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diff --git a/zerotierone/node/Multicaster.hpp b/zerotierone/node/Multicaster.hpp
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+/*
+ * ZeroTier One - Network Virtualization Everywhere
+ * Copyright (C) 2011-2016  ZeroTier, Inc.  https://www.zerotier.com/
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef ZT_MULTICASTER_HPP
+#define ZT_MULTICASTER_HPP
+
+#include <stdint.h>
+#include <string.h>
+
+#include <map>
+#include <vector>
+#include <list>
+
+#include "Constants.hpp"
+#include "Hashtable.hpp"
+#include "Address.hpp"
+#include "MAC.hpp"
+#include "MulticastGroup.hpp"
+#include "OutboundMulticast.hpp"
+#include "Utils.hpp"
+#include "Mutex.hpp"
+#include "NonCopyable.hpp"
+
+namespace ZeroTier {
+
+class RuntimeEnvironment;
+class CertificateOfMembership;
+class Packet;
+
+/**
+ * Database of known multicast peers within a network
+ */
+class Multicaster : NonCopyable
+{
+private:
+	struct Key
+	{
+		Key() : nwid(0),mg() {}
+		Key(uint64_t n,const MulticastGroup &g) : nwid(n),mg(g) {}
+
+		uint64_t nwid;
+		MulticastGroup mg;
+
+		inline bool operator==(const Key &k) const throw() { return ((nwid == k.nwid)&&(mg == k.mg)); }
+		inline unsigned long hashCode() const throw() { return (mg.hashCode() ^ (unsigned long)(nwid ^ (nwid >> 32))); }
+	};
+
+	struct MulticastGroupMember
+	{
+		MulticastGroupMember() {}
+		MulticastGroupMember(const Address &a,uint64_t ts) : address(a),timestamp(ts) {}
+
+		Address address;
+		uint64_t timestamp; // time of last notification
+	};
+
+	struct MulticastGroupStatus
+	{
+		MulticastGroupStatus() : lastExplicitGather(0) {}
+
+		uint64_t lastExplicitGather;
+		std::list<OutboundMulticast> txQueue; // pending outbound multicasts
+		std::vector<MulticastGroupMember> members; // members of this group
+	};
+
+public:
+	Multicaster(const RuntimeEnvironment *renv);
+	~Multicaster();
+
+	/**
+	 * Add or update a member in a multicast group
+	 *
+	 * @param now Current time
+	 * @param nwid Network ID
+	 * @param mg Multicast group
+	 * @param member New member address
+	 */
+	inline void add(uint64_t now,uint64_t nwid,const MulticastGroup &mg,const Address &member)
+	{
+		Mutex::Lock _l(_groups_m);
+		_add(now,nwid,mg,_groups[Multicaster::Key(nwid,mg)],member);
+	}
+
+	/**
+	 * Add multiple addresses from a binary array of 5-byte address fields
+	 *
+	 * It's up to the caller to check bounds on the array before calling this.
+	 *
+	 * @param now Current time
+	 * @param nwid Network ID
+	 * @param mg Multicast group
+	 * @param addresses Raw binary addresses in big-endian format, as a series of 5-byte fields
+	 * @param count Number of addresses
+	 * @param totalKnown Total number of known addresses as reported by peer
+	 */
+	void addMultiple(uint64_t now,uint64_t nwid,const MulticastGroup &mg,const void *addresses,unsigned int count,unsigned int totalKnown);
+
+	/**
+	 * Remove a multicast group member (if present)
+	 *
+	 * @param nwid Network ID
+	 * @param mg Multicast group
+	 * @param member Member to unsubscribe
+	 */
+	void remove(uint64_t nwid,const MulticastGroup &mg,const Address &member);
+
+	/**
+	 * Append gather results to a packet by choosing registered multicast recipients at random
+	 *
+	 * This appends the following fields to the packet:
+	 *   <[4] 32-bit total number of known members in this multicast group>
+	 *   <[2] 16-bit number of members enumerated in this packet>
+	 *   <[...] series of 5-byte ZeroTier addresses of enumerated members>
+	 *
+	 * If zero is returned, the first two fields will still have been appended.
+	 *
+	 * @param queryingPeer Peer asking for gather (to skip in results)
+	 * @param nwid Network ID
+	 * @param mg Multicast group
+	 * @param appendTo Packet to append to
+	 * @param limit Maximum number of 5-byte addresses to append
+	 * @return Number of addresses appended
+	 * @throws std::out_of_range Buffer overflow writing to packet
+	 */
+	unsigned int gather(const Address &queryingPeer,uint64_t nwid,const MulticastGroup &mg,Buffer<ZT_PROTO_MAX_PACKET_LENGTH> &appendTo,unsigned int limit) const;
+
+	/**
+	 * Get subscribers to a multicast group
+	 *
+	 * @param nwid Network ID
+	 * @param mg Multicast group
+	 */
+	std::vector<Address> getMembers(uint64_t nwid,const MulticastGroup &mg,unsigned int limit) const;
+
+	/**
+	 * Send a multicast
+	 *
+	 * @param com Certificate of membership to include or NULL for none
+	 * @param limit Multicast limit
+	 * @param now Current time
+	 * @param nwid Network ID
+	 * @param alwaysSendTo Send to these peers first and even if not included in subscriber list
+	 * @param mg Multicast group
+	 * @param src Source Ethernet MAC address or NULL to skip in packet and compute from ZT address (non-bridged mode)
+	 * @param etherType Ethernet frame type
+	 * @param data Packet data
+	 * @param len Length of packet data
+	 */
+	void send(
+		const CertificateOfMembership *com,
+		unsigned int limit,
+		uint64_t now,
+		uint64_t nwid,
+		const std::vector<Address> &alwaysSendTo,
+		const MulticastGroup &mg,
+		const MAC &src,
+		unsigned int etherType,
+		const void *data,
+		unsigned int len);
+
+	/**
+	 * Clean up and resort database
+	 *
+	 * @param RR Runtime environment
+	 * @param now Current time
+	 */
+	void clean(uint64_t now);
+
+private:
+	void _add(uint64_t now,uint64_t nwid,const MulticastGroup &mg,MulticastGroupStatus &gs,const Address &member);
+
+	const RuntimeEnvironment *RR;
+	Hashtable<Multicaster::Key,MulticastGroupStatus> _groups;
+	Mutex _groups_m;
+};
+
+} // namespace ZeroTier
+
+#endif