main.go

package main

import (
	"compress/gzip"
	"embed"
	"io"
	"io/fs"
	"log"
	"net/http"
	"os"
	"strings"
)

//go:embed static
var staticFS embed.FS

func compressMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if !strings.Contains(r.Header.Get("Accept-Encoding"), "gzip") {
			next.ServeHTTP(w, r)
			return
		}

		w.Header().Set("Content-Encoding", "gzip")
		gz := gzip.NewWriter(w)
		defer gz.Close()

		gzResponseWriter := gzipResponseWriter{
			ResponseWriter: w,
			Writer:         gz,
		}

		next.ServeHTTP(gzResponseWriter, r)
	})
}

type gzipResponseWriter struct {
	http.ResponseWriter
	io.Writer
}

func (w gzipResponseWriter) Write(b []byte) (int, error) {
	return w.Writer.Write(b)
}

func main() {
	log.Print("starting server...")
	port := os.Getenv("PORT")
	if port == "" {
		port = "8080"
	}

	staticSub, _ := fs.Sub(fs.FS(staticFS), "static")
	fileServer := http.FileServer(http.FS(staticSub))
	handler := compressMiddleware(fileServer)

	http.Handle("/", handler)

	log.Printf("listening on port %s", port)
	if err := http.ListenAndServe(":"+port, nil); err != nil {
		log.Fatal(err)
	}
}