core/s2smanager.lua

   1 -- Prosody IM
   2 -- Copyright (C) 2008-2010 Matthew Wild
   3 -- Copyright (C) 2008-2010 Waqas Hussain
   4 --
   5 -- This project is MIT/X11 licensed. Please see the
   6 -- COPYING file in the source package for more information.
   7 --
   8
   9
  10
  11 local hosts = hosts;
  12 local sessions = sessions;
  13 local core_process_stanza = function(a, b) core_process_stanza(a, b); end
  14 local add_task = require "util.timer".add_task;
  15 local socket = require "socket";
  16 local format = string.format;
  17 local t_insert, t_sort = table.insert, table.sort;
  18 local get_traceback = debug.traceback;
  19 local tostring, pairs, ipairs, getmetatable, newproxy, error, tonumber, setmetatable
  20     = tostring, pairs, ipairs, getmetatable, newproxy, error, tonumber, setmetatable;
  21
  22 local idna_to_ascii = require "util.encodings".idna.to_ascii;
  23 local connlisteners_get = require "net.connlisteners".get;
  24 local initialize_filters = require "util.filters".initialize;
  25 local wrapclient = require "net.server".wrapclient;
  26 local modulemanager = require "core.modulemanager";
  27 local st = require "stanza";
  28 local stanza = st.stanza;
  29 local nameprep = require "util.encodings".stringprep.nameprep;
  30 local cert_verify_identity = require "util.x509".verify_identity;
  31
  32 local fire_event = prosody.events.fire_event;
  33 local uuid_gen = require "util.uuid".generate;
  34
  35 local logger_init = require "util.logger".init;
  36
  37 local log = logger_init("s2smanager");
  38
  39 local sha256_hash = require "util.hashes".sha256;
  40
  41 local adns, dns = require "net.adns", require "net.dns";
  42 local config = require "core.configmanager";
  43 local connect_timeout = config.get("*", "core", "s2s_timeout") or 60;
  44 local dns_timeout = config.get("*", "core", "dns_timeout") or 15;
  45 local max_dns_depth = config.get("*", "core", "dns_max_depth") or 3;
  46
  47 dns.settimeout(dns_timeout);
  48
  49 local prosody = _G.prosody;
  50 incoming_s2s = {};
  51 prosody.incoming_s2s = incoming_s2s;
  52 local incoming_s2s = incoming_s2s;
  53
  54 module "s2smanager"
  55
  56 function compare_srv_priorities(a,b)
  57         return a.priority < b.priority or (a.priority == b.priority and a.weight > b.weight);
  58 end
  59
  60 local bouncy_stanzas = { message = true, presence = true, iq = true };
  61 local function bounce_sendq(session, reason)
  62         local sendq = session.sendq;
  63         if sendq then
  64                 session.log("info", "sending error replies for "..#sendq.." queued stanzas because of failed outgoing connection to "..tostring(session.to_host));
  65                 local dummy = {
  66                         type = "s2sin";
  67                         send = function(s)
  68                                 (session.log or log)("error", "Replying to to an s2s error reply, please report this! Traceback: %s", get_traceback());
  69                         end;
  70                         dummy = true;
  71                 };
  72                 for i, data in ipairs(sendq) do
  73                         local reply = data[2];
  74                         if reply and not(reply.attr.xmlns) and bouncy_stanzas[reply.name] then
  75                                 reply.attr.type = "error";
  76                                 reply:tag("error", {type = "cancel"})
  77                                         :tag("remote-server-not-found", {xmlns = "urn:ietf:params:xml:ns:xmpp-stanzas"}):up();
  78                                 if reason then
  79                                         reply:tag("text", {xmlns = "urn:ietf:params:xml:ns:xmpp-stanzas"})
  80                                                 :text("Server-to-server connection failed: "..reason):up();
  81                                 end
  82                                 core_process_stanza(dummy, reply);
  83                         end
  84                         sendq[i] = nil;
  85                 end
  86                 session.sendq = nil;
  87         end
  88 end
  89
  90 function send_to_host(from_host, to_host, data)
  91         if not hosts[from_host] then
  92                 log("warn", "Attempt to send stanza from %s - a host we don't serve", from_host);
  93                 return false;
  94         end
  95         local host = hosts[from_host].s2sout[to_host];
  96         if host then
  97                 -- We have a connection to this host already
  98                 if host.type == "s2sout_unauthed" and (data.name ~= "db:verify" or not host.dialback_key) then
  99                         (host.log or log)("debug", "trying to send over unauthed s2sout to "..to_host);
 100
 101                         -- Queue stanza until we are able to send it
 102                         if host.sendq then t_insert(host.sendq, {tostring(data), data.attr.type ~= "error" and data.attr.type ~= "result" and st.reply(data)});
 103                         else host.sendq = { {tostring(data), data.attr.type ~= "error" and data.attr.type ~= "result" and st.reply(data)} }; end
 104                         host.log("debug", "stanza [%s] queued ", data.name);
 105                 elseif host.type == "local" or host.type == "component" then
 106                         log("error", "Trying to send a stanza to ourselves??")
