通向码农的道路（enet开源翻译计划 一）

QQ 324186207群 enet交流技术。主要是为了研究tcp内部执行机制，欢迎大家增加探讨。小弟水平有限。翻译难免有误。

。

Features:

ENet evolved specifically as a UDP networking layer for the multiplayer first person
shooter Cube.

ENet 最初衷设计为了第一人称射击类游戏。

为什么须要udp （參考，unix网络编程，假设不是为了进行多播，不要使用udp，我们应该使用tcp，让厂商来关注性能 ）由于无法容忍延迟。（參考tcp v1）





眼下我们游戏来看卡牌塔防类，根本不须要udp  就算有高延迟玩家有什么不能接受的。 看看梦幻细雨。有时候一回合延迟高达10秒？？  终于我们失去了tcp的又一次分组，高速恢复算法，高速重传，延迟确认机制 ，坚持定时器........ 



由于看到腾讯的 t3 面试问题 怎样提网络吞吐量？enet 正是怎样回答这个问题的最佳方案。我想enet 正是学习tcp最佳路程。假设仅仅是看内核tcp源代码学习。难免会有点不自量力。 

1.

     enet_host_create(
&address, 4095, 2, 0, 0 );
 // num of clients, num of channels, incoming bandwidth, outgoing bandwidth。

channels  这个设计眼下我理解的为了进行负载均衡， 比方 client    －》 zoneconnect     －》 zoneserver   

假设此时  client zoneconnect  1 num   ，zoneconnect  zoneserver   2  num ，     1 num  之间通信发生了拥塞，此时通过拥塞控制，降低发包频率，假设
2  num 也在发包呢？  然而此时的 1  num 已经发生了拥塞 。那么我们的所须要发送的数据包，仅仅有异步等待 1 num发送  为了解决问题的延迟，并降低对数据包的限制，使用多通道独立的进行发送。因此此时一个通道的数据包传送状态不会影响其它通道的包传送 。

假设默觉得0 则是禁止开启流量控制。和拥塞控制。（參考 tcpv2 内核源代码）

To combat this latency and reduce
the ordering restrictions on packets, ENet provides multiple channels of communication over a given connection. Each channel is independently sequenced, and so the delivery status of a packet in one channel will not stall the delivery of other packets in another
channel.



 ENetHost *

enet_host_create (const ENetAddress *
address, size_t peerCount, size_t channelLimit, enet_uint32 incomingBandwidth,enet_uint32 outgoingBandwidth)

{

ENetHost * host; //server本端 一个全局变量存储数据

ENetPeer * currentPeer;//当前client就是一个peer

//ENET_PROTOCOL_MAXIMUM_PEER_ID

//

if( peerCount > ENET_PROTOCOL_MAXIMUM_PEER_ID )

return NULL;

host = (ENetHost *) enet_malloc (sizeof (ENetHost));

if (host == NULL)

return NULL;

memset(host, 0, sizeof (ENetHost));

host ->peers = (ENetPeer *) enet_malloc (peerCount
* sizeof (ENetPeer));

if (host ->peers == NULL)

{

enet_free (host);

return NULL;

}

memset (host ->peers, 0,
peerCount * sizeof (ENetPeer));

host ->socket = enet_socket_create (ENET_SOCKET_TYPE_DATAGRAM);

if (host ->socket == ENET_SOCKET_NULL ||
(address != NULL && enet_socket_bind (host ->socket,
address) < 0))

{

if (host ->socket != ENET_SOCKET_NULL)

enet_socket_destroy (host ->socket);

enet_free (host ->peers);

enet_free (host);

return NULL;

