New simpler command interface via loopback UDP protected by a crypto token.

11 files changed, 194 insertions, 240 deletions

diff --git a/node/Constants.hpp b/node/Constants.hpp
index fbb309e6..b8dc9ebf 100644
--- a/node/Constants.hpp
+++ b/node/Constants.hpp
@@ -118,6 +118,11 @@ error_no_ZT_ARCH_defined;
 #define ZT_DEFAULT_UDP_PORT 8993
 
 /**
+ * Local control port, also used for multiple invocation check
+ */
+#define ZT_CONTROL_UDP_PORT 39393
+
+/**
  * Default payload MTU for UDP packets
  *
  * In the future we might support UDP path MTU discovery, but for now we
@@ -152,13 +157,6 @@ error_no_ZT_ARCH_defined;
 #define ZT_IF_MTU 2800
 
 /**
- * Maximum number of networks we can be a member of
- *
- * This is a safe value that's within the tap device limit on all known OSes.
- */
-#define ZT_MAX_NETWORK_MEMBERSHIPS 16
-
-/**
  * Maximum number of packet fragments we'll support
  * 
  * The actual spec allows 16, but this is the most we'll support right
@@ -233,21 +231,16 @@ error_no_ZT_ARCH_defined;
 #define ZT_MULTICAST_PROPAGATION_DEPTH 7
 
 /**
- * Length of circular ring buffer history of multicast packets
+ * Length of ring buffer history of recent multicast packets
  */
 #define ZT_MULTICAST_DEDUP_HISTORY_LENGTH 1024
 
 /**
- * Expiration time in ms for multicast history items
+ * Expiration time in ms for multicast deduplication history items
  */
 #define ZT_MULTICAST_DEDUP_HISTORY_EXPIRE 4000
 
 /**
- * Number of bits to randomly "decay" in bloom filter per hop
- */
-#define ZT_MULTICAST_BLOOM_FILTER_DECAY_RATE 2
-
-/**
  * Period between announcements of all multicast 'likes' in ms
  *
  * Announcement occurs when a multicast group is locally joined, but all
@@ -282,23 +275,6 @@ error_no_ZT_ARCH_defined;
 #define ZT_PEER_DIRECT_PING_DELAY 120000
 
 /**
- * Period between rechecks of autoconfigure URL
- *
- * This is in the absence of an external message ordering a recheck.
- */
-#define ZT_AUTOCONFIGURE_INTERVAL 3600000
-
-/**
- * Period between autoconfigure attempts if no successful autoconfig
- */
-#define ZT_AUTOCONFIGURE_CHECK_DELAY 15000
-
-/**
- * Delay between updates of status file in home directory
- */
-#define ZT_STATUS_OUTPUT_PERIOD 120000
-
-/**
  * Minimum delay in Node service loop
  * 
  * This is the shortest of the check delays/periods.
@@ -348,9 +324,4 @@ error_no_ZT_ARCH_defined;
  */
 #define ZT_RENDEZVOUS_NAT_T_DELAY 500
 
-/**
- * Generate a new ownership verify secret on launch if older than this
- */
-#define ZT_OVS_GENERATE_NEW_IF_OLDER_THAN 86400000
-
 #endif
diff --git a/node/Defaults.cpp b/node/Defaults.cpp
index f1454796..3e936b2d 100644
--- a/node/Defaults.cpp
+++ b/node/Defaults.cpp
@@ -68,9 +68,7 @@ static inline std::map< Identity,std::vector<InetAddress> > _mkSupernodeMap()
 
 Defaults::Defaults()
 	throw(std::runtime_error) :
-	supernodes(_mkSupernodeMap()),
-	configUrlPrefix("http://api.zerotier.com/one/nc/"),
-	configAuthority("f9f34184ac:1:AwGgrWjb8dARXzruqxiy1+Qf+gz4iM5IMfQTCWrJXkwERdvbvxTPZvtIyitw4gS90TGIxW+e7uJxweg9Vyq5lZJBrg==:QeEQLm9ymLC3EcnIw2OUqufUwb2wgHSAg6wQOXKyhT779p/8Hz5485PZLJCbr/aVHjwzop8APJk9B45Zm0Mb/LEhQTBMH2jvc7qqoYnMCNCO9jpADeMJwMW5e1VFgIObWl9uNjhRbf5/m8dZcn0pKKGwjSoP1QTeVWOC8GkZhE25bUWj")
+	supernodes(_mkSupernodeMap())
 {
 }
 
