDocument
       .getPage(pageNumber)
       .then(function (pdfPage) {
+        if (currentRenderTask) {
+          currentRenderTask.cancel();
+          currentRenderTask = null;
+        }
         const renderContext = {
           canvasContext: ctx,
           transform: [PRINT_UNITS, 0, 0, PRINT_UNITS, 0, 0],
@@ -61,15 +74,25 @@ function composePage(
           annotationStorage: pdfDocument.annotationStorage,
           optionalContentConfigPromise,
         };
-        return pdfPage.render(renderContext).promise;
+        currentRenderTask = thisRenderTask = pdfPage.render(renderContext);
+        return thisRenderTask.promise;
       })
       .then(
         function () {
           // Tell the printEngine that rendering this canvas/page has finished.
+          if (currentRenderTask === thisRenderTask) {
+            currentRenderTask = null;
+          }
           obj.done();
         },
         function (error) {
           console.error(error);
+
+          if (currentRenderTask === thisRenderTask) {
+            currentRenderTask.cancel();
+            currentRenderTask = null;
+          }
+
           // Tell the printEngine that rendering this canvas/page has failed.
           // This will make the print process stop.
           if ("abort" in obj) {