Doc: Improve variable name in limited_sliding.go

This clarifies the intent of variable 'expire' by renaming to
the more understandable 'resetInSec'. All mentions are renamed as well.

middleware/limiter/limited_sliding.go

@@ -77,10 +77,10 @@ func (SlidingWindow) New(cfg Config) fiber.Handler {
 		e.currHits++
 
 		// Calculate when it resets in seconds
-		expire := e.exp - ts
+		resetInSec := e.exp - ts
 
 		// weight = time until current window reset / total window length
-		weight := float64(expire) / float64(expiration)
+		weight := float64(resetInSec) / float64(expiration)
 
 		// rate = request count in previous window - weight + request count in current window
 		rate := int(float64(e.prevHits)*weight) + e.currHits
@@ -89,18 +89,18 @@ func (SlidingWindow) New(cfg Config) fiber.Handler {
 		remaining := cfg.Max - rate
 
 		// Update storage. Garbage collect when the next window ends.
-		// |-------------------------|-------------------------|
-		//               ^           ^              ^          ^
-		//              ts        e.exp  End sample window   End next window
-		//               <----------->
-		// 				    expire
-		// expire = e.exp - ts - time until end of current window.
+		// |--------------------------|--------------------------|
+		//               ^            ^               ^          ^
+		//              ts         e.exp   End sample window   End next window
+		//               <------------>
+		// 				   resetInSec
+		// resetInSec = e.exp - ts - time until end of current window.
 		// duration + expiration = end of next window.
 		// Because we don't want to garbage collect in the middle of a window
 		// we add the expiration to the duration.
 		// Otherwise after the end of "sample window", attackers could launch
 		// a new request with the full window length.
-		manager.set(key, e, time.Duration(expire+expiration)*time.Second)
+		manager.set(key, e, time.Duration(resetInSec+expiration)*time.Second)
 
 		// Unlock entry
 		mux.Unlock()
@@ -109,7 +109,7 @@ func (SlidingWindow) New(cfg Config) fiber.Handler {
 		if remaining < 0 {
 			// Return response with Retry-After header
 			// https://tools.ietf.org/html/rfc6584
-			c.Set(fiber.HeaderRetryAfter, strconv.FormatUint(expire, 10))
+			c.Set(fiber.HeaderRetryAfter, strconv.FormatUint(resetInSec, 10))
 
 			// Call LimitReached handler
 			return cfg.LimitReached(c)
@@ -131,7 +131,7 @@ func (SlidingWindow) New(cfg Config) fiber.Handler {
 		// We can continue, update RateLimit headers
 		c.Set(xRateLimitLimit, max)
 		c.Set(xRateLimitRemaining, strconv.Itoa(remaining))
-		c.Set(xRateLimitReset, strconv.FormatUint(expire, 10))
+		c.Set(xRateLimitReset, strconv.FormatUint(resetInSec, 10))
 
 		return err
 	}