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pdftract/notes/bf-1m30m.md
jedarden 6c668c7e42 docs(bf-ttbb5): document no-mapping.pdf generation verification 
Successfully executed generate_unicode_recovery_fixtures_bin to create
no-mapping.pdf fixture (650 bytes). Validated PDF structure includes
custom /CustomNoMap font with /Differences encoding, non-AGL glyph
names, and no ToUnicode entry. Ground truth contains U+FFFD × 3.

Closes bf-ttbb5.
2026-07-03 16:13:27 -04:00

2.7 KiB
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bf-1m30m: Generate no-mapping.pdf Fixture

Date: 2026-07-03 Parent Bead: bf-f0xqd Prerequisite: bf-2g412 (Research and design approach)

Implementation

Generated the no-mapping.pdf fixture using the existing Rust script: tests/fixtures/encoding/generate_unicode_recovery_fixtures.rs

Verification Results

Acceptance Criteria - All PASS

  1. ✓ Valid PDF exists: tests/fixtures/encoding/no-mapping.pdf (660 bytes)

    • Valid PDF 1.4 structure
    • Single page with 612x792 pts (letter size)

  2. ✓ Font has no ToUnicode CMap: Verified with grep -a "ToUnicode"

    • No /ToUnicode entry in font dictionary

  3. ✓ Font has no standard encoding: Verified with pdffonts and grep

    • pdffonts shows: Encoding: Custom
    • No /WinAnsiEncoding, /MacRomanEncoding, or /StandardEncoding present

  4. ✓ PDF contains test text content: Verified in content stream

    • Content stream: <g001><g002><g003> Tj
    • Codes: [0, 1, 2] mapped to non-AGL glyph names /g001, /g002, /g003
    • Ground truth file: Three U+FFFD replacement characters (0xEF 0xBF 0xBD × 3)

Font Dictionary Structure

/Type /Font
/Subtype /Type1
/BaseFont /CustomNoMap
/Encoding <<
    /Type /Encoding
    /Differences [0 /g001 /g002 /g003]
>>

Key characteristics:

  • Type1 font (simplest for custom encodings)
  • Custom base font name (prevents standard 14 font matching)
  • Custom encoding with /Differences array
  • Non-AGL glyph names (/g001-3 not in Adobe Glyph List)
  • No embedded font program (prevents Level 3 fingerprinting)
  • No ToUnicode CMap (prevents direct Unicode mapping)

Testing Purpose

This fixture tests the ENCODING_NO_MAPPING failure mode — the worst case for Unicode recovery:

  • Level 1 (Standard Encoding): FAIL — No standard encoding
  • Level 2 (AGL Lookup): FAIL — Glyph names not in AGL
  • Level 3 (Font Fingerprinting): FAIL — No embedded font program
  • Level 4 (Shape Recognition): FAIL/Partial — Intentionally no shape DB match
  • Fallback: Emit U+FFFD × 3 with GLYPH_UNMAPPED diagnostic

Files Modified

  • tests/fixtures/encoding/no-mapping.pdf - Generated fixture (660 bytes)
  • tests/fixtures/encoding/no-mapping.txt - Ground truth (3 × U+FFFD)

Files Unchanged

  • tests/fixtures/encoding/generate_unicode_recovery_fixtures.rs - Generation script (already existed)
  • tests/fixtures/encoding/agl-only.pdf - Companion fixture
  • tests/fixtures/encoding/fingerprint-match.pdf - Companion fixture
  • tests/fixtures/encoding/shape-match.pdf - Companion fixture

Reference

  • Technical approach documented in notes/bf-f0xqd-research.md
  • Failure Mode Taxonomy: ENCODING_NO_MAPPING