Since signing_key is now required at config load time, sessMgr, encGen,
and signer are always initialized. Remove unnecessary nil checks that
were runtime failure paths that can no longer be reached.
- handlers.go: Remove conditional init, always create sessMgr/encGen
- auth.go: Remove nil checks for sessMgr
- imageenc.go: Remove nil check for encGen
- service.go: Require signing_key in NewService, remove signer nil checks
- Update tests to provide signing_key
- Middleware now tracks and logs bytes written via response_bytes
- Handler logs cache_key for cache hit debugging
- Changed "served encrypted image" to "image served" (only URL is encrypted)
- Capture TLS version, cipher suite, HTTP version, and remote addr
- Add download bitrate using go-humanize SI formatting
- Use consistent WxH format for dimensions (not struct notation)
- Rename input/output to src/dst for consistency
- Add separate "upstream fetched" log with connection details
- Return ErrUnsupportedOutputFormat for WebP/AVIF encoding
- Return ErrInvalidFitMode for unknown fit mode values
- Add ValidateFitMode() for input validation
- Validate fit mode at handler level before processing
Silent fallbacks violate the principle of least surprise and mask bugs.
When a user explicitly specifies a value, we should either honor it or
return an error - never silently substitute a different value.
- Make ExpiresAt optional in CBOR (omitempty) for smaller tokens
- Treat ExpiresAt=0 as 'never expires' in parser
- URL-encode token with url.PathEscape() for safety
- Add 'Never' as default TTL option in generator form
TDD: Write tests first before implementation for:
- ETag generation and consistency in service layer
- HEAD request support (headers only, no body)
- Conditional requests with If-None-Match header (304 responses)
- StoreOutput now returns output hash for immediate retrieval
- Cache misses now serve from disk file after storing (same as hits)
- Log served_bytes from actual io.Copy result (avoids stat calls)
- Remove ContentLength field usage for cache hits (stream from file)
- Fix tests to properly check all return values
