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Merged
ReneWerner87 merged 7 commits into from
Jan 13, 2026
Merged

🔥 feat(limiter): Add ExpirationFunc for dynamic expiration #3984

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5c23d3d
feat(limiter): Add ExpirationFunc for dynamic expiration
Jan 4, 2026
8dc5341
chore: omit redundant comments
Jan 4, 2026
65dab38
style: fix lint issue
Jan 4, 2026
4cc236e
refactor: improve
Jan 6, 2026
8dd54e8
test: increase coverage
Jan 7, 2026
cdedcf1
test: increase coverage
Jan 8, 2026
6505229
test: increase coverage
Jan 8, 2026
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24 changes: 24 additions & 0 deletions docs/middleware/limiter.md
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Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,13 @@ app.Use(limiter.New(limiter.Config{
return 20
},
Expiration: 30 * time.Second,
ExpirationFunc: func(c fiber.Ctx) time.Duration {
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Copilot AI Jan 4, 2026

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The ExpirationFunc in this example is redundant because it returns the same value as the static Expiration field above it (30 * time.Second). For a more useful demonstration, consider showing either a different value or a dynamic calculation based on the request context, similar to the dynamic expiration example below.

Suggested change
ExpirationFunc: func(c fiber.Ctx) time.Duration {
ExpirationFunc: func(c fiber.Ctx) time.Duration {
if c.Path() == "/login" {
return 60 * time.Second
}

Copilot uses AI. Check for mistakes.
// Use longer expiration for sensitive endpoints
if c.Path() == "/login" {
return 60 * time.Second
}
return 30 * time.Second
},
KeyGenerator: func(c fiber.Ctx) string {
return c.Get("x-forwarded-for")
},
Expand Down Expand Up @@ -99,6 +106,21 @@ app.Use(limiter.New(limiter.Config{
}))
```

## Dynamic expiration

You can also calculate the expiration dynamically using the `ExpirationFunc` parameter. It receives the request context and allows you to set a different expiration window for each request.

Example:

