(pdfbox-jbig2) branch master updated: PDFBOX-6155: Fix JBIG2 symbol dictionary coding context reuse (§7.4.2.2 steps 3–4)

[msahyoun]

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asf-gitbox-commits pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/pdfbox-jbig2.git


The following commit(s) were added to refs/heads/master by this push:
     new 44fe469  PDFBOX-6155: Fix JBIG2 symbol dictionary coding context reuse 
(§7.4.2.2 steps 3–4)
44fe469 is described below

commit 44fe469f741f128ecf8847d87030bbd398654adb
Author: Maruan Sahyoun <sahy...@fileaffairs.de>
AuthorDate: Sun Apr 19 18:14:40 2026 +0200

    PDFBOX-6155: Fix JBIG2 symbol dictionary coding context reuse (§7.4.2.2 
steps 3–4)
---
 .../pdfbox/jbig2/segments/SymbolDictionary.java    | 67 +++++++++++++++++-----
 1 file changed, 53 insertions(+), 14 deletions(-)

diff --git 
a/src/main/java/org/apache/pdfbox/jbig2/segments/SymbolDictionary.java 
b/src/main/java/org/apache/pdfbox/jbig2/segments/SymbolDictionary.java
index 3803414..dd6cf1d 100644
--- a/src/main/java/org/apache/pdfbox/jbig2/segments/SymbolDictionary.java
+++ b/src/main/java/org/apache/pdfbox/jbig2/segments/SymbolDictionary.java
@@ -128,28 +128,41 @@ public class SymbolDictionary implements Dictionary
         readAmountOfNewSymbols();
         setInSyms();
 
-        if (isCodingContextUsed)
-        {
-            SegmentHeader[] rtSegments = segmentHeader.getRtSegments();
+        boolean isContextAdopted = false;
+        SymbolDictionary lastSymbolDictionary = null;
+
+        SegmentHeader[] rtSegments = segmentHeader.getRtSegments();
 
+        if (rtSegments != null)
+        {
             for (int i = rtSegments.length - 1; i >= 0; i--)
             {
 
                 if (rtSegments[i].getSegmentType() == 0)
                 {
-                    SymbolDictionary symbolDictionary = (SymbolDictionary) 
rtSegments[i]
-                            .getSegmentData();
+                    lastSymbolDictionary = (SymbolDictionary) rtSegments[i]
+                        .getSegmentData();
 
-                    if (symbolDictionary.isCodingContextRetained)
+                    if (isCodingContextUsed && 
lastSymbolDictionary.isCodingContextRetained)
                     {
                         /* 7.4.2.2 3) */
-                        setRetainedCodingContexts(symbolDictionary);
+                        adoptRetainedCodingContexts(lastSymbolDictionary);
+                        isContextAdopted = true;
                     }
                     break;
                 }
             }
         }
 
+        if (isCodingContextUsed && !isContextAdopted)
+        {
+            throw new InvalidHeaderValueException(
+                lastSymbolDictionary == null
+                    ? "Coding context reuse requested, but no referred symbol 
dictionary found"
+                    : "Coding context reuse requested, but last referred 
symbol dictionary does not retain coding context"
+            );
+        }
+
         this.checkInput();
     }
 
@@ -271,16 +284,42 @@ public class SymbolDictionary implements Dictionary
         }
     }
 
-    private void setRetainedCodingContexts(final SymbolDictionary sd)
+    /**
+     * Adopt retained arithmetic coding context from another symbol dictionary.
+     *
+     * Per spec §7.4.2.2:
+     * - Configuration MUST match (validated here)
+     * - Only bitmap coding statistics (CX) are reused
+     * - ArithmeticDecoder MUST NOT be reused (stream-bound)
+     * @throws InvalidHeaderValueException 
+     */
+    private void adoptRetainedCodingContexts(final SymbolDictionary sd) throws 
InvalidHeaderValueException
     {
-        this.sdTemplate = sd.sdTemplate;
-        this.sdrTemplate = sd.sdrTemplate;
-        this.sdATX = sd.sdATX;
-        this.sdATY = sd.sdATY;
-        this.sdrATX = sd.sdrATX;
-        this.sdrATY = sd.sdrATY;
+        validateContextValues(sd);
         this.cx = sd.cx;
     }
+    
+    /**
+     * The values of SDHUFF, SDREFAGG, SDTEMPLATE, SDRTEMPLATE, and all of the 
AT locations
+     * (both direct and refinement) for this symbol dictionary must match the 
corresponding
+     * values from the symbol dictionary whose context values are being used.
+     * @param sd
+     * @throws InvalidHeaderValueException 
+     */
+    private void validateContextValues(final SymbolDictionary sd) throws 
InvalidHeaderValueException
+    {
+        if ( this.isHuffmanEncoded != sd.isHuffmanEncoded
+            || this.useRefinementAggregation != sd.useRefinementAggregation
+            || this.sdTemplate != sd.sdTemplate
+            || this.sdrTemplate != sd.sdrTemplate
+            || !java.util.Arrays.equals(this.sdATX, sd.sdATX)
+            || !java.util.Arrays.equals(this.sdATY, sd.sdATY)
+            || !java.util.Arrays.equals(this.sdrATX, sd.sdrATX)
+            || !java.util.Arrays.equals(this.sdrATY, sd.sdrATY))
+        {
+            throw new InvalidHeaderValueException("SymbolDictionary reuse 
values don't match");
+        }
+    }
 
     private void checkInput() throws InvalidHeaderValueException
     {