archive/tar: adding from go as of a9dddb53f

archive/tar/common.go

@@ -0,0 +1,305 @@
+// 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 implements access to tar archives.
+// It aims to cover most of the variations, including those produced
+// by GNU and BSD tars.
+//
+// References:
+//   http://www.freebsd.org/cgi/man.cgi?query=tar&sektion=5
+//   http://www.gnu.org/software/tar/manual/html_node/Standard.html
+//   http://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html
+package tar
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"os"
+	"path"
+	"time"
+)
+
+const (
+	blockSize = 512
+
+	// Types
+	TypeReg           = '0'    // regular file
+	TypeRegA          = '\x00' // regular file
+	TypeLink          = '1'    // hard link
+	TypeSymlink       = '2'    // symbolic link
+	TypeChar          = '3'    // character device node
+	TypeBlock         = '4'    // block device node
+	TypeDir           = '5'    // directory
+	TypeFifo          = '6'    // fifo node
+	TypeCont          = '7'    // reserved
+	TypeXHeader       = 'x'    // extended header
+	TypeXGlobalHeader = 'g'    // global extended header
+	TypeGNULongName   = 'L'    // Next file has a long name
+	TypeGNULongLink   = 'K'    // Next file symlinks to a file w/ a long name
+	TypeGNUSparse     = 'S'    // sparse file
+)
+
+// A Header represents a single header in a tar archive.
+// Some fields may not be populated.
+type Header struct {
+	Name       string    // name of header file entry
+	Mode       int64     // permission and mode bits
+	Uid        int       // user id of owner
+	Gid        int       // group id of owner
+	Size       int64     // length in bytes
+	ModTime    time.Time // modified time
+	Typeflag   byte      // type of header entry
+	Linkname   string    // target name of link
+	Uname      string    // user name of owner
+	Gname      string    // group name of owner
+	Devmajor   int64     // major number of character or block device
+	Devminor   int64     // minor number of character or block device
+	AccessTime time.Time // access time
+	ChangeTime time.Time // status change time
+	Xattrs     map[string]string
+}
+
+// File name constants from the tar spec.
+const (
+	fileNameSize       = 100 // Maximum number of bytes in a standard tar name.
+	fileNamePrefixSize = 155 // Maximum number of ustar extension bytes.
+)
+
+// FileInfo returns an os.FileInfo for the Header.
+func (h *Header) FileInfo() os.FileInfo {
+	return headerFileInfo{h}
+}
+
+// headerFileInfo implements os.FileInfo.
+type headerFileInfo struct {
+	h *Header
+}
+
+func (fi headerFileInfo) Size() int64        { return fi.h.Size }
+func (fi headerFileInfo) IsDir() bool        { return fi.Mode().IsDir() }
+func (fi headerFileInfo) ModTime() time.Time { return fi.h.ModTime }
+func (fi headerFileInfo) Sys() interface{}   { return fi.h }
+
+// Name returns the base name of the file.
+func (fi headerFileInfo) Name() string {
+	if fi.IsDir() {
+		return path.Base(path.Clean(fi.h.Name))
+	}
+	return path.Base(fi.h.Name)
+}
+
+// Mode returns the permission and mode bits for the headerFileInfo.
+func (fi headerFileInfo) Mode() (mode os.FileMode) {
+	// Set file permission bits.
+	mode = os.FileMode(fi.h.Mode).Perm()
+
+	// Set setuid, setgid and sticky bits.
+	if fi.h.Mode&c_ISUID != 0 {
+		// setuid
+		mode |= os.ModeSetuid
+	}
+	if fi.h.Mode&c_ISGID != 0 {
+		// setgid
+		mode |= os.ModeSetgid
+	}
+	if fi.h.Mode&c_ISVTX != 0 {
+		// sticky
+		mode |= os.ModeSticky
+	}
+
+	// Set file mode bits.
+	// clear perm, setuid, setgid and sticky bits.
+	m := os.FileMode(fi.h.Mode) &^ 07777
+	if m == c_ISDIR {
+		// directory
+		mode |= os.ModeDir
+	}
+	if m == c_ISFIFO {
+		// named pipe (FIFO)
+		mode |= os.ModeNamedPipe
+	}
+	if m == c_ISLNK {
+		// symbolic link
+		mode |= os.ModeSymlink
+	}
+	if m == c_ISBLK {
+		// device file
+		mode |= os.ModeDevice
+	}
+	if m == c_ISCHR {
+		// Unix character device
+		mode |= os.ModeDevice
+		mode |= os.ModeCharDevice
+	}
+	if m == c_ISSOCK {
+		// Unix domain socket
+		mode |= os.ModeSocket
+	}
+
+	switch fi.h.Typeflag {
+	case TypeLink, TypeSymlink:
+		// hard link, symbolic link
+		mode |= os.ModeSymlink
+	case TypeChar:
+		// character device node
+		mode |= os.ModeDevice
+		mode |= os.ModeCharDevice
+	case TypeBlock:
+		// block device node
+		mode |= os.ModeDevice
+	case TypeDir:
+		// directory
+		mode |= os.ModeDir
+	case TypeFifo:
+		// fifo node
+		mode |= os.ModeNamedPipe
+	}
+
+	return mode
+}
+
+// sysStat, if non-nil, populates h from system-dependent fields of fi.
+var sysStat func(fi os.FileInfo, h *Header) error
+
+// Mode constants from the tar spec.
+const (
+	c_ISUID  = 04000   // Set uid
+	c_ISGID  = 02000   // Set gid
+	c_ISVTX  = 01000   // Save text (sticky bit)
+	c_ISDIR  = 040000  // Directory
+	c_ISFIFO = 010000  // FIFO
+	c_ISREG  = 0100000 // Regular file
+	c_ISLNK  = 0120000 // Symbolic link
+	c_ISBLK  = 060000  // Block special file
+	c_ISCHR  = 020000  // Character special file
+	c_ISSOCK = 0140000 // Socket
+)
+
+// Keywords for the PAX Extended Header
+const (
+	paxAtime    = "atime"
+	paxCharset  = "charset"
+	paxComment  = "comment"
+	paxCtime    = "ctime" // please note that ctime is not a valid pax header.
+	paxGid      = "gid"
+	paxGname    = "gname"
+	paxLinkpath = "linkpath"
+	paxMtime    = "mtime"
+	paxPath     = "path"
+	paxSize     = "size"
+	paxUid      = "uid"
+	paxUname    = "uname"
+	paxXattr    = "SCHILY.xattr."
+	paxNone     = ""
+)
+
+// FileInfoHeader creates a partially-populated Header from fi.
+// If fi describes a symlink, FileInfoHeader records link as the link target.
+// If fi describes a directory, a slash is appended to the name.
+// Because os.FileInfo's Name method returns only the base name of
+// the file it describes, it may be necessary to modify the Name field
+// of the returned header to provide the full path name of the file.
+func FileInfoHeader(fi os.FileInfo, link string) (*Header, error) {
+	if fi == nil {
+		return nil, errors.New("tar: FileInfo is nil")
+	}
+	fm := fi.Mode()
+	h := &Header{
+		Name:    fi.Name(),
+		ModTime: fi.ModTime(),
+		Mode:    int64(fm.Perm()), // or'd with c_IS* constants later
+	}
+	switch {
+	case fm.IsRegular():
+		h.Mode |= c_ISREG
+		h.Typeflag = TypeReg
+		h.Size = fi.Size()
+	case fi.IsDir():
+		h.Typeflag = TypeDir
+		h.Mode |= c_ISDIR
+		h.Name += "/"
+	case fm&os.ModeSymlink != 0:
+		h.Typeflag = TypeSymlink
+		h.Mode |= c_ISLNK
+		h.Linkname = link
+	case fm&os.ModeDevice != 0:
+		if fm&os.ModeCharDevice != 0 {
+			h.Mode |= c_ISCHR
+			h.Typeflag = TypeChar
+		} else {
+			h.Mode |= c_ISBLK
+			h.Typeflag = TypeBlock
+		}
+	case fm&os.ModeNamedPipe != 0:
+		h.Typeflag = TypeFifo
+		h.Mode |= c_ISFIFO
+	case fm&os.ModeSocket != 0:
+		h.Mode |= c_ISSOCK
+	default:
+		return nil, fmt.Errorf("archive/tar: unknown file mode %v", fm)
+	}
+	if fm&os.ModeSetuid != 0 {
+		h.Mode |= c_ISUID
+	}
+	if fm&os.ModeSetgid != 0 {
+		h.Mode |= c_ISGID
+	}
+	if fm&os.ModeSticky != 0 {
+		h.Mode |= c_ISVTX
+	}
+	if sysStat != nil {
+		return h, sysStat(fi, h)
+	}
+	return h, nil
+}
+
+var zeroBlock = make([]byte, blockSize)
+
+// POSIX specifies a sum of the unsigned byte values, but the Sun tar uses signed byte values.
+// We compute and return both.
+func checksum(header []byte) (unsigned int64, signed int64) {
+	for i := 0; i < len(header); i++ {
+		if i == 148 {
+			// The chksum field (header[148:156]) is special: it should be treated as space bytes.
+			unsigned += ' ' * 8
+			signed += ' ' * 8
+			i += 7
+			continue
+		}
+		unsigned += int64(header[i])
+		signed += int64(int8(header[i]))
+	}
+	return
+}
+
+type slicer []byte
+
+func (sp *slicer) next(n int) (b []byte) {
+	s := *sp
+	b, *sp = s[0:n], s[n:]
+	return
+}
+
+func isASCII(s string) bool {
+	for _, c := range s {
+		if c >= 0x80 {
+			return false
+		}
+	}
+	return true
+}
+
+func toASCII(s string) string {
+	if isASCII(s) {
+		return s
+	}
+	var buf bytes.Buffer
+	for _, c := range s {
+		if c < 0x80 {
+			buf.WriteByte(byte(c))
+		}
+	}
+	return buf.String()
+}

