Create `ExponentialBackoff` helper class

1 files changed, 52 insertions, 0 deletions

diff --git a/android/src/main/kotlin/net/mullvad/mullvadvpn/util/ExponentialBackoff.kt b/android/src/main/kotlin/net/mullvad/mullvadvpn/util/ExponentialBackoff.kt
new file mode 100644
index 0000000000..1117b0b749
--- /dev/null
+++ b/android/src/main/kotlin/net/mullvad/mullvadvpn/util/ExponentialBackoff.kt
@@ -0,0 +1,52 @@
+package net.mullvad.mullvadvpn.util
+
+// Calculates a series of delays that increase exponentially.
+//
+// The delays follow the formula:
+//
+// (base ^ retryAttempt) * scale
+//
+// but it is never larger than the specified cap value.
+class ExponentialBackoff : Iterator<Long> {
+    private var unscaledValue = 1L
+    private var current = 1L
+
+    var iteration = 1
+        private set
+
+    var base = 2L
+    var scale = 1000L
+    var cap = Long.MAX_VALUE
+    var count: Int? = null
+
+    override fun hasNext(): Boolean {
+        val maxIterations = count
+
+        if (maxIterations != null) {
+            return iteration < maxIterations
+        } else {
+            return true
+        }
+    }
+
+    override fun next(): Long {
+        iteration += 1
+
+        if (current >= cap) {
+            return cap
+        } else {
+            val value = current
+
+            unscaledValue *= base
+            current = Math.min(cap, scale * unscaledValue)
+
+            return value
+        }
+    }
+
+    fun reset() {
+        unscaledValue = 1L
+        current = 1L
+        iteration = 1
+    }
+}