diff --git a/node/Defaults.hpp b/node/Defaults.hpp
index b9c8ecf5..3a350865 100644
--- a/node/Defaults.hpp
+++ b/node/Defaults.hpp
@@ -55,16 +55,6 @@ public:
 	 * Supernodes on the ZeroTier network
 	 */
 	const std::map< Identity,std::vector<InetAddress> > supernodes;
-
-	/**
-	 * URL prefix for autoconfiguration
-	 */
-	const std::string configUrlPrefix;
-
-	/**
-	 * Identity used to encrypt and authenticate configuration from URL
-	 */
-	const std::string configAuthority;
 };
 
 extern const Defaults ZT_DEFAULTS;
diff --git a/node/Demarc.cpp b/node/Demarc.cpp
index 5efe55bc..b935ce53 100644
--- a/node/Demarc.cpp
+++ b/node/Demarc.cpp
@@ -100,7 +100,7 @@ bool Demarc::bindLocalUdp(unsigned int localPort)
 		DemarcPortObj *v4r = &(_ports[(Port)v4p]);
 		v4r->port = (Port)v4p;
 		v4r->parent = this;
-		v4r->obj = v4 = new UdpSocket(localPort,false,&Demarc::_CBudpSocketPacketHandler,v4r);
+		v4r->obj = v4 = new UdpSocket(false,localPort,false,&Demarc::_CBudpSocketPacketHandler,v4r);
 		v4r->type = PORT_TYPE_UDP_SOCKET_V4;
 	} catch ( ... ) {
 		_ports.erase((Port)v4p);
@@ -112,7 +112,7 @@ bool Demarc::bindLocalUdp(unsigned int localPort)
 		DemarcPortObj *v6r = &(_ports[(Port)v6p]);
 		v6r->port = (Port)v6p;
 		v6r->parent = this;
-		v6r->obj = v6 = new UdpSocket(localPort,true,&Demarc::_CBudpSocketPacketHandler,v6r);
+		v6r->obj = v6 = new UdpSocket(false,localPort,true,&Demarc::_CBudpSocketPacketHandler,v6r);
 		v6r->type = PORT_TYPE_UDP_SOCKET_V6;
 	} catch ( ... ) {
 		_ports.erase((Port)v6p);
diff --git a/node/NodeConfig.cpp b/node/NodeConfig.cpp
index 763a5899..f05fb97e 100644
--- a/node/NodeConfig.cpp
+++ b/node/NodeConfig.cpp
@@ -27,34 +27,48 @@
 
 #include <stdio.h>
 #include <string.h>
+#include <stdlib.h>
+#include <stdint.h>
+
 #include <memory>
 #include <string>
 
-#include <json/json.h>
+#include <openssl/sha.h>
 
 #include "NodeConfig.hpp"
 #include "RuntimeEnvironment.hpp"
 #include "Defaults.hpp"
 #include "Utils.hpp"
 #include "Logger.hpp"
+#include "Topology.hpp"
+#include "Demarc.hpp"
+#include "InetAddress.hpp"
+#include "Peer.hpp"
+#include "Salsa20.hpp"
+#include "HMAC.hpp"
 
 namespace ZeroTier {
 
-NodeConfig::NodeConfig(const RuntimeEnvironment *renv,const std::string &url) :
+NodeConfig::NodeConfig(const RuntimeEnvironment *renv,const char *authToken)
+	throw(std::runtime_error) :
 	_r(renv),
-	_lastAutoconfigure(0),
-	_lastAutoconfigureLastModified(),
-	_url(url),
-	_autoconfigureLock(),
-	_networks(),
-	_networks_m()
+	_authToken(authToken),
+	_controlSocket(true,ZT_CONTROL_UDP_PORT,false,&_CBcontrolPacketHandler,this)
 {
+	SHA256_CTX sha;
+
+	SHA256_Init(&sha);
+	SHA256_Update(&sha,_authToken.data(),_authToken.length());
+	SHA256_Final(_keys,&sha); // first 32 bytes of keys[]: Salsa20 key
+
+	SHA256_Init(&sha);
+	SHA256_Update(&sha,_keys,32);
+	SHA256_Update(&sha,_authToken.data(),_authToken.length());
+	SHA256_Final(_keys + 32,&sha); // second 32 bytes of keys[]: HMAC key
 }
 
