go web framework gin 启动流程分析
最主要的package : gin
最主要的struct: Engine
Engine 是整个framework的实例,它包含了muxer, middleware, configuration settings. 通过New() 或者Default()来创建一个Engine 的实例。
type Engine struct {
RouterGroup // Enables automatic redirection if the current route can't be matched but a
// handler for the path with (without) the trailing slash exists.
// For example if /foo/ is requested but a route only exists for /foo, the
// client is redirected to /foo with http status code 301 for GET requests
// and 307 for all other request methods.
RedirectTrailingSlash bool // If enabled, the router tries to fix the current request path, if no
// handle is registered for it.
// First superfluous path elements like ../ or // are removed.
// Afterwards the router does a case-insensitive lookup of the cleaned path.
// If a handle can be found for this route, the router makes a redirection
// to the corrected path with status code 301 for GET requests and 307 for
// all other request methods.
// For example /FOO and /..//Foo could be redirected to /foo.
// RedirectTrailingSlash is independent of this option.
RedirectFixedPath bool // If enabled, the router checks if another method is allowed for the
// current route, if the current request can not be routed.
// If this is the case, the request is answered with 'Method Not Allowed'
// and HTTP status code 405.
// If no other Method is allowed, the request is delegated to the NotFound
// handler.
HandleMethodNotAllowed bool
ForwardedByClientIP bool // #726 #755 If enabled, it will thrust some headers starting with
// 'X-AppEngine...' for better integration with that PaaS.
AppEngine bool // If enabled, the url.RawPath will be used to find parameters.
UseRawPath bool // If true, the path value will be unescaped.
// If UseRawPath is false (by default), the UnescapePathValues effectively is true,
// as url.Path gonna be used, which is already unescaped.
UnescapePathValues bool // Value of 'maxMemory' param that is given to http.Request's ParseMultipartForm
// method call.
MaxMultipartMemory int64 delims render.Delims
secureJsonPrefix string
HTMLRender render.HTMLRender
FuncMap template.FuncMap
allNoRoute HandlersChain
allNoMethod HandlersChain
noRoute HandlersChain
noMethod HandlersChain
pool sync.Pool
trees methodTrees
}
获取一个gin Engin的实例:r := gin.Default()
查看gin.Default()方法的实现:
// Default returns an Engine instance with the Logger and Recovery middleware already attached.
func Default() *Engine {
debugPrintWARNINGDefault()
engine := New() #实例化一个engine
engine.Use(Logger(), Recovery())
return engine
}
查看New()的实现:
// New returns a new blank Engine instance without any middleware attached.
// By default the configuration is:
// - RedirectTrailingSlash: true
// - RedirectFixedPath: false
// - HandleMethodNotAllowed: false
// - ForwardedByClientIP: true
// - UseRawPath: false
// - UnescapePathValues: true
func New() *Engine {
debugPrintWARNINGNew()
engine := &Engine{
RouterGroup: RouterGroup{
Handlers: nil,
basePath: "/",
root: true,
},
FuncMap: template.FuncMap{},
RedirectTrailingSlash: true,
RedirectFixedPath: false,
HandleMethodNotAllowed: false,
ForwardedByClientIP: true,
AppEngine: defaultAppEngine,
UseRawPath: false,
UnescapePathValues: true,
MaxMultipartMemory: defaultMultipartMemory,
trees: make(methodTrees, 0, 9),
delims: render.Delims{Left: "{{", Right: "}}"},
secureJsonPrefix: "while(1);",
}
engine.RouterGroup.engine = engine
engine.pool.New = func() interface{} { //这里定义了engine.pool.New方法,所以在Get()的时候,如果为nil,那么直接执行New 方法
return engine.allocateContext()
}
return engine
}
如果engine.pool.New被执行,那么将返回一个*Context类型的指针。
func (engine *Engine) allocateContext() *Context {
return &Context{engine: engine}
}
然后调用r.Run(":8080"), 在本地网卡上监听8080端口,等待连接。实际上调用的是:http.ListenAndServe(address, engine)
查看http.ListenAndServe方法:
func ListenAndServe(addr string, handler Handler) error {
server := &Server{Addr: addr, Handler: handler}
return server.ListenAndServe()
}
它且将addr 和handler作为参数实例化了一个Server, 然后调用server.ListenAndServe()方法等待连接。
查看Handler的定义:
type Handler interface {
ServeHTTP(ResponseWriter, *Request)
}
它是一个interface, 那么也就是说它作为参数的话,那么这个struct必须实现ServeHTTP(ResponseWriter, *Request) 这个方法。
在gin.go中查看ServeHTTP方法的定义:
// ServeHTTP conforms to the http.Handler interface.
func (engine *Engine) ServeHTTP(w http.ResponseWriter, req *http.Request) {
c := engine.pool.Get().(*Context) 返回的是New()里面定义的func,然后执行。
c.writermem.reset(w)
c.Request = req
c.reset() engine.handleHTTPRequest(c) engine.pool.Put(c)
}
这里的engine.pool.Get().(*Context) 方法,实际上执行的是上面的New方法,所以得到的是一个Context类型的指针。
分析到这里,也就是说,如果有一个HTTP请求到来,那么会先触发ServeHTTP方法得到一个Context请求上下文,然后调用engine.handleHTTPRequest(C),处理这个请求,同时将处理的内容写入到http.ResponseWriter中。
关于engine.handleHTTPRequest()如何实现的,参考gin 路由表的设计
处理完以后为什么还要执行engine.pool.Put(c)呢?
因为:engine.pool需要一个buffer来存储内容,当下一个请求到达的时候,就可以直接来使用,避免又调用一次New函数,节省了内存。
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