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https://issues.apache.org/jira/browse/FOP-3329?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18099487#comment-18099487
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Rafael Witak commented on FOP-3329:
-----------------------------------
Attaching a git-format-patch [^multibytefont-sentinel-glyph.patch] (applies
cleanly on current main via `git am`) with the
fix plus two JUnit test cases. Happy to open a GitHub PR instead if preferred.
> ArrayIndexOutOfBoundsException/NPE in MultiByteFont for out-of-range/sentinel
> glyph index
> -----------------------------------------------------------------------------------------
>
> Key: FOP-3329
> URL: https://issues.apache.org/jira/browse/FOP-3329
> Project: FOP
> Issue Type: Bug
> Components: font/opentype
> Affects Versions: 2.11
> Reporter: Rafael Witak
> Priority: Major
> Attachments: multibytefont-sentinel-glyph.patch, reproduce.fo,
> reproduce.xconf
>
>
> h3. Overview
> When complex-script (GSUB) processing maps a code point to an out-of-range
> glyph
> index, {{MultiByteFont}} uses that index to access the
> {{{}width[]{}}}/{{{}boundingBoxes[]{}}}
> arrays directly and throws an {{ArrayIndexOutOfBoundsException}} in
> {{{}getWidth{}}}/{{{}getBoundingBox{}}}. The offending index can be:
> * the sentinel index {{0xFFFF}} (65535) emitted by GSUB for unsupported
> sequences,
> * a code point passed through as a glyph index that exceeds the metric array
> length
> (some fonts pass the variation selector U+FE0F through as {{0xFE0F}} = 65039),
> * or {{{}-1{}}}, returned by {{CIDSubset}} for an index it has not
> registered.
> When such an index additionally reaches the embedded subset
> ({{{}CIDSubset{}}}), it later
> causes a {{NullPointerException}} in
> {{OTFSubSetFile#createCharStringDataCID}} during
> CFF subsetting.
> This is NOT limited to emoji: it also affects ordinary text containing
> typographic
> characters (e.g. U+22EF MIDLINE HORIZONTAL ELLIPSIS) that route to a large
> CID-keyed
> fallback font.
> h3. Steps to Reproduce
> # Configure a font stack whose fallback font is a large CID-keyed
> OpenType/CFF font
> with about 65535 glyphs and active GSUB (e.g. Noto Sans CJK).
> # Render the attached minimal XSL-FO ([^reproduce.fo]) to PDF with the
> attached
> configuration ([^reproduce.xconf]). The document contains a code point whose
> GSUB
> processing yields an out-of-range glyph index. Verified triggers include:
> ** U+27A1 followed by U+FE0F ("right arrow" + variation selector), and
> ** the plain character U+22EF, i.e. {{"A" + U+22EF + "B"}} already crashes.
> # Observe the rendering.
> h3. Actual Results
> {{ArrayIndexOutOfBoundsException}} in {{MultiByteFont.getWidth}} (or
> {{{}getBoundingBox{}}}).
> The exact message depends only on which invalid index occurs, e.g.
> {{"Index 65535 out of bounds for length 65535"}} (fallback font has exactly
> 65535
> glyphs and GSUB emits the sentinel), or {{"Index -1 out of bounds for length
> <N>"}}
> ({{{}CIDSubset{}}} returns -1 for an unregistered index).
> {noformat}
> java.lang.ArrayIndexOutOfBoundsException: Index 65535 out of bounds for
> length 65535
> at org.apache.fop.fonts.MultiByteFont.getWidth(MultiByteFont.java:198)
> at org.apache.fop.fonts.LazyFont.getWidth(LazyFont.java:292)
> at org.apache.fop.fonts.Font.getWidth(Font.java:224)
> <... full stack trace from the attached console log ...>
> {noformat}
> When the invalid index reaches the embedded subset, a
> {{NullPointerException}} follows
> in {{OTFSubSetFile#createCharStringDataCID}} during CFF subsetting.
> h3. Expected Results
> The unmapped/out-of-range glyph index should fall back to {{.notdef}} (glyph
> index 0)
> so that metric lookups and subsetting do not crash. The page renders without
> exception
> (the offending character simply produces no visible glyph).
> h3. Build & Environment
> Verified against current {{main}} (HEAD 3791b92, 2026-07-08) and FOP 2.11
> ({{{}MultiByteFont{}}}
> accesses {{{}width[glyphIndex]{}}}/{{{}boundingBoxes[index]{}}} without a
> bounds check on both).
> Java 17 (also reproducible on 8/21). OS-independent (Windows 11 here). The
> defect is
> font-independent: with the guard removed, the provided JUnit tests fail on
> the real
> {{CIDSubset}} path with {{"Index -1 out of bounds for length 10"}} - i.e.
> neither a
> specific font nor the value 65535 is required to trigger it.
> h3. Fonts
> The trigger fonts are freely available under the SIL Open Font License 1.1:
> * Noto Sans CJK: [https://github.com/notofonts/noto-cjk]
> * Noto Emoji: [https://github.com/google/fonts/tree/main/ofl/notoemoji]
> Noto Sans CJK has exactly 65535 glyphs and produces the 65535 sentinel; Noto
> Emoji
> passes U+FE0F through as glyph index 65039 (same out-of-range bug class).
> h3. Additional Information
> {*}Fix{*}: clamp any out-of-range or negative glyph index to 0
> ({{{}.notdef{}}}) before it is
> used to index {{{}width[]{}}}/{{{}boundingBoxes[]{}}} and before it is added
> to the embedded
> subset via {{{}cidSet.mapChar{}}}/{{{}mapCodePoint{}}}. The guard is
> range-based
> ({{{}index < 0 || index >= length{}}}), not tied to a single magic value;
> valid indices are
> unaffected.
> Empirically verified on unpatched current {{{}main{}}}: the attached
> {{MultiByteFontTestCase}}
> (13 tests, synthetic width arrays + the real {{CIDSubset}} -1 path) and
> {{MultiByteFontRealFontTestCase}} (3 tests, using the bundled
> {{AndroidEmoji.ttf}} and
> {{{}DejaVuLGCSerif.ttf{}}}) fail with {{ArrayIndexOutOfBoundsException}}
> without the fix and
> all pass with it. Checkstyle is clean. A GitHub pull request with the fix and
> both tests
> will be linked in a comment.
>
> ??with assistance of Claude Opus 4.8??
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