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// Copyright 2020 Google LLC
//
// 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 storage
import (
"crypto"
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"encoding/base64"
"encoding/json"
"errors"
"fmt"
"net/url"
"strings"
"time"
)
// PostPolicyV4Options are used to construct a signed post policy.
// Please see https://cloud.google.com/storage/docs/xml-api/post-object
// for reference about the fields.
type PostPolicyV4Options struct {
// GoogleAccessID represents the authorizer of the signed URL generation.
// It is typically the Google service account client email address from
// the Google Developers Console in the form of "xxx@developer.gserviceaccount.com".
// Required.
GoogleAccessID string
// PrivateKey is the Google service account private key. It is obtainable
// from the Google Developers Console.
// At https://console.developers.google.com/project/<your-project-id>/apiui/credential,
// create a service account client ID or reuse one of your existing service account
// credentials. Click on the "Generate new P12 key" to generate and download
// a new private key. Once you download the P12 file, use the following command
// to convert it into a PEM file.
//
// $ openssl pkcs12 -in key.p12 -passin pass:notasecret -out key.pem -nodes
//
// Provide the contents of the PEM file as a byte slice.
// Exactly one of PrivateKey or SignBytes must be non-nil.
PrivateKey []byte
// SignBytes is a function for implementing custom signing. For example, if
// your application is running on Google App Engine, you can use
// appengine's internal signing function:
// ctx := appengine.NewContext(request)
// acc, _ := appengine.ServiceAccount(ctx)
// url, err := SignedURL("bucket", "object", &SignedURLOptions{
// GoogleAccessID: acc,
// SignBytes: func(b []byte) ([]byte, error) {
// _, signedBytes, err := appengine.SignBytes(ctx, b)
// return signedBytes, err
// },
// // etc.
// })
//
// Exactly one of PrivateKey or SignBytes must be non-nil.
SignBytes func(hashBytes []byte) (signature []byte, err error)
// Expires is the expiration time on the signed URL.
// It must be a time in the future.
// Required.
Expires time.Time
// Style provides options for the type of URL to use. Options are
// PathStyle (default), BucketBoundHostname, and VirtualHostedStyle. See
// https://cloud.google.com/storage/docs/request-endpoints for details.
// Optional.
Style URLStyle
// Insecure when set indicates that the generated URL's scheme
// will use "http" instead of "https" (default).
// Optional.
Insecure bool
// Fields specifies the attributes of a PostPolicyV4 request.
// When Fields is non-nil, its attributes must match those that will
// passed into field Conditions.
// Optional.
Fields *PolicyV4Fields
// The conditions that the uploaded file will be expected to conform to.
// When used, the failure of an upload to satisfy a condition will result in
// a 4XX status code, back with the message describing the problem.
// Optional.
Conditions []PostPolicyV4Condition
}
// PolicyV4Fields describes the attributes for a PostPolicyV4 request.
type PolicyV4Fields struct {
// ACL specifies the access control permissions for the object.
// Optional.
ACL string
// CacheControl specifies the caching directives for the object.
// Optional.
CacheControl string
// ContentType specifies the media type of the object.
// Optional.
ContentType string
// ContentDisposition specifies how the file will be served back to requesters.
// Optional.
ContentDisposition string
// ContentEncoding specifies the decompressive transcoding that the object.
// This field is complementary to ContentType in that the file could be
// compressed but ContentType specifies the file's original media type.
// Optional.
ContentEncoding string
// Metadata specifies custom metadata for the object.
// If any key doesn't begin with "x-goog-meta-", an error will be returned.
// Optional.
Metadata map[string]string
// StatusCodeOnSuccess when set, specifies the status code that Cloud Storage
// will serve back on successful upload of the object.
// Optional.
StatusCodeOnSuccess int
// RedirectToURLOnSuccess when set, specifies the URL that Cloud Storage
// will serve back on successful upload of the object.
// Optional.
RedirectToURLOnSuccess string
}
// PostPolicyV4 describes the URL and respective form fields for a generated PostPolicyV4 request.
type PostPolicyV4 struct {
// URL is the generated URL that the file upload will be made to.