archive/tar/example_test.go

@@ -0,0 +1,80 @@
+// Copyright 2013 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_test
+
+import (
+	"archive/tar"
+	"bytes"
+	"fmt"
+	"io"
+	"log"
+	"os"
+)
+
+func Example() {
+	// Create a buffer to write our archive to.
+	buf := new(bytes.Buffer)
+
+	// Create a new tar archive.
+	tw := tar.NewWriter(buf)
+
+	// Add some files to the archive.
+	var files = []struct {
+		Name, Body string
+	}{
+		{"readme.txt", "This archive contains some text files."},
+		{"gopher.txt", "Gopher names:\nGeorge\nGeoffrey\nGonzo"},
+		{"todo.txt", "Get animal handling licence."},
+	}
+	for _, file := range files {
+		hdr := &tar.Header{
+			Name: file.Name,
+			Mode: 0600,
+			Size: int64(len(file.Body)),
+		}
+		if err := tw.WriteHeader(hdr); err != nil {
+			log.Fatalln(err)
+		}
+		if _, err := tw.Write([]byte(file.Body)); err != nil {
+			log.Fatalln(err)
+		}
+	}
+	// Make sure to check the error on Close.
+	if err := tw.Close(); err != nil {
+		log.Fatalln(err)
+	}
+
+	// Open the tar archive for reading.
+	r := bytes.NewReader(buf.Bytes())
+	tr := tar.NewReader(r)
+
+	// Iterate through the files in the archive.
+	for {
+		hdr, err := tr.Next()
+		if err == io.EOF {
+			// end of tar archive
+			break
+		}
+		if err != nil {
+			log.Fatalln(err)
+		}
+		fmt.Printf("Contents of %s:\n", hdr.Name)
+		if _, err := io.Copy(os.Stdout, tr); err != nil {
+			log.Fatalln(err)
+		}
+		fmt.Println()
+	}
+
+	// Output:
+	// Contents of readme.txt:
+	// This archive contains some text files.
+	// Contents of gopher.txt:
+	// Gopher names:
+	// George
+	// Geoffrey
+	// Gonzo
+	// Contents of todo.txt:
+	// Get animal handling licence.
+}

