go-performance/main.go

package main

import (
	"bytes"
	"compress/gzip"
	"encoding/json"
	"fmt"
	"html/template"
	"log/slog"
	"net/http"
	"os"
	"os/signal"
	"regexp"
	"strconv"
	"strings"
	"syscall"
	"time"

	"example.com/go-performance/assets"
	"example.com/go-performance/internal/config"
)

const (
	cTcss   string = "text/css"
	cTxpem  string = "application/x-pem-file"
	cTpdf   string = "application/pdf"
	cTmpeg  string = "audio/mpeg"
	cTwoff  string = "font/woff"
	cTwoff2 string = "font/woff2"
	cTpng   string = "image/png"
	cTjpeg  string = "image/jpg"
	cTjs    string = "text/javascript"
	cTjson  string = "application/json"
	cTplain string = "text/plain"
	cTraw   string = "text/raw"
	cThtml  string = "text/html"
)

type webErrStruct struct {
	Error    bool   `json:"error"         yaml:"error"`
	ErrorMsg string `json:"error_message" yaml:"errorMessage"`
}

var (
	validFiles map[string]string = map[string]string{
		"/images/game.png": cTpng,
	}
	cfg config.Config
)

func forever(log *slog.Logger) {
	c := make(chan os.Signal, 1)
	signal.Notify(c, os.Interrupt, syscall.SIGTERM)

	sig := <-c
	log.Warn("Shutting down, triggered by signal", "signal", sig)
}

func main() {
	// initialize all parameters
	cfg = config.Init()

	// configure shutdown sequence
	defer func() {
		cfg.Log.Info("Shutdown sequence complete")
	}()

	// start webserver
	go httpServer(cfg.Log)

	forever(cfg.Log)
}

func httpServer(log *slog.Logger) {
	path := http.NewServeMux()

	connection := &http.Server{
		Addr:         cfg.WebServerIP + ":" + strconv.FormatInt(int64(cfg.WebServerPort), 10),
		Handler:      path,
		ReadTimeout:  time.Duration(cfg.WebServerReadTimeout) * time.Second,
		WriteTimeout: time.Duration(cfg.WebServerWriteTimeout) * time.Second,
		IdleTimeout:  time.Duration(cfg.WebServerIdleTimeout) * time.Second,
	}

	path.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) { webRoot(log, w, r) })

	if err := connection.ListenAndServe(); err != nil {
		log.Error("Unable to create webserver", "function", "httpServer", "error", err)
		panic(err)
	}
}

func isValidReq(file string) (string, error) {
	for f, t := range validFiles {
		if file == f {
			return t, nil
		}
	}

	return "", fmt.Errorf("Invalid file requested: %s", file)
}

func webRoot(log *slog.Logger, w http.ResponseWriter, r *http.Request) {
	httpAccessLog(log, r)

	if strings.ToLower(r.Method) != "get" {
		log.Debug("Request made using the wrong method", "function", "webRoot", "url", r.URL.Path, "expected-method", "GET", "requested-method", r.Method)
		tmpltError(log, w, http.StatusBadRequest, "Invalid http method.")
		return
	}

	if r.URL.Path == "/" {
		tmpltWebRoot(log, w)
		return
	}

	cType, err := isValidReq(r.URL.Path)
	if err != nil {
		log.Debug("Request not found", "function", "webRoot", "url", r.URL.Path)
		tmpltStatusNotFound(log, w, r.URL.Path)
		return
	}

	w.Header().Add("Content-Type", cType)
	o, err := assets.EmbedData.ReadFile("html" + r.URL.Path)
	if err != nil {
		log.Error("Unable to read local embedded file", "function", "webRoot", "error", err)
		tmpltError(log, w, http.StatusInternalServerError, "Server unable to retrieve file data.")
		return
	}

	if regexp.MustCompile(`gzip`).Match([]byte(r.Header.Get("Accept-Encoding"))) {
		w.Header().Add("Content-Encoding", "gzip")
		gw := gzip.NewWriter(w)
		defer gw.Close()
		gw.Write(o) //nolint: errcheck
	} else {
		w.Write(o) //nolint: errcheck
	}
}

func httpAccessLog(log *slog.Logger, req *http.Request) {
	log.Debug("AccessLog", "method", req.Method, "remote-addr", req.RemoteAddr, "uri", req.RequestURI)
}

func tmpltWebRoot(log *slog.Logger, w http.ResponseWriter) {
	tmplt, err := template.ParseFS(
		assets.EmbedData,
		"html/index.tplt",
	)
	if err != nil {
		log.Debug("Unable to parse HTML template", "function", "tmpltWebRoot", "error", err)
		tmpltError(log, w, http.StatusInternalServerError, "Template Parse Error.")
		return
	}

	var msgBuffer bytes.Buffer
	if err := tmplt.Execute(&msgBuffer, struct {
		Time    string
		Title   string
		Version string
	}{
		Time:    time.Now().In(cfg.TZLocal).Format(cfg.TimeFormat),
		Title:   "Performance Test",
		Version: "v1.0.0",
	}); err != nil {
		log.Debug("Unable to execute HTML template", "function", "tmpltWebRoot", "error", err)
		tmpltError(log, w, http.StatusInternalServerError, "Template Parse Error.")
		return
	}

	w.Write(msgBuffer.Bytes()) //nolint: errcheck
}

func tmpltError(log *slog.Logger, w http.ResponseWriter, serverStatus int, message string) {
	var (
		output []byte
		o      = webErrStruct{
			Error:    true,
			ErrorMsg: message,
		}
		err error
	)

	w.Header().Add("Content-Type", "application/json")
	output, err = json.MarshalIndent(o, "", "  ")
	if err != nil {
		log.Warn("Unable to marshal error", "function", "tmpltError", "error", err)
		w.WriteHeader(serverStatus)
		w.Write(output) //nolint:errcheck
	}
}

func tmpltStatusNotFound(log *slog.Logger, w http.ResponseWriter, path string) {
	tmplt, err := template.ParseFS(assets.EmbedData, "html/file-not-found.tplt")
	if err != nil {
		log.Debug("Unable to parse HTML template", "function", "tmpltStatusNotFound", "error", err)
		tmpltError(log, w, http.StatusInternalServerError, "Template Parse Error.")
		return
	}

	var msgBuffer bytes.Buffer
	if err := tmplt.Execute(&msgBuffer, struct {
		Title     string
		ErrorCode int
	}{
		Title:     path,
		ErrorCode: http.StatusNotFound,
	}); err != nil {
		log.Debug("Unable to execute HTML template", "function", "tmpltStatusNotFound", "error", err)
		tmpltError(log, w, http.StatusInternalServerError, "Template Parse Error.")
		return
	}
	w.Write(msgBuffer.Bytes()) //nolint: errcheck
}