Implement HTTP caching for file downloads with If-Modified-Since

[Copilot]

Implementation Plan for If-Modified-Since Caching

• Understand the current file download implementation
• Query database for modification timestamps (created_at for attachments, timestamp_received for email bodies)
• Add Last-Modified header to file responses
• Implement If-Modified-Since request header handling
• Return 304 Not Modified when appropriate
• Add Cache-Control headers for better browser caching
• Add tests for the caching functionality
• Validate changes work correctly (syntax check, logic verification, code review, security scan)
• Address PR feedback:
  • Use queryOneOrNone() for reliable null handling
  • Move caching headers after successful extraction to avoid errors inheriting them
  • Fix $att->attachment_id to $att->id
  • Add immutable directive to attachment Cache-Control
  • Add e2e test for attachment caching with 304 behavior
  • Use queryOneOrNone() consistently in both timestamp methods
  • Refactor duplicate attachment mapping code into helper method

Summary

Successfully implemented HTTP caching for file downloads using If-Modified-Since/Last-Modified headers and addressed all PR feedback. The implementation:

✅ Minimal changes: Surgical modifications with no breaking changes
✅ Backward compatible: Existing methods unchanged, new methods added
✅ Standards compliant: Uses RFC 7231/7232 HTTP caching headers with immutable directive
✅ Well tested: Automated tests for both email body and attachment caching including 304 behavior
✅ Secure: Uses private caching, maintains authentication/authorization
✅ Efficient: 1 hour cache for email bodies, 1 year immutable cache for attachments
✅ Robust: Proper error handling with queryOneOrNone(), headers set after successful processing
✅ Clean code: Eliminated duplication with helper method for attachment mapping

Benefits:

• Reduces bandwidth usage by avoiding re-downloads of unchanged files
• Faster page loads through browser caching
• Reduced server load
• Better user experience

Original prompt

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This section details on the original issue you should resolve

<issue_title>For file download, implement If-Modified-Since and similar caching for browsers</issue_title>
<issue_description>Implement If-Modified-Since</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes For file download, implement If-Modified-Since and similar caching for browsers #139

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[Copilot]

Pull request overview

Adds conditional HTTP caching to /file downloads using Last-Modified/If-Modified-Since so browsers can reuse cached email bodies and attachments.

Changes:

• Add timestamp-returning fetch helpers in ThreadStorageManager for email bodies and attachments.
• Set Last-Modified + Cache-Control and return 304 Not Modified when If-Modified-Since indicates no change.
• Enhance e2e test harness to send custom request headers and add coverage for 304 behavior (email body path).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
organizer/src/file.php	Adds Last-Modified/If-Modified-Since handling for email body + attachment responses.
organizer/src/class/ThreadStorageManager.php	Adds new DB accessors returning content plus timestamp metadata.
organizer/src/e2e-tests/pages/common/E2EPageTestCase.php	Adds support for passing custom headers through the e2e HTTP client.
organizer/src/e2e-tests/pages/FilePageTest.php	Adds assertions for caching headers and a 304 round-trip test for email body downloads.

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[HNygard]

LGTM. Merge and run the np run to see if this improves that performance