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// Copyright 2016 Google Inc.  All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package uuid
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import (
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	"sync"
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)
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var (
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	nodeMu sync.Mutex
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	ifname string  // name of interface being used
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	nodeID [6]byte // hardware for version 1 UUIDs
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	zeroID [6]byte // nodeID with only 0's
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)
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// NodeInterface returns the name of the interface from which the NodeID was
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// derived.  The interface "user" is returned if the NodeID was set by
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// SetNodeID.
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func NodeInterface() string {
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	defer nodeMu.Unlock()
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	nodeMu.Lock()
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	return ifname
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}
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// SetNodeInterface selects the hardware address to be used for Version 1 UUIDs.
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// If name is "" then the first usable interface found will be used or a random
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// Node ID will be generated.  If a named interface cannot be found then false
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// is returned.
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//
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// SetNodeInterface never fails when name is "".
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func SetNodeInterface(name string) bool {
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	defer nodeMu.Unlock()
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	nodeMu.Lock()
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	return setNodeInterface(name)
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}
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func setNodeInterface(name string) bool {
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	iname, addr := getHardwareInterface(name) // null implementation for js
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	if iname != "" && addr != nil {
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		ifname = iname
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		copy(nodeID[:], addr)
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		return true
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	}
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	// We found no interfaces with a valid hardware address.  If name
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	// does not specify a specific interface generate a random Node ID
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	// (section 4.1.6)
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	if name == "" {
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		ifname = "random"
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		randomBits(nodeID[:])
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		return true
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	}
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	return false
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}
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// NodeID returns a slice of a copy of the current Node ID, setting the Node ID
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// if not already set.
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func NodeID() []byte {
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	defer nodeMu.Unlock()
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	nodeMu.Lock()
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	if nodeID == zeroID {
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		setNodeInterface("")
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	}
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	nid := nodeID
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	return nid[:]
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}
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// SetNodeID sets the Node ID to be used for Version 1 UUIDs.  The first 6 bytes
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// of id are used.  If id is less than 6 bytes then false is returned and the
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// Node ID is not set.
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func SetNodeID(id []byte) bool {
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	if len(id) < 6 {
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		return false
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	}
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	defer nodeMu.Unlock()
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	nodeMu.Lock()
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	copy(nodeID[:], id)
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	ifname = "user"
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	return true
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}
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// NodeID returns the 6 byte node id encoded in uuid.  It returns nil if uuid is
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// not valid.  The NodeID is only well defined for version 1 and 2 UUIDs.
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func (uuid UUID) NodeID() []byte {
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	var node [6]byte
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	copy(node[:], uuid[10:])
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	return node[:]
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}
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