进阶技法-断线重连

“断线重连”是手机游戏的必备功能。除了网络连接不稳定外，部分手机系统为了节省电量，在默认情况下黑屏十几秒后就会断开网络连接。如果没有重连机制，玩家只要短时间不在手机旁(比如去喝杯水)，回来后就得退出游戏重新打开，大大影响游戏体验。图是《Unity3D网络游戏实战(第2版)》的范例游戏《铁流的轮印》在断线后会自动重连。它是如何实现的呢?下面一起来看看。

 

一、原理解析

图展示了服务端断线重连的流程。以3.2节《球球大作战》的服务端架构为例，gateway作为中介连接客户端与内部服务，当客户端断开连接(阶段)时，只要gateway不去触发下线流程，agent和scene就都不会受到影响。当客户端重新发起连接(阶段②)时，经过校验，如果gateway认为它是合法的连接(阶段③)，则会将新连接与agent关联起来，这样便完成了重连。整个重连过程只有qatewav参与，服务端系统中的其他服务均不受影响。

 

二、身份标识

为验证重连客户端的合法性，需给每个玩家生成代表身份标识的密码，如代码中的key变量，gateway会为每个玩家生成身份标识码(读者可以将它设计得更加复杂)，并让其随着登录协议返回给客户端(代码略)。在发起重连时，客户端必须将标识码发回给服务端，以验证身份。如果不是重连的客户端，它无法得知标识码就无法以断线的名义冒充身份。下图展示了断线重连的完整流程

gateway/init.lua

-- player class
function gate_player()
  local m = {
    player_id = nil,
    agent = nil,
    conn = nil,
    key = math.random(1, 999999999),
    lost_conn_time = nil,
    msgcache = {}, -- not send msg cache
  }
  return m
end

除了key，代码中还定义了两个变量，lost_conn_time用于记录最后一次断开连接的时间，msgcache用于缓存服务端未能发出的协议。

 

三、消息缓存

断线期间服务端可能会向客户端发送消息，由于这些消息不能传达，因此需由gateway缓存起来，待重连后发送，见如下代码。修改gateway向客户端发送消息的远程调用send，可实现如下功能:

1. 如果没有断线，调用s.resp.send_by_fd正常发送消息。
2. 如果在断线期间，将消息存入gplayer.msgcache中。
3. 为避免占用过多内存，在缓存了大于500条的消息后，触发下线逻辑，不允许重连。

gateway/init.lua

s.resp.send = function(source, player_id, msg)
  local gplayer = players[player_id]
  if gplayer == nil then
    return
  end

  local c = gplayer.conn
  if c == nil then
    table.insert(gplayer.msgcache, msg)
    local len = #gplayer.msgcache
    if len > 500 then
      skynet.call("agentmgr", "lua", "reqkick", player_id, "gate消息缓存过多")
    end
    return
  end
  s.resp.send_by_fd(nil, c.fd, msg)
end

 

四、处理重连请求

定义如图所示的重连协议reconnect，客户端会发送玩家id和身份标识，服务端会回应重连成功或者失败。

由于reconnect协议由gateway处理，因此在处理消息的process msg方法中，要做个特殊判断，即如果收到reconnect协议，交由processreconnect方法处理。

gateway/init.lua

-- 消息处理
local process_msg = function(fd, msgstr)
  local cmd,msg = str_unpack(msgstr)
  skynet.error("recv "..fd.." ["..cmd.."] {"..table.concat( msg, ",").."}")
  -- 连接对象
  local conn = conns[fd]
  -- 如果完成登录,player_id不为空，否则为空
  local player_id = conn.player_id
  if cmd == "reconnect" then
    process_reconnect(fd, msg)
    return
  end
  -- ...
end

 process_reconnect

代码展示了断线重连的具体处理方法，它有如下几个要点:

