From 94171d9d720f4bfe2cf1737c0aa7ccfad04c7c81 Mon Sep 17 00:00:00 2001
From: huzjakd <huzjakd@gmail.com>
Date: Wed, 2 Oct 2019 14:13:49 +0200
Subject: [PATCH] Attempt to fallback to a default font, for non-available
 ones, in `PartialEvaluator.loadFont`

This handles the two different ways that fonts can be loaded, either by Name (which is the common case) or by Reference.
Furthermore, this also takes the `ignoreErrors` option into account when deciding whether to fallback or Error.
Finally, by creating a minimal but valid Font dictionary, there's no special-cases necessary in any of the font parsing code.

Co-authored-by: huzjakd <huzjakd@gmail.com>
Co-Authored-By: Jonas Jenwald <jonas.jenwald@gmail.com>
---
 src/core/evaluator.js | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/src/core/evaluator.js b/src/core/evaluator.js
index 9bc1e75ef..46c45fd58 100644
--- a/src/core/evaluator.js
+++ b/src/core/evaluator.js
@@ -711,21 +711,35 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
       var fontRef, xref = this.xref;
       if (font) { // Loading by ref.
         if (!isRef(font)) {
-          throw new Error('The "font" object should be a reference.');
+          throw new FormatError('The "font" object should be a reference.');
         }
         fontRef = font;
       } else { // Loading by name.
         var fontRes = resources.get('Font');
         if (fontRes) {
           fontRef = fontRes.getRaw(fontName);
-        } else {
-          warn('fontRes not available');
-          return errorFont();
         }
       }
       if (!fontRef) {
-        warn('fontRef not available');
-        return errorFont();
+        const partialMsg =
+          `Font "${fontName || (font && font.toString())}" is not available`;
+
+        if (!this.options.ignoreErrors && !this.parsingType3Font) {
+          warn(`${partialMsg}.`);
+          return errorFont();
+        }
+        // Font not found -- sending unsupported feature notification.
+        this.handler.send('UnsupportedFeature',
+                          { featureId: UNSUPPORTED_FEATURES.font, });
+        warn(`${partialMsg} -- attempting to fallback to a default font.`);
+
+        // Falling back to a default font to avoid completely broken rendering,
+        // but note that there're no guarantees that things will look "correct".
+        fontRef = new Dict();
+        fontRef.set('BaseFont', Name.get('PDFJS-FallbackFont'));
+        fontRef.set('Type', Name.get('FallbackType'));
+        fontRef.set('Subtype', Name.get('FallbackType'));
+        fontRef.set('Encoding', Name.get('WinAnsiEncoding'));
       }
 
       if (this.fontCache.has(fontRef)) {