s3-proxy/main.go

package main

import (
	"context"
	"io"
	"log"
	"net/http"
	"strings"

	"github.com/alexflint/go-arg"
	"github.com/minio/minio-go/v7"
	"github.com/minio/minio-go/v7/pkg/credentials"
)

type args struct {
	S3Endpoint   string `arg:"--s3-endpoint,required,env:S3_ENDPOINT" help:"host[:port]" placeholder:"ENDPOINT"`
	S3Bucket     string `arg:"--s3-bucket,required,env:S3_BUCKET" placeholder:"BUCKET"`
	S3AccessKey  string `arg:"--s3-access-key,env:S3_ACCESS_KEY" placeholder:"ACCESS_KEY"`
	S3SecretKey  string `arg:"--s3-secret-key,env:S3_SECRET_KEY" placeholder:"SECRET_KEY"`
	S3DisableSSL bool   `arg:"--s3-disable-ssl,env:S3_DISABLE_SSL" default:"false"`
	Address      string `arg:"--address,env:ADDRESS" default:":3000" help:"what address to listen on" placeholder:"ADDRESS"`
}

func (args) Version() string {
	// TODO
	return "s3-proxy 0.1"
}

var s3Client *minio.Client

func main() {
	// Warning: Shitty code

	var args args
	arg.MustParse(&args)

	client, err := newClientFromArgs(args)

	if err != nil {
		log.Panicf("Failed to create s3 client: %s", err.Error())
	}

	s3Client = client

	log.Printf("Starting webserver on: %s", args.Address)

	err = http.ListenAndServe(args.Address, http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
		path := r.URL.Path

		// Only allow GET and HEAD request
		if r.Method != http.MethodGet && r.Method != http.MethodHead {
			rw.WriteHeader(http.StatusMethodNotAllowed)
			return
		}

		// Edge case with root "/"
		if path == "/" {
			succ, err := tryObject(createIndexPath(path), rw, r)

			if err != nil {
				handleError(err, rw, r)
				return
			}

			if !succ {
				handle404(rw, r)
				return
			}

			return
		}

		// Edge case with paths ending with "/index.html"
		if strings.HasSuffix(path, "/index.html") {
			http.Redirect(rw, r, strings.TrimSuffix(path, "index.html"), http.StatusMovedPermanently)
			return
		}

		// If path ends with "/"
		if strings.HasSuffix(path, "/") {
			// Try the index file first
			succ, err := tryObject(createIndexPath(path), rw, r)

			if err != nil {
				handleError(err, rw, r)
				return
			}

			if succ {
				return
			}

			// If file without the "/" exists then redirect
			if objectExists(r.Context(), strings.TrimSuffix(path, "/")) {
				// Redirect
				http.Redirect(rw, r, strings.TrimSuffix(path, "/"), http.StatusMovedPermanently)
				return
			}

			// Else 404
			handle404(rw, r)
			return
		} else {
			// Try file first
			succ, err := tryObject(path, rw, r)

			if err != nil {
				handleError(err, rw, r)
				return
			}

			if succ {
				return
			}

			// If if path + "/" + "index.html" exists then redirect to path + "/"
			if objectExists(r.Context(), createIndexPath(path)) {
				redirectUrl := path + "/"
				http.Redirect(rw, r, redirectUrl, http.StatusMovedPermanently)
				return
			}

			// else 404
			handle404(rw, r)
			return
		}

	}))

	if err != nil {
		log.Printf("Failed to start webserver: %s", err.Error())
	}
}

func objectExists(ctx context.Context, key string) bool {
	_, err := s3Client.StatObject(ctx, "www", key, minio.GetObjectOptions{})
	response := minio.ToErrorResponse(err)

	return !(response.StatusCode == http.StatusNotFound)
}

func tryObject(key string, rw http.ResponseWriter, r *http.Request) (bool, error) {
	stat, err := s3Client.StatObject(r.Context(), "www", key, minio.GetObjectOptions{})

	if err != nil {
		if is404(err) {
			return false, nil
		} else {
			return false, err
		}
	}

	reqEtag := r.Header.Get("If-None-Match")
	if reqEtag == stat.ETag {
		rw.WriteHeader(http.StatusNotModified)
		return true, nil
	}

	rw.Header().Add("content-type", stat.ContentType)
	rw.Header().Add("ETag", stat.ETag)
	rw.Header().Add("Server", "Yo mama lol")

	if r.Method == http.MethodGet {
		obj, err := s3Client.GetObject(r.Context(), "www", key, minio.GetObjectOptions{})

		if err != nil {
			return false, err
		}

		_, err = io.Copy(rw, obj)

		if err != nil {
			return false, err
		}
	}

	return true, nil
}

func createIndexPath(s string) string {
	index := s

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

	index += "index.html"

	return index
}

func handleError(err error, rw http.ResponseWriter, r *http.Request) {
	log.Printf("error: %s : %s", r.URL.Path, err.Error())
	rw.WriteHeader(http.StatusInternalServerError)
}

func handle404(rw http.ResponseWriter, r *http.Request) {
	rw.WriteHeader(http.StatusNotFound)
}

func is404(err error) bool {
	resp := minio.ToErrorResponse(err)
	return resp.StatusCode == http.StatusNotFound
}

func newClientFromArgs(args args) (*minio.Client, error) {
	if args.S3AccessKey == "" {
		return minio.New(args.S3Endpoint, &minio.Options{
			Secure: !args.S3DisableSSL,
		})
	} else {
		return minio.New(args.S3Endpoint, &minio.Options{
			Secure: !args.S3DisableSSL,
			Creds:  credentials.NewStaticV4(args.S3AccessKey, args.S3SecretKey, ""),
		})
	}
}