initial, tests passing

README.md

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+# Backoff
+
+A simple backoff algorithm in Go (Golang)
+
+# Usage
+
+Starts at `Min`, multiplied by `Factor` every call to
+`Duration()` where it is capped at `Max`. Commonly used
+in conjunction with `time.Sleep(duration)`.
+
+``` go
+
+b := &backoff.Backoff{
+	//These are the defaults
+	Min:    100 * time.Millisecond,
+	Max:    10 * time.Second,
+	Factor: 2,
+}
+
+fmt.Printf("%s\n", b.Duration())
+fmt.Printf("%s\n", b.Duration())
+fmt.Printf("%s\n", b.Duration())
+
+fmt.Printf("Reset!\n")
+b.Reset()
+
+fmt.Printf("%s\n", b.Duration())
+```
+
+```
+100ms
+200ms
+400ms
+Reset!
+100ms
+```
+
+#### Credits
+
+Ported from some JavaScript written by [@tj](https://github.com/tj)
+
+#### MIT License
+
+Copyright © 2015 Jaime Pillora <dev@jpillora.com>
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+'Software'), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

backoff.go

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+package backoff
+
+import (
+	"math"
+	"time"
+)
+
+type Backoff struct {
+	attempts, Factor int
+	curr, Min, Max   time.Duration
+}
+
+func (b *Backoff) Duration() time.Duration {
+	//abit hacky though, if zero-value, apply defaults
+	if b.Min == 0 {
+		b.Min = 100 * time.Millisecond
+	}
+	if b.Max == 0 {
+		b.Max = 10 * time.Second
+	}
+	if b.Factor == 0 {
+		b.Factor = 2
+	}
+	if b.curr == 0 {
+		b.curr = b.Min
+	}
+
+	//calculate next duration in ms
+	ms := float64(b.curr) * math.Pow(float64(b.Factor), float64(b.attempts))
+	//bump attempts count
+	b.attempts++
+	//return as a time.Duration
+	return time.Duration(math.Min(ms, float64(b.Max)))
+}
+
+func (b *Backoff) Reset() {
+	b.attempts = 0
+}

backoff_test.go

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+package backoff
+
+import (
+	"testing"
+	"time"
+)
+
+func Test1(t *testing.T) {
+
+	b := &Backoff{
+		Min:    100 * time.Millisecond,
+		Max:    10 * time.Second,
+		Factor: 2,
+	}
+
+	if b.Duration() != 100*time.Millisecond {
+		t.Error("Should be 100ms")
+	}
+
+	if b.Duration() != 200*time.Millisecond {
+		t.Error("Should be 200ms")
+	}
+
+	if b.Duration() != 400*time.Millisecond {
+		t.Error("Should be 400ms")
+	}
+
+	b.Reset()
+
+	if b.Duration() != 100*time.Millisecond {
+		t.Error("Should be 100ms again")
+	}
+}