Imported Upstream version 60upstream/60

1 files changed, 221 insertions, 0 deletions

diff --git a/src/pkg/archive/tar/reader.go b/src/pkg/archive/tar/reader.go
new file mode 100644
index 000000000..45d95c3df
--- /dev/null
+++ b/src/pkg/archive/tar/reader.go
@@ -0,0 +1,221 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tar
+
+// TODO(dsymonds):
+//   - pax extensions
+
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+	"os"
+	"strconv"
+)
+
+var (
+	HeaderError = os.NewError("invalid tar header")
+)
+
+// A Reader provides sequential access to the contents of a tar archive.
+// A tar archive consists of a sequence of files.
+// The Next method advances to the next file in the archive (including the first),
+// and then it can be treated as an io.Reader to access the file's data.
+//
+// Example:
+//	tr := tar.NewReader(r)
+//	for {
+//		hdr, err := tr.Next()
+//		if err == os.EOF {
+//			// end of tar archive
+//			break
+//		}
+//		if err != nil {
+//			// handle error
+//		}
+//		io.Copy(data, tr)
+//	}
+type Reader struct {
+	r   io.Reader
+	err os.Error
+	nb  int64 // number of unread bytes for current file entry
+	pad int64 // amount of padding (ignored) after current file entry
+}
+
+// NewReader creates a new Reader reading from r.
+func NewReader(r io.Reader) *Reader { return &Reader{r: r} }
+
+// Next advances to the next entry in the tar archive.
+func (tr *Reader) Next() (*Header, os.Error) {
+	var hdr *Header
+	if tr.err == nil {
+		tr.skipUnread()
+	}
+	if tr.err == nil {
+		hdr = tr.readHeader()
+	}
+	return hdr, tr.err
+}
+
+// Parse bytes as a NUL-terminated C-style string.
+// If a NUL byte is not found then the whole slice is returned as a string.
+func cString(b []byte) string {
+	n := 0
+	for n < len(b) && b[n] != 0 {
+		n++
+	}
+	return string(b[0:n])
+}
+
+func (tr *Reader) octal(b []byte) int64 {
+	// Removing leading spaces.
+	for len(b) > 0 && b[0] == ' ' {
+		b = b[1:]
+	}
+	// Removing trailing NULs and spaces.
+	for len(b) > 0 && (b[len(b)-1] == ' ' || b[len(b)-1] == '\x00') {
+		b = b[0 : len(b)-1]
+	}
+	x, err := strconv.Btoui64(cString(b), 8)
+	if err != nil {
+		tr.err = err
+	}
+	return int64(x)
+}
+
+// Skip any unread bytes in the existing file entry, as well as any alignment padding.
+func (tr *Reader) skipUnread() {
+	nr := tr.nb + tr.pad // number of bytes to skip
+	tr.nb, tr.pad = 0, 0
+	if sr, ok := tr.r.(io.Seeker); ok {
+		if _, err := sr.Seek(nr, os.SEEK_CUR); err == nil {
+			return
+		}
+	}
+	_, tr.err = io.Copyn(ioutil.Discard, tr.r, nr)
+}
+
+func (tr *Reader) verifyChecksum(header []byte) bool {
+	if tr.err != nil {
+		return false
+	}
+
+	given := tr.octal(header[148:156])
+	unsigned, signed := checksum(header)
+	return given == unsigned || given == signed
+}
+
+func (tr *Reader) readHeader() *Header {
+	header := make([]byte, blockSize)
+	if _, tr.err = io.ReadFull(tr.r, header); tr.err != nil {
+		return nil
+	}
+
+	// Two blocks of zero bytes marks the end of the archive.
+	if bytes.Equal(header, zeroBlock[0:blockSize]) {
+		if _, tr.err = io.ReadFull(tr.r, header); tr.err != nil {
+			return nil
+		}
+		if bytes.Equal(header, zeroBlock[0:blockSize]) {
+			tr.err = os.EOF
+		} else {
+			tr.err = HeaderError // zero block and then non-zero block
+		}
+		return nil
+	}
+
+	if !tr.verifyChecksum(header) {
+		tr.err = HeaderError
+		return nil
+	}
+
+	// Unpack
+	hdr := new(Header)
+	s := slicer(header)
+
+	hdr.Name = cString(s.next(100))
+	hdr.Mode = tr.octal(s.next(8))
+	hdr.Uid = int(tr.octal(s.next(8)))
+	hdr.Gid = int(tr.octal(s.next(8)))
+	hdr.Size = tr.octal(s.next(12))
+	hdr.Mtime = tr.octal(s.next(12))
+	s.next(8) // chksum
+	hdr.Typeflag = s.next(1)[0]
+	hdr.Linkname = cString(s.next(100))
+
+	// The remainder of the header depends on the value of magic.
+	// The original (v7) version of tar had no explicit magic field,
+	// so its magic bytes, like the rest of the block, are NULs.
+	magic := string(s.next(8)) // contains version field as well.
+	var format string
+	switch magic {
+	case "ustar\x0000": // POSIX tar (1003.1-1988)
+		if string(header[508:512]) == "tar\x00" {
+			format = "star"
+		} else {
+			format = "posix"
+		}
+	case "ustar  \x00": // old GNU tar
+		format = "gnu"
+	}
+
+	switch format {
+	case "posix", "gnu", "star":
+		hdr.Uname = cString(s.next(32))
+		hdr.Gname = cString(s.next(32))
+		devmajor := s.next(8)
+		devminor := s.next(8)
+		if hdr.Typeflag == TypeChar || hdr.Typeflag == TypeBlock {
+			hdr.Devmajor = tr.octal(devmajor)
+			hdr.Devminor = tr.octal(devminor)
+		}
+		var prefix string
+		switch format {
+		case "posix", "gnu":
+			prefix = cString(s.next(155))
+		case "star":
+			prefix = cString(s.next(131))
+			hdr.Atime = tr.octal(s.next(12))
+			hdr.Ctime = tr.octal(s.next(12))
+		}
+		if len(prefix) > 0 {
+			hdr.Name = prefix + "/" + hdr.Name
+		}
+	}
+
+	if tr.err != nil {
+		tr.err = HeaderError
+		return nil
+	}
+
+	// Maximum value of hdr.Size is 64 GB (12 octal digits),
+	// so there's no risk of int64 overflowing.
+	tr.nb = int64(hdr.Size)
+	tr.pad = -tr.nb & (blockSize - 1) // blockSize is a power of two
+
+	return hdr
+}
+
+// Read reads from the current entry in the tar archive.
+// It returns 0, os.EOF when it reaches the end of that entry,
+// until Next is called to advance to the next entry.
+func (tr *Reader) Read(b []byte) (n int, err os.Error) {
+	if tr.nb == 0 {
+		// file consumed
+		return 0, os.EOF
+	}
+
+	if int64(len(b)) > tr.nb {
+		b = b[0:tr.nb]
+	}
+	n, err = tr.r.Read(b)
+	tr.nb -= int64(n)
+
+	if err == os.EOF && tr.nb > 0 {
+		err = io.ErrUnexpectedEOF
+	}
+	tr.err = err
+	return
+}