feature: add size for humanize byte size

CHANGELOG.md

@@ -11,6 +11,7 @@
 - [#46](https://github.com/influxdata/kapacitor/issue/46): Can now create combinations of points within the same stream.
 	This is kind of like join but instead joining a stream with itself.
 
+- [#669](https://github.com/influxdata/kapacitor/pull/669): Add size function for humanize byte size.
 
 ### Bugfixes
 

tick/stateful/functions.go

@@ -7,6 +7,7 @@ import (
 	"strconv"
 	"time"
 
+	"github.com/dustin/go-humanize"
 	"github.com/influxdata/influxdb/influxql"
 )
 
@@ -83,6 +84,9 @@ func init() {
 	statelessFuncs["day"] = &day{}
 	statelessFuncs["month"] = &month{}
 	statelessFuncs["year"] = &year{}
+
+	// Humanize functions
+	statelessFuncs["humanBytes"] = &humanBytes{}
 }
 
 // Return set of built-in Funcs
@@ -598,3 +602,25 @@ func (*year) Call(args ...interface{}) (v interface{}, err error) {
 	}
 	return
 }
+
+type humanBytes struct {
+}
+
+func (*humanBytes) Reset() {
+
+}
+
+func (*humanBytes) Call(args ...interface{}) (v interface{}, err error) {
+	if len(args) != 1 {
+		return 0, errors.New("humanBytes expects exactly one argument")
+	}
+	switch a := args[0].(type) {
+	case float64:
+		v = humanize.Bytes(uint64(a))
+	case int64:
+		v = humanize.Bytes(uint64(a))
+	default:
+		err = fmt.Errorf("cannot convert %T to humanBytes", a)
+	}
+	return
+}