🐛 bug: delegate Ctx context methods to SetContext

ctx.go

@@ -151,9 +151,15 @@ func (c *DefaultCtx) SetContext(ctx context.Context) {
 // should be canceled. Deadline returns ok==false when no deadline is
 // set. Successive calls to Deadline return the same results.
 //
-// Due to current limitations in how fasthttp works, Deadline operates as a nop.
+// If no context was set with SetContext, Deadline operates as a nop due to
+// current limitations in how fasthttp works.
 // See: https://github.com/valyala/fasthttp/issues/965#issuecomment-777268945
-func (*DefaultCtx) Deadline() (time.Time, bool) {
+func (c *DefaultCtx) Deadline() (time.Time, bool) {
+	if c.fasthttp != nil {
+		if ctx, ok := c.fasthttp.UserValue(userContextKey).(context.Context); ok && ctx != nil {
+			return ctx.Deadline()
+		}
+	}
 	return time.Time{}, false
 }
 
@@ -163,17 +169,29 @@ func (*DefaultCtx) Deadline() (time.Time, bool) {
 // The close of the Done channel may happen asynchronously,
 // after the cancel function returns.
 //
-// Due to current limitations in how fasthttp works, Done operates as a nop.
+// If no context was set with SetContext, Done operates as a nop due to
+// current limitations in how fasthttp works.
 // See: https://github.com/valyala/fasthttp/issues/965#issuecomment-777268945
-func (*DefaultCtx) Done() <-chan struct{} {
+func (c *DefaultCtx) Done() <-chan struct{} {
+	if c.fasthttp != nil {
+		if ctx, ok := c.fasthttp.UserValue(userContextKey).(context.Context); ok && ctx != nil {
+			return ctx.Done()
+		}
+	}
 	return nil
 }
 
 // Err mirrors context.Err, returning nil until cancellation and then the terminal error value.
 //
-// Due to current limitations in how fasthttp works, Err operates as a nop.
+// If no context was set with SetContext, Err operates as a nop due to
+// current limitations in how fasthttp works.
 // See: https://github.com/valyala/fasthttp/issues/965#issuecomment-777268945
-func (*DefaultCtx) Err() error {
+func (c *DefaultCtx) Err() error {
+	if c.fasthttp != nil {
+		if ctx, ok := c.fasthttp.UserValue(userContextKey).(context.Context); ok && ctx != nil {
+			return ctx.Err() //nolint:wrapcheck // Err mirrors the stored context.
+		}
+	}
 	return nil
 }
 

ctx_test.go

@@ -3739,6 +3739,27 @@ func Test_Ctx_Err(t *testing.T) {
 	require.Equal(t, StatusOK, resp.StatusCode, "Status code")
 }
 
+// go test -run Test_Ctx_ContextMethods_UseCustomContext
+func Test_Ctx_ContextMethods_UseCustomContext(t *testing.T) {
+	t.Parallel()
+	app := New()
+	deadline := time.Now().Add(time.Hour)
+	parent, cancel := context.WithDeadline(context.Background(), deadline)
+	cancel()
+	c := app.AcquireCtx(&fasthttp.RequestCtx{})
+	t.Cleanup(func() {
+		app.ReleaseCtx(c)
+	})
+
+	c.SetContext(parent)
+
+	actualDeadline, ok := c.Deadline()
+	require.True(t, ok)
+	require.Equal(t, deadline, actualDeadline)
+	require.Equal(t, parent.Done(), c.Done())
+	require.ErrorIs(t, c.Err(), context.Canceled)
+}
+
 // go test -run Test_Ctx_Value
 func Test_Ctx_Value(t *testing.T) {
 	t.Parallel()

docs/api/ctx.md

@@ -80,7 +80,7 @@ app.Get("/", func(c fiber.Ctx) error {
 
 ### context.Context
 
-`Ctx` implements `context.Context`. However due to [current limitations in how fasthttp](https://github.com/valyala/fasthttp/issues/965#issuecomment-777268945) works, `Deadline()`, `Done()` and `Err()` are no-ops. The `fiber.Ctx` instance is reused after the handler returns and must not be used for asynchronous operations once the handler has completed. Call [`Context`](#context) within the handler to obtain a `context.Context` that can be used outside the handler.
+`Ctx` implements `context.Context`. `Deadline()`, `Done()` and `Err()` delegate to the context set with [`SetContext`](#setcontext). If no context was set, these methods are no-ops because of [current limitations in how fasthttp](https://github.com/valyala/fasthttp/issues/965#issuecomment-777268945) works. The `fiber.Ctx` instance is reused after the handler returns and must not be used for asynchronous operations once the handler has completed. Call [`Context`](#context) within the handler to obtain a `context.Context` that can be used outside the handler.
 
 ```go title="Signature"
 func (c fiber.Ctx) Deadline() (deadline time.Time, ok bool)

docs/guide/context.md

@@ -19,7 +19,8 @@ Fiber's [`Ctx`](../api/ctx.md) implements Go's
 You can pass `c` directly to functions that expect a `context.Context`
 without adapters.
 However, `fasthttp` doesn't support cancellation yet, so
-`Deadline`, `Done`, and `Err` are no-ops.
+`Deadline`, `Done`, and `Err` are no-ops unless you set a custom context with
+`c.SetContext`. When a custom context is set, those methods delegate to it.
 
 :::caution
 The `fiber.Ctx` instance is only valid within the lifetime of the handler.
@@ -262,8 +263,9 @@ This approach provides safe cancellation semantics for goroutine-based work whil
 
 ## Summary
 
-- `fiber.Ctx` satisfies `context.Context` but its `Deadline`, `Done`, and `Err`
-  methods are currently no-ops.
+- `fiber.Ctx` satisfies `context.Context`. Its `Deadline`, `Done`, and `Err`
+  methods delegate to `c.SetContext` when a custom context is set; otherwise
+  they remain no-ops.
 - `RequestCtx` exposes the raw `fasthttp` context. Its `Done` channel
   closes only on server shutdown, not on client disconnect.
 - Use `fiber.StoreInContext(c, key, value)` to store request-scoped values in both

log/default.go

@@ -73,7 +73,7 @@ func (l *defaultLogger) privateLog(lv Level, fmtArgs []any) {
 	buf.Reset()
 	bytebufferpool.Put(buf)
 	if lv == LevelFatal {
-		os.Exit(1) //nolint:revive // we want to exit the program when Fatal is called
+		os.Exit(1) //revive:disable-line:deep-exit // Fatal logs intentionally terminate the process.
 	}
 }
 
@@ -101,7 +101,7 @@ func (l *defaultLogger) privateLogf(lv Level, format string, fmtArgs []any) {
 	buf.Reset()
 	bytebufferpool.Put(buf)
 	if lv == LevelFatal {
-		os.Exit(1) //nolint:revive // we want to exit the program when Fatal is called
+		os.Exit(1) //revive:disable-line:deep-exit // Fatal logs intentionally terminate the process.
 	}
 }
 
@@ -148,7 +148,7 @@ func (l *defaultLogger) privateLogw(lv Level, format string, keysAndValues []any
 	buf.Reset()
 	bytebufferpool.Put(buf)
 	if lv == LevelFatal {
-		os.Exit(1) //nolint:revive // we want to exit the program when Fatal is called
+		os.Exit(1) //revive:disable-line:deep-exit // Fatal logs intentionally terminate the process.
 	}
 }