archive/tar/reader.go

@@ -0,0 +1,822 @@
+// 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"
+	"errors"
+	"io"
+	"io/ioutil"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+)
+
+var (
+	ErrHeader = errors.New("archive/tar: invalid tar header")
+)
+
+const maxNanoSecondIntSize = 9
+
+// 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.
+type Reader struct {
+	r       io.Reader
+	err     error
+	pad     int64           // amount of padding (ignored) after current file entry
+	curr    numBytesReader  // reader for current file entry
+	hdrBuff [blockSize]byte // buffer to use in readHeader
+}
+
+// A numBytesReader is an io.Reader with a numBytes method, returning the number
+// of bytes remaining in the underlying encoded data.
+type numBytesReader interface {
+	io.Reader
+	numBytes() int64
+}
+
+// A regFileReader is a numBytesReader for reading file data from a tar archive.
+type regFileReader struct {
+	r  io.Reader // underlying reader
+	nb int64     // number of unread bytes for current file entry
+}
+
+// A sparseFileReader is a numBytesReader for reading sparse file data from a tar archive.
+type sparseFileReader struct {
+	rfr *regFileReader // reads the sparse-encoded file data
+	sp  []sparseEntry  // the sparse map for the file
+	pos int64          // keeps track of file position
+	tot int64          // total size of the file
+}
+
+// Keywords for GNU sparse files in a PAX extended header
+const (
+	paxGNUSparseNumBlocks = "GNU.sparse.numblocks"
+	paxGNUSparseOffset    = "GNU.sparse.offset"
+	paxGNUSparseNumBytes  = "GNU.sparse.numbytes"
+	paxGNUSparseMap       = "GNU.sparse.map"
+	paxGNUSparseName      = "GNU.sparse.name"
+	paxGNUSparseMajor     = "GNU.sparse.major"
+	paxGNUSparseMinor     = "GNU.sparse.minor"
+	paxGNUSparseSize      = "GNU.sparse.size"
+	paxGNUSparseRealSize  = "GNU.sparse.realsize"
+)
+
+// Keywords for old GNU sparse headers
+const (
+	oldGNUSparseMainHeaderOffset               = 386
+	oldGNUSparseMainHeaderIsExtendedOffset     = 482
+	oldGNUSparseMainHeaderNumEntries           = 4
+	oldGNUSparseExtendedHeaderIsExtendedOffset = 504
+	oldGNUSparseExtendedHeaderNumEntries       = 21
+	oldGNUSparseOffsetSize                     = 12
+	oldGNUSparseNumBytesSize                   = 12
+)
+
+// 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.
+//
+// io.EOF is returned at the end of the input.
+func (tr *Reader) Next() (*Header, error) {
+	var hdr *Header
+	if tr.err == nil {
+		tr.skipUnread()
+	}
+	if tr.err != nil {
+		return hdr, tr.err
+	}
+	hdr = tr.readHeader()
+	if hdr == nil {
+		return hdr, tr.err
+	}
+	// Check for PAX/GNU header.
+	switch hdr.Typeflag {
+	case TypeXHeader:
+		//  PAX extended header
+		headers, err := parsePAX(tr)
+		if err != nil {
+			return nil, err
+		}
+		// We actually read the whole file,
+		// but this skips alignment padding
+		tr.skipUnread()
+		hdr = tr.readHeader()
+		mergePAX(hdr, headers)
+
+		// Check for a PAX format sparse file
+		sp, err := tr.checkForGNUSparsePAXHeaders(hdr, headers)
+		if err != nil {
+			tr.err = err
+			return nil, err
+		}
+		if sp != nil {
+			// Current file is a PAX format GNU sparse file.
+			// Set the current file reader to a sparse file reader.
+			tr.curr = &sparseFileReader{rfr: tr.curr.(*regFileReader), sp: sp, tot: hdr.Size}
+		}
+		return hdr, nil
+	case TypeGNULongName:
+		// We have a GNU long name header. Its contents are the real file name.
+		realname, err := ioutil.ReadAll(tr)
+		if err != nil {
+			return nil, err
+		}
+		hdr, err := tr.Next()
+		hdr.Name = cString(realname)
+		return hdr, err
+	case TypeGNULongLink:
+		// We have a GNU long link header.
+		realname, err := ioutil.ReadAll(tr)
+		if err != nil {
+			return nil, err
+		}
+		hdr, err := tr.Next()
+		hdr.Linkname = cString(realname)
+		return hdr, err
+	}
+	return hdr, tr.err
+}
+
+// checkForGNUSparsePAXHeaders checks the PAX headers for GNU sparse headers. If they are found, then
+// this function reads the sparse map and returns it. Unknown sparse formats are ignored, causing the file to
+// be treated as a regular file.
+func (tr *Reader) checkForGNUSparsePAXHeaders(hdr *Header, headers map[string]string) ([]sparseEntry, error) {
+	var sparseFormat string
+
+	// Check for sparse format indicators
+	major, majorOk := headers[paxGNUSparseMajor]
+	minor, minorOk := headers[paxGNUSparseMinor]
+	sparseName, sparseNameOk := headers[paxGNUSparseName]
+	_, sparseMapOk := headers[paxGNUSparseMap]
+	sparseSize, sparseSizeOk := headers[paxGNUSparseSize]
+	sparseRealSize, sparseRealSizeOk := headers[paxGNUSparseRealSize]
+
+	// Identify which, if any, sparse format applies from which PAX headers are set
+	if majorOk && minorOk {
+		sparseFormat = major + "." + minor
+	} else if sparseNameOk && sparseMapOk {
+		sparseFormat = "0.1"
+	} else if sparseSizeOk {
+		sparseFormat = "0.0"
+	} else {
+		// Not a PAX format GNU sparse file.
+		return nil, nil
+	}
+
+	// Check for unknown sparse format
+	if sparseFormat != "0.0" && sparseFormat != "0.1" && sparseFormat != "1.0" {
+		return nil, nil
+	}
+
+	// Update hdr from GNU sparse PAX headers
+	if sparseNameOk {
+		hdr.Name = sparseName
+	}
+	if sparseSizeOk {
+		realSize, err := strconv.ParseInt(sparseSize, 10, 0)
+		if err != nil {
+			return nil, ErrHeader
+		}
+		hdr.Size = realSize
+	} else if sparseRealSizeOk {
+		realSize, err := strconv.ParseInt(sparseRealSize, 10, 0)
+		if err != nil {
+			return nil, ErrHeader
+		}
+		hdr.Size = realSize
+	}
+
+	// Set up the sparse map, according to the particular sparse format in use
+	var sp []sparseEntry
+	var err error
+	switch sparseFormat {
+	case "0.0", "0.1":
+		sp, err = readGNUSparseMap0x1(headers)
+	case "1.0":
+		sp, err = readGNUSparseMap1x0(tr.curr)
+	}
+	return sp, err
+}
+
+// mergePAX merges well known headers according to PAX standard.
+// In general headers with the same name as those found
+// in the header struct overwrite those found in the header
+// struct with higher precision or longer values. Esp. useful
+// for name and linkname fields.
+func mergePAX(hdr *Header, headers map[string]string) error {
+	for k, v := range headers {
+		switch k {
+		case paxPath:
+			hdr.Name = v
+		case paxLinkpath:
+			hdr.Linkname = v
+		case paxGname:
+			hdr.Gname = v
+		case paxUname:
+			hdr.Uname = v
+		case paxUid:
+			uid, err := strconv.ParseInt(v, 10, 0)
+			if err != nil {
+				return err
+			}
+			hdr.Uid = int(uid)
+		case paxGid:
+			gid, err := strconv.ParseInt(v, 10, 0)
+			if err != nil {
+				return err
+			}
+			hdr.Gid = int(gid)
+		case paxAtime:
+			t, err := parsePAXTime(v)
+			if err != nil {
+				return err
+			}
+			hdr.AccessTime = t
+		case paxMtime:
+			t, err := parsePAXTime(v)
+			if err != nil {
+				return err
+			}
+			hdr.ModTime = t
+		case paxCtime:
+			t, err := parsePAXTime(v)
+			if err != nil {
+				return err
+			}
+			hdr.ChangeTime = t
+		case paxSize:
+			size, err := strconv.ParseInt(v, 10, 0)
+			if err != nil {
+				return err
+			}
+			hdr.Size = int64(size)
+		default:
+			if strings.HasPrefix(k, paxXattr) {
+				if hdr.Xattrs == nil {
+					hdr.Xattrs = make(map[string]string)
+				}
+				hdr.Xattrs[k[len(paxXattr):]] = v
+			}
+		}
+	}
+	return nil
+}
+
+// parsePAXTime takes a string of the form %d.%d as described in
+// the PAX specification.
+func parsePAXTime(t string) (time.Time, error) {
+	buf := []byte(t)
+	pos := bytes.IndexByte(buf, '.')
+	var seconds, nanoseconds int64
+	var err error
+	if pos == -1 {
+		seconds, err = strconv.ParseInt(t, 10, 0)
+		if err != nil {
+			return time.Time{}, err
+		}
+	} else {
+		seconds, err = strconv.ParseInt(string(buf[:pos]), 10, 0)
+		if err != nil {
+			return time.Time{}, err
+		}
+		nano_buf := string(buf[pos+1:])
+		// Pad as needed before converting to a decimal.
+		// For example .030 -> .030000000 -> 30000000 nanoseconds
+		if len(nano_buf) < maxNanoSecondIntSize {
+			// Right pad
+			nano_buf += strings.Repeat("0", maxNanoSecondIntSize-len(nano_buf))
+		} else if len(nano_buf) > maxNanoSecondIntSize {
+			// Right truncate
+			nano_buf = nano_buf[:maxNanoSecondIntSize]
+		}
+		nanoseconds, err = strconv.ParseInt(string(nano_buf), 10, 0)
+		if err != nil {
+			return time.Time{}, err
+		}
+	}
+	ts := time.Unix(seconds, nanoseconds)
+	return ts, nil
+}
+
+// parsePAX parses PAX headers.
+// If an extended header (type 'x') is invalid, ErrHeader is returned
+func parsePAX(r io.Reader) (map[string]string, error) {
+	buf, err := ioutil.ReadAll(r)
+	if err != nil {
+		return nil, err
+	}
+
+	// For GNU PAX sparse format 0.0 support.
+	// This function transforms the sparse format 0.0 headers into sparse format 0.1 headers.
+	var sparseMap bytes.Buffer
+
+	headers := make(map[string]string)
+	// Each record is constructed as
+	//     "%d %s=%s\n", length, keyword, value
+	for len(buf) > 0 {
+		// or the header was empty to start with.
+		var sp int
+		// The size field ends at the first space.
+		sp = bytes.IndexByte(buf, ' ')
+		if sp == -1 {
+			return nil, ErrHeader
+		}
+		// Parse the first token as a decimal integer.
+		n, err := strconv.ParseInt(string(buf[:sp]), 10, 0)
+		if err != nil {
+			return nil, ErrHeader
+		}
+		// Extract everything between the decimal and the n -1 on the
+		// beginning to eat the ' ', -1 on the end to skip the newline.
+		var record []byte
+		record, buf = buf[sp+1:n-1], buf[n:]
+		// The first equals is guaranteed to mark the end of the key.
+		// Everything else is value.
+		eq := bytes.IndexByte(record, '=')
+		if eq == -1 {
+			return nil, ErrHeader
+		}
+		key, value := record[:eq], record[eq+1:]
+
+		keyStr := string(key)
+		if keyStr == paxGNUSparseOffset || keyStr == paxGNUSparseNumBytes {
+			// GNU sparse format 0.0 special key. Write to sparseMap instead of using the headers map.
+			sparseMap.Write(value)
+			sparseMap.Write([]byte{','})
+		} else {
+			// Normal key. Set the value in the headers map.
+			headers[keyStr] = string(value)
+		}
+	}
+	if sparseMap.Len() != 0 {
+		// Add sparse info to headers, chopping off the extra comma
+		sparseMap.Truncate(sparseMap.Len() - 1)
+		headers[paxGNUSparseMap] = sparseMap.String()
+	}
+	return headers, nil
+}
+
+// cString parses 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 {
+	// Check for binary format first.
+	if len(b) > 0 && b[0]&0x80 != 0 {
+		var x int64
+		for i, c := range b {
+			if i == 0 {