 NodeConfig::~NodeConfig()
 {
-	_autoconfigureLock.lock(); // wait for any autoconfs to finish
-	_autoconfigureLock.unlock();
 }
 
 void NodeConfig::whackAllTaps()
@@ -65,150 +79,128 @@ void NodeConfig::whackAllTaps()
 		n->second->tap().whack();
 }
 
-void NodeConfig::refreshConfiguration()
+// Macro used in execute()
+#undef _P
+#define _P(f,...) { r.push_back(std::string()); Utils::stdsprintf(r.back(),(f),##__VA_ARGS__); }
+
+// Used with Topology::eachPeer to dump peer stats
+class _DumpPeerStatistics
 {
-	_autoconfigureLock.lock(); // unlocked when handler gets called
+public:
+	_DumpPeerStatistics(std::vector<std::string> &out) :
+		r(out),
+		_now(Utils::now())
+	{
+	}
+
+	inline void operator()(Topology &t,const SharedPtr<Peer> &p)
+	{
+		InetAddress v4(p->ipv4ActivePath(_now));
+		InetAddress v6(p->ipv6ActivePath(_now));
+		_P("200 listpeers %s %s %s %u",
+			p->address().toString().c_str(),
+			((v4) ? v4.toString().c_str() : "(none)"),
+			((v6) ? v6.toString().c_str() : "(none)"),
+			(((v4)||(v6)) ? p->latency() : 0));
+	}
 
-	TRACE("refreshing autoconfigure URL %s (if modified since: '%s')",_url.c_str(),_lastAutoconfigureLastModified.c_str());
+private:
+	std::vector<std::string> &r;
+	uint64_t _now;
+};
 
-	std::map<std::string,std::string> reqHeaders;
-	reqHeaders["X-ZT-ID"] = _r->identity.toString(false);
-	reqHeaders["X-ZT-OVSH"] = _r->ownershipVerificationSecretHash;
-	if (_lastAutoconfigureLastModified.length())
-		reqHeaders["If-Modified-Since"] = _lastAutoconfigureLastModified;
+std::vector<std::string> NodeConfig::execute(const char *command)
+{
+	std::vector<std::string> r;
+	std::vector<std::string> cmd(Utils::split(command,"\r\n \t","\\","'"));
+
+	//
+	// Not coincidentally, response type codes correspond with HTTP
+	// status codes.
+	//
+
+	if ((cmd.empty())||(cmd[0] == "help")) {
+		_P("200 help help");
+		_P("200 help listpeers");
+		_P("200 help listnetworks");
+		_P("200 help join <network ID> [<network invitation code>]");
+		_P("200 help leave <network ID>");
+	} else if (cmd[0] == "listpeers") {
+		_r->topology->eachPeer(_DumpPeerStatistics(r));
+	} else if (cmd[0] == "listnetworks") {
+		Mutex::Lock _l(_networks_m);
+		for(std::map< uint64_t,SharedPtr<Network> >::const_iterator nw(_networks.begin());nw!=_networks.end();++nw) {
+			_P("200 listnetworks %llu %s %s",
+				nw->first,
+				nw->second->tap().deviceName().c_str(),
+				(nw->second->open() ? "public" : "private"));
+		}
+	} else if (cmd[0] == "join") {
+		_P("404 join Not implemented yet.");
+	} else if (cmd[0] == "leave") {
+		_P("404 leave Not implemented yet.");
+	} else {
+		_P("404 %s No such command. Use 'help' for help.",cmd[0].c_str());
+	}
 
-	new Http::Request(Http::HTTP_METHOD_GET,_url,reqHeaders,std::string(),&NodeConfig::_CBautoconfHandler,this);
+	return r;
 }
 
