From 26cffd03b0f54a37b22c6a4ecee50fef66aceab5 Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Sat, 11 Apr 2020 15:49:25 +0200
Subject: [PATCH] [src/core/jpg.js] Remove some redundant marker validation
 during the MCU parsing in the `decodeScan` function

Some of the code in `src/core/jpg.js` is fairly old, and has with time become unnecessary when the surrounding code has been updated to handle various types of JPEG corruption.
In particular the `if (!marker || marker <= 0xff00) { ... }` branch is now dead code, since:

 - The `!marker` case can no longer happen, since we would already have broken out of the loop thanks to the `!fileMarker` branch a handful of lines above.

 - The `marker <= 0xff00` case can also no longer happen, since the `findNextFileMarker` function validate markers much more thoroughly (by checking `marker >= 0xffc0 && marker <= 0xfffe`). Hence we'd again have broken out of the loop via the `!fileMarker` branch above when no valid marker was found.
---
 src/core/jpg.js | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/src/core/jpg.js b/src/core/jpg.js
index 3433dadce..53a2c1498 100644
--- a/src/core/jpg.js
+++ b/src/core/jpg.js
@@ -429,23 +429,17 @@ var JpegImage = (function JpegImageClosure() {
       bitsCount = 0;
       fileMarker = findNextFileMarker(data, offset);
       if (!fileMarker) {
-        // Reached the end of the image data without finding an EOI marker.
-        break;
-      } else if (fileMarker.invalid) {
+        break; // Reached the end of the image data without finding any marker.
+      }
+      if (fileMarker.invalid) {
         // Some bad images seem to pad Scan blocks with e.g. zero bytes, skip
         // past those to attempt to find a valid marker (fixes issue4090.pdf).
         warn(
-          "decodeScan - unexpected MCU data, current marker is: " +
-            fileMarker.invalid
+          `decodeScan - unexpected MCU data, current marker is: ${fileMarker.invalid}`
         );
         offset = fileMarker.offset;
       }
-      var marker = fileMarker && fileMarker.marker;
-      if (!marker || marker <= 0xff00) {
-        throw new JpegError("decodeScan - a valid marker was not found.");
-      }
-
-      if (marker >= 0xffd0 && marker <= 0xffd7) {
+      if (fileMarker.marker >= 0xffd0 && fileMarker.marker <= 0xffd7) {
         // RSTx
         offset += 2;
       } else {
@@ -458,8 +452,7 @@ var JpegImage = (function JpegImageClosure() {
     // attempt to find the next valid marker (fixes issue8182.pdf).
     if (fileMarker && fileMarker.invalid) {
       warn(
-        "decodeScan - unexpected Scan data, current marker is: " +
-          fileMarker.invalid
+        `decodeScan - unexpected Scan data, current marker is: ${fileMarker.invalid}`
       );
       offset = fileMarker.offset;
     }