如何在http.HandleFunc中设置上下文值？ [英] How to set context value inside http.HandleFunc?

问题描述

我想在http.HandleFunc中设置一个上下文值。以下方法似乎起作用。

I want to set a context value inside an http.HandleFunc. The following approach seems to work.

虽然我有点担心 * r = * r.WithContext（ctx）。

type contextKey string
var myContext = contextKey("myContext")

func setValue(r *http.Request, val string)  {
  ctx := context.WithValue(r.Context(), myContext, val)
  *r = *r.WithContext(ctx)
}

http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
    setValue(r, "foobar")
})

在http.HandleFunc中设置上下文变量的最佳方法是什么？

What's the best approach to set a context variable inside an http.HandleFunc?

推荐答案

问题中的代码覆盖请求对象。这可能导致使用错误的上下文值对代码进行编码。 Request.WithContext创建请求的浅表副本以避免这种情况。
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The code in the question overwrites the request object. This can result in code up the stack using the wrong context value. Request.WithContext creates a shallow copy of the request to avoid this. Return a pointer to that shallow copy.

func setValue(r *http.Request, val string) *http.Requesst {
  return r.WithContext(context.WithValue(r.Context(), myContext, val))
}

http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
    r = setValue(r, "foobar")
})

如果处理程序调用其他处理程序，则将新请求传递给新处理程序：

If then handler invokes some other handler, then pass the new request along to the new handler:

http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
    r = setValue(r, "foobar")
    someOtherHandler.ServeHTTP(w, r)
})

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