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v4.go
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v4.go
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package v4
import (
"crypto/hmac"
"crypto/sha256"
"encoding/hex"
"fmt"
"io"
"net/http"
"net/url"
"sort"
"strconv"
"strings"
"time"
"github.com/awslabs/aws-sdk-go/aws/credentials"
"github.com/awslabs/aws-sdk-go/aws"
)
const (
authHeaderPrefix = "AWS4-HMAC-SHA256"
timeFormat = "20060102T150405Z"
shortTimeFormat = "20060102"
)
var ignoredHeaders = map[string]bool{
"Authorization": true,
"Content-Type": true,
"Content-Length": true,
"User-Agent": true,
}
type signer struct {
Request *http.Request
Time time.Time
ExpireTime time.Duration
ServiceName string
Region string
AccessKeyID string
SecretAccessKey string
SessionToken string
Query url.Values
Body io.ReadSeeker
Debug uint
Logger io.Writer
isPresign bool
formattedTime string
formattedShortTime string
signedHeaders string
canonicalHeaders string
canonicalString string
credentialString string
stringToSign string
signature string
authorization string
}
// Sign requests with signature version 4.
//
// Will sign the requests with the service config's Credentials object
// Signing is skipped if the credentials is the credentials.AnonymousCredentials
// object.
func Sign(req *aws.Request) {
// If the request does not need to be signed ignore the signing of the
// request if the AnonymousCredentials object is used.
if req.Service.Config.Credentials == credentials.AnonymousCredentials {
return
}
creds, err := req.Service.Config.Credentials.Get()
if err != nil {
req.Error = err
return
}
region := req.Service.SigningRegion
if region == "" {
region = req.Service.Config.Region
}
name := req.Service.SigningName
if name == "" {
name = req.Service.ServiceName
}
s := signer{
Request: req.HTTPRequest,
Time: req.Time,
ExpireTime: req.ExpireTime,
Query: req.HTTPRequest.URL.Query(),
Body: req.Body,
ServiceName: name,
Region: region,
AccessKeyID: creds.AccessKeyID,
SecretAccessKey: creds.SecretAccessKey,
SessionToken: creds.SessionToken,
Debug: req.Service.Config.LogLevel,
Logger: req.Service.Config.Logger,
}
s.sign()
return
}
func (v4 *signer) sign() {
if v4.ExpireTime != 0 {
v4.isPresign = true
}
if v4.isPresign {
v4.Query.Set("X-Amz-Algorithm", authHeaderPrefix)
if v4.SessionToken != "" {
v4.Query.Set("X-Amz-Security-Token", v4.SessionToken)
} else {
v4.Query.Del("X-Amz-Security-Token")
}
} else if v4.SessionToken != "" {
v4.Request.Header.Set("X-Amz-Security-Token", v4.SessionToken)
}
v4.build()
if v4.Debug > 0 {
out := v4.Logger
fmt.Fprintf(out, "---[ CANONICAL STRING ]-----------------------------\n")
fmt.Fprintln(out, v4.canonicalString)
fmt.Fprintf(out, "---[ STRING TO SIGN ]--------------------------------\n")
fmt.Fprintln(out, v4.stringToSign)
if v4.isPresign {
fmt.Fprintf(out, "---[ SIGNED URL ]--------------------------------\n")
fmt.Fprintln(out, v4.Request.URL)
}
fmt.Fprintf(out, "-----------------------------------------------------\n")
}
}
func (v4 *signer) build() {
v4.buildTime() // no depends
v4.buildCredentialString() // no depends
if v4.isPresign {
v4.buildQuery() // no depends
}
v4.buildCanonicalHeaders() // depends on cred string
v4.buildCanonicalString() // depends on canon headers / signed headers
v4.buildStringToSign() // depends on canon string
v4.buildSignature() // depends on string to sign
if v4.isPresign {
v4.Request.URL.RawQuery += "&X-Amz-Signature=" + v4.signature
} else {
parts := []string{
authHeaderPrefix + " Credential=" + v4.AccessKeyID + "/" + v4.credentialString,
"SignedHeaders=" + v4.signedHeaders,
"Signature=" + v4.signature,
}
v4.Request.Header.Set("Authorization", strings.Join(parts, ", "))
}
}
