如何全局访问处理程序值

Question

I have this simple http server. How can i access the request data to a global variable and use it in any part of the application.

package main

import (
    "io"
    "net/http"
)

var data string // Get URL data globally and use it in other part of the  application

func hello(w http.ResponseWriter, r *http.Request) {
    data := r.URL.Query().Get("somestring")
}

func main() {
    mux := http.NewServeMux()
    mux.HandleFunc("/", hello)

    http.ListenAndServe(":8000", mux)
}

Answer 1

You could use net/context with http.Handler. for example you have "X-Request-ID" in header, you could define middlware like this:

func middleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
        ctx := newContextWithRequestID(req.Context(), req)
        next.ServeHTTP(rw, req.WithContext(ctx))
    })
}
type key int
const requestIDKey key = 0

func newContextWithRequestID(ctx context.Context, req *http.Request) context.Context {
    reqID := req.Header.Get("X-Request-ID")
    if reqID == "" {
        reqID = generateRandomID()
    }

    return context.WithValue(ctx, requestIDKey, reqID)
}

func requestIDFromContext(ctx context.Context) string {
    return ctx.Value(requestIDKey).(string)
}

you could get requestIDKey in any handler with Context object.

func handler(rw http.ResponseWriter, req *http.Request) {
    reqID := requestIDFromContext(req.Context())
    fmt.Fprintf(rw, "Hello request ID %v\n", reqID)
}

this is just an example. insted of requestIDKey you could have any data which you should put in Context and read from it with a key. for more detail information visit this blog.