pdftract/notes/pdftract-68wfa.md

Verification Note: pdftract-68wfa

Bead: 6.6.2: AtomicFileWriter (temp + rename) + Drop cleanup + panic safety

Implementation Summary

Changes Made

1. Created AtomicFileWriter module (crates/pdftract-core/src/atomic_file_writer.rs)

   • Implements atomic file writes using temp-file-and-rename pattern
   • Creates temp file as <target>.tmp.<pid>.<random> in same directory as target
   • commit() method atomically renames temp file to target on success
   • Drop implementation removes temp file if not committed
   • Special case for stdout ("-") passthrough

2. Updated CLI extract command (crates/pdftract-cli/src/main.rs)

   • Added --output option (default: "-" for stdout)
   • Integrated AtomicFileWriter for file outputs
   • All formats (json, text, markdown) now write through atomic file writer

3. Added dependencies (crates/pdftract-core/Cargo.toml)

   • rand = "0.8" for random suffix generation
   • tempfile = "3.10" for test fixtures

Acceptance Criteria Status

Criterion	Status	Notes
Critical test: panic mid-extraction → no partial output files	PASS	Unit test test_drop_without_commit_removes_temp verifies temp file cleanup on Drop
Successful extraction: temp file renamed to target	PASS	Unit test test_successful_commit verifies rename on commit
Concurrent extractions: no collision	PASS	Unit test test_concurrent_writes_no_collision verifies 10 concurrent writers get unique temp paths
Drop cleanup: orphaned temp files removed on Drop	PASS	Drop impl removes temp file if not committed
File-backed sinks wrap Box in AtomicFileWriter	PASS	CLI extract command now uses AtomicFileWriter for all file outputs
Stdout sinks (path == "-") pass through	PASS	stdout() method and "-" special case implemented

Test Results

All 7 unit tests pass:

test atomic_file_writer::tests::test_empty_file ... ok
test atomic_file_writer::tests::test_drop_without_commit_removes_temp ... ok
test atomic_file_writer::tests::test_stdout_passthrough ... ok
test atomic_file_writer::tests::test_successful_commit ... ok
test atomic_file_writer::tests::test_concurrent_writes_no_collision ... ok
test atomic_file_writer::tests::test_overwrite_existing_file ... ok
test atomic_file_writer::tests::test_large_file ... ok

Git Commits

• feat(pdftract-68wfa): implement AtomicFileWriter for atomic file writes
  • Added atomic_file_writer.rs module with temp-file-and-rename pattern
  • Added --output option to extract command
  • Updated output handling to use AtomicFileWriter
  • Added unit tests for commit, drop, and concurrent write scenarios

Files Modified

• crates/pdftract-core/src/atomic_file_writer.rs (new)
• crates/pdftract-core/src/lib.rs (module export)
• crates/pdftract-core/Cargo.toml (rand, tempfile deps)
• crates/pdftract-cli/src/main.rs (output option, AtomicFileWriter integration)

Known Limitations

1. Multi-sink transactional commit: The plan mentions "For multi-sink: all sinks must commit successfully or NONE commit (transactional)". This is not yet implemented as the full multi-output CLI (Phase 6.6) is a separate feature. Current implementation handles single-file atomic writes.
2. Cross-device rename: The code detects and reports cross-device renames (non-atomic), but falls back to copy+delete is not implemented. This is acceptable for the current scope.

Integration Notes

The AtomicFileWriter is now integrated into the CLI extract command:

• pdftract extract file.pdf --output out.json writes atomically to out.json
• pdftract extract file.pdf (default) writes to stdout (no atomic behavior needed)
• pdftract extract file.pdf --output - --format json explicitly writes to stdout

Next Steps

This implementation provides the foundation for Phase 6.6 multi-output architecture. The full multi-output CLI (--json out.json --md out.md --text out.txt) will be implemented in a separate bead, building on this atomic file writer infrastructure.