+				c &= 0x7f // ignore signal bit in first byte
+			}
+			x = x<<8 | int64(c)
+		}
+		return x
+	}
+
+	// Because unused fields are filled with NULs, we need
+	// to skip leading NULs. Fields may also be padded with
+	// spaces or NULs.
+	// So we remove leading and trailing NULs and spaces to
+	// be sure.
+	b = bytes.Trim(b, " \x00")
+
+	if len(b) == 0 {
+		return 0
+	}
+	x, err := strconv.ParseUint(cString(b), 8, 64)
+	if err != nil {
+		tr.err = err
+	}
+	return int64(x)
+}
+
+// skipUnread skips any unread bytes in the existing file entry, as well as any alignment padding.
+func (tr *Reader) skipUnread() {
+	nr := tr.numBytes() + tr.pad // number of bytes to skip
+	tr.curr, tr.pad = nil, 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 := tr.hdrBuff[:]
+	copy(header, zeroBlock)
+
+	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 = io.EOF
+		} else {
+			tr.err = ErrHeader // zero block and then non-zero block
+		}
+		return nil
+	}
+
+	if !tr.verifyChecksum(header) {
+		tr.err = ErrHeader
+		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.ModTime = time.Unix(tr.octal(s.next(12)), 0)
+	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 {
+	case magic[:6] == "ustar\x00": // POSIX tar (1003.1-1988)
+		if string(header[508:512]) == "tar\x00" {
+			format = "star"
+		} else {
+			format = "posix"
+		}
+	case magic == "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.AccessTime = time.Unix(tr.octal(s.next(12)), 0)
+			hdr.ChangeTime = time.Unix(tr.octal(s.next(12)), 0)
+		}
+		if len(prefix) > 0 {
+			hdr.Name = prefix + "/" + hdr.Name
+		}
+	}
+
+	if tr.err != nil {
+		tr.err = ErrHeader
+		return nil
+	}
+
+	// Maximum value of hdr.Size is 64 GB (12 octal digits),
+	// so there's no risk of int64 overflowing.
+	nb := int64(hdr.Size)
+	tr.pad = -nb & (blockSize - 1) // blockSize is a power of two
+
+	// Set the current file reader.
+	tr.curr = &regFileReader{r: tr.r, nb: nb}
+
+	// Check for old GNU sparse format entry.
+	if hdr.Typeflag == TypeGNUSparse {
+		// Get the real size of the file.
+		hdr.Size = tr.octal(header[483:495])
+
+		// Read the sparse map.
+		sp := tr.readOldGNUSparseMap(header)
+		if tr.err != nil {
+			return nil
+		}
+		// Current file is a GNU sparse file. Update the current file reader.
+		tr.curr = &sparseFileReader{rfr: tr.curr.(*regFileReader), sp: sp, tot: hdr.Size}
+	}
+
+	return hdr
+}
+
+// A sparseEntry holds a single entry in a sparse file's sparse map.
+// A sparse entry indicates the offset and size in a sparse file of a
+// block of data.
+type sparseEntry struct {
+	offset   int64
+	numBytes int64
+}
+
+// readOldGNUSparseMap reads the sparse map as stored in the old GNU sparse format.
+// The sparse map is stored in the tar header if it's small enough. If it's larger than four entries,
+// then one or more extension headers are used to store the rest of the sparse map.
+func (tr *Reader) readOldGNUSparseMap(header []byte) []sparseEntry {
+	isExtended := header[oldGNUSparseMainHeaderIsExtendedOffset] != 0
+	spCap := oldGNUSparseMainHeaderNumEntries
+	if isExtended {
+		spCap += oldGNUSparseExtendedHeaderNumEntries
+	}
+	sp := make([]sparseEntry, 0, spCap)
+	s := slicer(header[oldGNUSparseMainHeaderOffset:])
+
+	// Read the four entries from the main tar header
+	for i := 0; i < oldGNUSparseMainHeaderNumEntries; i++ {
+		offset := tr.octal(s.next(oldGNUSparseOffsetSize))
+		numBytes := tr.octal(s.next(oldGNUSparseNumBytesSize))
+		if tr.err != nil {
+			tr.err = ErrHeader
+			return nil
+		}
+		if offset == 0 && numBytes == 0 {
+			break
+		}
+		sp = append(sp, sparseEntry{offset: offset, numBytes: numBytes})
+	}
+
+	for isExtended {
+		// There are more entries. Read an extension header and parse its entries.
+		sparseHeader := make([]byte, blockSize)
+		if _, tr.err = io.ReadFull(tr.r, sparseHeader); tr.err != nil {
+			return nil
+		}
+		isExtended = sparseHeader[oldGNUSparseExtendedHeaderIsExtendedOffset] != 0
+		s = slicer(sparseHeader)
+		for i := 0; i < oldGNUSparseExtendedHeaderNumEntries; i++ {
+			offset := tr.octal(s.next(oldGNUSparseOffsetSize))
+			numBytes := tr.octal(s.next(oldGNUSparseNumBytesSize))
+			if tr.err != nil {
+				tr.err = ErrHeader
+				return nil
+			}
+			if offset == 0 && numBytes == 0 {
+				break
+			}
+			sp = append(sp, sparseEntry{offset: offset, numBytes: numBytes})
+		}
+	}
+	return sp
+}
+
+// readGNUSparseMap1x0 reads the sparse map as stored in GNU's PAX sparse format version 1.0.
+// The sparse map is stored just before the file data and padded out to the nearest block boundary.
+func readGNUSparseMap1x0(r io.Reader) ([]sparseEntry, error) {
+	buf := make([]byte, 2*blockSize)
+	sparseHeader := buf[:blockSize]
+
+	// readDecimal is a helper function to read a decimal integer from the sparse map
+	// while making sure to read from the file in blocks of size blockSize
+	readDecimal := func() (int64, error) {
+		// Look for newline
+		nl := bytes.IndexByte(sparseHeader, '\n')
+		if nl == -1 {
+			if len(sparseHeader) >= blockSize {
+				// This is an error
+				return 0, ErrHeader
+			}
+			oldLen := len(sparseHeader)
+			newLen := oldLen + blockSize
+			if cap(sparseHeader) < newLen {
+				// There's more header, but we need to make room for the next block
+				copy(buf, sparseHeader)
+				sparseHeader = buf[:newLen]
+			} else {
+				// There's more header, and we can just reslice
+				sparseHeader = sparseHeader[:newLen]
+			}
+
+			// Now that sparseHeader is large enough, read next block
+			if _, err := io.ReadFull(r, sparseHeader[oldLen:newLen]); err != nil {
+				return 0, err
+			}
+
+			// Look for a newline in the new data
+			nl = bytes.IndexByte(sparseHeader[oldLen:newLen], '\n')
+			if nl == -1 {
+				// This is an error
+				return 0, ErrHeader
+			}
+			nl += oldLen // We want the position from the beginning
+		}
+		// Now that we've found a newline, read a number
+		n, err := strconv.ParseInt(string(sparseHeader[:nl]), 10, 0)
+		if err != nil {
+			return 0, ErrHeader
+		}
+
+		// Update sparseHeader to consume this number
+		sparseHeader = sparseHeader[nl+1:]
+		return n, nil
+	}
+
+	// Read the first block
+	if _, err := io.ReadFull(r, sparseHeader); err != nil {
+		return nil, err
+	}
+
+	// The first line contains the number of entries
+	numEntries, err := readDecimal()
+	if err != nil {
+		return nil, err
+	}
+
+	// Read all the entries
+	sp := make([]sparseEntry, 0, numEntries)
+	for i := int64(0); i < numEntries; i++ {
+		// Read the offset
+		offset, err := readDecimal()
+		if err != nil {
+			return nil, err
+		}
+		// Read numBytes
+		numBytes, err := readDecimal()
+		if err != nil {
+			return nil, err
+		}
+
+		sp = append(sp, sparseEntry{offset: offset, numBytes: numBytes})
+	}
+
+	return sp, nil
+}
+
+// readGNUSparseMap0x1 reads the sparse map as stored in GNU's PAX sparse format version 0.1.
+// The sparse map is stored in the PAX headers.
+func readGNUSparseMap0x1(headers map[string]string) ([]sparseEntry, error) {
+	// Get number of entries
+	numEntriesStr, ok := headers[paxGNUSparseNumBlocks]
+	if !ok {
+		return nil, ErrHeader
+	}
+	numEntries, err := strconv.ParseInt(numEntriesStr, 10, 0)
+	if err != nil {
+		return nil, ErrHeader
+	}
+
+	sparseMap := strings.Split(headers[paxGNUSparseMap], ",")
+
+	// There should be two numbers in sparseMap for each entry
+	if int64(len(sparseMap)) != 2*numEntries {
+		return nil, ErrHeader
+	}
+
+	// Loop through the entries in the sparse map
+	sp := make([]sparseEntry, 0, numEntries)
+	for i := int64(0); i < numEntries; i++ {
+		offset, err := strconv.ParseInt(sparseMap[2*i], 10, 0)
+		if err != nil {
+			return nil, ErrHeader
+		}
+		numBytes, err := strconv.ParseInt(sparseMap[2*i+1], 10, 0)
+		if err != nil {
+			return nil, ErrHeader
+		}
+		sp = append(sp, sparseEntry{offset: offset, numBytes: numBytes})
+	}
+
+	return sp, nil
+}
+
+// numBytes returns the number of bytes left to read in the current file's entry
+// in the tar archive, or 0 if there is no current file.
+func (tr *Reader) numBytes() int64 {
+	if tr.curr == nil {
+		// No current file, so no bytes
+		return 0
+	}
+	return tr.curr.numBytes()
+}
+
+// Read reads from the current entry in the tar archive.
+// It returns 0, io.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 error) {
+	if tr.curr == nil {
+		return 0, io.EOF
+	}
+	n, err = tr.curr.Read(b)
+	if err != nil && err != io.EOF {
+		tr.err = err
+	}
+	return
+}
+
+func (rfr *regFileReader) Read(b []byte) (n int, err error) {
+	if rfr.nb == 0 {
+		// file consumed
+		return 0, io.EOF
+	}
+	if int64(len(b)) > rfr.nb {
+		b = b[0:rfr.nb]
+	}
+	n, err = rfr.r.Read(b)
+	rfr.nb -= int64(n)
+
+	if err == io.EOF && rfr.nb > 0 {
+		err = io.ErrUnexpectedEOF
+	}
+	return
+}
+
+// numBytes returns the number of bytes left to read in the file's data in the tar archive.
+func (rfr *regFileReader) numBytes() int64 {
+	return rfr.nb
+}
+
+// readHole reads a sparse file hole ending at offset toOffset
+func (sfr *sparseFileReader) readHole(b []byte, toOffset int64) int {
+	n64 := toOffset - sfr.pos
+	if n64 > int64(len(b)) {
+		n64 = int64(len(b))
+	}
+	n := int(n64)
+	for i := 0; i < n; i++ {
+		b[i] = 0
+	}
+	sfr.pos += n64
+	return n
+}
+
+// Read reads the sparse file data in expanded form.
+func (sfr *sparseFileReader) Read(b []byte) (n int, err error) {
+	if len(sfr.sp) == 0 {
+		// No more data fragments to read from.
+		if sfr.pos < sfr.tot {
+			// We're in the last hole
+			n = sfr.readHole(b, sfr.tot)
+			return
+		}
+		// Otherwise, we're at the end of the file
+		return 0, io.EOF
+	}
+	if sfr.pos < sfr.sp[0].offset {
+		// We're in a hole
+		n = sfr.readHole(b, sfr.sp[0].offset)
+		return
+	}
+
+	// We're not in a hole, so we'll read from the next data fragment
+	posInFragment := sfr.pos - sfr.sp[0].offset
+	bytesLeft := sfr.sp[0].numBytes - posInFragment
+	if int64(len(b)) > bytesLeft {
+		b = b[0:bytesLeft]
+	}
+
+	n, err = sfr.rfr.Read(b)
+	sfr.pos += int64(n)
+
+	if int64(n) == bytesLeft {
+		// We're done with this fragment
+		sfr.sp = sfr.sp[1:]
+	}
+
+	if err == io.EOF && sfr.pos < sfr.tot {
+		// We reached the end of the last fragment's data, but there's a final hole
+		err = nil
+	}
+	return
+}
+
+// numBytes returns the number of bytes left to read in the sparse file's
+// sparse-encoded data in the tar archive.
+func (sfr *sparseFileReader) numBytes() int64 {
+	return sfr.rfr.nb
+}

