perkeep/internal/amazon/s3/auth.go

/*
Copyright 2011 The Perkeep Authors

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package s3

import (
	"bytes"
	"crypto/hmac"
	"crypto/sha1"
	"encoding/base64"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"sort"
	"strings"
	"time"
)

// See http://docs.amazonwebservices.com/AmazonS3/latest/dev/index.html?RESTAuthentication.html

type Auth struct {
	AccessKey       string
	SecretAccessKey string

	// Hostname is the S3 hostname to use.
	// If empty, the standard US region of "s3.amazonaws.com" is
	// used.
	Hostname string
}

const standardUSRegionAWS = "s3.amazonaws.com"

func (a *Auth) hostname() string {
	if a.Hostname != "" {
		return a.Hostname
	}
	return standardUSRegionAWS
}

func (a *Auth) SignRequest(req *http.Request) {
	if date := req.Header.Get("Date"); date == "" {
		req.Header.Set("Date", time.Now().UTC().Format(http.TimeFormat))
	}
	hm := hmac.New(sha1.New, []byte(a.SecretAccessKey))
	ss := a.stringToSign(req)
	// log.Printf("String to sign: %q (%x)", ss, ss)
	io.WriteString(hm, ss)

	authHeader := new(bytes.Buffer)
	fmt.Fprintf(authHeader, "AWS %s:", a.AccessKey)
	encoder := base64.NewEncoder(base64.StdEncoding, authHeader)
	encoder.Write(hm.Sum(nil))
	encoder.Close()
	req.Header.Set("Authorization", authHeader.String())
}

// From the Amazon docs:
//
// StringToSign = HTTP-Verb + "\n" +
// 	 Content-MD5 + "\n" +
//	 Content-Type + "\n" +
//	 Date + "\n" +
//	 CanonicalizedAmzHeaders +
//	 CanonicalizedResource;
func (a *Auth) stringToSign(req *http.Request) string {
	buf := new(bytes.Buffer)
	buf.WriteString(req.Method)
	buf.WriteByte('\n')
	buf.WriteString(req.Header.Get("Content-MD5"))
	buf.WriteByte('\n')
	buf.WriteString(req.Header.Get("Content-Type"))
	buf.WriteByte('\n')
	if req.Header.Get("x-amz-date") == "" {
		buf.WriteString(req.Header.Get("Date"))
	}
	buf.WriteByte('\n')
	a.writeCanonicalizedAmzHeaders(buf, req)
	a.writeCanonicalizedResource(buf, req)
	return buf.String()
}

func hasPrefixCaseInsensitive(s, pfx string) bool {
	if len(pfx) > len(s) {
		return false
	}
	shead := s[:len(pfx)]
	if shead == pfx {
		return true
	}
	shead = strings.ToLower(shead)
	return shead == pfx || shead == strings.ToLower(pfx)
}

func (a *Auth) writeCanonicalizedAmzHeaders(buf *bytes.Buffer, req *http.Request) {
	amzHeaders := make([]string, 0)
	vals := make(map[string][]string)
	for k, vv := range req.Header {
		if hasPrefixCaseInsensitive(k, "x-amz-") {
			lk := strings.ToLower(k)
			amzHeaders = append(amzHeaders, lk)
			vals[lk] = vv
		}
	}
	sort.Strings(amzHeaders)
	for _, k := range amzHeaders {
		buf.WriteString(k)
		buf.WriteByte(':')
		for idx, v := range vals[k] {
			if idx > 0 {
				buf.WriteByte(',')
			}
			if strings.Contains(v, "\n") {
				// TODO: "Unfold" long headers that
				// span multiple lines (as allowed by
				// RFC 2616, section 4.2) by replacing
				// the folding white-space (including
				// new-line) by a single space.
				buf.WriteString(v)
			} else {
				buf.WriteString(v)
			}
		}
		buf.WriteByte('\n')
	}
}

// Must be sorted:
var subResList = []string{"acl", "lifecycle", "location", "logging", "notification", "partNumber", "policy", "requestPayment", "torrent", "uploadId", "uploads", "versionId", "versioning", "versions", "website"}

// From the Amazon docs:
//
// CanonicalizedResource = [ "/" + Bucket ] +
// 	  <HTTP-Request-URI, from the protocol name up to the query string> +
// 	  [ sub-resource, if present. For example "?acl", "?location", "?logging", or "?torrent"];
func (a *Auth) writeCanonicalizedResource(buf *bytes.Buffer, req *http.Request) {
	bucket := a.bucketFromHostname(req)
	if bucket != "" {
		buf.WriteByte('/')
		buf.WriteString(bucket)
	}
	buf.WriteString(req.URL.Path)
	if req.URL.RawQuery != "" {
		n := 0
		vals, _ := url.ParseQuery(req.URL.RawQuery)
		for _, subres := range subResList {
			if vv, ok := vals[subres]; ok && len(vv) > 0 {
				n++
				if n == 1 {
					buf.WriteByte('?')
				} else {
					buf.WriteByte('&')
				}
				buf.WriteString(subres)
				if len(vv[0]) > 0 {
					buf.WriteByte('=')
					buf.WriteString(url.QueryEscape(vv[0]))
				}
			}
		}
	}
}

// hasDotSuffix reports whether s ends with "." + suffix.
func hasDotSuffix(s string, suffix string) bool {
	return len(s) >= len(suffix)+1 && strings.HasSuffix(s, suffix) && s[len(s)-len(suffix)-1] == '.'
}

func (a *Auth) bucketFromHostname(req *http.Request) string {
	host := req.Host
	if host == "" {
		host = req.URL.Host
	}
	if host == a.hostname() {
		return ""
	}
	if hostSuffix := a.hostname(); hasDotSuffix(host, hostSuffix) {
		return host[:len(host)-len(hostSuffix)-1]
	}
	if lastColon := strings.LastIndex(host, ":"); lastColon != -1 {
		return host[:lastColon]
	}
	return host
}