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pack.go
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pack.go
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package crx3
import (
"bytes"
"crypto"
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"crypto/x509"
"encoding/binary"
"io"
"os"
"path"
"strings"
"github.com/mediabuyerbot/go-crx3/pb"
"google.golang.org/protobuf/proto"
)
const (
crxExt = ".crx"
zipExt = ".zip"
pemExt = ".pem"
)
// Pack packs a zip file or unzipped directory into a crx extension.
// It takes the source 'src' (zip file or directory), target 'dst' CRX file path,
// and a private key 'pk' (optional). If 'pk' is nil, it generates a new private key.
// It creates a CRX extension from the source and writes it to the destination.
func Pack(src string, dst string, pk *rsa.PrivateKey) (err error) {
var (
publicKey []byte
signedData []byte
signature []byte
header []byte
hasDst = len(dst) > 0
isDefaultPk bool
isNotCrxSuffix = path.Ext(dst) != crxExt
)
if len(src) == 0 || len(dst) == 0 {
return ErrPathNotFound
}
if hasDst && isNotCrxSuffix {
return ErrUnknownFileExtension
}
zipData, err := readZipFile(src)
if err != nil {
return err
}
// make default private key
if pk == nil {
pk, err = NewPrivateKey()
if err != nil {
return err
}
isDefaultPk = true
}
if publicKey, err = makePublicKey(pk); err != nil {
return err
}
if signedData, err = makeSignedData(publicKey); err != nil {
return err
}
if signature, err = makeSign(zipData, signedData, pk); err != nil {
return err
}
if header, err = makeHeader(publicKey, signature, signedData); err != nil {
return err
}
if _, err := zipData.Seek(0, 0); err != nil {
return err
}
if !hasDst {
crxFilename := strings.TrimSuffix(src, zipExt)
crxFilename = crxFilename + crxExt
dst = crxFilename
}
if err := writeToCRX(dst, zipData, header); err != nil {
return err
}
if isDefaultPk {
if err := saveDefaultPrivateKey(dst, pk); err != nil {
return err
}
}
return nil
}
func readZipFile(filename string) (data io.ReadSeeker, err error) {
var zipData bytes.Buffer
switch {
case isDir(filename):
if err := Zip(&zipData, filename); err != nil {
return nil, err
}
case isZip(filename):
file, err := os.Open(filename)
if err != nil {
return nil, err
}
defer file.Close()
if _, err := io.Copy(&zipData, file); err != nil {
return nil, err
}
default:
return nil, ErrUnknownFileExtension
}
return bytes.NewReader(zipData.Bytes()), nil
}
func writeToCRX(filename string, zipFile io.ReadSeeker, header []byte) error {
crx, err := os.Create(filename)
if err != nil {
return err
}
if _, err = crx.Write([]byte("Cr24")); err != nil {
return err
}
if err := binary.Write(crx, binary.LittleEndian, uint32(3)); err != nil {
return err
}
if err := binary.Write(crx, binary.LittleEndian, uint32(len(header))); err != nil {
return err
}
if _, err := crx.Write(header); err != nil {
return err
}
if _, err := io.Copy(crx, zipFile); err != nil {
return err
}
return nil
}
func makeCRXID(publicKey []byte) []byte {
hash := sha256.New()
hash.Write(publicKey)
return hash.Sum(nil)[0:16]
}
func makePublicKey(pk *rsa.PrivateKey) ([]byte, error) {
return x509.MarshalPKIXPublicKey(&pk.PublicKey)
}
func makeSignedData(publicKey []byte) ([]byte, error) {
signedData := &pb.SignedData{
CrxId: makeCRXID(publicKey),
}
return proto.Marshal(signedData)
}
func makeSign(r io.Reader, signedData []byte, pk *rsa.PrivateKey) ([]byte, error) {
sign := sha256.New()
sign.Write([]byte("CRX3 SignedData\x00"))
if err := binary.Write(sign, binary.LittleEndian, uint32(len(signedData))); err != nil {
return nil, err
}
sign.Write(signedData)
if _, err := io.Copy(sign, r); err != nil {
return nil, err
}
return rsa.SignPKCS1v15(rand.Reader, pk, crypto.SHA256, sign.Sum(nil))
}
func makeHeader(pubKey, signature, signedData []byte) ([]byte, error) {
header := &pb.CrxFileHeader{
Sha256WithRsa: []*pb.AsymmetricKeyProof{
{
PublicKey: pubKey,
Signature: signature,
},
},
SignedHeaderData: signedData,
}
return proto.Marshal(header)
}
func saveDefaultPrivateKey(filename string, pk *rsa.PrivateKey) error {
pemFilename := strings.TrimSuffix(filename, zipExt)
pemFilename = pemFilename + pemExt
return SavePrivateKey(pemFilename, pk)
}