HTTP request tracing middleware

Bogdan Ungureanu
Programming

Request-based tracing provides a way to determine what exactly is happening with your requests and why.

It is handy when you want to reproduce and understand the problem that you are experiencing.

package middleware

import (
	"context"
	"net/http"
)
const RequestIDKey = "requestID"

func Tracing(nextRequestID func() string) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			requestID := r.Header.Get("X-Request-Id")
			if requestID == "" {
				requestID = nextRequestID()
			}

			ctx := context.WithValue(r.Context(), RequestIDKey, requestID)
			w.Header().Set("X-Request-Id", requestID)

			next.ServeHTTP(w, r.WithContext(ctx))
		})
	}
}

Example using the middleware with mux router and standard http package.

package main

import (
	"net/http"
	"github.com/some-user/some-project/pkg/http/middleware"
	"github.com/gorilla/mux"
	"github.com/google/uuid"
)

func main() {
	r := mux.NewRouter()

	nextIDfn := func() string {
	    return uuid.New().String()
	}

	r.Use(
		middleware.Tracing(nextIDfn),
	)

	http.ListenAndServe(":8080",r)
}