Split the application into modules

Splitting into modules will help keep concerns separate,
at the cost of a slightly more verbose code.

common/node.go

@@ -0,0 +1,51 @@
+package common
+
+import (
+	"bytes"
+	"encoding/gob"
+	"net"
+
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+)
+
+// NodeMeta holds metadata sent over the cluster
+type NodeMeta struct {
+	OverlayAddr net.IPNet
+	PubKey      string
+}
+
+// Node holds the memberlist node structure
+type Node struct {
+	Name string
+	Addr net.IP
+	Meta []byte
+	NodeMeta
+}
+
+func (n *Node) String() string {
+	return n.Addr.String()
+}
+
+func EncodeNodeMeta(nm NodeMeta, limit int) []byte {
+	buf := &bytes.Buffer{}
+	if err := gob.NewEncoder(buf).Encode(nm); err != nil {
+		logrus.Errorf("could not encode local state: %s", err)
+		return nil
+	}
+	if buf.Len() > limit {
+		logrus.Errorf("could not fit node metadata into %d bytes", limit)
+		return nil
+	}
+	return buf.Bytes()
+}
+
+func DecodeNodeMeta(b []byte) (NodeMeta, error) {
+	// TODO: we blindly trust the info we get from the peers; We should be more defensive to limit the damage a leaked
+	// PSK can cause.
+	nm := NodeMeta{}
+	if err := gob.NewDecoder(bytes.NewReader(b)).Decode(&nm); err != nil {
+		return nm, errors.Wrap(err, "could not decode node meta")
+	}
+	return nm, nil
+}