wip: migrate to mono-repo. SPN has already been moved to spn/

spn/terminal/rate_limit.go

@@ -0,0 +1,39 @@
+package terminal
+
+import "time"
+
+// RateLimiter is a data flow rate limiter.
+type RateLimiter struct {
+	maxBytesPerSlot uint64
+	slotBytes       uint64
+	slotStarted     time.Time
+}
+
+// NewRateLimiter returns a new rate limiter.
+// The given MBit/s are transformed to bytes, so giving a multiple of 8 is
+// advised for accurate results.
+func NewRateLimiter(mbits uint64) *RateLimiter {
+	return &RateLimiter{
+		maxBytesPerSlot: (mbits / 8) * 1_000_000,
+		slotStarted:     time.Now(),
+	}
+}
+
+// Limit is given the current transferred bytes and blocks until they may be sent.
+func (rl *RateLimiter) Limit(xferBytes uint64) {
+	// Check if we need to limit transfer if we go over to max bytes per slot.
+	if rl.slotBytes > rl.maxBytesPerSlot {
+		// Wait if we are still within the slot.
+		sinceSlotStart := time.Since(rl.slotStarted)
+		if sinceSlotStart < time.Second {
+			time.Sleep(time.Second - sinceSlotStart)
+		}
+
+		// Reset state for next slot.
+		rl.slotBytes = 0
+		rl.slotStarted = time.Now()
+	}
+
+	// Add new bytes after checking, as first step over the limit is fully using the limit.
+	rl.slotBytes += xferBytes
+}