通过 golang 中的多个 HTTP 处理程序包含上下文对象

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问题内容

我刚刚阅读了这篇关于创建函数类型并在该函数上实现方法以处理错误的[博客文章。](http://blog.golang.org/error-handling- and-go#TOC_3.).ServeHTTP()例如：

type appError struct {
    Error   error
    Message string
    Code    int
}

type appHandler func(http.ResponseWriter, *http.Request) *appError

func (fn appHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    if e := fn(w, r); e != nil { // e is *appError, not os.Error.
        http.Error(w, e.Message, e.Code)
    }
}

func init() {
    http.Handle("/view", appHandler(viewRecord)) //viewRecord is an appHandler function
}

我喜欢这种方法，但我无法从概念上弄清楚如何通过处理程序层包含上下文对象。例如：

func init() {
    http.Handle("/view", AuthHandler(appHandler(viewRecord))) 
}

AuthHandler可能会为每个请求创建一个&SessionToken{User: user}对象并将其设置在context.Context对象中。我不知道如何把它交给viewRecord处理程序。想法？

正确答案

我可以想到几种方法来做到这一点。

传递上下文

首先，您可以更改签名以接受上下文

type appHandler func(http.ResponseWriter, *http.Request, context.Context) *appError

func (fn appHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
        if e := fn(w, r, nil); e != nil { // e is *appError, not os.Error.
                http.Error(w, e.Message, e.Code)
        }
}

现在我假设 AuthHandler 与身份验证有关，并在上下文对象中设置用户。

您可以做的是创建另一个设置上下文的类型处理程序。像这样

type authHandler func(http.ResponseWriter, *http.Request, context.Context) *appError

func (fn authHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {           
    // setup authentication here                                                    
    uid := 1                                                                        

    // setup the context the way you want                                           
    parent := context.TODO()                                                        
    ctx := context.WithValue(parent, userIdKey, uid)                                
    if e := fn(w, r, ctx); e != nil { // e is *appError, not os.Error.              
        http.Error(w, e.Message, e.Code)                                            
    }                                                                               
}

这样你就可以通过以下方式使用它

func init() {                                                                         
    http.Handle("/view", appHandler(viewRecord))      // don't require authentication 
    http.Handle("/viewAuth", authHandler(viewRecord)) // require authentication       
}                                                                                     

这是完整的代码

package main

import (
        "fmt"
        "net/http"

        "code.google.com/p/go.net/context"
)

type appError struct {
        Error   error
        Message string
        Code    int
}

type key int

const userIdKey key = 0

type appHandler func(http.ResponseWriter, *http.Request, context.Context) *appError

func (fn appHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
        if e := fn(w, r, nil); e != nil { // e is *appError, not os.Error.
                http.Error(w, e.Message, e.Code)
        }
}

type authHandler func(http.ResponseWriter, *http.Request, context.Context) *appError

func (fn authHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
        // setup authentication here
        uid := 1

        // setup the context the way you want
        parent := context.TODO()
        ctx := context.WithValue(parent, userIdKey, uid)
        if e := fn(w, r, ctx); e != nil { // e is *appError, not os.Error.
                http.Error(w, e.Message, e.Code)
        }
}

func viewRecord(w http.ResponseWriter, r *http.Request, c context.Context) *appError {

        if c == nil {
                fmt.Fprintf(w, "User are not logged in")
        } else {
                uid := c.Value(userIdKey)
                fmt.Fprintf(w, "User logged in with uid: %d", uid)
        }

        return nil
}

func init() {
        http.Handle("/view", appHandler(viewRecord))      // viewRecord is an appHandler function
        http.Handle("/viewAuth", authHandler(viewRecord)) // viewRecord is an authHandler function
}

func main() {
        http.ListenAndServe(":8080", nil)
}

创建地图上下文

您无需传递上下文，而是创建

var contexts map[*http.Request]context.Context

view并在with中获取上下文contexts[r]。

但是由于 map 不是线程安全的，所以必须使用互斥锁来保护对 map 的访问。

猜猜看，这就是 gorilla context 正在为你做的事情，我认为这是更好的方法

https://github.com/gorilla/context/blob/master/context.go#l20-28

这是完整的代码

package main

import (
        "fmt"
        "net/http"

        "github.com/gorilla/context"
)

type appError struct {
        Error   error
        Message string
        Code    int
}

type key int

const userIdKey key = 0

type appHandler func(http.ResponseWriter, *http.Request) *appError

func (fn appHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
        if e := fn(w, r); e != nil { // e is *appError, not os.Error.
                http.Error(w, e.Message, e.Code)
        }
}

type authHandler func(http.ResponseWriter, *http.Request) *appError

func (fn authHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
        // setup authentication here
        uid := 1

        context.Set(r, userIdKey, uid)
        if e := fn(w, r); e != nil { // e is *appError, not os.Error.
                http.Error(w, e.Message, e.Code)
        }
}

func viewRecord(w http.ResponseWriter, r *http.Request) *appError {

        if uid, ok := context.GetOk(r, userIdKey); !ok {
                fmt.Fprintf(w, "User are not logged in")
        } else {
                fmt.Fprintf(w, "User logged in with uid: %d", uid)
        }

        return nil
}

func init() {
        http.Handle("/view", appHandler(viewRecord))      // don't require authentication
        http.Handle("/viewAuth", authHandler(viewRecord)) // require authentication
}

func main() {
        http.ListenAndServe(":8080", nil)
}

您还可以选择包装函数而不是类型函数进行身份验证

func AuthHandler(h appHandler) appHandler {                                   
    return func(w http.ResponseWriter, r *http.Request) *appError {
        // setup authentication here                                          
        uid := 1                                                              

        context.Set(r, userIdKey, uid)                                        
        return h(w, r)                                                        
    }                                                                        
}  

func init() {                                                                                    
    http.Handle("/view", appHandler(viewRecord))                  // don't require authentication
    http.Handle("/viewAuth", appHandler(AuthHandler(viewRecord))) // require authentication      
}                                                                                               

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