archive/tar/reader_test.go

@@ -0,0 +1,743 @@
+// 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
+
+import (
+	"bytes"
+	"crypto/md5"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"reflect"
+	"strings"
+	"testing"
+	"time"
+)
+
+type untarTest struct {
+	file    string
+	headers []*Header
+	cksums  []string
+}
+
+var gnuTarTest = &untarTest{
+	file: "testdata/gnu.tar",
+	headers: []*Header{
+		{
+			Name:     "small.txt",
+			Mode:     0640,
+			Uid:      73025,
+			Gid:      5000,
+			Size:     5,
+			ModTime:  time.Unix(1244428340, 0),
+			Typeflag: '0',
+			Uname:    "dsymonds",
+			Gname:    "eng",
+		},
+		{
+			Name:     "small2.txt",
+			Mode:     0640,
+			Uid:      73025,
+			Gid:      5000,
+			Size:     11,
+			ModTime:  time.Unix(1244436044, 0),
+			Typeflag: '0',
+			Uname:    "dsymonds",
+			Gname:    "eng",
+		},
+	},
+	cksums: []string{
+		"e38b27eaccb4391bdec553a7f3ae6b2f",
+		"c65bd2e50a56a2138bf1716f2fd56fe9",
+	},
+}
+
+var sparseTarTest = &untarTest{
+	file: "testdata/sparse-formats.tar",
+	headers: []*Header{
+		{
+			Name:     "sparse-gnu",
+			Mode:     420,
+			Uid:      1000,
+			Gid:      1000,
+			Size:     200,
+			ModTime:  time.Unix(1392395740, 0),
+			Typeflag: 0x53,
+			Linkname: "",
+			Uname:    "david",
+			Gname:    "david",
+			Devmajor: 0,
+			Devminor: 0,
+		},
+		{
+			Name:     "sparse-posix-0.0",
+			Mode:     420,
+			Uid:      1000,
+			Gid:      1000,
+			Size:     200,
+			ModTime:  time.Unix(1392342187, 0),
+			Typeflag: 0x30,
+			Linkname: "",
+			Uname:    "david",
+			Gname:    "david",
+			Devmajor: 0,
+			Devminor: 0,
+		},
+		{
+			Name:     "sparse-posix-0.1",
+			Mode:     420,
+			Uid:      1000,
+			Gid:      1000,
+			Size:     200,
+			ModTime:  time.Unix(1392340456, 0),
+			Typeflag: 0x30,
+			Linkname: "",
+			Uname:    "david",
+			Gname:    "david",
+			Devmajor: 0,
+			Devminor: 0,
+		},
+		{
+			Name:     "sparse-posix-1.0",
+			Mode:     420,
+			Uid:      1000,
+			Gid:      1000,
+			Size:     200,
+			ModTime:  time.Unix(1392337404, 0),
+			Typeflag: 0x30,
+			Linkname: "",
+			Uname:    "david",
+			Gname:    "david",
+			Devmajor: 0,
+			Devminor: 0,
+		},
+		{
+			Name:     "end",
+			Mode:     420,
+			Uid:      1000,
+			Gid:      1000,
+			Size:     4,
+			ModTime:  time.Unix(1392398319, 0),
+			Typeflag: 0x30,
+			Linkname: "",
+			Uname:    "david",
+			Gname:    "david",
+			Devmajor: 0,
+			Devminor: 0,
+		},
+	},
+	cksums: []string{
+		"6f53234398c2449fe67c1812d993012f",
+		"6f53234398c2449fe67c1812d993012f",
+		"6f53234398c2449fe67c1812d993012f",
+		"6f53234398c2449fe67c1812d993012f",
+		"b0061974914468de549a2af8ced10316",
+	},
+}
+
+var untarTests = []*untarTest{
+	gnuTarTest,
+	sparseTarTest,
+	{
+		file: "testdata/star.tar",
+		headers: []*Header{
+			{
+				Name:       "small.txt",
+				Mode:       0640,
+				Uid:        73025,
+				Gid:        5000,
+				Size:       5,
+				ModTime:    time.Unix(1244592783, 0),
+				Typeflag:   '0',
+				Uname:      "dsymonds",
+				Gname:      "eng",
+				AccessTime: time.Unix(1244592783, 0),
+				ChangeTime: time.Unix(1244592783, 0),
+			},
+			{
+				Name:       "small2.txt",
+				Mode:       0640,
+				Uid:        73025,
+				Gid:        5000,
+				Size:       11,
+				ModTime:    time.Unix(1244592783, 0),
+				Typeflag:   '0',
+				Uname:      "dsymonds",
+				Gname:      "eng",
+				AccessTime: time.Unix(1244592783, 0),
+				ChangeTime: time.Unix(1244592783, 0),
+			},
+		},
+	},
+	{
+		file: "testdata/v7.tar",
+		headers: []*Header{
+			{
+				Name:     "small.txt",
+				Mode:     0444,
+				Uid:      73025,
+				Gid:      5000,
+				Size:     5,
+				ModTime:  time.Unix(1244593104, 0),
+				Typeflag: '\x00',
+			},
+			{
+				Name:     "small2.txt",
+				Mode:     0444,
+				Uid:      73025,
+				Gid:      5000,
+				Size:     11,
+				ModTime:  time.Unix(1244593104, 0),
+				Typeflag: '\x00',
+			},
+		},
+	},
+	{
+		file: "testdata/pax.tar",
+		headers: []*Header{
+			{
+				Name:       "a/123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100",
+				Mode:       0664,
+				Uid:        1000,
+				Gid:        1000,
+				Uname:      "shane",
+				Gname:      "shane",
+				Size:       7,
+				ModTime:    time.Unix(1350244992, 23960108),
+				ChangeTime: time.Unix(1350244992, 23960108),
+				AccessTime: time.Unix(1350244992, 23960108),
+				Typeflag:   TypeReg,
+			},
+			{
+				Name:       "a/b",
+				Mode:       0777,
+				Uid:        1000,
+				Gid:        1000,
+				Uname:      "shane",
+				Gname:      "shane",
+				Size:       0,
+				ModTime:    time.Unix(1350266320, 910238425),
+				ChangeTime: time.Unix(1350266320, 910238425),
+				AccessTime: time.Unix(1350266320, 910238425),
+				Typeflag:   TypeSymlink,
+				Linkname:   "123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100",
+			},
+		},
+	},
+	{
+		file: "testdata/nil-uid.tar", // golang.org/issue/5290
+		headers: []*Header{
+			{
+				Name:     "P1050238.JPG.log",
+				Mode:     0664,
+				Uid:      0,
+				Gid:      0,
+				Size:     14,
+				ModTime:  time.Unix(1365454838, 0),
+				Typeflag: TypeReg,
+				Linkname: "",
+				Uname:    "eyefi",
+				Gname:    "eyefi",
+				Devmajor: 0,
+				Devminor: 0,
+			},
+		},
+	},
+	{
+		file: "testdata/xattrs.tar",
+		headers: []*Header{
+			{
+				Name:       "small.txt",
+				Mode:       0644,
+				Uid:        1000,
+				Gid:        10,
+				Size:       5,
+				ModTime:    time.Unix(1386065770, 448252320),
+				Typeflag:   '0',
+				Uname:      "alex",
+				Gname:      "wheel",
+				AccessTime: time.Unix(1389782991, 419875220),
+				ChangeTime: time.Unix(1389782956, 794414986),
+				Xattrs: map[string]string{
+					"user.key":  "value",
+					"user.key2": "value2",
+					// Interestingly, selinux encodes the terminating null inside the xattr
+					"security.selinux": "unconfined_u:object_r:default_t:s0\x00",
+				},
+			},
+			{
+				Name:       "small2.txt",
+				Mode:       0644,
+				Uid:        1000,
+				Gid:        10,
+				Size:       11,
+				ModTime:    time.Unix(1386065770, 449252304),
+				Typeflag:   '0',
+				Uname:      "alex",
+				Gname:      "wheel",
+				AccessTime: time.Unix(1389782991, 419875220),
+				ChangeTime: time.Unix(1386065770, 449252304),
+				Xattrs: map[string]string{
+					"security.selinux": "unconfined_u:object_r:default_t:s0\x00",
+				},
+			},
+		},
+	},
+}
+
+func TestReader(t *testing.T) {
+testLoop:
+	for i, test := range untarTests {
+		f, err := os.Open(test.file)
+		if err != nil {
+			t.Errorf("test %d: Unexpected error: %v", i, err)
+			continue
+		}
+		defer f.Close()
+		tr := NewReader(f)
+		for j, header := range test.headers {
+			hdr, err := tr.Next()
+			if err != nil || hdr == nil {
+				t.Errorf("test %d, entry %d: Didn't get entry: %v", i, j, err)
+				f.Close()
+				continue testLoop
+			}
+			if !reflect.DeepEqual(*hdr, *header) {
+				t.Errorf("test %d, entry %d: Incorrect header:\nhave %+v\nwant %+v",
+					i, j, *hdr, *header)
+			}
+		}
+		hdr, err := tr.Next()
+		if err == io.EOF {
+			continue testLoop
+		}
+		if hdr != nil || err != nil {
+			t.Errorf("test %d: Unexpected entry or error: hdr=%v err=%v", i, hdr, err)
+		}
+	}
+}
+
+func TestPartialRead(t *testing.T) {
+	f, err := os.Open("testdata/gnu.tar")
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	defer f.Close()
+
+	tr := NewReader(f)
+
+	// Read the first four bytes; Next() should skip the last byte.
+	hdr, err := tr.Next()
+	if err != nil || hdr == nil {
+		t.Fatalf("Didn't get first file: %v", err)
+	}
+	buf := make([]byte, 4)
+	if _, err := io.ReadFull(tr, buf); err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	if expected := []byte("Kilt"); !bytes.Equal(buf, expected) {
+		t.Errorf("Contents = %v, want %v", buf, expected)
+	}
+
+	// Second file
+	hdr, err = tr.Next()
+	if err != nil || hdr == nil {
+		t.Fatalf("Didn't get second file: %v", err)
+	}
+	buf = make([]byte, 6)
+	if _, err := io.ReadFull(tr, buf); err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	if expected := []byte("Google"); !bytes.Equal(buf, expected) {
+		t.Errorf("Contents = %v, want %v", buf, expected)
+	}
+}
+
+func TestIncrementalRead(t *testing.T) {
+	test := gnuTarTest
+	f, err := os.Open(test.file)
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	defer f.Close()
+
+	tr := NewReader(f)
+
+	headers := test.headers
+	cksums := test.cksums
+	nread := 0
+
+	// loop over all files
+	for ; ; nread++ {
+		hdr, err := tr.Next()
+		if hdr == nil || err == io.EOF {
+			break
+		}
+
+		// check the header
+		if !reflect.DeepEqual(*hdr, *headers[nread]) {
+			t.Errorf("Incorrect header:\nhave %+v\nwant %+v",
+				*hdr, headers[nread])
+		}
+
+		// read file contents in little chunks EOF,
+		// checksumming all the way
+		h := md5.New()
+		rdbuf := make([]uint8, 8)
+		for {
+			nr, err := tr.Read(rdbuf)
+			if err == io.EOF {
+				break
+			}
+			if err != nil {
+				t.Errorf("Read: unexpected error %v\n", err)
+				break
+			}
+			h.Write(rdbuf[0:nr])
+		}
+		// verify checksum
+		have := fmt.Sprintf("%x", h.Sum(nil))
+		want := cksums[nread]
+		if want != have {
+			t.Errorf("Bad checksum on file %s:\nhave %+v\nwant %+v", hdr.Name, have, want)
+		}
+	}
+	if nread != len(headers) {
+		t.Errorf("Didn't process all files\nexpected: %d\nprocessed %d\n", len(headers), nread)
+	}
+}
+
+func TestNonSeekable(t *testing.T) {
+	test := gnuTarTest
+	f, err := os.Open(test.file)
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	defer f.Close()
+
+	type readerOnly struct {
+		io.Reader
+	}
+	tr := NewReader(readerOnly{f})
+	nread := 0
+
+	for ; ; nread++ {
+		_, err := tr.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			t.Fatalf("Unexpected error: %v", err)
+		}
+	}
+
+	if nread != len(test.headers) {
+		t.Errorf("Didn't process all files\nexpected: %d\nprocessed %d\n", len(test.headers), nread)
+	}
+}
+
+func TestParsePAXHeader(t *testing.T) {
+	paxTests := [][3]string{
+		{"a", "a=name", "10 a=name\n"}, // Test case involving multiple acceptable lengths
+		{"a", "a=name", "9 a=name\n"},  // Test case involving multiple acceptable length
+		{"mtime", "mtime=1350244992.023960108", "30 mtime=1350244992.023960108\n"}}
+	for _, test := range paxTests {
+		key, expected, raw := test[0], test[1], test[2]
+		reader := bytes.NewReader([]byte(raw))
+		headers, err := parsePAX(reader)
+		if err != nil {
+			t.Errorf("Couldn't parse correctly formatted headers: %v", err)
+			continue
+		}
+		if strings.EqualFold(headers[key], expected) {
+			t.Errorf("mtime header incorrectly parsed: got %s, wanted %s", headers[key], expected)
+			continue
+		}
+		trailer := make([]byte, 100)
+		n, err := reader.Read(trailer)
+		if err != io.EOF || n != 0 {
+			t.Error("Buffer wasn't consumed")
+		}
+	}
+	badHeader := bytes.NewReader([]byte("3 somelongkey="))
+	if _, err := parsePAX(badHeader); err != ErrHeader {
+		t.Fatal("Unexpected success when parsing bad header")
+	}
+}
+
+func TestParsePAXTime(t *testing.T) {
+	// Some valid PAX time values
+	timestamps := map[string]time.Time{
+		"1350244992.023960108":  time.Unix(1350244992, 23960108), // The common case
+		"1350244992.02396010":   time.Unix(1350244992, 23960100), // Lower precision value
+		"1350244992.0239601089": time.Unix(1350244992, 23960108), // Higher precision value
+		"1350244992":            time.Unix(1350244992, 0),        // Low precision value
+	}
+	for input, expected := range timestamps {
+		ts, err := parsePAXTime(input)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if !ts.Equal(expected) {
+			t.Fatalf("Time parsing failure %s %s", ts, expected)
+		}
+	}
+}
+
+func TestMergePAX(t *testing.T) {
+	hdr := new(Header)
+	// Test a string, integer, and time based value.
+	headers := map[string]string{
+		"path":  "a/b/c",
+		"uid":   "1000",
+		"mtime": "1350244992.023960108",
+	}
+	err := mergePAX(hdr, headers)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := &Header{
+		Name:    "a/b/c",
+		Uid:     1000,
+		ModTime: time.Unix(1350244992, 23960108),
+	}
+	if !reflect.DeepEqual(hdr, want) {
+		t.Errorf("incorrect merge: got %+v, want %+v", hdr, want)
+	}
+}
+
+func TestSparseEndToEnd(t *testing.T) {
+	test := sparseTarTest
+	f, err := os.Open(test.file)
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	defer f.Close()
+
+	tr := NewReader(f)
+
+	headers := test.headers
+	cksums := test.cksums
+	nread := 0
+
+	// loop over all files
+	for ; ; nread++ {
+		hdr, err := tr.Next()
+		if hdr == nil || err == io.EOF {
+			break
+		}
+
+		// check the header
+		if !reflect.DeepEqual(*hdr, *headers[nread]) {
+			t.Errorf("Incorrect header:\nhave %+v\nwant %+v",
+				*hdr, headers[nread])
+		}
+
+		// read and checksum the file data
+		h := md5.New()
+		_, err = io.Copy(h, tr)
+		if err != nil {
+			t.Fatalf("Unexpected error: %v", err)
+		}
+
+		// verify checksum
+		have := fmt.Sprintf("%x", h.Sum(nil))
+		want := cksums[nread]
+		if want != have {
+			t.Errorf("Bad checksum on file %s:\nhave %+v\nwant %+v", hdr.Name, have, want)
+		}
+	}
+	if nread != len(headers) {
+		t.Errorf("Didn't process all files\nexpected: %d\nprocessed %d\n", len(headers), nread)
+	}
+}
+
+type sparseFileReadTest struct {
+	sparseData []byte
+	sparseMap  []sparseEntry
+	realSize   int64
+	expected   []byte
+}
+
+var sparseFileReadTests = []sparseFileReadTest{
+	{
+		sparseData: []byte("abcde"),
+		sparseMap: []sparseEntry{
+			{offset: 0, numBytes: 2},
+			{offset: 5, numBytes: 3},
+		},
+		realSize: 8,
+		expected: []byte("ab\x00\x00\x00cde"),
+	},
+	{
+		sparseData: []byte("abcde"),
+		sparseMap: []sparseEntry{
+			{offset: 0, numBytes: 2},
+			{offset: 5, numBytes: 3},
+		},
+		realSize: 10,
+		expected: []byte("ab\x00\x00\x00cde\x00\x00"),
+	},
+	{
+		sparseData: []byte("abcde"),
+		sparseMap: []sparseEntry{
+			{offset: 1, numBytes: 3},
+			{offset: 6, numBytes: 2},
+		},
+		realSize: 8,
+		expected: []byte("\x00abc\x00\x00de"),
+	},
+	{
+		sparseData: []byte("abcde"),
+		sparseMap: []sparseEntry{
+			{offset: 1, numBytes: 3},
+			{offset: 6, numBytes: 2},
+		},
+		realSize: 10,
+		expected: []byte("\x00abc\x00\x00de\x00\x00"),
+	},
+	{
+		sparseData: []byte(""),
+		sparseMap:  nil,
+		realSize:   2,
+		expected:   []byte("\x00\x00"),
+	},
+}
+
+func TestSparseFileReader(t *testing.T) {
+	for i, test := range sparseFileReadTests {
+		r := bytes.NewReader(test.sparseData)
+		nb := int64(r.Len())
+		sfr := &sparseFileReader{
+			rfr: &regFileReader{r: r, nb: nb},
+			sp:  test.sparseMap,
+			pos: 0,
+			tot: test.realSize,
+		}
+		if sfr.numBytes() != nb {
+			t.Errorf("test %d: Before reading, sfr.numBytes() = %d, want %d", i, sfr.numBytes(), nb)
+		}
+		buf, err := ioutil.ReadAll(sfr)
+		if err != nil {
+			t.Errorf("test %d: Unexpected error: %v", i, err)
+		}
+		if e := test.expected; !bytes.Equal(buf, e) {
+			t.Errorf("test %d: Contents = %v, want %v", i, buf, e)
+		}
+		if sfr.numBytes() != 0 {
+			t.Errorf("test %d: After draining the reader, numBytes() was nonzero", i)
+		}
+	}
+}
+
+func TestSparseIncrementalRead(t *testing.T) {
+	sparseMap := []sparseEntry{{10, 2}}
+	sparseData := []byte("Go")
+	expected := "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00Go\x00\x00\x00\x00\x00\x00\x00\x00"
+
+	r := bytes.NewReader(sparseData)
+	nb := int64(r.Len())
+	sfr := &sparseFileReader{
+		rfr: &regFileReader{r: r, nb: nb},
+		sp:  sparseMap,
+		pos: 0,
+		tot: int64(len(expected)),
+	}
+
+	// We'll read the data 6 bytes at a time, with a hole of size 10 at
+	// the beginning and one of size 8 at the end.
+	var outputBuf bytes.Buffer
+	buf := make([]byte, 6)
+	for {
+		n, err := sfr.Read(buf)
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			t.Errorf("Read: unexpected error %v\n", err)
+		}
+		if n > 0 {
+			_, err := outputBuf.Write(buf[:n])
+			if err != nil {
+				t.Errorf("Write: unexpected error %v\n", err)
+			}
+		}
+	}
+	got := outputBuf.String()
+	if got != expected {
+		t.Errorf("Contents = %v, want %v", got, expected)
+	}
+}
+
+func TestReadGNUSparseMap0x1(t *testing.T) {
+	headers := map[string]string{
+		paxGNUSparseNumBlocks: "4",
+		paxGNUSparseMap:       "0,5,10,5,20,5,30,5",
+	}
+	expected := []sparseEntry{
+		{offset: 0, numBytes: 5},
+		{offset: 10, numBytes: 5},
+		{offset: 20, numBytes: 5},
+		{offset: 30, numBytes: 5},
+	}
+
+	sp, err := readGNUSparseMap0x1(headers)
+	if err != nil {
+		t.Errorf("Unexpected error: %v", err)
+	}
+	if !reflect.DeepEqual(sp, expected) {
+		t.Errorf("Incorrect sparse map: got %v, wanted %v", sp, expected)
+	}
+}
+
+func TestReadGNUSparseMap1x0(t *testing.T) {
+	// This test uses lots of holes so the sparse header takes up more than two blocks
+	numEntries := 100
+	expected := make([]sparseEntry, 0, numEntries)
+	sparseMap := new(bytes.Buffer)
+
+	fmt.Fprintf(sparseMap, "%d\n", numEntries)
+	for i := 0; i < numEntries; i++ {
+		offset := int64(2048 * i)
+		numBytes := int64(1024)
+		expected = append(expected, sparseEntry{offset: offset, numBytes: numBytes})
+		fmt.Fprintf(sparseMap, "%d\n%d\n", offset, numBytes)
+	}
+
+	// Make the header the smallest multiple of blockSize that fits the sparseMap
+	headerBlocks := (sparseMap.Len() + blockSize - 1) / blockSize
+	bufLen := blockSize * headerBlocks
+	buf := make([]byte, bufLen)
+	copy(buf, sparseMap.Bytes())
+
+	// Get an reader to read the sparse map
+	r := bytes.NewReader(buf)
+
+	// Read the sparse map
+	sp, err := readGNUSparseMap1x0(r)
+	if err != nil {
+		t.Errorf("Unexpected error: %v", err)
+	}
+	if !reflect.DeepEqual(sp, expected) {
+		t.Errorf("Incorrect sparse map: got %v, wanted %v", sp, expected)
+	}
+}
+
+func TestUninitializedRead(t *testing.T) {
+	test := gnuTarTest
+	f, err := os.Open(test.file)
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	defer f.Close()
+
+	tr := NewReader(f)
+	_, err = tr.Read([]byte{})
+	if err == nil || err != io.EOF {
+		t.Errorf("Unexpected error: %v, wanted %v", err, io.EOF)
+	}
+
+}

