参考资料

1. https://study.163.com/course/courseMain.htm?courseId=1210171207 李文周Mooc
2. https://www.liwenzhou.com/posts/Go/read_gin_sourcecode/#autoid-0-1-3 李文周博客

   Gin实例

   func main() {
    r := gin.Default()
    r.GET("/", func(c *gin.Context) {
        c.JSON(200, gin.H{
            "status": "ok",
        })
    })
    err := r.Run(":9090")
    if err != nil {
        log.Printf("start server failed, err: %v\n", err)
    }
   }

初始化

gin.Defalut()

// 使用gin.Default()创建的Engine包含一个Logger和Recovery的中间件。
func Default() *Engine {
    debugPrintWARNINGDefault()
    engine := New()
    engine.Use(Logger(), Recovery())
    return engine
}

gin.New()

// 使用gin.New()创建的Engine不包含任何中间件
// 默认配置：
// - 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,
        RemoteIPHeaders:        []string{"X-Forwarded-For", "X-Real-IP"},
        TrustedProxies:         []string{"0.0.0.0/0"},
        AppEngine:              defaultAppEngine,
        UseRawPath:             false,
        RemoveExtraSlash:       false,
        UnescapePathValues:     true,
        MaxMultipartMemory:     defaultMultipartMemory,
        trees:                  make(methodTrees, 0, 9), // 初始化路由树数量（最多9个HTTP方法）
        delims:                 render.Delims{Left: "{{", Right: "}}"},
        secureJSONPrefix:       "while(1);",
    }
    engine.RouterGroup.engine = engine
    engine.pool.New = func() interface{} {
        return engine.allocateContext()
    }
    return engine
}

type Engine

// Engine是一个gin框架的实例，包括路由、中间件及其他的一些配置
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
    // If enabled, client IP will be parsed from the request's headers that
    // match those stored at `(*gin.Engine).RemoteIPHeaders`. If no IP was
    // fetched, it falls back to the IP obtained from
    // `(*gin.Context).Request.RemoteAddr`.
    ForwardedByClientIP bool
    // List of headers used to obtain the client IP when
    // `(*gin.Engine).ForwardedByClientIP` is `true` and
    // `(*gin.Context).Request.RemoteAddr` is matched by at least one of the
    // network origins of `(*gin.Engine).TrustedProxies`.
    RemoteIPHeaders []string
    // List of network origins (IPv4 addresses, IPv4 CIDRs, IPv6 addresses or
    // IPv6 CIDRs) from which to trust request's headers that contain
    // alternative client IP when `(*gin.Engine).ForwardedByClientIP` is
    // `true`.
    TrustedProxies []string
    // #726 #755 If enabled, it will trust 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
    // RemoveExtraSlash a parameter can be parsed from the URL even with extra slashes.
    // See the PR #1817 and issue #1644
    RemoveExtraSlash bool
    delims           render.Delims
    secureJSONPrefix string
    HTMLRender       render.HTMLRender
    FuncMap          template.FuncMap
    allNoRoute       HandlersChain
    allNoMethod      HandlersChain
    noRoute          HandlersChain
    noMethod         HandlersChain
    pool             sync.Pool
    trees            methodTrees // 各类HTTP请求路由树的集合
    maxParams        uint16
    trustedCIDRs     []*net.IPNet
}
// 确保Engine实现了IRouter接口
var _ IRouter = &Engine{}

Context

// Contex是gin中最重要的结构，它使我们能使用中间件，管理流，处理和返回JSON数据
type Context struct {
    writermem responseWriter
    Request   *http.Request
    Writer    ResponseWriter
    Params   Params
    handlers HandlersChain
    index    int8
    fullPath string
    engine *Engine
    params *Params
    // This mutex protect Keys map
    mu sync.RWMutex
    // Keys is a key/value pair exclusively for the context of each request.
    Keys map[string]interface{}
    // Errors is a list of errors attached to all the handlers/middlewares who used this context.
    Errors errorMsgs
    // Accepted defines a list of manually accepted formats for content negotiation.
    Accepted []string
    // queryCache use url.ParseQuery cached the param query result from c.Request.URL.Query()
    queryCache url.Values
    // formCache use url.ParseQuery cached PostForm contains the parsed form data from POST, PATCH,
    // or PUT body parameters.
    formCache url.Values
    // SameSite allows a server to define a cookie attribute making it impossible for
    // the browser to send this cookie along with cross-site requests.
    sameSite http.SameSite
}