1. 做出严格的条件判断，只有断线的玩家才能接受重连。未登录(ifnot gplayer为真)、未掉线(ifgplayer.conn为真)、身份标识错误(if gplayer.key~=key为真)均不可重连。
2. 绑定新连接(conn)和玩家对象(gplayer)。
3. 回应重连消息{"reconnect",0}。
4. 发送缓存中的消息。

local process_reconnect = function(fd, msg)
  local player_id = tonumber(msg[2])
  local key = tonumber(msg[3])
  --con
  local conn = conns[fd]
  if not conn then
    skynet.error("reconnect fail,conn not exist")
    return
  end
  --gplayer
  local gplayer = players[player_id]
  if not gplayer then
    skynet.error("reconnect fail,gplayer not exist")
    return
  end
  if gplayer.conn then
    skynet.error("reconnect fail,conn not break")
    return
  end
  if gplayer.key ~= key then
    skynet.error("reconnect fail,key error")
    return
  end
  --bind
  gplayer.conn = conn
  conn.player_id = player_id
  --response
  s.resp.send_by_fd(nil, fd, {"reconect", 0})
end

 

五、断线处理

与之前介绍的“登出流程”不同，当客户端掉线时，gateway不会去触发掉线请求(即向agentmgr请求regkick)。如代码所示，掉线时仅仅取消玩家对象(gplayer)与旧连接(conn)的关联(即gplayer.conn=nil)。
为防止客户端不再发起重连导致的资源占用，程序会开启一个定时器(skynet.timeout)，若15秒后依然是掉线状态(if gplayer.conn~=nil为假)，则向agentmgr请求下线。

gateway/init.lua

-- 断线
-- 如果agentmgr仲裁通过，或是agentmgr想直接把玩家踢下线，在保存数据后，它会通知gateway
-- 来删掉玩家对应的conn和gateplayer对象
local disconnect = function(fd)
  local c = conns[fd]
  if not c then
    return
  end

  local player_id = c.player_id
  -- 还没完成登录
  if not player_id  then
    return
  -- 已在游戏中
  else
    local gplayer = players[player_id]
    gplayer.conn = nil
    skynet.timeout(15*100, function()
      if gplayer.conn ~= nil then
        return
      end
      players[player_id] = nil
      local reason = "diconnect timeout"
      -- 向agentmgr发送下线请示
      skynet.call("agentmgr", "lua", "reqkick", player_id, reason)
    end)
  end
end

 

六、登录增加key返回

gateway/init.lua

-- 客户端关联agent
-- 功能：完成登录流程之后,login会通知gateway,将客户端连接和agent关联起来
s.resp.sure_agent = function(source, fd, player_id, agent)
  local conn = conns[fd]
  --登录过程中已下线
  if not conn then
    skynet.call("agentmgr", "lua", "reqkick", player_id, "未完成登录即下线")
    return false
  end

  conn.player_id = player_id

  local gplayer = gate_player()
  gplayer.player_id = player_id
  gplayer.agent = agent
  gplayer.conn = conn
  players[player_id] = gplayer

  return true,gplayer.key
end

login/init.lua

-- 登录消息
s.client.login = function(fd, msg, source)
    local player_id = tonumber(msg[2])
    local password = tonumber(msg[3])
    local gate = source
    node = skynet.getenv("node")
    --校验用户名密码
    if password ~= 123 then
        return {"login", 1, "password error"}
    end
    -- 通知agentmgr,分配agent
    local isok,agent = skynet.call("agentmgr","lua","reqlogin",player_id, node, gate)
    if not isok then
        return {"login", 1, "req mgr fail"}
    end
    -- 通知gate分配的agent
    local isok,key = skynet.call(gate, "lua", "sure_agent", fd, player_id, agent)
    skynet.error("login sure_agent key="..key)
    if not isok then
        return {"login", 1, "res gate fail"}
    end
    skynet.error("login success ".. player_id)
    return {"login", player_id, key, "login success"}
end

