Moving TransferParse from file to its own package (#1286)

* Moving TransferParse from file to its own package

* Adding tests for parse

plugin/pkg/parse/parse.go

@@ -0,0 +1,47 @@
+package parse
+
+import (
+	"fmt"
+
+	"github.com/coredns/coredns/plugin/pkg/dnsutil"
+	"github.com/mholt/caddy"
+)
+
+// Transfer parses transfer statements: 'transfer [to|from] [address...]'.
+func Transfer(c *caddy.Controller, secondary bool) (tos, froms []string, err error) {
+	if !c.NextArg() {
+		return nil, nil, c.ArgErr()
+	}
+	value := c.Val()
+	switch value {
+	case "to":
+		tos = c.RemainingArgs()
+		for i := range tos {
+			if tos[i] != "*" {
+				normalized, err := dnsutil.ParseHostPort(tos[i], "53")
+				if err != nil {
+					return nil, nil, err
+				}
+				tos[i] = normalized
+			}
+		}
+
+	case "from":
+		if !secondary {
+			return nil, nil, fmt.Errorf("can't use `transfer from` when not being a secondary")
+		}
+		froms = c.RemainingArgs()
+		for i := range froms {
+			if froms[i] != "*" {
+				normalized, err := dnsutil.ParseHostPort(froms[i], "53")
+				if err != nil {
+					return nil, nil, err
+				}
+				froms[i] = normalized
+			} else {
+				return nil, nil, fmt.Errorf("can't use '*' in transfer from")
+			}
+		}
+	}
+	return
+}