docs(logger): clarify ${bytesSent} behavior in logger middleware

[elton-peixoto-lu]

Summary

Clarifies the behavior of the ${bytesSent} logger tag in the middleware documentation.

Changes

• document that ${bytesSent} is based on the Content-Length response header
• mention that it may be 0 when Content-Length is not set
• mention that it may be -1 for streaming responses
• clarify that Fiber does not calculate the actual response body size for performance reasons

Notes

• documentation-only change
• no runtime behavior changed

Validation

• reviewed the logger middleware documentation location for ${bytesSent}
• confirmed the behavior from issue 🐛 [Bug]: bytesSent tag not working in logging middleware. #4226 discussion
• no code or runtime logic changed

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: dcc01f1b-4da1-4a75-8a1f-19918975a7ff

📥 Commits

Reviewing files that changed from the base of the PR and between dfec5f6 and 225074e.

📒 Files selected for processing (1)

• docs/middleware/logger.md

✅ Files skipped from review due to trivial changes (1)

• docs/middleware/logger.md

---

Walkthrough

This PR adds a documentation tip to the logger middleware explaining that ${bytesSent} is taken from the response Content-Length header; if the header is missing or the response is streaming/chunked, ${bytesSent} is -1, and Fiber does not compute the actual body size for performance.

Changes

Logger Middleware Documentation

Layer / File(s)	Summary
Documentation Insertion docs/middleware/logger.md	Inserted a tip (lines 209–212) clarifying ${bytesSent} is sourced from the response Content-Length header and is -1 when the header is missing or the response is streaming/chunked; notes Fiber does not compute body size for performance.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Possibly related PRs

• 🐛 bug: Use Content-Length for bytesReceived and bytesSent tags in Logger Middleware in v2 #3067: Implements/changes logger middleware to use Content-Length for bytesSent/bytesReceived — directly related to this docs clarification.
• 🐛 bug: Use Content-Length for bytesReceived and bytesSent tags in Logger Middleware #3066: Related change documenting bytesSent/bytesReceived semantics tied to Content-Length and streaming cases.

Suggested reviewers

• gaby
• ReneWerner87

Poem

Hop, hop, a doc update bright and spry 🐇
Bytes sent now follow the header's sky,
When streaming flows or headers hide,
-1 is written with performance pride ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description covers the purpose, changes made, and notes that this is documentation-only with no runtime changes. However, it does not follow the repository's required description template structure.	Reformat the description to follow the repository's template, including sections like 'Type of change', 'Changes introduced', and the 'Checklist' items to ensure consistency with project standards.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: clarifying the ${bytesSent} behavior in logger middleware documentation.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Review rate limit: 6/8 reviews remaining, refill in 12 minutes and 53 seconds.}

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[gemini-code-assist]

Code Review

This pull request adds documentation for the ${bytesSent} variable in the logger middleware. The review feedback suggests refining the technical accuracy of the explanation regarding missing headers and using a callout block to align with the project's documentation style.

[welcome]

Congrats on merging your first pull request! 🎉 We here at Fiber are proud of you! If you need help or want to chat with us, join us on Discord https://gofiber.io/discord