 107                         log("error", "Traceback: %s", get_traceback());
 108                         log("error", "Stanza: %s", tostring(data));
 109                         return false;
 110                 else
 111                         (host.log or log)("debug", "going to send stanza to "..to_host.." from "..from_host);
 112                         -- FIXME
 113                         if host.from_host ~= from_host then
 114                                 log("error", "WARNING! This might, possibly, be a bug, but it might not...");
 115                                 log("error", "We are going to send from %s instead of %s", tostring(host.from_host), tostring(from_host));
 116                         end
 117                         host.sends2s(data);
 118                         host.log("debug", "stanza sent over "..host.type);
 119                 end
 120         else
 121                 log("debug", "opening a new outgoing connection for this stanza");
 122                 local host_session = new_outgoing(from_host, to_host);
 123
 124                 -- Store in buffer
 125                 host_session.sendq = { {tostring(data), data.attr.type ~= "error" and data.attr.type ~= "result" and st.reply(data)} };
 126                 log("debug", "stanza [%s] queued until connection complete", tostring(data.name));
 127                 if (not host_session.connecting) and (not host_session.conn) then
 128                         log("warn", "Connection to %s failed already, destroying session...", to_host);
 129                         if not destroy_session(host_session, "Connection failed") then
 130                                 -- Already destroyed, we need to bounce our stanza
 131                                 bounce_sendq(host_session, host_session.destruction_reason);
 132                         end
 133                         return false;
 134                 end
 135         end
 136         return true;
 137 end
 138
 139 local open_sessions = 0;
 140
 141 function new_incoming(conn)
 142         local session = { conn = conn, type = "s2sin_unauthed", direction = "incoming", hosts = {} };
 143         if true then
 144                 session.trace = newproxy(true);
 145                 getmetatable(session.trace).__gc = function () open_sessions = open_sessions - 1; end;
 146         end
 147         open_sessions = open_sessions + 1;
 148         local w, log = conn.write, logger_init("s2sin"..tostring(conn):match("[a-f0-9]+$"));
 149         session.log = log;
 150         local filter = initialize_filters(session);
 151         session.sends2s = function (t)
 152                 log("debug", "sending: %s", t.top_tag and t:top_tag() or t:match("^([^>]*>?)"));
 153                 if t.name then
 154                         t = filter("stanzas/out", t);
 155                 end
 156                 if t then
 157                         t = filter("bytes/out", tostring(t));
 158                         if t then
 159                                 return w(conn, t);
 160                         end
 161                 end
 162         end
 163         incoming_s2s[session] = true;
 164         add_task(connect_timeout, function ()
 165                 if session.conn ~= conn or
 166                    session.type == "s2sin" then
 167                         return; -- Ok, we're connect[ed|ing]
 168                 end
 169                 -- Not connected, need to close session and clean up
 170                 (session.log or log)("debug", "Destroying incomplete session %s->%s due to inactivity",
 171                     session.from_host or "(unknown)", session.to_host or "(unknown)");
 172                 session:close("connection-timeout");
 173         end);
 174         return session;
 175 end
 176
 177 function new_outgoing(from_host, to_host, connect)
 178                 local host_session = { to_host = to_host, from_host = from_host, host = from_host,
 179                                        notopen = true, type = "s2sout_unauthed", direction = "outgoing",
 180                                        open_stream = session_open_stream };
 181
 182                 hosts[from_host].s2sout[to_host] = host_session;
 183
 184                 host_session.close = destroy_session; -- This gets replaced by xmppserver_listener later
 185
 186                 local log;
 187                 do
 188                         local conn_name = "s2sout"..tostring(host_session):match("[a-f0-9]*$");
 189                         log = logger_init(conn_name);
 190                         host_session.log = log;
 191                 end
 192
 193                 initialize_filters(host_session);
 194
 195                 if connect ~= false then
 196                         -- Kick the connection attempting machine into life
