Disable ZIP+LZMA (#226)

* Disable zip(lzma)

7z seems to have adopted a different strategy to create ZIP+lzma

* Improve register decompressor

* remove extraneous comments

zip.go

@@ -15,20 +15,22 @@ import (
 
 	"github.com/dsnet/compress/bzip2"
 	"github.com/klauspost/compress/zstd"
-	"github.com/ulikunitz/xz/lzma"
+	"github.com/ulikunitz/xz"
 )
 
 // ZipCompressionMethod Compression type
 type ZipCompressionMethod uint16
 
 // Compression methods.
 // see https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT.
+// Note LZMA: Disabled - because 7z isn't able to unpack ZIP+LZMA ZIP+LZMA2 archives made this way - and vice versa.
 const (
 	Store   ZipCompressionMethod = 0
 	Deflate ZipCompressionMethod = 8
 	BZIP2   ZipCompressionMethod = 12
 	LZMA    ZipCompressionMethod = 14
 	ZSTD    ZipCompressionMethod = 93
+	XZ      ZipCompressionMethod = 95
 )
 
 // Zip provides facilities for operating ZIP archives.
@@ -90,32 +92,28 @@ func (*Zip) CheckExt(filename string) error {
 }
 
 // Registering a global decompressor is not reentrant and may panic
-func (z *Zip) registerDecompressor() {
-	if z.decinitialized {
-		return
-	}
-	z.decinitialized = true
+func registerDecompressor(zr *zip.Reader) {
 	// register zstd decompressor
-	z.zr.RegisterDecompressor(uint16(ZSTD), func(r io.Reader) io.ReadCloser {
+	zr.RegisterDecompressor(uint16(ZSTD), func(r io.Reader) io.ReadCloser {
 		zr, err := zstd.NewReader(r)
 		if err != nil {
 			return nil
 		}
 		return zr.IOReadCloser()
 	})
-	z.zr.RegisterDecompressor(uint16(BZIP2), func(r io.Reader) io.ReadCloser {
+	zr.RegisterDecompressor(uint16(BZIP2), func(r io.Reader) io.ReadCloser {
 		bz2r, err := bzip2.NewReader(r, nil)
 		if err != nil {
 			return nil
 		}
 		return bz2r
 	})
-	z.zr.RegisterDecompressor(uint16(LZMA), func(r io.Reader) io.ReadCloser {
-		lr, err := lzma.NewReader(r)
+	zr.RegisterDecompressor(uint16(XZ), func(r io.Reader) io.ReadCloser {
+		xr, err := xz.NewReader(r)
 		if err != nil {
 			return nil
 		}
-		return ioutil.NopCloser(lr)
+		return ioutil.NopCloser(xr)
 	})
 }
 
@@ -348,14 +346,14 @@ func (z *Zip) Create(out io.Writer) error {
 		z.zw.RegisterCompressor(uint16(BZIP2), func(out io.Writer) (io.WriteCloser, error) {
 			return bzip2.NewWriter(out, &bzip2.WriterConfig{Level: z.CompressionLevel})
 		})
-	case LZMA:
-		z.zw.RegisterCompressor(uint16(LZMA), func(out io.Writer) (io.WriteCloser, error) {
-			return lzma.NewWriter(out)
-		})
 	case ZSTD:
 		z.zw.RegisterCompressor(uint16(ZSTD), func(out io.Writer) (io.WriteCloser, error) {
 			return zstd.NewWriter(out)
 		})
+	case XZ:
+		z.zw.RegisterCompressor(uint16(XZ), func(out io.Writer) (io.WriteCloser, error) {
+			return xz.NewWriter(out)
+		})
 	}
 	return nil
 }
@@ -441,7 +439,7 @@ func (z *Zip) Open(in io.Reader, size int64) error {
 	if err != nil {
 		return fmt.Errorf("creating reader: %v", err)
 	}
-	z.registerDecompressor()
+	registerDecompressor(z.zr)
 	z.ridx = 0
 	return nil
 }
@@ -498,11 +496,13 @@ func (z *Zip) Walk(archive string, walkFn WalkFunc) error {
 		return fmt.Errorf("opening zip reader: %v", err)
 	}
 	defer zr.Close()
-	z.registerDecompressor()
+	registerDecompressor(&zr.Reader)
 	for _, zf := range zr.File {
 		zfrc, err := zf.Open()
 		if err != nil {
-			zfrc.Close()
+			if zfrc != nil {
+				zfrc.Close()
+			}
 			if z.ContinueOnError {
 				log.Printf("[ERROR] Opening %s: %v", zf.Name, err)
 				continue