-void NodeConfig::__CBautoconfHandler(const std::string &lastModified,const std::string &body)
+void NodeConfig::_CBcontrolPacketHandler(UdpSocket *sock,void *arg,const InetAddress &remoteAddr,const void *data,unsigned int len)
 {
-	try {
-		Json::Value root;
-		Json::Reader reader;
+	char hmacKey[32];
+	char hmac[32];
+	char buf[131072];
+	NodeConfig *nc = (NodeConfig *)arg;
+	const RuntimeEnvironment *_r = nc->_r;
 
-		std::string dec(_r->identity.decrypt(_r->configAuthority,body.data(),body.length()));
-		if (!dec.length()) {
-			LOG("autoconfigure from %s failed: data did not decrypt as from config authority %s",_url.c_str(),_r->configAuthority.address().toString().c_str());
+	try {
+		// Minimum length
+		if (len < 24)
 			return;
-		}
-		TRACE("decrypted autoconf: %s",dec.c_str());
-
-		if (!reader.parse(dec,root,false)) {
-			LOG("autoconfigure from %s failed: JSON parse error: %s",_url.c_str(),reader.getFormattedErrorMessages().c_str());
+		if (len >= sizeof(buf)) // only up to len - 24 bytes are used on receive/decrypt
 			return;
-		}
 
-		if (!root.isObject()) {
-			LOG("autoconfigure from %s failed: not a JSON object",_url.c_str());
+		// Compare first 16 bytes of HMAC, which is after IV in packet
+		memcpy(hmacKey,nc->_keys + 32,32);
+		*((uint64_t *)hmacKey) ^= *((const uint64_t *)data); // include IV in HMAC
+		HMAC::sha256(hmacKey,32,((const unsigned char *)data) + 24,len - 24,hmac);
+		if (memcmp(hmac,((const unsigned char *)data) + 8,16))
 			return;
-		}
 
-		// Configure networks
-		const Json::Value &networks = root["_networks"];
-		if (networks.isArray()) {
-			Mutex::Lock _l(_networks_m);
-			for(unsigned int ni=0;ni<networks.size();++ni) {
-				if (networks[ni].isObject()) {
-					const Json::Value &nwid_ = networks[ni]["id"];
-					uint64_t nwid = nwid_.isNumeric() ? (uint64_t)nwid_.asUInt64() : (uint64_t)strtoull(networks[ni]["id"].asString().c_str(),(char **)0,10);
-
-					if (nwid) {
-						SharedPtr<Network> nw;
-						std::map< uint64_t,SharedPtr<Network> >::iterator nwent(_networks.find(nwid));
-						if (nwent != _networks.end())
-							nw = nwent->second;
-						else {
-							try {
-								nw = SharedPtr<Network>(new Network(_r,nwid));
-								_networks[nwid] = nw;
-							} catch (std::exception &exc) {
-								LOG("unable to create network %llu: %s",nwid,exc.what());
-							} catch ( ... ) {
-								LOG("unable to create network %llu: unknown exception",nwid);
-							}
-						}
-
-						if (nw) {
-							Mutex::Lock _l2(nw->_lock);
-							nw->_open = networks[ni]["isOpen"].asBool();
-
-							// Ensure that TAP device has all the right IP addresses
-							// TODO: IPv6 might work a tad differently
-							std::set<InetAddress> allIps;
-							const Json::Value &addresses = networks[ni]["_addresses"];
-							if (addresses.isArray()) {
-								for(unsigned int ai=0;ai<addresses.size();++ai) {
-									if (addresses[ai].isString()) {
-										InetAddress addr(addresses[ai].asString());
-										if (addr) {
-											TRACE("network %llu IP/netmask: %s",nwid,addr.toString().c_str());
-											allIps.insert(addr);
-										}
-									}
-								}
-							}
-							nw->_tap.setIps(allIps);
-
-							// NOTE: the _members field is optional for open networks,
-							// since members of open nets do not need to check membership
-							// of packet senders and mutlicasters.
-							const Json::Value &members = networks[ni]["_members"];
-							nw->_members.clear();
-							if (members.isArray()) {
-								for(unsigned int mi=0;mi<members.size();++mi) {
-									std::string rawAddr(Utils::unhex(members[mi].asString()));
-									if (rawAddr.length() == ZT_ADDRESS_LENGTH) {
-										Address addr(rawAddr.data());
-										if ((addr)&&(!addr.isReserved())) {
-											//TRACE("network %llu member: %s",nwid,addr.toString().c_str());
-											nw->_members.insert(addr);
-										}
-									}
-								}
-							}
-						}
-					} else {
-						TRACE("ignored networks[%u], 'id' field missing");
-					}
-				} else {
-					TRACE("ignored networks[%u], not a JSON object",ni);
-				}
-			}
+		// Decrypt payload if we passed HMAC
+		Salsa20 s20(nc->_keys,256,data); // first 64 bits of data are IV
+		s20.decrypt(((const unsigned char *)data) + 24,buf,len - 24);
+
+		// Null-terminate string for execute()
+		buf[len - 24] = (char)0;
+
+		// Execute command
+		std::vector<std::string> r(nc->execute(buf));
+
+		// Result packet contains a series of null-terminated results
+		unsigned int resultLen = 24;
+		for(std::vector<std::string>::iterator i(r.begin());i!=r.end();++i) {
+			if ((resultLen + i->length() + 1) >= sizeof(buf))
+				return; // result too long
+			memcpy(buf + resultLen,i->c_str(),i->length() + 1);
+			resultLen += i->length() + 1;
 		}
 
