From 70a20b4d261036c01dad38134097ba34afa60461 Mon Sep 17 00:00:00 2001
From: Bryan Boreham <bjboreham@gmail.com>
Date: Mon, 19 Dec 2016 18:10:26 +0000
Subject: [PATCH] Generate peer name / mac address in Go

---
 net/mac.go                  | 38 +++++++++++++++++++++++++++++++++
 net/uuid.go                 | 42 +++++++++++++++++++++++++++++++++++++
 prog/weaveutil/main.go      |  1 +
 prog/weaveutil/unique_id.go | 20 ++++++++++++++++++
 4 files changed, 101 insertions(+)
 create mode 100644 net/mac.go
 create mode 100644 net/uuid.go
 create mode 100644 prog/weaveutil/unique_id.go

diff --git a/net/mac.go b/net/mac.go
new file mode 100644
index 00000000..05864970
--- /dev/null
+++ b/net/mac.go
@@ -0,0 +1,38 @@
+package net
+
+import (
+	"crypto/rand"
+	"crypto/sha256"
+	"net"
+)
+
+func RandomMAC() (net.HardwareAddr, error) {
+	mac := make([]byte, 6)
+	if _, err := rand.Read(mac); err != nil {
+		return nil, err
+	}
+
+	setUnicastAndLocal(mac)
+
+	return net.HardwareAddr(mac), nil
+}
+
+func MACfromUUID(uuid []byte) net.HardwareAddr {
+	hash := sha256.New()
+	// We salt the input just as a precaution to avoid clashes with
+	// other applications who might have had the bright idea of
+	// generating MACs in the same way.
+	hash.Write([]byte("9oBJ0Jmip-"))
+	hash.Write(uuid)
+	sum := hash.Sum(nil)
+
+	setUnicastAndLocal(sum)
+
+	return net.HardwareAddr(sum[:6])
+}
+
+// In the first byte of the MAC, the 'multicast' bit should be
+// clear and 'locally administered' bit should be set.
+func setUnicastAndLocal(mac []byte) {
+	mac[0] = (mac[0] & 0xFE) | 0x02
+}
diff --git a/net/uuid.go b/net/uuid.go
new file mode 100644
index 00000000..f3cd2ebc
--- /dev/null
+++ b/net/uuid.go
@@ -0,0 +1,42 @@
+package net
+
+import (
+	"fmt"
+	"io/ioutil"
+	"net"
+	"os"
+)
+
+func getSystemUUID(hostRoot string) ([]byte, error) {
+	machineid, err := ioutil.ReadFile(hostRoot + "/etc/machine-id")
+	if os.IsNotExist(err) {
+		machineid, _ = ioutil.ReadFile(hostRoot + "/var/lib/dbus/machine-id")
+	}
+	uuid, err := ioutil.ReadFile(hostRoot + "/sys/class/dmi/id/product_uuid")
+	if os.IsNotExist(err) {
+		uuid, _ = ioutil.ReadFile(hostRoot + "/sys/hypervisor/uuid")
+	}
+	if err != nil && !os.IsNotExist(err) {
+		return nil, err
+	}
+	if len(machineid)+len(uuid) == 0 {
+		return nil, fmt.Errorf("Empty system uuid")
+	}
+	return append(machineid, uuid...), nil
+}
+
+// GetSystemPeerName returns an ID derived from concatenated machine-id
+// (either systemd or dbus), the system (aka bios) UUID and the
+// hypervisor UUID.  It is tweaked and formatted to be usable as a mac address
+func GetSystemPeerName(hostRoot string) (string, error) {
+	var mac net.HardwareAddr
+	if uuid, err := getSystemUUID(hostRoot); err == nil {
+		mac = MACfromUUID(uuid)
+	} else {
+		mac, err = RandomMAC()
+		if err != nil {
+			return "", err
+		}
+	}
+	return mac.String(), nil
+}
diff --git a/prog/weaveutil/main.go b/prog/weaveutil/main.go
index 8322a013..10e771f3 100644
--- a/prog/weaveutil/main.go
+++ b/prog/weaveutil/main.go
@@ -36,6 +36,7 @@ func init() {
 		"cni-ipam":               cniIPAM,
 		"expose-nat":             exposeNAT,
 		"bridge-ip":              bridgeIP,
+		"unique-id":              uniqueID,
 	}
 }
 
diff --git a/prog/weaveutil/unique_id.go b/prog/weaveutil/unique_id.go
new file mode 100644
index 00000000..456c69eb
--- /dev/null
+++ b/prog/weaveutil/unique_id.go
@@ -0,0 +1,20 @@
+package main
+
+import (
+	"fmt"
+
+	weavenet "github.com/weaveworks/weave/net"
+)
+
+func uniqueID(args []string) error {
+	if len(args) != 1 {
+		cmdUsage("unique-id", "<host-root>")
+	}
+	hostRoot := args[0]
+	uid, err := weavenet.GetSystemPeerName(hostRoot)
+	if err != nil {
+		return err
+	}
+	fmt.Printf(uid)
+	return nil
+}