}

enet_socket_set_option (host ->socket, ENET_SOCKOPT_NONBLOCK, 1); //设置非堵塞

enet_socket_set_option (host ->socket, ENET_SOCKOPT_BROADCAST, 1);//设置广播

enet_socket_set_option (host ->socket, ENET_SOCKOPT_RCVBUF, ENET_HOST_RECEIVE_BUFFER_SIZE); //设置socket
接受缓冲区

enet_socket_set_option (host ->socket, ENET_SOCKOPT_SNDBUF, ENET_HOST_SEND_BUFFER_SIZE);//设置socket发送缓冲区

if (address != NULL && enet_socket_get_address (host
->socket, & host -> address) < 0)  //
绑定socket  设置地址

host -> address = * address;

if (! channelLimit || channelLimit > ENET_PROTOCOL_MAXIMUM_CHANNEL_COUNT)

channelLimit = ENET_PROTOCOL_MAXIMUM_CHANNEL_COUNT;

else

if (channelLimit < ENET_PROTOCOL_MINIMUM_CHANNEL_COUNT)

channelLimit = ENET_PROTOCOL_MINIMUM_CHANNEL_COUNT;

host ->randomSeed = (enet_uint32) (size_t)
host;

host ->randomSeed += enet_host_random_seed ();

host ->randomSeed = (host ->randomSeed << 16)
| (host ->randomSeed >> 16);

host ->channelLimit = channelLimit;

host ->incomingBandwidth = incomingBandwidth;

host ->outgoingBandwidth = outgoingBandwidth;

host ->bandwidthThrottleEpoch = 0;

host ->recalculateBandwidthLimits = 0;

host ->mtu = ENET_HOST_DEFAULT_MTU; //通信最大包限制，
本身自带分包发送。

host ->peerCount = peerCount;

host ->commandCount = 0;

host ->bufferCount = 0;

host ->checksum = NULL;

host ->receivedAddress.host = ENET_HOST_ANY;

host ->receivedAddress.port = 0;

host ->receivedData = NULL;

host ->receivedDataLength = 0;

host ->totalSentData = 0;

host ->totalSentPackets = 0;

host ->totalReceivedData = 0;

host ->totalReceivedPackets = 0;

host ->connectedPeers = 0;

host ->bandwidthLimitedPeers = 0;

host ->duplicatePeers = ENET_PROTOCOL_MAXIMUM_PEER_ID;

host ->maximumPacketSize = ENET_HOST_DEFAULT_MAXIMUM_PACKET_SIZE;

host ->maximumWaitingData = ENET_HOST_DEFAULT_MAXIMUM_WAITING_DATA;

host ->compressor.context = NULL; //
这里开启压缩包算法

host ->compressor.compress = NULL;

host ->compressor.decompress = NULL;

host ->compressor.destroy = NULL;

host ->intercept = NULL;

enet_list_clear (& host ->dispatchQueue); //双向链表
每次必须clear 使得双指针指向头节点

for (currentPeer = host ->peers;

currentPeer < & host ->peers [host -> peerCount];

++ currentPeer)

{

currentPeer ->host = host;

currentPeer ->incomingPeerID = currentPeer - host ->peers;

currentPeer ->outgoingSessionID = currentPeer ->incomingSessionID = 0xFF;

currentPeer ->data = NULL;

enet_list_clear (& currentPeer ->acknowledgements);

enet_list_clear (& currentPeer ->sentReliableCommands);

enet_list_clear (& currentPeer ->sentUnreliableCommands);

enet_list_clear (& currentPeer ->outgoingReliableCommands);

enet_list_clear (& currentPeer ->outgoingUnreliableCommands);

enet_list_clear (& currentPeer ->dispatchedCommands);

enet_peer_reset (currentPeer);

}

return host;

}

2.



  /**
Forcefully disconnects a peer.

@param peer peer to forcefully disconnect

@remarks The foreign host represented by the peer is not notified of the disconnection
and will timeout

on its connection to the local host.

*/

void

enet_peer_reset (ENetPeer * peer)

{

enet_peer_on_disconnect (peer);

peer -> outgoingPeerID = ENET_PROTOCOL_MAXIMUM_PEER_ID;

peer -> connectID = 0;

peer -> state = ENET_PEER_STATE_DISCONNECTED;

peer -> incomingBandwidth = 0;

peer -> outgoingBandwidth = 0;

peer -> incomingBandwidthThrottleEpoch = 0;

peer -> outgoingBandwidthThrottleEpoch = 0;

peer -> incomingDataTotal = 0;

peer -> outgoingDataTotal = 0;

peer -> lastSendTime = 0;

peer -> lastReceiveTime = 0;

peer -> nextTimeout = 0;   client下次超时时间

peer -> earliestTimeout = 0;  最早的超时时间

peer -> packetLossEpoch = 0;