 197                         if not attempt_connection(host_session) then
 198                                 -- Intentionally not returning here, the
 199                                 -- session is needed, connected or not
 200                                 destroy_session(host_session);
 201                         end
 202                 end
 203
 204                 if not host_session.sends2s then
 205                         -- A sends2s which buffers data (until the stream is opened)
 206                         -- note that data in this buffer will be sent before the stream is authed
 207                         -- and will not be ack'd in any way, successful or otherwise
 208                         local buffer;
 209                         function host_session.sends2s(data)
 210                                 if not buffer then
 211                                         buffer = {};
 212                                         host_session.send_buffer = buffer;
 213                                 end
 214                                 log("debug", "Buffering data on unconnected s2sout to %s", to_host);
 215                                 buffer[#buffer+1] = data;
 216                                 log("debug", "Buffered item %d: %s", #buffer, tostring(data));
 217                         end
 218                 end
 219
 220                 return host_session;
 221 end
 222
 223
 224 function attempt_connection(host_session, err)
 225         local from_host, to_host = host_session.from_host, host_session.to_host;
 226         local connect_host, connect_port = to_host and idna_to_ascii(to_host), 5269;
 227
 228         if not connect_host then
 229                 return false;
 230         end
 231
 232         if not err then -- This is our first attempt
 233                 log("debug", "First attempt to connect to %s, starting with SRV lookup...", to_host);
 234                 host_session.connecting = true;
 235                 local handle;
 236                 handle = adns.lookup(function (answer)
 237                         handle = nil;
 238                         host_session.connecting = nil;
 239                         if answer then
 240                                 log("debug", to_host.." has SRV records, handling...");
 241                                 local srv_hosts = {};
 242                                 host_session.srv_hosts = srv_hosts;
 243                                 for _, record in ipairs(answer) do
 244                                         t_insert(srv_hosts, record.srv);
 245                                 end
 246                                 t_sort(srv_hosts, compare_srv_priorities);
 247
 248                                 local srv_choice = srv_hosts[1];
 249                                 host_session.srv_choice = 1;
 250                                 if srv_choice then
 251                                         connect_host, connect_port = srv_choice.target or to_host, srv_choice.port or connect_port;
 252                                         log("debug", "Best record found, will connect to %s:%d", connect_host, connect_port);
 253                                 end
 254                         else
 255                                 log("debug", to_host.." has no SRV records, falling back to A");
 256                         end
 257                         -- Try with SRV, or just the plain hostname if no SRV
 258                         local ok, err = try_connect(host_session, connect_host, connect_port);
 259                         if not ok then
 260                                 if not attempt_connection(host_session, err) then
 261                                         -- No more attempts will be made
 262                                         destroy_session(host_session, err);
 263                                 end
 264                         end
 265                 end, "_xmpp-server._tcp."..connect_host..".", "SRV");
 266
 267                 return true; -- Attempt in progress
 268         elseif host_session.srv_hosts and #host_session.srv_hosts > host_session.srv_choice then -- Not our first attempt, and we also have SRV
 269                 host_session.srv_choice = host_session.srv_choice + 1;
 270                 local srv_choice = host_session.srv_hosts[host_session.srv_choice];
 271                 connect_host, connect_port = srv_choice.target or to_host, srv_choice.port or connect_port;
 272                 host_session.log("info", "Connection failed (%s). Attempt #%d: This time to %s:%d", tostring(err), host_session.srv_choice, connect_host, connect_port);
 273         else
 274                 host_session.log("info", "Out of connection options, can't connect to %s", tostring(host_session.to_host));
