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// Copyright 2018 The Hugo Authors. All rights reserved.
//
// 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 integrity
import (
"crypto/md5"
"crypto/sha256"
"crypto/sha512"
"encoding/base64"
"encoding/hex"
"fmt"
"hash"
"html/template"
"io"
"github.com/gohugoio/hugo/resource"
)
const defaultHashAlgo = "sha256"
// Client contains methods to fingerprint (cachebusting) and other integrity-related
// methods.
type Client struct {
rs *resource.Spec
}
// New creates a new Client with the given specification.
func New(rs *resource.Spec) *Client {
return &Client{rs: rs}
}
type fingerprintTransformation struct {
algo string
}
func (t *fingerprintTransformation) Key() resource.ResourceTransformationKey {
return resource.NewResourceTransformationKey("fingerprint", t.algo)
}
// Transform creates a MD5 hash of the Resource content and inserts that hash before
// the extension in the filename.
func (t *fingerprintTransformation) Transform(ctx *resource.ResourceTransformationCtx) error {
algo := t.algo
var h hash.Hash
switch algo {
case "md5":
h = md5.New()
case "sha256":
h = sha256.New()
case "sha512":
h = sha512.New()
default:
return fmt.Errorf("unsupported crypto algo: %q, use either md5, sha256 or sha512", algo)
}
io.Copy(io.MultiWriter(h, ctx.To), ctx.From)
d, err := digest(h)
if err != nil {
return err
}
ctx.Data["Integrity"] = integrity(algo, d)
ctx.AddOutPathIdentifier("." + hex.EncodeToString(d[:]))
return nil
}
// Fingerprint applies fingerprinting of the given resource and hash algorithm.
// It defaults to sha256 if none given, and the options are md5, sha256 or sha512.
// The same algo is used for both the fingerprinting part (aka cache busting) and
// the base64-encoded Subresource Integrity hash, so you will have to stay away from
// md5 if you plan to use both.
// See https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity
func (c *Client) Fingerprint(res resource.Resource, algo string) (resource.Resource, error) {
if algo == "" {
algo = defaultHashAlgo
}
return c.rs.Transform(
res,
&fingerprintTransformation{algo: algo},
)
}
func integrity(algo string, sum []byte) template.HTMLAttr {
encoded := base64.StdEncoding.EncodeToString(sum)
return template.HTMLAttr(algo + "-" + encoded)
}
func digest(h hash.Hash) ([]byte, error) {
sum := h.Sum(nil)
return sum, nil
}
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