func (v4 *signer) buildTime() {
v4.formattedTime = v4.Time.UTC().Format(timeFormat)
v4.formattedShortTime = v4.Time.UTC().Format(shortTimeFormat)
if v4.isPresign {
duration := int64(v4.ExpireTime / time.Second)
v4.Query.Set("X-Amz-Date", v4.formattedTime)
v4.Query.Set("X-Amz-Expires", strconv.FormatInt(duration, 10))
} else {
v4.Request.Header.Set("X-Amz-Date", v4.formattedTime)
}
}
func (v4 *signer) buildCredentialString() {
v4.credentialString = strings.Join([]string{
v4.formattedShortTime,
v4.Region,
v4.ServiceName,
"aws4_request",
}, "/")
if v4.isPresign {
v4.Query.Set("X-Amz-Credential", v4.AccessKeyID+"/"+v4.credentialString)
}
}
func (v4 *signer) buildQuery() {
for k, h := range v4.Request.Header {
if strings.HasPrefix(http.CanonicalHeaderKey(k), "X-Amz-") {
continue // never hoist x-amz-* headers, they must be signed
}
if _, ok := ignoredHeaders[http.CanonicalHeaderKey(k)]; ok {
continue // never hoist ignored headers
}
v4.Request.Header.Del(k)
v4.Query.Del(k)
for _, v := range h {
v4.Query.Add(k, v)
}
}
}
func (v4 *signer) buildCanonicalHeaders() {
var headers []string
headers = append(headers, "host")
for k := range v4.Request.Header {
if _, ok := ignoredHeaders[http.CanonicalHeaderKey(k)]; ok {
continue // ignored header
}
headers = append(headers, strings.ToLower(k))
}
sort.Strings(headers)
v4.signedHeaders = strings.Join(headers, ";")
if v4.isPresign {
v4.Query.Set("X-Amz-SignedHeaders", v4.signedHeaders)
}
headerValues := make([]string, len(headers))
for i, k := range headers {
if k == "host" {
headerValues[i] = "host:" + v4.Request.URL.Host
} else {
headerValues[i] = k + ":" +
strings.Join(v4.Request.Header[http.CanonicalHeaderKey(k)], ",")
}
}
v4.canonicalHeaders = strings.Join(headerValues, "\n")
}
func (v4 *signer) buildCanonicalString() {
v4.Request.URL.RawQuery = strings.Replace(v4.Query.Encode(), "+", "%20", -1)
uri := v4.Request.URL.Opaque
if uri != "" {
uri = "/" + strings.Join(strings.Split(uri, "/")[3:], "/")
} else {
uri = v4.Request.URL.Path
}
if uri == "" {
uri = "/"
}
v4.canonicalString = strings.Join([]string{
v4.Request.Method,
uri,
v4.Request.URL.RawQuery,
v4.canonicalHeaders + "\n",
v4.signedHeaders,
v4.bodyDigest(),
}, "\n")
}
func (v4 *signer) buildStringToSign() {
v4.stringToSign = strings.Join([]string{
authHeaderPrefix,
v4.formattedTime,
v4.credentialString,
hex.EncodeToString(makeSha256([]byte(v4.canonicalString))),
}, "\n")
}
func (v4 *signer) buildSignature() {
secret := v4.SecretAccessKey
date := makeHmac([]byte("AWS4"+secret), []byte(v4.formattedShortTime))
region := makeHmac(date, []byte(v4.Region))
service := makeHmac(region, []byte(v4.ServiceName))
credentials := makeHmac(service, []byte("aws4_request"))
signature := makeHmac(credentials, []byte(v4.stringToSign))
v4.signature = hex.EncodeToString(signature)
}
func (v4 *signer) bodyDigest() string {
hash := v4.Request.Header.Get("X-Amz-Content-Sha256")
if hash == "" {
if v4.isPresign && v4.ServiceName == "s3" {
hash = "UNSIGNED-PAYLOAD"
} else if v4.Body == nil {
hash = hex.EncodeToString(makeSha256([]byte{}))
} else {
hash = hex.EncodeToString(makeSha256Reader(v4.Body))
}
v4.Request.Header.Add("X-Amz-Content-Sha256", hash)
}
return hash
}
func makeHmac(key []byte, data []byte) []byte {
hash := hmac.New(sha256.New, key)
hash.Write(data)
return hash.Sum(nil)
}
func makeSha256(data []byte) []byte {
hash := sha256.New()
hash.Write(data)
return hash.Sum(nil)
}
func makeSha256Reader(reader io.ReadSeeker) []byte {
packet := make([]byte, 4096)
hash := sha256.New()
start, _ := reader.Seek(0, 1)
defer reader.Seek(start, 0)
for {
n, err := reader.Read(packet)
if n > 0 {
hash.Write(packet[0:n])
}
if err == io.EOF || n == 0 {
break
}
}
return hash.Sum(nil)
}