六、测试

1、重连

server

root@server-VirtualBox:/home/bbb_fight# sh start.sh 1
[:00000002] LAUNCH snlua bootstrap
[:00000003] LAUNCH snlua launcher
[:00000004] LAUNCH snlua cdummy
[:00000005] LAUNCH harbor 0 4
[:00000006] LAUNCH snlua datacenterd
[:00000007] LAUNCH snlua service_mgr
[:00000008] LAUNCH snlua main
[:00000009] LAUNCH snlua clusterd
[:0000000a] LAUNCH snlua nodemgr nodemgr 0
[:0000000a] [service][start] name=nodemgr id=0
[:0000000b] LAUNCH snlua gate
[:0000000b] Listen on 127.0.0.1:7771
[:0000000c] LAUNCH snlua gateway gateway 1
[:0000000c] [service][start] name=gateway id=1
[:0000000c] gate init port=8001
[:0000000c] Listen socket: 0.0.0.0 8001
[:0000000d] LAUNCH snlua gateway gateway 2
[:0000000d] [service][start] name=gateway id=2
[:0000000d] gate init port=8002
[:0000000d] Listen socket: 0.0.0.0 8002
[:0000000e] LAUNCH snlua login login 1
[:0000000e] [service][start] name=login id=1
[:0000000f] LAUNCH snlua login login 2
[:0000000f] [service][start] name=login id=2
[:00000010] LAUNCH snlua agentmgr agentmgr 0
[:00000010] [service][start] name=agentmgr id=0
[:00000011] LAUNCH snlua scene scene 1001
[:00000011] [service][start] name=scene id=1001
[:00000012] LAUNCH snlua scene scene 1002
[:00000012] [service][start] name=scene id=1002
[:00000013] LAUNCH snlua admin admin 1001
[:00000013] [service][start] name=admin id=1001
[:00000013] admin init listenfd=4
[:00000008] KILL self
[:00000002] KILL self
connect from 127.0.0.1:42378 5
[:0000000c] socket connectted 5
[:0000000c] recv 5 [login] {login,101,123}
[:0000000f] [login][client]login
[:0000000a] [nodemgr] newservice begin name=agent
[:00000014] LAUNCH snlua agent agent 101
[:00000014] [service][start] name=agent id=101
[:00000014] last_day=19885 now_day=19888
[:00000014] kuatian...
[:0000000a] [nodemgr] newservice end name=agent
[:00000010] reqlogin player_id=101 success
[:0000000f] login sure_agent key=629613317
[:0000000f] login success 101
[:0000000c] send 5 [login] {login,0,101,629613317,login success}
[:0000000c] socket close 5
connect from 127.0.0.1:37462 6
[:0000000c] socket connectted 6
[:0000000c] recv 6 [reconnect] {reconnect,101,629613317}
[:0000000c] send 6 [reconect] {reconect,0}

 client

server@server-VirtualBox:~$ telnet 0.0.0.0 8001
Trying 0.0.0.0...
Connected to 0.0.0.0.
Escape character is '^]'.
login,101,123
login,0,101,629613317,login success
^]
telnet> q
Connection closed.
server@server-VirtualBox:~$ telnet 0.0.0.0 8001
Trying 0.0.0.0...
Connected to 0.0.0.0.
Escape character is '^]'.
reconnect,101,629613317
reconect,0

 

2、掉线超时踢下线

agentmgr/init.lua

s.resp.reqkick = function(source, player_id, reason)
    local mplayer = players[player_id]
    if not mplayer then
        return false
    end

    -- 游戏中不能登出
    if mplayer.status ~= STATUS.GAME then
        return false
    end

    local pnode = mplayer.node
    local pagent = mplayer.agent
    local pgate = mplayer.gate
    mplayer.status = STATUS.LOGOUT

    s.call(pnode, pagent, "kick")
    s.send(pnode, pagent, "exit")
    s.send(pnode, pgate, "kick", player_id)
    players[player_id] = nil
    skynet.error("agentmgr reqkick player_id="..player_id.." reason="..reason)
    return true
end

