1 // This file is public domain, in case it's useful to anyone. -comex
2
3 // The central server implementation.
4 #include <arpa/inet.h>
5 #include <cerrno>
6 #include <chrono>
7 #include <cstdio>
8 #include <cstdlib>
9 #include <cstring>
10 #include <fcntl.h>
11 #include <netinet/in.h>
12 #include <sys/socket.h>
13 #include <sys/types.h>
14 #include <unistd.h>
15 #include <unordered_map>
16 #include <utility>
17 #include <vector>
18
19 #ifdef HAVE_LIBSYSTEMD
20 #include <systemd/sd-daemon.h>
21 #endif
22
23 #include "Common/Random.h"
24 #include "Common/TraversalProto.h"
25
26 #define DEBUG 0
27 #define NUMBER_OF_TRIES 5
28 #define PORT 6262
29
30 static u64 currentTime;
31
32 struct OutgoingPacketInfo
33 {
34 TraversalPacket packet;
35 TraversalRequestId misc;
36 sockaddr_in6 dest;
37 int tries;
38 u64 sendTime;
39 };
40
41 template <typename T>
42 struct EvictEntry
43 {
44 u64 updateTime;
45 T value;
46 };
47
48 template <typename V>
49 struct EvictFindResult
50 {
51 bool found;
52 V* value;
53 };
54
55 template <typename K, typename V>
EvictFind(std::unordered_map<K,EvictEntry<V>> & map,const K & key,bool refresh=false)56 EvictFindResult<V> EvictFind(std::unordered_map<K, EvictEntry<V>>& map, const K& key,
57 bool refresh = false)
58 {
59 retry:
60 const u64 expiryTime = 30 * 1000000; // 30s
61 EvictFindResult<V> result;
62 if (map.bucket_count())
63 {
64 auto bucket = map.bucket(key);
65 auto it = map.begin(bucket);
66 for (; it != map.end(bucket); ++it)
67 {
68 if (currentTime - it->second.updateTime > expiryTime)
69 {
70 map.erase(it->first);
71 goto retry;
72 }
73 if (it->first == key)
74 {
75 if (refresh)
76 it->second.updateTime = currentTime;
77 result.found = true;
78 result.value = &it->second.value;
79 return result;
80 }
81 }
82 }
83 #if DEBUG
84 printf("failed to find key '");
85 for (size_t i = 0; i < sizeof(key); i++)
86 {
87 printf("%02x", ((u8*)&key)[i]);
88 }
89 printf("'\n");
90 #endif
91 result.found = false;
92 return result;
93 }
94
95 template <typename K, typename V>
EvictSet(std::unordered_map<K,EvictEntry<V>> & map,const K & key)96 V* EvictSet(std::unordered_map<K, EvictEntry<V>>& map, const K& key)
97 {
98 // can't use a local_iterator to emplace...
99 auto& result = map[key];
100 result.updateTime = currentTime;
101 return &result.value;
102 }
103
104 namespace std
105 {
106 template <>
107 struct hash<TraversalHostId>
108 {
operator ()std::hash109 size_t operator()(const TraversalHostId& id) const
110 {
111 auto p = (u32*)id.data();
112 return p[0] ^ ((p[1] << 13) | (p[1] >> 19));
113 }
114 };
115 } // namespace std
116
117 static int sock;
118 static std::unordered_map<TraversalRequestId, OutgoingPacketInfo> outgoingPackets;
119 static std::unordered_map<TraversalHostId, EvictEntry<TraversalInetAddress>> connectedClients;
120
MakeInetAddress(const sockaddr_in6 & addr)121 static TraversalInetAddress MakeInetAddress(const sockaddr_in6& addr)
122 {
123 if (addr.sin6_family != AF_INET6)
124 {
125 fprintf(stderr, "bad sockaddr_in6\n");
126 exit(1);
127 }
128 u32* words = (u32*)addr.sin6_addr.s6_addr;
129 TraversalInetAddress result = {0};
130 if (words[0] == 0 && words[1] == 0 && words[2] == 0xffff0000)
131 {
132 result.isIPV6 = false;
133 result.address[0] = words[3];
134 }
135 else
136 {
137 result.isIPV6 = true;
138 memcpy(result.address, words, sizeof(result.address));
139 }
140 result.port = addr.sin6_port;
141 return result;
142 }
143
MakeSinAddr(const TraversalInetAddress & addr)144 static sockaddr_in6 MakeSinAddr(const TraversalInetAddress& addr)
145 {
146 sockaddr_in6 result;
147 #ifdef SIN6_LEN
148 result.sin6_len = sizeof(result);
149 #endif
150 result.sin6_family = AF_INET6;
151 result.sin6_port = addr.port;
152 result.sin6_flowinfo = 0;
153 if (addr.isIPV6)
154 {
155 memcpy(&result.sin6_addr, addr.address, 16);
156 }
157 else
158 {
159 u32* words = (u32*)result.sin6_addr.s6_addr;
160 words[0] = 0;
161 words[1] = 0;
162 words[2] = 0xffff0000;
163 words[3] = addr.address[0];
164 }
165 result.sin6_scope_id = 0;
166 return result;
167 }
168
GetRandomHostId(TraversalHostId * hostId)169 static void GetRandomHostId(TraversalHostId* hostId)
170 {
171 char buf[9];
172 const u32 num = Common::Random::GenerateValue<u32>();
