gateway: Fix Send rate limiting

Prior to this commit, gateways can send 120 events before being
throttled at a terribly slow rate of 1 send per minute.

This commit permits gateways to send 5 events before being throttled at
a rate of slightly less than 120 events per minute.

utils/ws/throttler.go

@@ -6,18 +6,34 @@ import (
 	"golang.org/x/time/rate"
 )
 
+// SendBurst determines the number of gateway commands that can be sent all at
+// once before being throttled. The higher the burst, the slower the rate
+// limiter recovers.
+var SendBurst = 5
+
+// NewSendLimiter returns a rate limiter for throttling gateway commands.
 func NewSendLimiter() *rate.Limiter {
-	return rate.NewLimiter(rate.Every(time.Minute), 120)
+	const perMinute = 120
+	return rate.NewLimiter(
+		// Permit r = minute / (120 - b) commands per second.
+		rate.Every(time.Minute/(perMinute-time.Duration(SendBurst))),
+		SendBurst,
+	)
 }
 
+// NewDialLimiter returns a rate limiter for throttling new gateway connections.
 func NewDialLimiter() *rate.Limiter {
 	return rate.NewLimiter(rate.Every(5*time.Second), 1)
 }
 
+// NewIdentityLimiter returns a rate limiter for throttling gateway Identify
+// commands.
 func NewIdentityLimiter() *rate.Limiter {
 	return NewDialLimiter() // same
 }
 
+// NewGlobalIdentityLimiter returns a rate limiter for throttling global
+// gateway Identify commands.
 func NewGlobalIdentityLimiter() *rate.Limiter {
 	return rate.NewLimiter(rate.Every(24*time.Hour), 1000)
 }