Change README to include example

Author: yeka

README.md

@@ -0,0 +1,91 @@
+This fork add support for Standard Zip Encryption.
+
+The work is based on https://github.com/alexmullins/zip
+
+Available encryption:
+
+```
+zip.StandardEncryption
+zip.AES128Encryption
+zip.AES192Encryption
+zip.AES256Encryption
+```
+
+## Warning
+
+Zip Standard Encryption isn't actually secure.
+Unless you have to work with it, please use AES encryption instead.
+
+## Example Encrypt Zip
+
+```
+package main
+
+import (
+	"bytes"
+	"log"
+	"os"
+
+	"github.com/yeka/zip"
+)
+
+func main() {
+	contents := []byte("Hello World")
+	fzip, err := os.Create(`./test.zip`)
+	if err != nil {
+		log.Fatalln(err)
+	}
+	zipw := zip.NewWriter(fzip)
+	defer zipw.Close()
+	w, err := zipw.Encrypt(`test.txt`, `golang`, zip.AES256Encryption)
+	if err != nil {
+		log.Fatal(err)
+	}
+	_, err = io.Copy(w, bytes.NewReader(contents))
+	if err != nil {
+		log.Fatal(err)
+	}
+	zipw.Flush()
+}
+```
+
+## Example Decrypt Zip
+
+```
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"log"
+
+	"github.com/yeka/zip"
+)
+
+func main() {
+	r, err := zip.OpenReader("encrypted.zip")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer r.Close()
+
+	for _, f := range r.File {
+		if f.IsEncrypted() {
+			f.SetPassword("12345")
+		}
+
+		r, err := f.Open()
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		buf, err := ioutil.ReadAll(r)
+		if err != nil {
+			log.Fatal(err)
+		}
+		defer r.Close()
+
+		fmt.Printf("Size of %v: %v byte(s)\n", f.Name, len(buf))
+	}
+}
+```

README.txt

@@ -22,10 +22,10 @@ import (
 type EncryptionMethod int
 
 const (
-	ZipStandardEncryption EncryptionMethod = 1
-	AES128Encryption EncryptionMethod = 2
-	AES192Encryption EncryptionMethod = 3
-	AES256Encryption EncryptionMethod = 4
+	StandardEncryption EncryptionMethod = 1
+	AES128Encryption   EncryptionMethod = 2
+	AES192Encryption   EncryptionMethod = 3
+	AES256Encryption   EncryptionMethod = 4
 
 	// AES key lengths
 	aes128 = 16

crypto.go

@@ -175,7 +175,7 @@ func TestPasswordWriteSimple(t *testing.T) {
 	contents := []byte("Hello World")
 	conLen := len(contents)
 
-	for _, enc := range []EncryptionMethod{ZipStandardEncryption, AES128Encryption, AES192Encryption, AES256Encryption} {
+	for _, enc := range []EncryptionMethod{StandardEncryption, AES128Encryption, AES192Encryption, AES256Encryption} {
 		raw := new(bytes.Buffer)
 		zipw := NewWriter(raw)
 		w, err := zipw.Encrypt("hello.txt", "golang", enc)
@@ -223,7 +223,7 @@ func TestZipCrypto(t *testing.T) {
 
 	raw := new(bytes.Buffer)
 	zipw := NewWriter(raw)
-	w, err := zipw.Encrypt("hello.txt", "golang", ZipStandardEncryption)
+	w, err := zipw.Encrypt("hello.txt", "golang", StandardEncryption)
 	if err != nil {
 		t.Errorf("Expected to create a new FileHeader")
 	}

crypto_test.go

@@ -229,7 +229,7 @@ func (w *Writer) CreateHeader(fh *FileHeader) (io.Writer, error) {
 	// check for password
 	var sw io.Writer = fw.compCount
 	if fh.password != nil {
-		if fh.encryption == ZipStandardEncryption {
+		if fh.encryption == StandardEncryption {
 			ew, err := ZipCryptoEncryptor(sw, fh.password, fw)
 			if err != nil {
 				return nil, err
@@ -321,7 +321,7 @@ func (w *fileWriter) close() error {
 		return err
 	}
 	// if encrypted grab the hmac and write it out
-	if w.header.IsEncrypted() && w.header.encryption != ZipStandardEncryption {
+	if w.header.IsEncrypted() && w.header.encryption != StandardEncryption {
 		authCode := w.hmac.Sum(nil)
 		authCode = authCode[:10]
 		_, err := w.compCount.Write(authCode)
@@ -332,7 +332,7 @@ func (w *fileWriter) close() error {
 	// update FileHeader
 	fh := w.header.FileHeader
 	// ae-2 we don't write out CRC
-	if !fh.IsEncrypted() || fh.encryption == ZipStandardEncryption {
+	if !fh.IsEncrypted() || fh.encryption == StandardEncryption {
 		fh.CRC32 = w.crc32.Sum32()
 	}
 	fh.CompressedSize64 = uint64(w.compCount.count)