 275                 -- We're out of options
 276                 return false;
 277         end
 278
 279         if not (connect_host and connect_port) then
 280                 -- Likely we couldn't resolve DNS
 281                 log("warn", "Hmm, we're without a host (%s) and port (%s) to connect to for %s, giving up :(", tostring(connect_host), tostring(connect_port), tostring(to_host));
 282                 return false;
 283         end
 284
 285         return try_connect(host_session, connect_host, connect_port);
 286 end
 287
 288 function try_connect(host_session, connect_host, connect_port)
 289         host_session.connecting = true;
 290         local handle;
 291         handle = adns.lookup(function (reply, err)
 292                 handle = nil;
 293                 host_session.connecting = nil;
 294
 295                 -- COMPAT: This is a compromise for all you CNAME-(ab)users :)
 296                 if not (reply and reply[#reply] and reply[#reply].a) then
 297                         local count = max_dns_depth;
 298                         reply = dns.peek(connect_host, "CNAME", "IN");
 299                         while count > 0 and reply and reply[#reply] and not reply[#reply].a and reply[#reply].cname do
 300                                 log("debug", "Looking up %s (DNS depth is %d)", tostring(reply[#reply].cname), count);
 301                                 reply = dns.peek(reply[#reply].cname, "A", "IN") or dns.peek(reply[#reply].cname, "CNAME", "IN");
 302                                 count = count - 1;
 303                         end
 304                 end
 305                 -- end of CNAME resolving
 306
 307                 if reply and reply[#reply] and reply[#reply].a then
 308                         log("debug", "DNS reply for %s gives us %s", connect_host, reply[#reply].a);
 309                         local ok, err = make_connect(host_session, reply[#reply].a, connect_port);
 310                         if not ok then
 311                                 if not attempt_connection(host_session, err or "closed") then
 312                                         err = err and (": "..err) or "";
 313                                         destroy_session(host_session, "Connection failed"..err);
 314                                 end
 315                         end
 316                 else
 317                         log("debug", "DNS lookup failed to get a response for %s", connect_host);
 318                         if not attempt_connection(host_session, "name resolution failed") then -- Retry if we can
 319                                 log("debug", "No other records to try for %s - destroying", host_session.to_host);
 320                                 err = err and (": "..err) or "";
 321                                 destroy_session(host_session, "DNS resolution failed"..err); -- End of the line, we can't
 322                         end
 323                 end
 324         end, connect_host, "A", "IN");
 325
 326         return true;
 327 end
 328
 329 function make_connect(host_session, connect_host, connect_port)
 330         (host_session.log or log)("info", "Beginning new connection attempt to %s (%s:%d)", host_session.to_host, connect_host, connect_port);
 331         -- Ok, we're going to try to connect
 332
 333         local from_host, to_host = host_session.from_host, host_session.to_host;
 334
 335         local conn, handler = socket.tcp();
 336
 337         if not conn then
 338                 log("warn", "Failed to create outgoing connection, system error: %s", handler);
 339                 return false, handler;
 340         end
 341
 342         conn:settimeout(0);
 343         local success, err = conn:connect(connect_host, connect_port);
 344         if not success and err ~= "timeout" then
 345                 log("warn", "s2s connect() to %s (%s:%d) failed: %s", host_session.to_host, connect_host, connect_port, err);
 346                 return false, err;
 347         end
 348
 349         local cl = connlisteners_get("xmppserver");
 350         conn = wrapclient(conn, connect_host, connect_port, cl, cl.default_mode or 1 );
 351         host_session.conn = conn;
 352
 353         local filter = initialize_filters(host_session);
 354         local w, log = conn.write, host_session.log;
 355         host_session.sends2s = function (t)
 356                 log("debug", "sending: %s", (t.top_tag and t:top_tag()) or t:match("^[^>]*>?"));
 357                 if t.name then
 358                         t = filter("stanzas/out", t);
 359                 end
 360                 if t then
 361                         t = filter("bytes/out", tostring(t));
 362                         if t then
 363                                 return w(conn, tostring(t));
 364                         end