173 sprintf(buf, "%08x", num);
174 memcpy(hostId->data(), buf, 8);
175 }
176
SenderName(sockaddr_in6 * addr)177 static const char* SenderName(sockaddr_in6* addr)
178 {
179 static char buf[INET6_ADDRSTRLEN + 10];
180 inet_ntop(PF_INET6, &addr->sin6_addr, buf, sizeof(buf));
181 sprintf(buf + strlen(buf), ":%d", ntohs(addr->sin6_port));
182 return buf;
183 }
184
TrySend(const void * buffer,size_t size,sockaddr_in6 * addr)185 static void TrySend(const void* buffer, size_t size, sockaddr_in6* addr)
186 {
187 #if DEBUG
188 printf("-> %d %llu %s\n", ((TraversalPacket*)buffer)->type,
189 (long long)((TraversalPacket*)buffer)->requestId, SenderName(addr));
190 #endif
191 if ((size_t)sendto(sock, buffer, size, 0, (sockaddr*)addr, sizeof(*addr)) != size)
192 {
193 perror("sendto");
194 }
195 }
196
AllocPacket(const sockaddr_in6 & dest,TraversalRequestId misc=0)197 static TraversalPacket* AllocPacket(const sockaddr_in6& dest, TraversalRequestId misc = 0)
198 {
199 TraversalRequestId requestId;
200 Common::Random::Generate(&requestId, sizeof(requestId));
201 OutgoingPacketInfo* info = &outgoingPackets[requestId];
202 info->dest = dest;
203 info->misc = misc;
204 info->tries = 0;
205 info->sendTime = currentTime;
206 TraversalPacket* result = &info->packet;
207 memset(result, 0, sizeof(*result));
208 result->requestId = requestId;
209 return result;
210 }
211
SendPacket(OutgoingPacketInfo * info)212 static void SendPacket(OutgoingPacketInfo* info)
213 {
214 info->tries++;
215 info->sendTime = currentTime;
216 TrySend(&info->packet, sizeof(info->packet), &info->dest);
217 }
218
ResendPackets()219 static void ResendPackets()
220 {
221 std::vector<std::pair<TraversalInetAddress, TraversalRequestId>> todoFailures;
222 todoFailures.clear();
223 for (auto it = outgoingPackets.begin(); it != outgoingPackets.end();)
224 {
225 OutgoingPacketInfo* info = &it->second;
226 if (currentTime - info->sendTime >= (u64)(300000 * info->tries))
227 {
228 if (info->tries >= NUMBER_OF_TRIES)
229 {
230 if (info->packet.type == TraversalPacketPleaseSendPacket)
231 {
232 todoFailures.push_back(std::make_pair(info->packet.pleaseSendPacket.address, info->misc));
233 }
234 it = outgoingPackets.erase(it);
235 continue;
236 }
237 else
238 {
239 SendPacket(info);
240 }
241 }
242 ++it;
243 }
244
245 for (const auto& p : todoFailures)
246 {
247 TraversalPacket* fail = AllocPacket(MakeSinAddr(p.first));
248 fail->type = TraversalPacketConnectFailed;
249 fail->connectFailed.requestId = p.second;
250 fail->connectFailed.reason = TraversalConnectFailedClientDidntRespond;
251 }
252 }
253
HandlePacket(TraversalPacket * packet,sockaddr_in6 * addr)254 static void HandlePacket(TraversalPacket* packet, sockaddr_in6* addr)
255 {
256 #if DEBUG
257 printf("<- %d %llu %s\n", packet->type, (long long)packet->requestId, SenderName(addr));
258 #endif
259 bool packetOk = true;
260 switch (packet->type)
261 {
262 case TraversalPacketAck:
263 {
264 auto it = outgoingPackets.find(packet->requestId);
265 if (it == outgoingPackets.end())
266 break;
267
268 OutgoingPacketInfo* info = &it->second;
269
270 if (info->packet.type == TraversalPacketPleaseSendPacket)
271 {
272 TraversalPacket* ready = AllocPacket(MakeSinAddr(info->packet.pleaseSendPacket.address));
273 if (packet->ack.ok)
274 {
275 ready->type = TraversalPacketConnectReady;
276 ready->connectReady.requestId = info->misc;
277 ready->connectReady.address = MakeInetAddress(info->dest);
278 }
279 else
280 {
281 ready->type = TraversalPacketConnectFailed;
282 ready->connectFailed.requestId = info->misc;
283 ready->connectFailed.reason = TraversalConnectFailedClientFailure;
284 }
285 }
286
287 outgoingPackets.erase(it);
288 break;
289 }
290 case TraversalPacketPing:
291 {
292 auto r = EvictFind(connectedClients, packet->ping.hostId, true);
293 packetOk = r.found;
294 break;
295 }
296 case TraversalPacketHelloFromClient:
297 {
298 u8 ok = packet->helloFromClient.protoVersion <= TraversalProtoVersion;
299 TraversalPacket* reply = AllocPacket(*addr);
300 reply->type = TraversalPacketHelloFromServer;
301 reply->helloFromServer.ok = ok;
302 if (ok)
303 {
304 TraversalHostId hostId;
305 TraversalInetAddress* iaddr;
306 // not that there is any significant change of
307 // duplication, but...