```go
app.Use(limiter.New(limiter.Config{
Max: 20,
ExpirationFunc: func(c fiber.Ctx) time.Duration {
return getExpirationForRoute(c.Path())
},
}))
```

## Config

| Property | Type | Description | Default |
Expand All @@ -108,6 +130,7 @@ app.Use(limiter.New(limiter.Config{
| MaxFunc | `func(fiber.Ctx) int` | Function that calculates the maximum number of recent connections within `Expiration` seconds before sending a 429 response. | A function that returns `cfg.Max` |
| KeyGenerator | `func(fiber.Ctx) string` | Function to generate custom keys; uses `c.IP()` by default. | A function using `c.IP()` as the default |
| Expiration | `time.Duration` | Duration to keep request records in memory. | 1 * time.Minute |
| ExpirationFunc | `func(fiber.Ctx) time.Duration` | Function that calculates the expiration duration dynamically. | A function that returns `cfg.Expiration` |
| LimitReached | `fiber.Handler` | Called when a request exceeds the limit. | A function sending a 429 response |
| SkipFailedRequests | `bool` | When set to `true`, requests with status code ≥ 400 aren't counted. | false |
| SkipSuccessfulRequests | `bool` | When set to `true`, requests with status code < 400 aren't counted. | false |
Expand All @@ -129,6 +152,7 @@ var ConfigDefault = Config{
return 5
},
Expiration: 1 * time.Minute,
// ExpirationFunc defaults to nil and is set dynamically to return cfg.Expiration
KeyGenerator: func(c fiber.Ctx) string {
return c.IP()
},
Expand Down
22 changes: 17 additions & 5 deletions middleware/limiter/config.go
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,11 @@ type Config struct {
// }
MaxFunc func(c fiber.Ctx) int

// A function to dynamically calculate the expiration time for rate limiter entries
//
// Default: A function that returns the static `Expiration` value from the config.
ExpirationFunc func(c fiber.Ctx) time.Duration

// KeyGenerator allows you to generate custom keys, by default c.IP() is used
//
// Default: func(c fiber.Ctx) string {
Expand Down Expand Up @@ -83,6 +88,8 @@ var ConfigDefault = Config{
MaxFunc: func(_ fiber.Ctx) int {
return defaultLimiterMax
},
// Note: ExpirationFunc is intentionally nil here so that configDefault()
// can create a proper closure that references the configured Expiration value.
KeyGenerator: func(c fiber.Ctx) string {
return c.IP()
},
Expand All @@ -98,14 +105,14 @@ var ConfigDefault = Config{

// Helper function to set default values
func configDefault(config ...Config) Config {
// Return default config if nothing provided
// Use default config if nothing provided
var cfg Config
if len(config) < 1 {
return ConfigDefault
cfg = ConfigDefault
} else {
cfg = config[0]
}

// Override default config
cfg := config[0]

// Set default values
if cfg.Next == nil {
cfg.Next = ConfigDefault.Next
Expand All @@ -130,5 +137,10 @@ func configDefault(config ...Config) Config {
return cfg.Max
}
}
if cfg.ExpirationFunc == nil {
cfg.ExpirationFunc = func(_ fiber.Ctx) time.Duration {
return cfg.Expiration
}
}
return cfg
}
18 changes: 11 additions & 7 deletions middleware/limiter/limiter_fixed.go
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Original file line number Diff line number Diff line change
Expand Up @@ -19,11 +19,8 @@ func (FixedWindow) New(cfg *Config) fiber.Handler {
cfg = &defaultCfg
}

var (
// Limiter variables
mux = &sync.RWMutex{}
expiration = uint64(cfg.Expiration.Seconds())
)
// Limiter variables
mux := &sync.RWMutex{}

// Create manager to simplify storage operations ( see manager.go )
manager := newManager(cfg.Storage, !cfg.DisableValueRedaction)
Expand All @@ -41,6 +38,13 @@ func (FixedWindow) New(cfg *Config) fiber.Handler {
return c.Next()
}

// Generate expiration from generator
expirationDuration := cfg.ExpirationFunc(c)
if expirationDuration <= 0 {
expirationDuration = ConfigDefault.Expiration
}
expiration := uint64(expirationDuration.Seconds())
Comment on lines 41 to 46
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@coderabbitai coderabbitai bot Jan 4, 2026

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🛠️ Refactor suggestion | 🟠 Major

Same duration validation needed here.

The same conversion safety concerns from limiter_sliding.go apply here. Please add validation to ensure ExpirationFunc returns a positive, reasonable duration before converting to uint64.

🔎 Suggested validation 
 // Generate expiration from generator
 expirationDuration := cfg.ExpirationFunc(c)
+if expirationDuration <= 0 {
+	return fmt.Errorf("limiter: ExpirationFunc must return a positive duration, got %v", expirationDuration)
+}
 expiration := uint64(expirationDuration.Seconds())
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
// Generate expiration from generator
expirationDuration := cfg.ExpirationFunc(c)
expiration := uint64(expirationDuration.Seconds())
// Generate expiration from generator
expirationDuration := cfg.ExpirationFunc(c)
if expirationDuration <= 0 {
return fmt.Errorf("limiter: ExpirationFunc must return a positive duration, got %v", expirationDuration)
}
expiration := uint64(expirationDuration.Seconds())
🤖 Prompt for AI Agents 
In middleware/limiter/limiter_fixed.go around lines 41-43, validate the duration
returned by cfg.ExpirationFunc(c) before converting to uint64: ensure the
duration is positive (>0) and clamp it to a safe upper bound to avoid overflow
when calling Seconds(); if the duration is <=0, set a sensible default (e.g.,
1s) and log or warn; if Seconds() exceeds the max uint64 value, clamp to
math.MaxUint64 (or a defined max) before casting to uint64. Implement these
checks immediately after calling ExpirationFunc and use the validated/clamped
value for expiration.


// Get key from request
key := cfg.KeyGenerator(c)

Expand Down Expand Up @@ -78,7 +82,7 @@ func (FixedWindow) New(cfg *Config) fiber.Handler {
remaining := maxRequests - e.currHits

// Update storage
if setErr := manager.set(reqCtx, key, e, cfg.Expiration); setErr != nil {
if setErr := manager.set(reqCtx, key, e, expirationDuration); setErr != nil {
mux.Unlock()
return fmt.Errorf("limiter: failed to persist state: %w", setErr)
}
Expand Down Expand Up @@ -118,7 +122,7 @@ func (FixedWindow) New(cfg *Config) fiber.Handler {
e = entry
e.currHits--
remaining++
if setErr := manager.set(reqCtx, key, e, cfg.Expiration); setErr != nil {
if setErr := manager.set(reqCtx, key, e, expirationDuration); setErr != nil {
mux.Unlock()
return fmt.Errorf("limiter: failed to persist state: %w", setErr)
}
Expand Down
14 changes: 9 additions & 5 deletions middleware/limiter/limiter_sliding.go
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Original file line number Diff line number Diff line change
Expand Up @@ -21,11 +21,8 @@ func (SlidingWindow) New(cfg *Config) fiber.Handler {
cfg = &defaultCfg
}

var (
// Limiter variables
mux = &sync.RWMutex{}
expiration = uint64(cfg.Expiration.Seconds())
)
// Limiter variables
mux := &sync.RWMutex{}

// Create manager to simplify storage operations ( see manager.go )
manager := newManager(cfg.Storage, !cfg.DisableValueRedaction)
Expand All @@ -43,6 +40,13 @@ func (SlidingWindow) New(cfg *Config) fiber.Handler {
return c.Next()
}

// Generate expiration from generator
expirationDuration := cfg.ExpirationFunc(c)
if expirationDuration <= 0 {
expirationDuration = ConfigDefault.Expiration
}
expiration := uint64(expirationDuration.Seconds())

// Get key from request
key := cfg.KeyGenerator(c)

Expand Down
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