-		_lastAutoconfigure = Utils::now();
-		_lastAutoconfigureLastModified = lastModified;
-	} catch (std::exception &exc) {
-		TRACE("exception parsing autoconf URL response: %s",exc.what());
-	} catch ( ... ) {
-		TRACE("unexpected exception parsing autoconf URL response");
-	}
-}
+		// Generate result packet IV
+		Utils::getSecureRandom(buf,8);
 
-bool NodeConfig::_CBautoconfHandler(Http::Request *req,void *arg,const std::string &url,int code,const std::map<std::string,std::string> &headers,const std::string &body)
-{
-#ifdef ZT_TRACE
-	const RuntimeEnvironment *_r = ((NodeConfig *)arg)->_r;
-#endif
-
-	if (code == 200) {
-		TRACE("200 got autoconfigure response from %s: %u bytes",url.c_str(),(unsigned int)body.length());
-
-		std::map<std::string,std::string>::const_iterator lm(headers.find("Last-Modified"));
-		if (lm != headers.end())
-			((NodeConfig *)arg)->__CBautoconfHandler(lm->second,body);
-		else ((NodeConfig *)arg)->__CBautoconfHandler(std::string(),body);
-	} else if (code == 304) {
-		TRACE("304 autoconfigure deferred, remote URL %s not modified",url.c_str());
-		((NodeConfig *)arg)->_lastAutoconfigure = Utils::now(); // still considered a success
-	} else if (code == 409) { // conflict, ID address in use by another ID
-		TRACE("%d autoconfigure failed from %s",code,url.c_str());
-	} else {
-		TRACE("%d autoconfigure failed from %s",code,url.c_str());
-	}
+		// Generate result packet HMAC
+		memcpy(hmacKey,nc->_keys + 32,32);
+		*((uint64_t *)hmacKey) ^= *((const uint64_t *)buf); // include IV in HMAC
+		HMAC::sha256(hmacKey,32,((const unsigned char *)buf) + 24,resultLen - 24,hmac);
+		memcpy(buf + 8,hmac,16);
 
-	((NodeConfig *)arg)->_autoconfigureLock.unlock();
-	return false; // causes Request to delete itself
+		// Send encrypted result back to requester
+		sock->send(remoteAddr,buf,resultLen,-1);
+	} catch ( ... ) {
+		TRACE("unexpected exception parsing control packet or generating response");
+	}
 }
 
 } // namespace ZeroTier
diff --git a/node/NodeConfig.hpp b/node/NodeConfig.hpp
index 5c412c9b..bb24d815 100644
--- a/node/NodeConfig.hpp
+++ b/node/NodeConfig.hpp
@@ -31,11 +31,14 @@
 #include <map>
 #include <set>
 #include <string>
+#include <vector>
+#include <stdexcept>
 #include <stdint.h>
 #include "SharedPtr.hpp"
 #include "Network.hpp"
 #include "Utils.hpp"
 #include "Http.hpp"
+#include "UdpSocket.hpp"
 
 namespace ZeroTier {
 
@@ -49,9 +52,11 @@ class NodeConfig
 public:
 	/**
 	 * @param renv Runtime environment
-	 * @param url Autoconfiguration URL (http:// or file://)
+	 * @param authToken Configuration authentication token
+	 * @throws std::runtime_error Unable to bind to local control port
 	 */
-	NodeConfig(const RuntimeEnvironment *renv,const std::string &url);
+	NodeConfig(const RuntimeEnvironment *renv,const char *authToken)
+		throw(std::runtime_error);
 
