网关服务 (GateSever) 是游戏的接入层, 基本功能是管理客户端的连接, 分割完整的数据包, 转发给逻辑处理服务.

GateServer is the access layer of a game server and the basic functionalities are managing client connections, unpacking data packages, redirecting them to the logic layer.

skynet 提供了一个通用模板 lualib/snax/gateserver.lua. 同时基于 gateserver.lua, 实现了一个网关服务 gate.lua.

Skynet provides a general template in lualib/snax/gateserver.lua and also implements GateServer in gate.lua based on gateserver.lua.

TCP 是面向字节流的协议，我们需要把字节流流切割成数据包, 具体的方式见 分包.

TCP is a byte-oriented protocol, we need to unpack byte stream into data packages, check detail in 分包.

local gateserver = require "snax.gateserver"

local handler = {}

-- register handlers here

gateserver.start(handler)

注：gateserver.start 会调用 skynet.start 。如果你希望自己控制 skynet.start 的时机，那么可以将 handler.embed 设置为 true 。

Notice : gateserver.start will call skynet.start unless handler.embed == true .

这样就可以启动一个网关服务。handler 是一组自定义的消息回调函数.

Then gate server gets started. Handler is a set of user-defined callback functions.

function handler.connect(fd, ipaddr)

当一个新客户端被accept后，connect 方法会被回调。 fd 是socket句柄 (不是系统fd). ipaddr是客户端地址, 例如 "127.0.0.1:8000".

connect function will be called when a new client has been accepted. fd is a socket handler (not the system fd). ipaddr is the client address, eg: "127.0.0.1:8000".

function handler.disconnect(fd)

当一个连接断开，disconnect 被回调，fd 表示是哪个连接。

disconnect will be called for disconnection, fd is the specified connection.

function handler.error(fd, msg)

当一个连接异常（通常意味着断开），error 被调用，除了 fd ，还会拿到错误信息 msg（通常用于 log 输出）。

error will be called when there is an exception (which usually means disconnect). Besides fd, you'll get an error message: msg (for logging purpose).

function handler.command(cmd, source, ...)

如果你希望让服务处理一些 skynet 内部消息，可以注册 command 方法。收到 lua 协议的 skynet 消息，会调用这个方法。cmd 是消息的第一个值，通常约定为一个字符串，指明是什么指令。source 是消息的来源地址。这个方法的返回值，会通过 skynet.ret/skynet.pack 返回给来源服务。

If you want your service to handle Skeynet internal messages, you can register the command function. This function will be called when receiving Skynet messages of lua protocol. cmd is the first value of a message and it's usually a string telling what the command it is. source is the source address of the message. The return of this function will be passed to the caller through skynet.ret/skynet.pack.

open 和 close 这两个指令是保留的。它用于 gate 打开监听端口，和关闭监听端口。

open and close functions are kept, which are used for closing/opening a listening port for the gate.

function handler.open(source, conf)

如果你希望在监听端口打开的时候，做一些初始化操作，可以提供 open 这个方法。source 是请求来源地址，conf 是开启 gate 服务的参数表。

If you need init functions after opening a listening port, use the open function. source is the source address of the request, config is the parameters to start a gate server.

function handler.message(fd, msg, sz)

当一个完整的包被切分好后，message 方法被调用。这里 msg 是一个 C 指针、sz 是一个数字，表示包的长度（C 指针指向的内存块的长度）。注意：这个 C 指针需要在处理完毕后调用 C 方法 skynet_free 释放。（通常建议直接用封装好的库 netpack.tostring 来做这些底层的数据处理）；或是通过 skynet.redirect 转发给别的 skynet 服务处理。

The message function will be called when a package has been unpacked. msg is a C pointer, sz is a number meaning the size of the package (the size of memory c pointer points to). Note: the c pointer needs to be freed using the C function skynet_free once it's processed. (It's recommended to use netpack.tostring for basic data processing); or use skynet.redirect redirecting it to other Skynet services.

function handler.warning(fd, size)

当 fd 上待发送的数据累积超过 1M 字节后，将回调这个方法。你也可以忽略这个消息。

This function will be called if the accumulated pending data from fd is bigger than 1M, you can ignore this message though.

在这些方法中，还可以调用 gateserver 模块的方法如下：

Out of all these functions, here is how to call gateserver module function:

gateserver.openclient(fd)   -- 允许 fd 接收消息

每次收到 handler.connect 后，你都需要调用 openclient 让 fd 上的消息进入。默认状态下， fd 仅仅是连接上你的服务器，但无法发送消息给你。这个步骤需要你显式的调用是因为，或许你需要在新连接建立后，把 fd 的控制权转交给别的服务。那么你可以在一切准备好以后，再放行消息。

Every time you received handle.connect, you'll need to call openclient and allow messages in from fd. By default, fd only connects the server but doesn't allow sending messages. It's required to call this function explicitly because you may want to pass the controller of fd to other services when a connection is established. In that case, you can allow messages in after everything is ready.

gateserver.closeclient(fd) -- 关闭 fd

通常用于主动踢掉一个连接。

Close a connection explicitly.

包格式：

The format of data package:

每个包就是 2 个字节 + 数据内容。这两个字节是 Big-Endian 编码的一个数字。数据内容可以是任意字节。

Each package contains two bytes header + payload. These two bytes are Big-Endian encoded number. The payload can be any size.

