plugin/rewrite: use request.Request and other cleanups (#1920)

This was done anyway, but only deep in the functions, just do this
everywhere; allows for shorter code and request.Request allows for
caching as well.

Cleanups, make it more Go like.
* remove unneeded switches
* remove testdir (why was this there??)
* simplify the logic
* remove unneeded variables
* put short functions on a single line
* fix documentation.
* spin off wire funcs in wire.go, make them functions.

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/rewrite/wire.go

@@ -0,0 +1,37 @@
+package rewrite
+
+import (
+	"encoding/binary"
+	"fmt"
+	"net"
+	"strconv"
+)
+
+// ipToWire writes IP address to wire/binary format, 4 or 16 bytes depends on IPV4 or IPV6.
+func ipToWire(family int, ipAddr string) ([]byte, error) {
+
+	switch family {
+	case 1:
+		return net.ParseIP(ipAddr).To4(), nil
+	case 2:
+		return net.ParseIP(ipAddr).To16(), nil
+	}
+	return nil, fmt.Errorf("invalid IP address family (i.e. version) %d", family)
+}
+
+// uint16ToWire writes unit16 to wire/binary format
+func uint16ToWire(data uint16) []byte {
+	buf := make([]byte, 2)
+	binary.BigEndian.PutUint16(buf, uint16(data))
+	return buf
+}
+
+// portToWire writes port to wire/binary format, 2 bytes
+func portToWire(portStr string) ([]byte, error) {
+
+	port, err := strconv.ParseUint(portStr, 10, 16)
+	if err != nil {
+		return nil, err
+	}
+	return uint16ToWire(uint16(port)), nil
+}