URL string
// Fields specifies the generated key-values that the file uploader
// must include in their multipart upload form.
Fields map[string]string
}
// PostPolicyV4Condition describes the constraints that the subsequent
// object upload's multipart form fields will be expected to conform to.
type PostPolicyV4Condition interface {
isEmpty() bool
json.Marshaler
}
type startsWith struct {
key, value string
}
func (sw *startsWith) MarshalJSON() ([]byte, error) {
return json.Marshal([]string{"starts-with", sw.key, sw.value})
}
func (sw *startsWith) isEmpty() bool {
return sw.value == ""
}
// ConditionStartsWith checks that an attributes starts with value.
// An empty value will cause this condition to be ignored.
func ConditionStartsWith(key, value string) PostPolicyV4Condition {
return &startsWith{key, value}
}
type contentLengthRangeCondition struct {
start, end uint64
}
func (clr *contentLengthRangeCondition) MarshalJSON() ([]byte, error) {
return json.Marshal([]interface{}{"content-length-range", clr.start, clr.end})
}
func (clr *contentLengthRangeCondition) isEmpty() bool {
return clr.start == 0 && clr.end == 0
}
type singleValueCondition struct {
name, value string
}
func (svc *singleValueCondition) MarshalJSON() ([]byte, error) {
return json.Marshal(map[string]string{svc.name: svc.value})
}
func (svc *singleValueCondition) isEmpty() bool {
return svc.value == ""
}
// ConditionContentLengthRange constraints the limits that the
// multipart upload's range header will be expected to be within.
func ConditionContentLengthRange(start, end uint64) PostPolicyV4Condition {
return &contentLengthRangeCondition{start, end}
}
func conditionRedirectToURLOnSuccess(redirectURL string) PostPolicyV4Condition {
return &singleValueCondition{"success_action_redirect", redirectURL}
}
func conditionStatusCodeOnSuccess(statusCode int) PostPolicyV4Condition {
svc := &singleValueCondition{name: "success_action_status"}
if statusCode > 0 {
svc.value = fmt.Sprintf("%d", statusCode)
}
return svc
}
// GenerateSignedPostPolicyV4 generates a PostPolicyV4 value from bucket, object and opts.
// The generated URL and fields will then allow an unauthenticated client to perform multipart uploads.
func GenerateSignedPostPolicyV4(bucket, object string, opts *PostPolicyV4Options) (*PostPolicyV4, error) {
if bucket == "" {
return nil, errors.New("storage: bucket must be non-empty")
}
if object == "" {
return nil, errors.New("storage: object must be non-empty")
}
now := utcNow()
if err := validatePostPolicyV4Options(opts, now); err != nil {
return nil, err
}
var signingFn func(hashedBytes []byte) ([]byte, error)
switch {
case opts.SignBytes != nil:
signingFn = opts.SignBytes
case len(opts.PrivateKey) != 0:
parsedRSAPrivKey, err := parseKey(opts.PrivateKey)
if err != nil {
return nil, err
}
signingFn = func(hashedBytes []byte) ([]byte, error) {
return rsa.SignPKCS1v15(rand.Reader, parsedRSAPrivKey, crypto.SHA256, hashedBytes)
}
default:
return nil, errors.New("storage: exactly one of PrivateKey or SignedBytes must be set")
}
var descFields PolicyV4Fields
if opts.Fields != nil {
descFields = *opts.Fields
}
if err := validateMetadata(descFields.Metadata); err != nil {
return nil, err
}
// Build the policy.