 365                 end
 366         end
 367
 368         -- Register this outgoing connection so that xmppserver_listener knows about it
 369         -- otherwise it will assume it is a new incoming connection
 370         cl.register_outgoing(conn, host_session);
 371
 372         host_session:open_stream(from_host, to_host);
 373
 374         log("debug", "Connection attempt in progress...");
 375         add_task(connect_timeout, function ()
 376                 if host_session.conn ~= conn or
 377                    host_session.type == "s2sout" or
 378                    host_session.connecting then
 379                         return; -- Ok, we're connect[ed|ing]
 380                 end
 381                 -- Not connected, need to close session and clean up
 382                 (host_session.log or log)("warn", "Destroying incomplete session %s->%s due to inactivity",
 383                     host_session.from_host or "(unknown)", host_session.to_host or "(unknown)");
 384                 host_session:close("connection-timeout");
 385         end);
 386         return true;
 387 end
 388
 389 function session_open_stream(session, from, to)
 390         session.sends2s(st.stanza("stream:stream", {
 391                 xmlns='jabber:server', ["xmlns:db"]='jabber:server:dialback',
 392                 ["xmlns:stream"]='http://etherx.jabber.org/streams',
 393                 from=from, to=to, version='1.0', ["xml:lang"]='en'}):top_tag());
 394 end
 395
 396 local function check_cert_status(session)
 397         local conn = session.conn:socket()
 398         local cert
 399         if conn.getpeercertificate then
 400                 cert = conn:getpeercertificate()
 401         end
 402
 403         if cert then
 404                 local chain_valid, err = conn:getpeerchainvalid()
 405                 if not chain_valid then
 406                         session.cert_chain_status = "invalid";
 407                         (session.log or log)("debug", "certificate chain validation result: %s", err);
 408                 else
 409                         session.cert_chain_status = "valid";
 410
 411                         local host = session.direction == "incoming" and session.from_host or session.to_host
 412
 413                         -- We'll go ahead and verify the asserted identity if the
 414                         -- connecting server specified one.
 415                         if host then
 416                                 if cert_verify_identity(host, "xmpp-server", cert) then
 417                                         session.cert_identity_status = "valid"
 418                                 else
 419                                         session.cert_identity_status = "invalid"
 420                                 end
 421                         end
 422                 end
 423         end
 424 end
 425
 426 function streamopened(session, attr)
 427         local send = session.sends2s;
 428
 429         -- TODO: #29: SASL/TLS on s2s streams
 430         session.version = tonumber(attr.version) or 0;
 431
 432         -- TODO: Rename session.secure to session.encrypted
 433         if session.secure == false then
 434                 session.secure = true;
 435         end
 436
 437         if session.direction == "incoming" then
 438                 -- Send a reply stream header
 439                 session.to_host = attr.to and nameprep(attr.to);
 440                 session.from_host = attr.from and nameprep(attr.from);
 441
 442                 session.streamid = uuid_gen();
 443                 (session.log or log)("debug", "incoming s2s received <stream:stream>");
 444                 if session.to_host then
 445                         if not hosts[session.to_host] then
 446                                 -- Attempting to connect to a host we don't serve
 447                                 session:close({
 448                                         condition = "host-unknown";
 449                                         text = "This host does not serve "..session.to_host
 450                                 });
 451                                 return;
 452                         elseif hosts[session.to_host].disallow_s2s then
 453                                 -- Attempting to connect to a host that disallows s2s
 454                                 session:close({
 455                                         condition = "policy-violation";
 456                                         text = "Server-to-server communication is not allowed to this host";
 457                                 });
 458                                 return;
 459                         end
 460                 end
 461
 462                 if session.secure and not session.cert_chain_status then check_cert_status(session); end
