Add HTTP cache headers for static files

[Copilot]

Implementation Plan for HTTP Cache Headers

• Analyze current static file serving implementation
• Add Last-Modified header for static files
• Add proper Cache-Control headers for static files (max-age=31536000)
• Handle If-Modified-Since conditional requests
• Fix 304 response to preserve cache headers
• Test the implementation manually
• Increment version in package.json (0.9.12 -> 0.9.13)
• Run code review and security checks
• Remove redundant ETag implementation per feedback
• Simplify code: inline variables, use return instead of throw

Summary

Simplified implementation to use only Last-Modified/If-Modified-Since for HTTP caching:

Features:

• Last-Modified header with file's modification time
• Cache-Control header with max-age=31536000 (1 year)
• If-Modified-Since conditional request handling returns 304 when appropriate

Code simplifications:

• Inlined mtime_ms and last_modified variables
• Set response headers immediately where they're computed
• Use response.statusCode = 304; response.end(); return; instead of throw 304
• Removed special 304 handling from catch block

Testing:

• ✅ Initial requests return 200 with Last-Modified and Cache-Control headers
• ✅ If-Modified-Since with matching time returns 304
• ✅ If-Modified-Since with old time returns 200

Security Summary:
No security vulnerabilities detected by CodeQL analysis.

Original prompt

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This section details on the original issue you should resolve

<issue_title>http cache headers for static files</issue_title>
<issue_description>handle stuff like max-age and etag.

for static files, send headers like etag, cache, last modified and similar.

generate the etag from the modification time and file size of the raw file.</issue_description>

<agent_instructions>dont forget to increment the version in package.json, but only the patch digit.</agent_instructions>

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

• Fixes http cache headers for static files #9

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[L3P3]

@copilot Is there even a value in using etag here? Is it redundant? If the if-modified-since is serving the same function already, remove the etag stuff again. I am not sure.

[Copilot]

@copilot Is there even a value in using etag here? Is it redundant? If the if-modified-since is serving the same function already, remove the etag stuff again. I am not sure.

You're correct - the ETag was redundant since it was just encoding the same mtime + size that Last-Modified already provides. I've removed the ETag implementation and simplified to use only Last-Modified/If-Modified-Since, which is sufficient for static file caching. (8537cd2)

[L3P3]

Make the changes shorter please.
Inline the mtime_ms and last_modified variable.
Set the two response headers where above variables were defined.
Instead of throw 304, set the status, call end and return directly and leave the catch block as it is.

[Copilot]

Make the changes shorter please.
Inline the mtime_ms and last_modified variable.
Set the two response headers where above variables were defined....

Done. Inlined variables, set headers immediately, and used response.statusCode = 304; response.end(); return; instead of throw 304. Removed special handling from catch block. (953213f)