 	~NodeConfig();
 
@@ -106,32 +111,22 @@ public:
 	}
 
 	/**
-	 * @return Time of last successful autoconfigure or refresh
+	 * Execute a command
+	 *
+	 * @param command Command and arguments separated by whitespace (must already be trimmed of CR+LF, etc.)
+	 * @return One or more command results (lines of output)
 	 */
-	inline uint64_t lastAutoconfigure() const { return _lastAutoconfigure; }
-
-	/**
-	 * @return Autoconfiguration URL
-	 */
-	inline const std::string &url() const { return _url; }
-
-	/**
-	 * Refresh configuration from autoconf URL
-	 */
-	void refreshConfiguration();
+	std::vector<std::string> execute(const char *command);
 
 private:
-	void __CBautoconfHandler(const std::string &lastModified,const std::string &body);
-	static bool _CBautoconfHandler(Http::Request *req,void *arg,const std::string &url,int code,const std::map<std::string,std::string> &headers,const std::string &body);
+	static void _CBcontrolPacketHandler(UdpSocket *sock,void *arg,const InetAddress &remoteAddr,const void *data,unsigned int len);
 
 	const RuntimeEnvironment *_r;
 
-	volatile uint64_t _lastAutoconfigure;
-
-	std::string _lastAutoconfigureLastModified;
-	std::string _url;
-	Mutex _autoconfigureLock;
+	const std::string _authToken;
+	unsigned char _keys[64]; // Salsa20 key, HMAC key
 
+	UdpSocket _controlSocket;
 	std::map< uint64_t,SharedPtr<Network> > _networks;
 	Mutex _networks_m;
 };
diff --git a/node/Topology.hpp b/node/Topology.hpp
index ae1a15b4..2a977aa8 100644
--- a/node/Topology.hpp
+++ b/node/Topology.hpp
@@ -271,35 +271,6 @@ public:
 		std::vector< SharedPtr<Peer> > &_v;
 	};
 
-	/**
-	 * Dump peer I/O statistics to an open FILE (for status reporting and debug)
-	 */
-	class DumpPeerStatistics
-	{
-	public:
-		DumpPeerStatistics(FILE *out) :
-			_out(out),
-			_now(Utils::now())
-		{
-			fprintf(_out,"Peer       Direct IPv4           Direct IPv6                                         Latency(ms)"ZT_EOL_S);
-		}
-
-		inline void operator()(Topology &t,const SharedPtr<Peer> &p)
-		{
-			InetAddress v4(p->ipv4ActivePath(_now));
-			InetAddress v6(p->ipv6ActivePath(_now));
-			fprintf(_out,"%-10s %-21s %-51s %u"ZT_EOL_S,
-				p->address().toString().c_str(),
-				((v4) ? v4.toString().c_str() : "(none)"),
-				((v6) ? v6.toString().c_str() : "(none)"),
-				p->latency());
-		}
-
-	private:
-		FILE *_out;
-		uint64_t _now;
-	};
-
 protected:
 	virtual void main()
 		throw();
diff --git a/node/UdpSocket.cpp b/node/UdpSocket.cpp
index 95156fcc..8b48b3b0 100644
--- a/node/UdpSocket.cpp
+++ b/node/UdpSocket.cpp
@@ -49,6 +49,7 @@
 namespace ZeroTier {
 