 463
 464                 send("<?xml version='1.0'?>");
 465                 send(stanza("stream:stream", { xmlns='jabber:server', ["xmlns:db"]='jabber:server:dialback',
 466                                 ["xmlns:stream"]='http://etherx.jabber.org/streams', id=session.streamid, from=session.to_host, to=session.from_host, version=(session.version > 0 and "1.0" or nil) }):top_tag());
 467                 if session.version >= 1.0 then
 468                         local features = st.stanza("stream:features");
 469
 470                         if session.to_host then
 471                                 hosts[session.to_host].events.fire_event("s2s-stream-features", { origin = session, features = features });
 472                         else
 473                                 (session.log or log)("warn", "No 'to' on stream header from %s means we can't offer any features", session.from_host or "unknown host");
 474                         end
 475
 476                         log("debug", "Sending stream features: %s", tostring(features));
 477                         send(features);
 478                 end
 479         elseif session.direction == "outgoing" then
 480                 -- If we are just using the connection for verifying dialback keys, we won't try and auth it
 481                 if not attr.id then error("stream response did not give us a streamid!!!"); end
 482                 session.streamid = attr.id;
 483
 484                 if session.secure and not session.cert_chain_status then check_cert_status(session); end
 485
 486                 -- Send unauthed buffer
 487                 -- (stanzas which are fine to send before dialback)
 488                 -- Note that this is *not* the stanza queue (which
 489                 -- we can only send if auth succeeds) :)
 490                 local send_buffer = session.send_buffer;
 491                 if send_buffer and #send_buffer > 0 then
 492                         log("debug", "Sending s2s send_buffer now...");
 493                         for i, data in ipairs(send_buffer) do
 494                                 session.sends2s(tostring(data));
 495                                 send_buffer[i] = nil;
 496                         end
 497                 end
 498                 session.send_buffer = nil;
 499
 500                 -- If server is pre-1.0, don't wait for features, just do dialback
 501                 if session.version < 1.0 then
 502                         if not session.dialback_verifying then
 503                                 log("debug", "Initiating dialback...");
 504                                 initiate_dialback(session);
 505                         else
 506                                 mark_connected(session);
 507                         end
 508                 end
 509         end
 510         session.notopen = nil;
 511 end
 512
 513 function streamclosed(session)
 514         (session.log or log)("debug", "Received </stream:stream>");
 515         session:close();
 516 end
 517
 518 function initiate_dialback(session)
 519         -- generate dialback key
 520         session.dialback_key = generate_dialback(session.streamid, session.to_host, session.from_host);
 521         session.sends2s(format("<db:result from='%s' to='%s'>%s</db:result>", session.from_host, session.to_host, session.dialback_key));
 522         session.log("info", "sent dialback key on outgoing s2s stream");
 523 end
 524
 525 function generate_dialback(id, to, from)
 526         return sha256_hash(id..to..from..hosts[from].dialback_secret, true);
 527 end
 528
 529 function verify_dialback(id, to, from, key)
 530         return key == generate_dialback(id, to, from);
 531 end
 532
 533 function make_authenticated(session, host)
 534         if not session.secure then
 535                 local local_host = session.direction == "incoming" and session.to_host or session.from_host;
 536                 if config.get(local_host, "core", "s2s_require_encryption") then
 537                         session:close({
 538                                 condition = "policy-violation",
 539                                 text = "Encrypted server-to-server communication is required but was not "
 540                                        ..((session.direction == "outgoing" and "offered") or "used")
 541                         });
 542                 end
 543         end
 544         if session.type == "s2sout_unauthed" then
 545                 session.type = "s2sout";
 546         elseif session.type == "s2sin_unauthed" then
 547                 session.type = "s2sin";
 548                 if host then
 549                         if not session.hosts[host] then session.hosts[host] = {}; end
 550                         session.hosts[host].authed = true;