archive/tar/stat_atim.go

@@ -0,0 +1,20 @@
+// Copyright 2012 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.
+
+// +build linux dragonfly openbsd solaris
+
+package tar
+
+import (
+	"syscall"
+	"time"
+)
+
+func statAtime(st *syscall.Stat_t) time.Time {
+	return time.Unix(st.Atim.Unix())
+}
+
+func statCtime(st *syscall.Stat_t) time.Time {
+	return time.Unix(st.Ctim.Unix())
+}

archive/tar/stat_atimespec.go

@@ -0,0 +1,20 @@
+// Copyright 2012 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.
+
+// +build darwin freebsd netbsd
+
+package tar
+
+import (
+	"syscall"
+	"time"
+)
+
+func statAtime(st *syscall.Stat_t) time.Time {
+	return time.Unix(st.Atimespec.Unix())
+}
+
+func statCtime(st *syscall.Stat_t) time.Time {
+	return time.Unix(st.Ctimespec.Unix())
+}

archive/tar/stat_unix.go

@@ -0,0 +1,32 @@
+// Copyright 2012 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.
+
+// +build linux darwin dragonfly freebsd openbsd netbsd solaris
+
+package tar
+
+import (
+	"os"
+	"syscall"
+)
+
+func init() {
+	sysStat = statUnix
+}
+
+func statUnix(fi os.FileInfo, h *Header) error {
+	sys, ok := fi.Sys().(*syscall.Stat_t)
+	if !ok {
+		return nil
+	}
+	h.Uid = int(sys.Uid)
+	h.Gid = int(sys.Gid)
+	// TODO(bradfitz): populate username & group.  os/user
+	// doesn't cache LookupId lookups, and lacks group
+	// lookup functions.
+	h.AccessTime = statAtime(sys)
+	h.ChangeTime = statCtime(sys)
+	// TODO(bradfitz): major/minor device numbers?
+	return nil
+}