server

root@server-VirtualBox:/home/bbb_fight# sh start.sh 1
[:00000002] LAUNCH snlua bootstrap
[:00000003] LAUNCH snlua launcher
[:00000004] LAUNCH snlua cdummy
[:00000005] LAUNCH harbor 0 4
[:00000006] LAUNCH snlua datacenterd
[:00000007] LAUNCH snlua service_mgr
[:00000008] LAUNCH snlua main
[:00000009] LAUNCH snlua clusterd
[:0000000a] LAUNCH snlua nodemgr nodemgr 0
[:0000000a] [service][start] name=nodemgr id=0
[:0000000b] LAUNCH snlua gate
[:0000000b] Listen on 127.0.0.1:7771
[:0000000c] LAUNCH snlua gateway gateway 1
[:0000000c] [service][start] name=gateway id=1
[:0000000c] gate init port=8001
[:0000000c] Listen socket: 0.0.0.0 8001
[:0000000d] LAUNCH snlua gateway gateway 2
[:0000000d] [service][start] name=gateway id=2
[:0000000d] gate init port=8002
[:0000000d] Listen socket: 0.0.0.0 8002
[:0000000e] LAUNCH snlua login login 1
[:0000000e] [service][start] name=login id=1
[:0000000f] LAUNCH snlua login login 2
[:0000000f] [service][start] name=login id=2
[:00000010] LAUNCH snlua agentmgr agentmgr 0
[:00000010] [service][start] name=agentmgr id=0
[:00000011] LAUNCH snlua scene scene 1001
[:00000011] [service][start] name=scene id=1001
[:00000012] LAUNCH snlua scene scene 1002
[:00000012] [service][start] name=scene id=1002
[:00000013] LAUNCH snlua admin admin 1001
[:00000013] [service][start] name=admin id=1001
[:00000013] admin init listenfd=4
[:00000008] KILL self
[:00000002] KILL self
connect from 127.0.0.1:39760 5
[:0000000c] socket connectted 5
[:0000000c] recv 5 [login] {login,101,123}
[:0000000e] [login][client]login
[:0000000a] [nodemgr] newservice begin name=agent
[:00000014] LAUNCH snlua agent agent 101
[:00000014] [service][start] name=agent id=101
[:00000014] last_day=19885 now_day=19888
[:00000014] kuatian...
[:0000000a] [nodemgr] newservice end name=agent
[:00000010] reqlogin player_id=101 success
[:0000000e] login sure_agent key=435252744
[:0000000e] login success 101
[:0000000c] send 5 [login] {login,0,101,435252744,login success}
[:0000000c] socket close 5
#15秒后
[:00000010] agentmgr reqkick player_id=101 reason=diconnect timeout
[:00000014] KILL self

client

server@server-VirtualBox:~$ telnet 0.0.0.0 8001
Trying 0.0.0.0...
Connected to 0.0.0.0.
Escape character is '^]'.
login,101,123
login,0,101,435252744,login success
^]
telnet> q
Connection closed.

可以看到，服务端掉线后agent服务(014)并没有退出，而是等待一段时间后(代码设置的定时器)才触发下线流程。

 

3、消息缓存

gateway/init.lua

local process_reconnect = function(fd, msg)
  local player_id = tonumber(msg[2])
  local key = tonumber(msg[3])
  --con
  local conn = conns[fd]
  if not conn then
    skynet.error("reconnect fail,conn not exist")
    return
  end
  --gplayer
  local gplayer = players[player_id]
  if not gplayer then
    skynet.error("reconnect fail,gplayer not exist")
    return
  end
  if gplayer.conn then
    skynet.error("reconnect fail,conn not break")
    return
  end
  if gplayer.key ~= key then
    skynet.error("reconnect fail,key error")
    return
  end
  --bind
  gplayer.conn = conn
  conn.player_id = player_id
  --response
  s.resp.send_by_fd(nil, fd, {"reconect", 0})
  --msgcache
  for _,_msg in ipairs(gplayer.msgcache) do
    s.resp.send_by_fd(nil, fd, _msg)
  end
end