 551                 end
 552         elseif session.type == "s2sin" and host then
 553                 if not session.hosts[host] then session.hosts[host] = {}; end
 554                 session.hosts[host].authed = true;
 555         else
 556                 return false;
 557         end
 558         session.log("debug", "connection %s->%s is now authenticated", session.from_host or "(unknown)", session.to_host or "(unknown)");
 559
 560         mark_connected(session);
 561
 562         return true;
 563 end
 564
 565 -- Stream is authorised, and ready for normal stanzas
 566 function mark_connected(session)
 567         local sendq, send = session.sendq, session.sends2s;
 568
 569         local from, to = session.from_host, session.to_host;
 570
 571         session.log("info", session.direction.." s2s connection "..from.."->"..to.." complete");
 572
 573         local send_to_host = send_to_host;
 574         function session.send(data) return send_to_host(to, from, data); end
 575
 576         local event_data = { session = session };
 577         if session.type == "s2sout" then
 578                 prosody.events.fire_event("s2sout-established", event_data);
 579                 hosts[session.from_host].events.fire_event("s2sout-established", event_data);
 580         else
 581                 prosody.events.fire_event("s2sin-established", event_data);
 582                 hosts[session.to_host].events.fire_event("s2sin-established", event_data);
 583         end
 584
 585         if session.direction == "outgoing" then
 586                 if sendq then
 587                         session.log("debug", "sending "..#sendq.." queued stanzas across new outgoing connection to "..session.to_host);
 588                         for i, data in ipairs(sendq) do
 589                                 send(data[1]);
 590                                 sendq[i] = nil;
 591                         end
 592                         session.sendq = nil;
 593                 end
 594
 595                 session.srv_hosts = nil;
 596         end
 597 end
 598
 599 local resting_session = { -- Resting, not dead
 600                 destroyed = true;
 601                 type = "s2s_destroyed";
 602                 open_stream = function (session)
 603                         session.log("debug", "Attempt to open stream on resting session");
 604                 end;
 605                 close = function (session)
 606                         session.log("debug", "Attempt to close already-closed session");
 607                 end;
 608                 filter = function (type, data) return data; end;
 609         }; resting_session.__index = resting_session;
 610
 611 function retire_session(session, reason)
 612         local log = session.log or log;
 613         for k in pairs(session) do
 614                 if k ~= "trace" and k ~= "log" and k ~= "id" then
 615                         session[k] = nil;
 616                 end
 617         end
 618
 619         session.destruction_reason = reason;
 620
 621         function session.send(data) log("debug", "Discarding data sent to resting session: %s", tostring(data)); end
 622         function session.data(data) log("debug", "Discarding data received from resting session: %s", tostring(data)); end
 623         return setmetatable(session, resting_session);
 624 end
 625
 626 function destroy_session(session, reason)
 627         if session.destroyed then return; end
 628         (session.log or log)("debug", "Destroying "..tostring(session.direction).." session "..tostring(session.from_host).."->"..tostring(session.to_host)..(reason and (": "..reason) or ""));
 629
 630         if session.direction == "outgoing" then
 631                 hosts[session.from_host].s2sout[session.to_host] = nil;
 632                 bounce_sendq(session, reason);
 633         elseif session.direction == "incoming" then
 634                 incoming_s2s[session] = nil;
 635         end
 636
 637         local event_data = { session = session, reason = reason };
 638         if session.type == "s2sout" then
 639                 prosody.events.fire_event("s2sout-destroyed", event_data);
 640                 if hosts[session.from_host] then
 641                         hosts[session.from_host].events.fire_event("s2sout-destroyed", event_data);
 642                 end
 643         elseif session.type == "s2sin" then
 644                 prosody.events.fire_event("s2sin-destroyed", event_data);
 645                 if hosts[session.to_host] then
 646                         hosts[session.to_host].events.fire_event("s2sin-destroyed", event_data);
 647                 end
 648         end
 649
 650         retire_session(session, reason); -- Clean session until it is GC'd
 651         return true;
 652 end
 653
 654 return _M;