archive/tar/tar_test.go

@@ -0,0 +1,284 @@
+// Copyright 2012 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
+
+import (
+	"bytes"
+	"io/ioutil"
+	"os"
+	"path"
+	"reflect"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestFileInfoHeader(t *testing.T) {
+	fi, err := os.Stat("testdata/small.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	h, err := FileInfoHeader(fi, "")
+	if err != nil {
+		t.Fatalf("FileInfoHeader: %v", err)
+	}
+	if g, e := h.Name, "small.txt"; g != e {
+		t.Errorf("Name = %q; want %q", g, e)
+	}
+	if g, e := h.Mode, int64(fi.Mode().Perm())|c_ISREG; g != e {
+		t.Errorf("Mode = %#o; want %#o", g, e)
+	}
+	if g, e := h.Size, int64(5); g != e {
+		t.Errorf("Size = %v; want %v", g, e)
+	}
+	if g, e := h.ModTime, fi.ModTime(); !g.Equal(e) {
+		t.Errorf("ModTime = %v; want %v", g, e)
+	}
+	// FileInfoHeader should error when passing nil FileInfo
+	if _, err := FileInfoHeader(nil, ""); err == nil {
+		t.Fatalf("Expected error when passing nil to FileInfoHeader")
+	}
+}
+
+func TestFileInfoHeaderDir(t *testing.T) {
+	fi, err := os.Stat("testdata")
+	if err != nil {
+		t.Fatal(err)
+	}
+	h, err := FileInfoHeader(fi, "")
+	if err != nil {
+		t.Fatalf("FileInfoHeader: %v", err)
+	}
+	if g, e := h.Name, "testdata/"; g != e {
+		t.Errorf("Name = %q; want %q", g, e)
+	}
+	// Ignoring c_ISGID for golang.org/issue/4867
+	if g, e := h.Mode&^c_ISGID, int64(fi.Mode().Perm())|c_ISDIR; g != e {
+		t.Errorf("Mode = %#o; want %#o", g, e)
+	}
+	if g, e := h.Size, int64(0); g != e {
+		t.Errorf("Size = %v; want %v", g, e)
+	}
+	if g, e := h.ModTime, fi.ModTime(); !g.Equal(e) {
+		t.Errorf("ModTime = %v; want %v", g, e)
+	}
+}
+
+func TestFileInfoHeaderSymlink(t *testing.T) {
+	h, err := FileInfoHeader(symlink{}, "some-target")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if g, e := h.Name, "some-symlink"; g != e {
+		t.Errorf("Name = %q; want %q", g, e)
+	}
+	if g, e := h.Linkname, "some-target"; g != e {
+		t.Errorf("Linkname = %q; want %q", g, e)
+	}
+}
+
+type symlink struct{}
+
+func (symlink) Name() string       { return "some-symlink" }
+func (symlink) Size() int64        { return 0 }
+func (symlink) Mode() os.FileMode  { return os.ModeSymlink }
+func (symlink) ModTime() time.Time { return time.Time{} }
+func (symlink) IsDir() bool        { return false }
+func (symlink) Sys() interface{}   { return nil }
+
+func TestRoundTrip(t *testing.T) {
+	data := []byte("some file contents")
+
+	var b bytes.Buffer
+	tw := NewWriter(&b)
+	hdr := &Header{
+		Name:    "file.txt",
+		Uid:     1 << 21, // too big for 8 octal digits
+		Size:    int64(len(data)),
+		ModTime: time.Now(),
+	}
+	// tar only supports second precision.
+	hdr.ModTime = hdr.ModTime.Add(-time.Duration(hdr.ModTime.Nanosecond()) * time.Nanosecond)
+	if err := tw.WriteHeader(hdr); err != nil {
+		t.Fatalf("tw.WriteHeader: %v", err)
+	}
+	if _, err := tw.Write(data); err != nil {
+		t.Fatalf("tw.Write: %v", err)
+	}
+	if err := tw.Close(); err != nil {
+		t.Fatalf("tw.Close: %v", err)
+	}
+
+	// Read it back.
+	tr := NewReader(&b)
+	rHdr, err := tr.Next()
+	if err != nil {
+		t.Fatalf("tr.Next: %v", err)
+	}
+	if !reflect.DeepEqual(rHdr, hdr) {
+		t.Errorf("Header mismatch.\n got %+v\nwant %+v", rHdr, hdr)
+	}
+	rData, err := ioutil.ReadAll(tr)
+	if err != nil {
+		t.Fatalf("Read: %v", err)
+	}
+	if !bytes.Equal(rData, data) {
+		t.Errorf("Data mismatch.\n got %q\nwant %q", rData, data)
+	}
+}
+
+type headerRoundTripTest struct {
+	h  *Header
+	fm os.FileMode
+}
+
+func TestHeaderRoundTrip(t *testing.T) {
+	golden := []headerRoundTripTest{
+		// regular file.
+		{
+			h: &Header{
+				Name:     "test.txt",
+				Mode:     0644 | c_ISREG,
+				Size:     12,
+				ModTime:  time.Unix(1360600916, 0),
+				Typeflag: TypeReg,
+			},
+			fm: 0644,
+		},
+		// hard link.
+		{
+			h: &Header{
+				Name:     "hard.txt",
+				Mode:     0644 | c_ISLNK,
+				Size:     0,
+				ModTime:  time.Unix(1360600916, 0),
+				Typeflag: TypeLink,
+			},
+			fm: 0644 | os.ModeSymlink,
+		},
+		// symbolic link.
+		{
+			h: &Header{
+				Name:     "link.txt",
+				Mode:     0777 | c_ISLNK,
+				Size:     0,
+				ModTime:  time.Unix(1360600852, 0),
+				Typeflag: TypeSymlink,
+			},
+			fm: 0777 | os.ModeSymlink,
+		},
+		// character device node.
+		{
+			h: &Header{
+				Name:     "dev/null",
+				Mode:     0666 | c_ISCHR,
+				Size:     0,
+				ModTime:  time.Unix(1360578951, 0),
+				Typeflag: TypeChar,
+			},
+			fm: 0666 | os.ModeDevice | os.ModeCharDevice,
+		},
+		// block device node.
+		{
+			h: &Header{
+				Name:     "dev/sda",
+				Mode:     0660 | c_ISBLK,
+				Size:     0,
+				ModTime:  time.Unix(1360578954, 0),
+				Typeflag: TypeBlock,
+			},
+			fm: 0660 | os.ModeDevice,
+		},
+		// directory.
+		{
+			h: &Header{
+				Name:     "dir/",
+				Mode:     0755 | c_ISDIR,
+				Size:     0,
+				ModTime:  time.Unix(1360601116, 0),
+				Typeflag: TypeDir,
+			},
+			fm: 0755 | os.ModeDir,
+		},
+		// fifo node.
+		{
+			h: &Header{
+				Name:     "dev/initctl",
+				Mode:     0600 | c_ISFIFO,
+				Size:     0,
+				ModTime:  time.Unix(1360578949, 0),
+				Typeflag: TypeFifo,
+			},
+			fm: 0600 | os.ModeNamedPipe,
+		},
+		// setuid.
+		{
+			h: &Header{
+				Name:     "bin/su",
+				Mode:     0755 | c_ISREG | c_ISUID,
+				Size:     23232,
+				ModTime:  time.Unix(1355405093, 0),
+				Typeflag: TypeReg,
+			},
+			fm: 0755 | os.ModeSetuid,
+		},
+		// setguid.
+		{
+			h: &Header{
+				Name:     "group.txt",
+				Mode:     0750 | c_ISREG | c_ISGID,
+				Size:     0,
+				ModTime:  time.Unix(1360602346, 0),
+				Typeflag: TypeReg,
+			},
+			fm: 0750 | os.ModeSetgid,
+		},
+		// sticky.
+		{
+			h: &Header{
+				Name:     "sticky.txt",
+				Mode:     0600 | c_ISREG | c_ISVTX,
+				Size:     7,
+				ModTime:  time.Unix(1360602540, 0),
+				Typeflag: TypeReg,
+			},
+			fm: 0600 | os.ModeSticky,
+		},
+	}
+
+	for i, g := range golden {
+		fi := g.h.FileInfo()
+		h2, err := FileInfoHeader(fi, "")
+		if err != nil {
+			t.Error(err)
+			continue
+		}
+		if strings.Contains(fi.Name(), "/") {
+			t.Errorf("FileInfo of %q contains slash: %q", g.h.Name, fi.Name())
+		}
+		name := path.Base(g.h.Name)
+		if fi.IsDir() {
+			name += "/"
+		}
+		if got, want := h2.Name, name; got != want {
+			t.Errorf("i=%d: Name: got %v, want %v", i, got, want)
+		}
+		if got, want := h2.Size, g.h.Size; got != want {
+			t.Errorf("i=%d: Size: got %v, want %v", i, got, want)
+		}
+		if got, want := h2.Mode, g.h.Mode; got != want {
+			t.Errorf("i=%d: Mode: got %o, want %o", i, got, want)
+		}
+		if got, want := fi.Mode(), g.fm; got != want {
+			t.Errorf("i=%d: fi.Mode: got %o, want %o", i, got, want)
+		}
+		if got, want := h2.ModTime, g.h.ModTime; got != want {
+			t.Errorf("i=%d: ModTime: got %v, want %v", i, got, want)
+		}
+		if sysh, ok := fi.Sys().(*Header); !ok || sysh != g.h {
+			t.Errorf("i=%d: Sys didn't return original *Header", i)
+		}
+	}
+}