peer -> packetsSent = 0;

peer -> packetsLost = 0;

peer -> packetLoss = 0;

peer -> packetLossVariance = 0;

peer -> packetThrottle = ENET_PEER_DEFAULT_PACKET_THROTTLE;

peer -> packetThrottleLimit = ENET_PEER_PACKET_THROTTLE_SCALE;

peer -> packetThrottleCounter = 0;

peer -> packetThrottleEpoch = 0;

peer -> packetThrottleAcceleration = ENET_PEER_PACKET_THROTTLE_ACCELERATION;

peer -> packetThrottleDeceleration = ENET_PEER_PACKET_THROTTLE_DECELERATION;

peer -> packetThrottleInterval = ENET_PEER_PACKET_THROTTLE_INTERVAL;

peer -> pingInterval = ENET_PEER_PING_INTERVAL;
   心跳检測时间

peer -> timeoutLimit = ENET_PEER_TIMEOUT_LIMIT;

peer -> timeoutMinimum = ENET_PEER_TIMEOUT_MINIMUM;

peer -> timeoutMaximum = ENET_PEER_TIMEOUT_MAXIMUM;
 最大超时时间  假设没有收到对端的ack确认，会一直重传，至道最大超时，而且踢掉玩家

peer -> lastRoundTripTime = ENET_PEER_DEFAULT_ROUND_TRIP_TIME;

peer -> lowestRoundTripTime = ENET_PEER_DEFAULT_ROUND_TRIP_TIME;

peer -> lastRoundTripTimeVariance = 0;

peer -> highestRoundTripTimeVariance = 0;

peer -> roundTripTime = ENET_PEER_DEFAULT_ROUND_TRIP_TIME;
 client和server通信往返时间设置，用于推断是否超时

peer -> roundTripTimeVariance = 0;

peer -> mtu = peer -> host -> mtu;

peer -> reliableDataInTransit = 0;

peer -> outgoingReliableSequenceNumber = 0;

peer -> windowSize = ENET_PROTOCOL_MAXIMUM_WINDOW_SIZE; 滑动窗体大小

peer -> incomingUnsequencedGroup = 0;

peer -> outgoingUnsequencedGroup = 0;

peer -> eventData = 0;

peer -> totalWaitingData = 0;

memset (peer -> unsequencedWindow, 0, sizeof (peer
-> unsequencedWindow));

enet_peer_reset_queues (peer);

}





3.

void

enet_peer_reset_queues (ENetPeer * peer)

{

ENetChannel * channel;

if (peer -> needsDispatch)

{

enet_list_remove (& peer -> dispatchList); 收到收到的数据包都会增加到调度队列

peer -> needsDispatch = 0;

}

while (! enet_list_empty (& peer -> acknowledgements))
 对端确认协议

enet_free (enet_list_remove (enet_list_begin (&
peer -> acknowledgements)));

enet_peer_reset_outgoing_commands (& peer -> sentReliableCommands); 可靠数据包协议
（每次发送send包后，须要存储到这个双向链表。目的在于存储，用于超时重传，仅仅有收到ack确认。才会删除）

enet_peer_reset_outgoing_commands (& peer -> sentUnreliableCommands); 不可靠数据包协议

enet_peer_reset_outgoing_commands (& peer -> outgoingReliableCommands);
  发送数据全部都会优先增加到 进来的可靠数据包协议 然后send后。又会增加到peer -> sentReliableCommands 
假设检測超时，又会从新回到peer -> outgoingReliableCommands

enet_peer_reset_outgoing_commands (& peer -> outgoingUnreliableCommands);

enet_peer_reset_incoming_commands (& peer -> dispatchedCommands); 调度协议

if (peer -> channels != NULL &&
peer -> channelCount > 0) 初始化通道

{

for (channel = peer -> channels;

channel < & peer -> channels [peer -> channelCount];

++ channel)

{

enet_peer_reset_incoming_commands (& channel -> incomingReliableCommands);

enet_peer_reset_incoming_commands (& channel -> incomingUnreliableCommands);

}

enet_free (peer -> channels);

}

peer -> channels = NULL;

peer -> channelCount = 0;

}