Tc bits (#617)

* middleware/erratic: allow TC bit to be set

Add `truncate` as an option.

Fixes #593

middleware/erratic/setup.go

@@ -33,6 +33,8 @@ func setupErratic(c *caddy.Controller) error {
 
 func parseErratic(c *caddy.Controller) (*Erratic, error) {
 	e := &Erratic{drop: 2}
+	drop := false // true if we've seen the drop keyword
+
 	for c.Next() { // 'erratic'
 		for c.NextBlock() {
 			switch c.Val() {
@@ -54,6 +56,7 @@ func parseErratic(c *caddy.Controller) (*Erratic, error) {
 					return nil, fmt.Errorf("illegal amount value given %q", args[0])
 				}
 				e.drop = uint64(amount)
+				drop = true
 			case "delay":
 				args := c.RemainingArgs()
 				if len(args) > 2 {
@@ -83,8 +86,30 @@ func parseErratic(c *caddy.Controller) (*Erratic, error) {
 					}
 					e.duration = duration
 				}
+			case "truncate":
+				args := c.RemainingArgs()
+				if len(args) > 1 {
+					return nil, c.ArgErr()
+				}
+
+				if len(args) == 0 {
+					continue
+				}
+
+				amount, err := strconv.ParseInt(args[0], 10, 32)
+				if err != nil {
+					return nil, err
+				}
+				if amount < 0 {
+					return nil, fmt.Errorf("illegal amount value given %q", args[0])
+				}
+				e.truncate = uint64(amount)
 			}
 		}
 	}
+	if (e.delay > 0 || e.truncate > 0) && !drop { // delay is set, but we've haven't seen a drop keyword, remove default drop stuff
+		e.drop = 0
+	}
+
 	return e, nil
 }