First crack at backoff function

client/backoff.go

@@ -0,0 +1,18 @@
+package client
+
+import (
+	"math"
+	"time"
+
+	"golang.org/x/net/context"
+)
+
+type BackoffFunc func(ctx context.Context, req Request, attempts int) (time.Duration, error)
+
+// exponential backoff
+func exponentialBackoff(ctx context.Context, req Request, attempts int) (time.Duration, error) {
+	if attempts == 0 {
+		return time.Duration(0), nil
+	}
+	return time.Duration(math.Pow(10, float64(attempts))) * time.Millisecond, nil
+}