所以，单个数据包最长不能超过 65535 字节。如果业务层需要传输更大的数据块，请在上层业务协议中解决。

So, every single data package cannot exceed 65535 bytes. If you need to transfer a large data package, please resolve it in in the feature layer .

skynet 提供一个netpack库用于处理分包问题， 位于lua-netpack.c。netpack根据包格式处理分包问题， netpack.filter(queue, msg, size)接口，它返回一个type(“data”, “more”, “error”, “open”, “close”)代表具体IO事件，其后返回每个事件所需参数。

Skynet provides a netpack lib for processing data unpacking, it's in lua-netpack.c. netpack unpacks the data based on data format, netpack.filter(queue, msg, size) API returns a type value (“data”, “more”, “error”, “open”, “close”) to represents an IO event and the parameters needed for this event.

对于SOCKET_DATA事件，filter会进行数据分包，如果分包后刚好有一条完整消息，filter返回的type为”data”，其后跟fd msg size。 如果不止一条消息，那么数据将被依次压入queue参数中，并且仅返回一个type为”more”。 queue是一个userdata，可以通过netpack.pop 弹出queue中的一条消息。

filter unpacks SOCKET_DATA event, if there is a complete message right after unpacking, filter returns type of "data" followed by fd msg size. If there is more than one message, data will be pushed into a queue parameter and return a type: "more". queue is a type of userdata and use netpack.pop to pop message from queue.

其余type类型”open”，”error”, “close”分别SOCKET_ACCEPT, SOCKET_ERROR, SOCKET_CLOSE事件。

Other types like "open", "error", "close" are for SOCKET_ACCEPT, SOCKET_ERROR, SOCKET_CLOSE events respectively.

netpack的使用者可以通过filter返回的type来分别进行事件处理。

The caller of netpack should process events based on the returned type.

netpack会尽可能多地分包，交给上层。并且通过一个哈希表保存每个套接字ID对应的粘包，在下次数据到达时，取出上次留下的粘包数据，重新分包.

netpack unpacks as much data as possible and passes it to the upper layer. And it's using a hash table to map each socket ID to its sticky package, when extra data arrives it retrieves the remaining sticky package and unpacks it again.

lualib-src/lua-netpack.c 是处理这类数据包的库。

lualib-src/lua-netpack.c is the lib to process this type of data package.

local netpack = require "skynet.netpack"

可以加载这个库。

Use the above code to load this lib.

• netpack.pack(msg, [sz]) 把一个字符串（或一个 C 指针加一个长度）打包成带 2 字节包头的数据块。这个 api 返回一个lightuserdata 和一个 number 。你可以直接送到 socket.write 发送（socket.write 负责最终释放内存）。

• netpack.tostring(msg, sz) 把 handler.message 方法收到的 msg,sz 转换成一个 lua string，并释放 msg 占用的 C 内存。

• netpack.pack(msg, [sz]) pack a string (or a c pointer with a size) into a data package with 2 bytes header. This function returns a lightuserdata and a number. You can send it with socket.write (it'll handle memory free.)

• netpack.tostring(msg, sz) convert msg and sz from handle.message function into a lua string and release the c memory of msg.

netpack 还有一些内部 api 用于 gate server 的实现。

netpack also provides other internal APIs for the implementation of gate server.

注意：除非你认为已经了解了细节和具备出错调试的能力，否则请不要直接使用 netpack 。

Note: unless you know the detail and know how to debug it, don't use netpack directly.

service/gate.lua 是一个实现完整的网关服务器，同时也可以作为 snax.gateserver 的使用范例。examples/watchdog.lua 是一个可以参考的例子，它启动了一个 service/gate.lua 服务，并将处理外部连接的消息转发处理。

service/gate.lua is a complete gate serer, it can also be used as an example of snax.gateserver. Another example can be found in examples/watchdog.lua, which starts a service in service/gate.lua and redirects messages needed by external connections.

gate 服务启动后，并非立刻开始监听。要让 gate 服务器开启监听端口，可以通过 lua 协议向它发送一个 open 指令，附带一个启动参数表，下面是一个示范：

gate server won't be listening right away when it's started. To make it listen to a port, use an open command with starting parameters using lua protocol, here is an example:

skynet.call(gate, "lua", "open", {
    address = "127.0.0.1", -- 监听地址 127.0.0.1
	port = 8888,    -- 监听端口 8888
	maxclient = 1024,   -- 最多允许 1024 个外部连接同时建立
	nodelay = true,     -- 给外部连接设置  TCP_NODELAY 属性
})

注: 这个模板不可以和 Socket 库一起使用。因为这个模板接管了 socket 类的消息。

Note: It's not allowed to use this module with Socket lib because it takes over socket messages.

skynet 并不限制你怎样编写网关，比如你还可以使用以下模块:

Skynet doesn't have a limitation on how you implementing gate server, you can use the following modules:

(tcp)http:https://blog.codingnow.com/2016/03/skynet_tcp_package.html

(websocket)https://gist.github.com/cloudfreexiao/851af8acff4ae5cf225d2ff19a94d327

(websocket-gate)https://github.com/xzhovo/skynet-websocket-gate

(websocket-gate reponse转发模式)https://github.com/hanxi/skynet-demo/blob/master/service/ws_gate.lua