S3 Proxy in Go

s3proxy.go

package main

import (
	"crypto/sha256"
	"flag"
	"fmt"
	"github.com/gorilla/mux"
	"hash"
	"io"
	"launchpad.net/goamz/aws"
	"launchpad.net/goamz/s3"
	"log"
	"net/http"
)

var BucketName string

func main() {
	flag.StringVar(&BucketName, "bucket", "", "The name of the bucket to be used")
	flag.Parse()
	if BucketName == "" {
		log.Fatalf("Specify a bucket name")
	}

	r := mux.NewRouter()
	r.HandleFunc("/{path:.+}", download).Methods("GET")
	r.HandleFunc("/{path:.+}", upload).Methods("PUT")

	http.Handle("/", r)

	log.Println("Listening on :8000")
	log.Println("Bucket:", BucketName)
	log.Fatal(http.ListenAndServe(":8000", nil))
}

func getBucket() (*s3.Bucket, error) {
	auth, err := aws.EnvAuth()
	if err != nil {
		return nil, err
	}
	s3conn := s3.New(auth, aws.Region{S3Endpoint: "https://s3.amazonaws.com"})
	bucket := s3conn.Bucket(BucketName)
	return bucket, nil
}

func download(w http.ResponseWriter, r *http.Request) {
	b, err := getBucket()
	if err != nil {
		http.Error(w, err.Error(), 500)
		return
	}

	reader, err := b.GetReader(r.URL.Path)
	if err != nil {
		http.Error(w, err.Error(), 500)
		return
	}
	defer reader.Close()

	buf := make([]byte, 8192)
	for {
		n, err := reader.Read(buf)
		if n > 0 {
			w.Write(buf[:n])
		}
		if n == 0 {
			break
		}
		if err != nil {
			http.Error(w, err.Error(), 500)
			return
		}
	}
}

func upload(w http.ResponseWriter, r *http.Request) {
	b, err := getBucket()
	if err != nil {
		http.Error(w, err.Error(), 500)
		return
	}

	bodyReader := &ReadHasher{h: sha256.New(), r: r.Body}

	err = b.PutReader(r.URL.Path, bodyReader, r.ContentLength, "", "private")
	if err != nil {
		http.Error(w, err.Error(), 500)
		return
	}

	fmt.Fprintf(w, "%x", bodyReader.Sum(nil))
}

type ReadHasher struct {
	h hash.Hash
	r io.Reader
}

func (rh *ReadHasher) Read(buf []byte) (n int, err error) {
	n, err = rh.r.Read(buf)
	if err != nil {
		return n, err
	}

	rh.h.Write(buf[:n])

	return
}

func (rh *ReadHasher) Sum(b []byte) []byte {
	return rh.h.Sum(b)
}