通过golang中的多个HTTP处理程序包括上下文对象

Question

我刚刚读了这篇博客文章，内容涉及创建函数类型并.ServeHTTP()在该函数上实现方法以能够处理错误。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，但无法从概念上弄清楚如何通过处理程序层包括上下文对象。例如：

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

AuthHandler可能会创建一个&SessionToken{User: user}对象并在context.Context对象中为每个请求设置该对象。我不知道如何将其传递给viewRecord处理程序。有想法吗？

Answer 1

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了用户。

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)                                            
    }                                                                               
}

这样您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

并获得上下文中view使用contexts[r]。

但是由于映射不是线程安全的，因此必须使用互斥锁保护对映射的访问。

猜猜是什么，这就是大猩猩上下文正在为您做的事情，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      
}