server

root@server-VirtualBox:/home/bbb_fight# sh start.sh 1
[:00000002] LAUNCH snlua bootstrap
[:00000003] LAUNCH snlua launcher
[:00000004] LAUNCH snlua cdummy
[:00000005] LAUNCH harbor 0 4
[:00000006] LAUNCH snlua datacenterd
[:00000007] LAUNCH snlua service_mgr
[:00000008] LAUNCH snlua main
[:00000009] LAUNCH snlua clusterd
[:0000000a] LAUNCH snlua nodemgr nodemgr 0
[:0000000a] [service][start] name=nodemgr id=0
[:0000000b] LAUNCH snlua gate
[:0000000b] Listen on 127.0.0.1:7771
[:0000000c] LAUNCH snlua gateway gateway 1
[:0000000c] [service][start] name=gateway id=1
[:0000000c] gate init port=8001
[:0000000c] Listen socket: 0.0.0.0 8001
[:0000000d] LAUNCH snlua gateway gateway 2
[:0000000d] [service][start] name=gateway id=2
[:0000000d] gate init port=8002
[:0000000d] Listen socket: 0.0.0.0 8002
[:0000000e] LAUNCH snlua login login 1
[:0000000e] [service][start] name=login id=1
[:0000000f] LAUNCH snlua login login 2
[:0000000f] [service][start] name=login id=2
[:00000010] LAUNCH snlua agentmgr agentmgr 0
[:00000010] [service][start] name=agentmgr id=0
[:00000011] LAUNCH snlua scene scene 1001
[:00000011] [service][start] name=scene id=1001
[:00000012] LAUNCH snlua scene scene 1002
[:00000012] [service][start] name=scene id=1002
[:00000013] LAUNCH snlua admin admin 1001
[:00000013] [service][start] name=admin id=1001
[:00000013] admin init listenfd=4
[:00000008] KILL self
[:00000002] KILL self
connect from 127.0.0.1:37784 5
[:0000000c] socket connectted 5
[:0000000c] recv 5 [login] {login,101,123}
[:0000000f] [login][client]login
[:0000000a] [nodemgr] newservice begin name=agent
[:00000014] LAUNCH snlua agent agent 101
[:00000014] [service][start] name=agent id=101
[:00000014] last_day=19885 now_day=19888
[:00000014] kuatian...
[:0000000a] [nodemgr] newservice end name=agent
[:00000010] reqlogin player_id=101 success
[:0000000f] login sure_agent key=763086078
[:0000000f] login success 101
[:0000000c] send 5 [login] {login,0,101,763086078,login success}
[:0000000c] recv 5 [enter] {enter}
[:00000014] random_scene i=node2
[:00000014] random_scene i=node1
[:00000011] scene send log msg=enter,101,16,56,2
[:0000000c] send 5 [enter] {enter,101,16,56,2}
[:0000000c] send 5 [balllist] {balllist,16,56,2}
[:0000000c] send 5 [foodlist] {foodlist,1,45,86,2,80,4}
[:00000011] scene send log msg=addfood,3,79,4
[:0000000c] send 5 [addfood] {addfood,3,79,4}
[:0000000c] socket close 5
[:00000011] scene send log msg=addfood,4,87,78
[:00000011] scene send log msg=addfood,5,93,85
[:00000011] scene send log msg=addfood,6,21,34
connect from 127.0.0.1:43018 6
[:0000000c] socket connectted 6
[:00000011] scene send log msg=addfood,7,91,68
[:00000011] scene send log msg=addfood,8,77,41
[:00000011] scene send log msg=addfood,9,89,22
[:00000011] scene send log msg=addfood,10,34,90
[:0000000c] recv 6 [reconnect] {reconnect,101,763086078}
[:0000000c] send 6 [reconect] {reconect,0}
[:0000000c] send 6 [addfood] {addfood,4,87,78}
[:0000000c] send 6 [addfood] {addfood,5,93,85}
[:0000000c] send 6 [addfood] {addfood,6,21,34}
[:0000000c] send 6 [addfood] {addfood,7,91,68}
[:0000000c] send 6 [addfood] {addfood,8,77,41}
[:0000000c] send 6 [addfood] {addfood,9,89,22}
[:0000000c] send 6 [addfood] {addfood,10,34,90}
[:00000011] scene send log msg=addfood,11,86,21
[:0000000c] send 6 [addfood] {addfood,11,86,21}
[:00000011] scene send log msg=addfood,12,63,33
[:0000000c] send 6 [addfood] {addfood,12,63,33}

client

server@server-VirtualBox:~$ telnet 0.0.0.0 8001
Trying 0.0.0.0...
Connected to 0.0.0.0.
Escape character is '^]'.
login,101,123
login,0,101,763086078,login success
enter
enter,101,16,56,2
balllist,16,56,2
foodlist,1,45,86,2,80,4
addfood,3,79,4
^]
telnet> q
Connection closed.
server@server-VirtualBox:~$ telnet 0.0.0.0 8001
Trying 0.0.0.0...
Connected to 0.0.0.0.
Escape character is '^]'.
reconnect,101,763086078
reconect,0
addfood,4,87,78
addfood,5,93,85
addfood,6,21,34
addfood,7,91,68
addfood,8,77,41
addfood,9,89,22
addfood,10,34,90
addfood,11,86,21
addfood,12,63,33