308 GetRandomHostId(&hostId);
309 while (true)
310 {
311 auto r = EvictFind(connectedClients, hostId);
312 if (!r.found)
313 {
314 iaddr = EvictSet(connectedClients, hostId);
315 break;
316 }
317 }
318
319 *iaddr = MakeInetAddress(*addr);
320
321 reply->helloFromServer.yourAddress = *iaddr;
322 reply->helloFromServer.yourHostId = hostId;
323 }
324 break;
325 }
326 case TraversalPacketConnectPlease:
327 {
328 TraversalHostId& hostId = packet->connectPlease.hostId;
329 auto r = EvictFind(connectedClients, hostId);
330 if (!r.found)
331 {
332 TraversalPacket* reply = AllocPacket(*addr);
333 reply->type = TraversalPacketConnectFailed;
334 reply->connectFailed.requestId = packet->requestId;
335 reply->connectFailed.reason = TraversalConnectFailedNoSuchClient;
336 }
337 else
338 {
339 TraversalPacket* please = AllocPacket(MakeSinAddr(*r.value), packet->requestId);
340 please->type = TraversalPacketPleaseSendPacket;
341 please->pleaseSendPacket.address = MakeInetAddress(*addr);
342 }
343 break;
344 }
345 default:
346 fprintf(stderr, "received unknown packet type %d from %s\n", packet->type, SenderName(addr));
347 }
348 if (packet->type != TraversalPacketAck)
349 {
350 TraversalPacket ack = {};
351 ack.type = TraversalPacketAck;
352 ack.requestId = packet->requestId;
353 ack.ack.ok = packetOk;
354 TrySend(&ack, sizeof(ack), addr);
355 }
356 }
357
main()358 int main()
359 {
360 int rv;
361 sock = socket(PF_INET6, SOCK_DGRAM, 0);
362 if (sock == -1)
363 {
364 perror("socket");
365 return 1;
366 }
367 int no = 0;
368 rv = setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, &no, sizeof(no));
369 if (rv < 0)
370 {
371 perror("setsockopt IPV6_V6ONLY");
372 return 1;
373 }
374 in6_addr any = IN6ADDR_ANY_INIT;
375 sockaddr_in6 addr;
376 #ifdef SIN6_LEN
377 addr.sin6_len = sizeof(addr);
378 #endif
379 addr.sin6_family = AF_INET6;
380 addr.sin6_port = htons(PORT);
381 addr.sin6_flowinfo = 0;
382 addr.sin6_addr = any;
383 addr.sin6_scope_id = 0;
384
385 rv = bind(sock, (sockaddr*)&addr, sizeof(addr));
386 if (rv < 0)
387 {
388 perror("bind");
389 return 1;
390 }
391
392 timeval tv;
393 tv.tv_sec = 0;
394 tv.tv_usec = 300000;
395 rv = setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
396 if (rv < 0)
397 {
398 perror("setsockopt SO_RCVTIMEO");
399 return 1;
400 }
401
402 #ifdef HAVE_LIBSYSTEMD
403 sd_notifyf(0, "READY=1\nSTATUS=Listening on port %d", PORT);
404 #endif
405
406 while (true)
407 {
408 sockaddr_in6 raddr;
409 socklen_t addrLen = sizeof(raddr);
410 TraversalPacket packet;
411 // note: switch to recvmmsg (yes, mmsg) if this becomes
412 // expensive
413 rv = recvfrom(sock, &packet, sizeof(packet), 0, (sockaddr*)&raddr, &addrLen);
414 currentTime = std::chrono::duration_cast<std::chrono::microseconds>(
415 std::chrono::system_clock::now().time_since_epoch())
416 .count();
417 if (rv < 0)
418 {
419 if (errno != EINTR && errno != EAGAIN)
420 {
421 perror("recvfrom");
422 return 1;
423 }
424 }
425 else if ((size_t)rv < sizeof(packet))
426 {
427 fprintf(stderr, "received short packet from %s\n", SenderName(&raddr));
428 }
429 else
430 {
431 HandlePacket(&packet, &raddr);
432 }
433 ResendPackets();
434 #ifdef HAVE_LIBSYSTEMD
435 sd_notify(0, "WATCHDOG=1");
436 #endif
437 }
438 }
439