reverseproxy.go

package main

import (
    "fmt"
    "io"
    "log"
    "net/http"
    "net/url"
    "time"

    "golang.org/x/time/rate"
)

var limiter = rate.NewLimiter(rate.Every(time.Second*1), 10)

func main() {
    originServers := make([]*url.URL, 10)
    for i := 0; i < 10; i++ {
        serverURL, err := url.Parse(fmt.Sprintf("http://127.0.0.1:800%d", i))
        if err != nil {
            log.Fatalf("invalid origin server URL for server %d", i)
        }
        originServers[i] = serverURL
    }
    serverIndex := 0 // initial server index

    reverseProxy := http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
        token := req.Header.Get("Authorization")
        fmt.Println(token)
        if token != "mySecretToken" {
            rw.WriteHeader(http.StatusUnauthorized)
            _, _ = fmt.Fprint(rw, "Unauthorized access. Invalid token.")
            return
        }
        if !limiter.Allow() {
            rw.WriteHeader(http.StatusTooManyRequests)
            _, _ = fmt.Fprint(rw, "Rate limit exceeded. Try again later.")
            return
        }
        serverURL := originServers[serverIndex]
        serverIndex = (serverIndex + 1) % 10
        fmt.Printf("[reverse proxy server] received request at: %s\n", time.Now())
        
        // set req Host, URL and Request URI to forward a request to the origin server
        req.URL.Host = serverURL.Host
        req.URL.Scheme = serverURL.Scheme
        req.RequestURI = ""
        req.Header.Add("X-Forwarded-For", "Rad")

        originServerResponse, err := http.DefaultClient.Do(req)
        if err != nil {
            rw.WriteHeader(http.StatusInternalServerError)
            _, _ = fmt.Fprint(rw, err)
            return
        }

        rw.Header().Set("Hello", "Hi")
        io.Copy(rw, originServerResponse.Body)
        rw.WriteHeader(http.StatusOK)
    })

    log.Fatal(http.ListenAndServe(":8080", reverseProxy))
}