 UdpSocket::UdpSocket(
+	bool localOnly,
 	int localPort,
 	bool ipv6,
 	void (*packetHandler)(UdpSocket *,void *,const InetAddress &,const void *,unsigned int),
@@ -87,7 +88,9 @@ UdpSocket::UdpSocket(
 		memset(&sin6,0,sizeof(sin6));
 		sin6.sin6_family = AF_INET6;
 		sin6.sin6_port = htons(localPort);
-		memcpy(&(sin6.sin6_addr),&in6addr_any,sizeof(struct in6_addr));
+		if (localOnly)
+			memcpy(&(sin6.sin6_addr.s6_addr),InetAddress::LO6.rawIpBytes(),16);
+		else memcpy(&(sin6.sin6_addr),&in6addr_any,sizeof(struct in6_addr));
 		if (::bind(_sock,(const struct sockaddr *)&sin6,sizeof(sin6))) {
 			::close(_sock);
 			throw std::runtime_error("unable to bind to port");
@@ -109,7 +112,9 @@ UdpSocket::UdpSocket(
 		memset(&sin,0,sizeof(sin));
 		sin.sin_family = AF_INET;
 		sin.sin_port = htons(localPort);
-		sin.sin_addr.s_addr = INADDR_ANY;
+		if (localOnly)
+			memcpy(&(sin.sin_addr.s_addr),InetAddress::LO4.rawIpBytes(),4);
+		else sin.sin_addr.s_addr = INADDR_ANY;
 		if (::bind(_sock,(const struct sockaddr *)&sin,sizeof(sin))) {
 			::close(_sock);
 			throw std::runtime_error("unable to bind to port");
diff --git a/node/UdpSocket.hpp b/node/UdpSocket.hpp
index be407d56..a3223f1f 100644
--- a/node/UdpSocket.hpp
+++ b/node/UdpSocket.hpp
@@ -46,6 +46,7 @@ public:
 	/**
 	 * Create and bind a local UDP socket
 	 *
+	 * @param localOnly If true, bind to loopback address only
 	 * @param localPort Local port to listen to
 	 * @param ipv6 If true, bind this as an IPv6 socket, otherwise IPv4
 	 * @param packetHandler Function to call when packets are read
@@ -53,6 +54,7 @@ public:
 	 * @throws std::runtime_error Unable to bind
 	 */
 	UdpSocket(
+		bool localOnly,
 		int localPort,
 		bool ipv6,
 		void (*packetHandler)(UdpSocket *,void *,const InetAddress &,const void *,unsigned int),
diff --git a/node/Utils.cpp b/node/Utils.cpp
index b9db07b9..7b2a17af 100644
--- a/node/Utils.cpp
+++ b/node/Utils.cpp
@@ -28,6 +28,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
+#include <stdarg.h>
 #include "Utils.hpp"
 #include "Mutex.hpp"
 
@@ -530,4 +531,20 @@ std::string Utils::trim(const std::string &s)
 	return s.substr(start,end - start);
 }
 
+void Utils::stdsprintf(std::string &s,const char *fmt,...)
+	throw(std::bad_alloc,std::length_error)
+{
+	char buf[65536];
+	va_list ap;
+
+	va_start(ap,fmt);
+	int n = vsnprintf(buf,sizeof(buf),fmt,ap);
+	va_end(ap);
+
+	if ((n >= (int)sizeof(buf))||(n < 0))
+		throw std::length_error("printf result too large");
+
+	s.append(buf);
+}
+
 } // namespace ZeroTier
diff --git a/node/Utils.hpp b/node/Utils.hpp
index e6bef5e5..b1917b27 100644
--- a/node/Utils.hpp
+++ b/node/Utils.hpp
@@ -34,6 +34,7 @@
 #include <time.h>
 #include <sys/time.h>
 #include <arpa/inet.h>
+
 #include <string>
 #include <stdexcept>
 #include <vector>
@@ -392,6 +393,18 @@ public:
 	static std::string trim(const std::string &s);
 
 	/**
+	 * Like sprintf, but appends to std::string
+	 *
+	 * @param s String to append to
+	 * @param fmt Printf format string
+	 * @param ... Format arguments
+	 * @throws std::bad_alloc Memory allocation failure
+	 * @throws std::length_error Format + args exceeds internal buffer maximum
+	 */
+	static void stdsprintf(std::string &s,const char *fmt,...)
+		throw(std::bad_alloc,std::length_error);
+
+	/**
 	 * Count the number of bits set in an integer
 	 *
 	 * @param v 32-bit integer