📚 Doc: correct fasthttpctx Done semantics in context guide

[gtoxlili]

Description

The "Working with RequestCtx and fasthttpctx" section in docs/guide/context.md (introduced in #3677) currently tells readers that RequestCtx.Done closes when the client connection ends and that "handlers can detect client disconnects" via this channel. That is not what fasthttp actually does:

• fasthttp server.go RequestCtx.Done carries the explicit comment "RequestCtx.s.done is only closed when the server is shutting down" — s.done is the shared server-wide channel, allocated once in Server.Serve and closed once in Server.Shutdown. There is no per-connection cancellation signal.
• Determine client connection was closed valyala/fasthttp#468 — "this is not possible and would be really hard to add"
• Request Cancellation valyala/fasthttp#965 — "fasthttp doesn't do any operations on the socket while your handler is running, this is impossible for us to implement"
• 🤗 Should we check for context done/cancel on every handler #805 — @Fenny: "I'm afraid that is not possible nor efficient with fasthttp sync.pool design"
• 🤗 Which context to use to detect client disconnected?  #1718 — same Q&A, closed in 2022 with the same answer
• 📝 [Proposal]: Provide an effective TCP disconnect handle #4145 — open proposal asking Fiber to add per-connection disconnect detection. Its existence is direct evidence that the capability the docs already advertised does not exist.

So the docs paragraph contradicts (a) the fasthttp source code, (b) two upstream fasthttp maintainers, (c) a four-year-old Fiber maintainer Q&A answer, and (d) an open Fiber proposal asking for the very capability the docs claim is already there.

Fixes #4263

Changes introduced

Three spots in docs/guide/context.md:

1. The fasthttpctx paragraph (~L100): now describes the actual semantics (server-shutdown-only, shared channel, no client-disconnect signal) and points readers to context.WithTimeout or Flush-error detection for long handlers.
2. The "Context Cancellation with Goroutines" paragraph (~L219): drops the misleading "or the client disconnects" phrasing and clarifies that the timeout (not a client-side cancellation) is what bounds the work.
3. The Summary bullet (~L263): matches the corrected description.

No code changes; no API changes.

• Benchmarks: n/a
• Documentation Update: docs/guide/context.md — three passages corrected, no new sections.
• Changelog/What's New: n/a (corrects an inaccurate claim, no behavior change)
• Migration Guide: n/a
• API Alignment with Express: n/a
• API Longevity: n/a (docs only)
• Examples: n/a

Type of change

• Documentation update (changes to documentation)

Checklist

• Conducted a self-review of the changes.
• Updated the documentation in the /docs/ directory.
• Added or updated unit tests — n/a, docs only.
• Verified the wording against the fasthttp source and the linked issues.

[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: d16e6ea9-e545-4592-9df4-a5ab5784a3ab

📥 Commits

Reviewing files that changed from the base of the PR and between 7a5eb8a and e1af685.

📒 Files selected for processing (1)

• docs/guide/context.md

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

• docs/guide/context.md

---

Walkthrough

Documentation updates to Fiber's context guide clarifying that RequestCtx.Done() is a shared server-wide channel closing only on server shutdown, not client disconnect. Deadline remains a no-op. Async goroutine guidance and summary bullets are updated to match.

Changes

Context Semantics Clarification

Layer / File(s)	Summary
RequestCtx Semantics docs/guide/context.md	Core documentation of fasthttpctx behavior corrected: Done is shared across all in-flight requests and closes only on server shutdown, not individual client disconnects; Deadline is no-op; Err returns context.Canceled after shutdown.
Async Goroutine Guidance docs/guide/context.md	Updated goroutine-in-Fiber cancellation guidance to emphasize exiting early on deadlines/timeouts (use context.WithTimeout) because fasthttp does not surface client disconnects via RequestCtx.Done.
Summary Bullets docs/guide/context.md	Updated summary statement that RequestCtx.Done is shared across in-flight requests and closes only on server shutdown, matching the clarified semantics.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• gofiber/fiber#3729: Related docs updates describing fiber.Ctx context behavior and Deadline/Done/Err semantics.
• gofiber/fiber#3884: Modifies the same context guide with examples and guidance for goroutine cancellation using derived contexts.
• gofiber/fiber#3677: Prior PR that updated the context guide's RequestCtx.Done semantics; directly related.

Suggested reviewers

• gaby
• sixcolors
• ReneWerner87
• efectn

Poem

🐰 I hopped through docs to clear the air,
Done stays shared — no single-client scare.
Deadline sleeps, Err wakes on shutdown's bell,
Timeouts bound the work so handlers well.
Hooray — the guide now tells the truth so fair.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the change as a documentation correction to fasthttp Done semantics in the context guide.
Description check	✅ Passed	The PR description is comprehensive, provides clear context from linked issue #4263, explains the three locations updated, and includes proper checklist completion.
Linked Issues check	✅ Passed	The PR fully addresses the objective of #4263 by correcting documentation to accurately reflect fasthttp's server-wide Done semantics and recommending alternatives for timeout/disconnect detection.
Out of Scope Changes check	✅ Passed	All changes are limited to correcting documentation in docs/guide/context.md to match the stated objective of fixing inaccurate Done semantics claims; no code or API changes are introduced.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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[gemini-code-assist]

Code Review

This pull request updates the documentation to clarify that Fiber's underlying fasthttp context does not signal client disconnects through the Done channel, which instead only closes during server shutdown. The feedback suggests improving the consistency of external issue links, clarifying the usage of w.Flush() within StreamWriter, and recommending c.RequestCtx() as a parent context for timeouts to ensure server shutdown signals are properly propagated to goroutines.

[gemini-code-assist]

For consistency and clarity, the second issue reference should include the repository name, as it refers to an external repository (valyala/fasthttp).

Suggested change

	provided by `fasthttp` (see [valyala/fasthttp#468](https://github.com/valyala/fasthttp/issues/468)
	and [#965](https://github.com/valyala/fasthttp/issues/965), and the
	provided by fasthttp (see [valyala/fasthttp#468](https://github.com/valyala/fasthttp/issues/468)
	and [valyala/fasthttp#965](https://github.com/valyala/fasthttp/issues/965), and the

[gemini-code-assist]

The mention of w.Flush() might be ambiguous for users unfamiliar with fasthttp's streaming implementation. It would be clearer to specify that this detection typically occurs within a StreamWriter (e.g., via c.Response().SetBodyStreamWriter) where the *bufio.Writer is available.

[gemini-code-assist]

While it is correct that client disconnects are not surfaced, the server shutdown signal (from c.RequestCtx().Done()) is available. To ensure goroutines also terminate during a graceful server shutdown, it is recommended to use c.RequestCtx() as the parent context for context.WithTimeout. The current examples (like the one on line 241) use c.Context(), which defaults to context.Background() and does not honor the shutdown signal.

[gaby]

@gtoxlili Please fix the wording and tone of the changes. These are official docs, not a forum.

[gtoxlili]

@gaby Tightened the wording — dropped the bold emphasis, the inline issue links, and the explanatory asides. Just states the actual semantics now and points to the timeout pattern below. PTAL.

[welcome]

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