conds := make([]PostPolicyV4Condition, len(opts.Conditions))
copy(conds, opts.Conditions)
conds = append(conds,
conditionRedirectToURLOnSuccess(descFields.RedirectToURLOnSuccess),
conditionStatusCodeOnSuccess(descFields.StatusCodeOnSuccess),
&singleValueCondition{"acl", descFields.ACL},
&singleValueCondition{"cache-control", descFields.CacheControl},
)
YYYYMMDD := now.Format(yearMonthDay)
policyFields := map[string]string{
"key": object,
"x-goog-date": now.Format(iso8601),
"x-goog-credential": opts.GoogleAccessID + "/" + YYYYMMDD + "/auto/storage/goog4_request",
"x-goog-algorithm": "GOOG4-RSA-SHA256",
"success_action_redirect": descFields.RedirectToURLOnSuccess,
"acl": descFields.ACL,
}
for key, value := range descFields.Metadata {
conds = append(conds, &singleValueCondition{key, value})
policyFields[key] = value
}
// Following from the order expected by the conformance test cases,
// hence manually inserting these fields in a specific order.
conds = append(conds,
&singleValueCondition{"bucket", bucket},
&singleValueCondition{"key", object},
&singleValueCondition{"x-goog-date", now.Format(iso8601)},
&singleValueCondition{
name: "x-goog-credential",
value: opts.GoogleAccessID + "/" + YYYYMMDD + "/auto/storage/goog4_request",
},
&singleValueCondition{"x-goog-algorithm", "GOOG4-RSA-SHA256"},
)
nonEmptyConds := make([]PostPolicyV4Condition, 0, len(opts.Conditions))
for _, cond := range conds {
if cond == nil || !cond.isEmpty() {
nonEmptyConds = append(nonEmptyConds, cond)
}
}
condsAsJSON, err := json.Marshal(map[string]interface{}{
"conditions": nonEmptyConds,
"expiration": opts.Expires.Format(time.RFC3339),
})
if err != nil {
return nil, fmt.Errorf("storage: PostPolicyV4 JSON serialization failed: %v", err)
}
b64Policy := base64.StdEncoding.EncodeToString(condsAsJSON)
shaSum := sha256.Sum256([]byte(b64Policy))
signature, err := signingFn(shaSum[:])
if err != nil {
return nil, err
}
policyFields["policy"] = b64Policy
policyFields["x-goog-signature"] = fmt.Sprintf("%x", signature)
// Construct the URL.
scheme := "https"
if opts.Insecure {
scheme = "http"
}
path := opts.Style.path(bucket, "") + "/"
u := &url.URL{
Path: path,
RawPath: pathEncodeV4(path),
Host: opts.Style.host(bucket),
Scheme: scheme,
}
if descFields.StatusCodeOnSuccess > 0 {
policyFields["success_action_status"] = fmt.Sprintf("%d", descFields.StatusCodeOnSuccess)
}
// Clear out fields with blanks values.
for key, value := range policyFields {
if value == "" {
delete(policyFields, key)
}
}
pp4 := &PostPolicyV4{
Fields: policyFields,
URL: u.String(),
}
return pp4, nil
}
// validatePostPolicyV4Options checks that:
// * GoogleAccessID is set
// * either but not both PrivateKey and SignBytes are set or nil, but not both
// * Expires, the deadline is not in the past
// * if Style is not set, it'll use PathStyle
func validatePostPolicyV4Options(opts *PostPolicyV4Options, now time.Time) error {
if opts == nil || opts.GoogleAccessID == "" {
return errors.New("storage: missing required GoogleAccessID")
}
if privBlank, signBlank := len(opts.PrivateKey) == 0, opts.SignBytes == nil; privBlank == signBlank {
return errors.New("storage: exactly one of PrivateKey or SignedBytes must be set")
}
if opts.Expires.Before(now) {
return errors.New("storage: expecting Expires to be in the future")
}
if opts.Style == nil {
opts.Style = PathStyle()
}
return nil
}
// validateMetadata ensures that all keys passed in have a prefix of "x-goog-meta-",
// otherwise it will return an error.
func validateMetadata(hdrs map[string]string) (err error) {
if len(hdrs) == 0 {
return nil
}
badKeys := make([]string, 0, len(hdrs))
for key := range hdrs {
if !strings.HasPrefix(key, "x-goog-meta-") {
badKeys = append(badKeys, key)
}
}
if len(badKeys) != 0 {
err = errors.New("storage: expected metadata to begin with x-goog-meta-, got " + strings.Join(badKeys, ", "))
}
return
}