How to access handler value globally - go

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.
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