vegvisir/server/server.go

package server

//           ___   ____               ___       ___
// \ \  / / | _   |  __| \ \  / / || | __  || || _ |
//  \ \/ /  |___  | |__   \ \/ /  || |___  || ||___|
//   \  /   | _   | _  |   \  /   ||  __ | || ||\\
//    \/    |___  |___ |    \/    || ____| || || \\

// Copyright (c) 2021 Piotr Biernat. https://pbiernat.dev. MIT License
// Repo: https://git.pbiernat.dev/golang/vegvisir

import (
	"context"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"log"
	"os"
	"os/signal"
	"regexp"
	"strings"
	"time"
	"vegvisir/config"

	"github.com/valyala/fasthttp"
)

const (
	Version = "0.1"
	Name    = "Vegvisir/" + Version
)

type Server struct {
	Config config.Config

	cFilePath    string
	foundBackend *config.Backend
	foundRoute   *config.Route
}

func NewServer(cPath string) *Server {
	return &Server{
		cFilePath: cPath,
	}
}

func (s *Server) Run() {
	if err := s.loadConfig(); err != nil {
		log.Fatalln("Unable to find config file: ", s.cFilePath, err)
	}

	go func() {
		serverAddress := s.Config.Server.Address + ":" + fmt.Sprint(s.Config.Server.Port)
		if err := fasthttp.ListenAndServe(serverAddress, s.mainHandler); err != nil {
			log.Fatalf("Server panic! Error message: %s", err)
		}
	}()

	log.Println("Server started")

	// Wait for an interrupt
	interrupt := make(chan os.Signal, 1)
	signal.Notify(interrupt, os.Interrupt, os.Kill)
	<-interrupt

	log.Println("SIGKILL or SIGINT caught, shutting down...")

	// Attempt a graceful shutdown
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()

	s.Shutdown(ctx)
	log.Println("Server shutdown successfully.")
}

func (s *Server) Shutdown(ctx context.Context) { // TODO: wait for all connections to finish
	log.Println("Shuting down finished")
}

func (s *Server) loadConfig() error {
	if _, err := os.Stat(s.cFilePath); err != nil {
		return err
	}

	data, err := ioutil.ReadFile(s.cFilePath)
	if err != nil {
		return err
	}

	err = json.Unmarshal(data, &s.Config)
	if err != nil {
		return err
	}

	return nil
}

func (s *Server) mainHandler(ctx *fasthttp.RequestCtx) {
	ctx.Response.Header.Add(fasthttp.HeaderServer, Name)

	// move all below logic to concrete handler or sth....?
	reqURI, sReqURI, sReqMethod := ctx.RequestURI(), string(ctx.RequestURI()), string(ctx.Method())
	log.Println("Incomming request:", sReqMethod, sReqURI)

	found, rgxp := s.findBackendAndRouteByRequestURI(reqURI)
	if !found {
		// FIXME: return 404/5xx error in repsonse, maybe define it in Backend config?
		ctx.Response.SetStatusCode(fasthttp.StatusNotFound)
		return
	}

	bckReqURI := s.buildBackendTargetURI(*rgxp, sReqURI)

	// prepare to send request to backend - separate
	bckReq := fasthttp.AcquireRequest()
	bckResp := fasthttp.AcquireResponse()
	defer fasthttp.ReleaseRequest(bckReq)
	defer fasthttp.ReleaseResponse(bckResp)

	// copy headers from backend response and prepare request for backend - separate
	bckReq.SetRequestURI(bckReqURI)
	bckReq.Header.SetMethod(sReqMethod)

	fasthttp.Do(bckReq, bckResp)

	ctx.Response.Header.SetBytesV(fasthttp.HeaderContentType, bckResp.Header.ContentType())
	ctx.SetBody(bckResp.Body())
}

func (s *Server) findBackendAndRouteByRequestURI(uri []byte) (bool, *regexp.Regexp) {
	for _, bck := range s.Config.Backends {
		if !strings.Contains(string(uri), bck.PrefixUrl) {
			continue
		}
		s.foundBackend = &bck // possibly errorneus...

		for _, r := range bck.Routes {
			rgxp := regexp.MustCompile(fmt.Sprintf("%s%s", bck.PrefixUrl, r.Pattern))
			// fmt.Println("pattern: ", bck.PrefixUrl+r.Pattern, rgxp.Match(uri))
			if rgxp.Match(uri) {
				s.foundBackend = &bck // 100% safe here
				s.foundRoute = &r

				return true, rgxp
			}
		}
	}

	return false, nil
}

func (s *Server) buildBackendTargetURI(rgxp regexp.Regexp, uri string) string {
	baseURI := s.foundBackend.BackendAddress
	url := rgxp.ReplaceAllString(uri, s.foundRoute.Target)

	// if !strings.HasSuffix(baseURI, "/") {
	// 	baseURI += "/"
	// }

	log.Println("Send req to backend url: ", baseURI+url)

	return baseURI + url
}