Let the modified date/time be settable when writing a zip file

.gitignore

@@ -24,3 +24,8 @@ _testmain.go
 *.exe
 *.test
 *.prof
+
+# Go dependencies
+vendor/
+Gopkg.toml
+Gopkg.lock

crypto.go

@@ -15,12 +15,15 @@ import (
 	"errors"
 	"hash"
 	"io"
+	"time"
 
 	"golang.org/x/crypto/pbkdf2"
 )
 
+// EncryptionMethod is a type which defines encryption methods
 type EncryptionMethod int
 
+// Encryption methods and constants
 const (
 	StandardEncryption EncryptionMethod = 1
 	AES128Encryption   EncryptionMethod = 2
@@ -388,7 +391,7 @@ func encryptStream(key []byte, w io.Writer) (io.Writer, error) {
 // data. The authcode will be written out in fileWriter.close().
 func newEncryptionWriter(w io.Writer, password passwordFn, fw *fileWriter, aesstrength byte) (io.Writer, error) {
 	keysize := aesKeyLen(aesstrength)
-	salt := make([]byte, keysize / 2)
+	salt := make([]byte, keysize/2)
 	_, err := rand.Read(salt[:])
 	if err != nil {
 		return nil, errors.New("zip: unable to generate random salt")
@@ -437,7 +440,8 @@ func (h *FileHeader) writeWinZipExtra() {
 	h.Extra = append(h.Extra, buf[:]...)
 }
 
-func (h *FileHeader) setEncryptionMethod(enc EncryptionMethod) {
+// SetEncryptionMethod sets the encryption method.
+func (h *FileHeader) SetEncryptionMethod(enc EncryptionMethod) {
 	h.encryption = enc
 	switch enc {
 	case AES128Encryption:
@@ -467,17 +471,29 @@ func (h *FileHeader) SetPassword(password string) {
 // as a byte slice
 type passwordFn func() []byte
 
-// Encrypt adds a file to the zip file using the provided name.
+// EncryptTime adds a file to the zip file using the provided name.
 // It returns a Writer to which the file contents should be written. File
 // contents will be encrypted with AES-256 using the given password. The
 // file's contents must be written to the io.Writer before the next call
-// to Create, CreateHeader, or Close.
-func (w *Writer) Encrypt(name string, password string, enc EncryptionMethod) (io.Writer, error) {
+// to Create, CreateHeader, or Close. It uses the provided modTime as
+// the file's last modified date&time
+func (w *Writer) EncryptTime(name string, password string, enc EncryptionMethod, modTime time.Time) (io.Writer, error) {
 	fh := &FileHeader{
 		Name:   name,
 		Method: Deflate,
 	}
+	fh.SetModTime(modTime)
 	fh.SetPassword(password)
-	fh.setEncryptionMethod(enc)
+	fh.SetEncryptionMethod(enc)
 	return w.CreateHeader(fh)
 }
+
+// Encrypt adds a file to the zip file using the provided name.
+// It returns a Writer to which the file contents should be written. File
+// contents will be encrypted with AES-256 using the given password. The
+// file's contents must be written to the io.Writer before the next call
+// to Create, CreateHeader, or Close. It uses the current time as
+// the file's last modified date&time
+func (w *Writer) Encrypt(name string, password string, enc EncryptionMethod) (io.Writer, error) {
+	return w.EncryptTime(name, password, enc, time.Now())
+}

crypto_test.go

@@ -5,6 +5,7 @@ import (
 	"io"
 	"path/filepath"
 	"testing"
+	"time"
 )
 
 // Test simple password reading.
@@ -56,7 +57,7 @@ func TestPasswordHelloWorldAes(t *testing.T) {
 	var b bytes.Buffer
 	for _, f := range r.File {
 		if !f.IsEncrypted() {
-			t.Errorf("Expected %s to be encrypted.", f.FileInfo().Name)
+			t.Errorf("Expected %s to be encrypted.", f.FileInfo().Name())
 		}
 		f.SetPassword("golang")
 		rc, err := f.Open()
@@ -235,6 +236,14 @@ func TestZipCrypto(t *testing.T) {
 
 	zipr, _ := NewReader(bytes.NewReader(raw.Bytes()), int64(raw.Len()))
 	zipr.File[0].SetPassword("golang")
+
+	modifiedTime := zipr.File[0].FileHeader.ModTime()
+	duration := time.Since(modifiedTime)
+	// Take care of the 2 seconds granularity
+	if duration.Seconds() <= -2000 || 4 <= duration.Seconds() {
+		t.Errorf("Modified time is expected to be very recent")
+	}
+
 	r, _ := zipr.File[0].Open()
 	res := new(bytes.Buffer)
 	io.Copy(res, r)