archive/tar/testdata/small.txt

@@ -0,0 +1 @@
+Kilts

archive/tar/testdata/small2.txt

@@ -0,0 +1 @@
+Google.com

archive/tar/writer.go

@@ -0,0 +1,396 @@
+// 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):
+// - catch more errors (no first header, etc.)
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path"
+	"strconv"
+	"strings"
+	"time"
+)
+
+var (
+	ErrWriteTooLong    = errors.New("archive/tar: write too long")
+	ErrFieldTooLong    = errors.New("archive/tar: header field too long")
+	ErrWriteAfterClose = errors.New("archive/tar: write after close")
+	errNameTooLong     = errors.New("archive/tar: name too long")
+	errInvalidHeader   = errors.New("archive/tar: header field too long or contains invalid values")
+)
+
+// A Writer provides sequential writing of a tar archive in POSIX.1 format.
+// A tar archive consists of a sequence of files.
+// Call WriteHeader to begin a new file, and then call Write to supply that file's data,
+// writing at most hdr.Size bytes in total.
+type Writer struct {
+	w          io.Writer
+	err        error
+	nb         int64 // number of unwritten bytes for current file entry
+	pad        int64 // amount of padding to write after current file entry
+	closed     bool
+	usedBinary bool            // whether the binary numeric field extension was used
+	preferPax  bool            // use pax header instead of binary numeric header
+	hdrBuff    [blockSize]byte // buffer to use in writeHeader when writing a regular header
+	paxHdrBuff [blockSize]byte // buffer to use in writeHeader when writing a pax header
+}
+
+// NewWriter creates a new Writer writing to w.
+func NewWriter(w io.Writer) *Writer { return &Writer{w: w} }
+
+// Flush finishes writing the current file (optional).
+func (tw *Writer) Flush() error {
+	if tw.nb > 0 {
+		tw.err = fmt.Errorf("archive/tar: missed writing %d bytes", tw.nb)
+		return tw.err
+	}
+
+	n := tw.nb + tw.pad
+	for n > 0 && tw.err == nil {
+		nr := n
+		if nr > blockSize {
+			nr = blockSize
+		}
+		var nw int
+		nw, tw.err = tw.w.Write(zeroBlock[0:nr])
+		n -= int64(nw)
+	}
+	tw.nb = 0
+	tw.pad = 0
+	return tw.err
+}
+
+// Write s into b, terminating it with a NUL if there is room.
+// If the value is too long for the field and allowPax is true add a paxheader record instead
+func (tw *Writer) cString(b []byte, s string, allowPax bool, paxKeyword string, paxHeaders map[string]string) {
+	needsPaxHeader := allowPax && len(s) > len(b) || !isASCII(s)
+	if needsPaxHeader {
+		paxHeaders[paxKeyword] = s
+		return
+	}
+	if len(s) > len(b) {
+		if tw.err == nil {
+			tw.err = ErrFieldTooLong
+		}
+		return
+	}
+	ascii := toASCII(s)
+	copy(b, ascii)
+	if len(ascii) < len(b) {
+		b[len(ascii)] = 0
+	}
+}
+
+// Encode x as an octal ASCII string and write it into b with leading zeros.
+func (tw *Writer) octal(b []byte, x int64) {
+	s := strconv.FormatInt(x, 8)
+	// leading zeros, but leave room for a NUL.
+	for len(s)+1 < len(b) {
+		s = "0" + s
+	}
+	tw.cString(b, s, false, paxNone, nil)
+}
+
+// Write x into b, either as octal or as binary (GNUtar/star extension).
+// If the value is too long for the field and writingPax is enabled both for the field and the add a paxheader record instead
+func (tw *Writer) numeric(b []byte, x int64, allowPax bool, paxKeyword string, paxHeaders map[string]string) {
+	// Try octal first.
+	s := strconv.FormatInt(x, 8)
+	if len(s) < len(b) {
+		tw.octal(b, x)
+		return
+	}
+
+	// If it is too long for octal, and pax is preferred, use a pax header
+	if allowPax && tw.preferPax {
+		tw.octal(b, 0)
+		s := strconv.FormatInt(x, 10)
+		paxHeaders[paxKeyword] = s
+		return
+	}
+
+	// Too big: use binary (big-endian).
+	tw.usedBinary = true
+	for i := len(b) - 1; x > 0 && i >= 0; i-- {
+		b[i] = byte(x)
+		x >>= 8
+	}
+	b[0] |= 0x80 // highest bit indicates binary format
+}
+
+var (
+	minTime = time.Unix(0, 0)
+	// There is room for 11 octal digits (33 bits) of mtime.
+	maxTime = minTime.Add((1<<33 - 1) * time.Second)
+)
+
+// WriteHeader writes hdr and prepares to accept the file's contents.
+// WriteHeader calls Flush if it is not the first header.
+// Calling after a Close will return ErrWriteAfterClose.
+func (tw *Writer) WriteHeader(hdr *Header) error {
+	return tw.writeHeader(hdr, true)
+}
+
+// WriteHeader writes hdr and prepares to accept the file's contents.
+// WriteHeader calls Flush if it is not the first header.
+// Calling after a Close will return ErrWriteAfterClose.
+// As this method is called internally by writePax header to allow it to
+// suppress writing the pax header.
+func (tw *Writer) writeHeader(hdr *Header, allowPax bool) error {
+	if tw.closed {
+		return ErrWriteAfterClose
+	}
+	if tw.err == nil {
+		tw.Flush()
+	}
+	if tw.err != nil {
+		return tw.err
+	}
+
+	// a map to hold pax header records, if any are needed
+	paxHeaders := make(map[string]string)
+
+	// TODO(shanemhansen): we might want to use PAX headers for
+	// subsecond time resolution, but for now let's just capture
+	// too long fields or non ascii characters
+
+	var header []byte
+
+	// We need to select which scratch buffer to use carefully,
+	// since this method is called recursively to write PAX headers.
+	// If allowPax is true, this is the non-recursive call, and we will use hdrBuff.
+	// If allowPax is false, we are being called by writePAXHeader, and hdrBuff is
+	// already being used by the non-recursive call, so we must use paxHdrBuff.
+	header = tw.hdrBuff[:]
+	if !allowPax {
+		header = tw.paxHdrBuff[:]
+	}
+	copy(header, zeroBlock)
+	s := slicer(header)
+
+	// keep a reference to the filename to allow to overwrite it later if we detect that we can use ustar longnames instead of pax
+	pathHeaderBytes := s.next(fileNameSize)
+
+	tw.cString(pathHeaderBytes, hdr.Name, true, paxPath, paxHeaders)
+
+	// Handle out of range ModTime carefully.
+	var modTime int64
+	if !hdr.ModTime.Before(minTime) && !hdr.ModTime.After(maxTime) {
+		modTime = hdr.ModTime.Unix()
+	}
+
+	tw.octal(s.next(8), hdr.Mode)                                   // 100:108
+	tw.numeric(s.next(8), int64(hdr.Uid), true, paxUid, paxHeaders) // 108:116
+	tw.numeric(s.next(8), int64(hdr.Gid), true, paxGid, paxHeaders) // 116:124
+	tw.numeric(s.next(12), hdr.Size, true, paxSize, paxHeaders)     // 124:136
+	tw.numeric(s.next(12), modTime, false, paxNone, nil)            // 136:148 --- consider using pax for finer granularity
+	s.next(8)                                                       // chksum (148:156)
+	s.next(1)[0] = hdr.Typeflag                                     // 156:157
+
+	tw.cString(s.next(100), hdr.Linkname, true, paxLinkpath, paxHeaders)
+
+	copy(s.next(8), []byte("ustar\x0000"))                        // 257:265
+	tw.cString(s.next(32), hdr.Uname, true, paxUname, paxHeaders) // 265:297
+	tw.cString(s.next(32), hdr.Gname, true, paxGname, paxHeaders) // 297:329
+	tw.numeric(s.next(8), hdr.Devmajor, false, paxNone, nil)      // 329:337
+	tw.numeric(s.next(8), hdr.Devminor, false, paxNone, nil)      // 337:345
+
+	// keep a reference to the prefix to allow to overwrite it later if we detect that we can use ustar longnames instead of pax
+	prefixHeaderBytes := s.next(155)
+	tw.cString(prefixHeaderBytes, "", false, paxNone, nil) // 345:500  prefix
+
+	// Use the GNU magic instead of POSIX magic if we used any GNU extensions.
+	if tw.usedBinary {
+		copy(header[257:265], []byte("ustar  \x00"))
+	}
+
+	_, paxPathUsed := paxHeaders[paxPath]
+	// try to use a ustar header when only the name is too long
+	if !tw.preferPax && len(paxHeaders) == 1 && paxPathUsed {
+		suffix := hdr.Name
+		prefix := ""
+		if len(hdr.Name) > fileNameSize && isASCII(hdr.Name) {
+			var err error
+			prefix, suffix, err = tw.splitUSTARLongName(hdr.Name)
+			if err == nil {
+				// ok we can use a ustar long name instead of pax, now correct the fields
+
+				// remove the path field from the pax header. this will suppress the pax header
+				delete(paxHeaders, paxPath)
+
+				// update the path fields
+				tw.cString(pathHeaderBytes, suffix, false, paxNone, nil)
+				tw.cString(prefixHeaderBytes, prefix, false, paxNone, nil)
+
+				// Use the ustar magic if we used ustar long names.
+				if len(prefix) > 0 && !tw.usedBinary {
+					copy(header[257:265], []byte("ustar\x00"))
+				}
+			}
+		}
+	}
+
+	// The chksum field is terminated by a NUL and a space.
+	// This is different from the other octal fields.
+	chksum, _ := checksum(header)
+	tw.octal(header[148:155], chksum)
+	header[155] = ' '
+
+	if tw.err != nil {
+		// problem with header; probably integer too big for a field.
+		return tw.err
+	}
+
+	if allowPax {
+		for k, v := range hdr.Xattrs {
+			paxHeaders[paxXattr+k] = v
+		}
+	}
+
+	if len(paxHeaders) > 0 {
+		if !allowPax {
+			return errInvalidHeader
+		}
+		if err := tw.writePAXHeader(hdr, paxHeaders); err != nil {
+			return err
+		}
+	}
+	tw.nb = int64(hdr.Size)
+	tw.pad = (blockSize - (tw.nb % blockSize)) % blockSize
+
+	_, tw.err = tw.w.Write(header)
+	return tw.err
+}
+
+// writeUSTARLongName splits a USTAR long name hdr.Name.
+// name must be < 256 characters. errNameTooLong is returned
+// if hdr.Name can't be split. The splitting heuristic
+// is compatible with gnu tar.
+func (tw *Writer) splitUSTARLongName(name string) (prefix, suffix string, err error) {
+	length := len(name)
+	if length > fileNamePrefixSize+1 {
+		length = fileNamePrefixSize + 1
+	} else if name[length-1] == '/' {
+		length--
+	}
+	i := strings.LastIndex(name[:length], "/")
+	// nlen contains the resulting length in the name field.
+	// plen contains the resulting length in the prefix field.
+	nlen := len(name) - i - 1
+	plen := i
+	if i <= 0 || nlen > fileNameSize || nlen == 0 || plen > fileNamePrefixSize {
+		err = errNameTooLong
+		return
+	}
+	prefix, suffix = name[:i], name[i+1:]
+	return
+}
+
+// writePaxHeader writes an extended pax header to the
+// archive.
+func (tw *Writer) writePAXHeader(hdr *Header, paxHeaders map[string]string) error {
+	// Prepare extended header
+	ext := new(Header)
+	ext.Typeflag = TypeXHeader
+	// Setting ModTime is required for reader parsing to
+	// succeed, and seems harmless enough.
+	ext.ModTime = hdr.ModTime
+	// The spec asks that we namespace our pseudo files
+	// with the current pid.
+	pid := os.Getpid()
+	dir, file := path.Split(hdr.Name)
+	fullName := path.Join(dir,
+		fmt.Sprintf("PaxHeaders.%d", pid), file)
+
+	ascii := toASCII(fullName)
+	if len(ascii) > 100 {
+		ascii = ascii[:100]
+	}
+	ext.Name = ascii
+	// Construct the body
+	var buf bytes.Buffer
+
+	for k, v := range paxHeaders {
+		fmt.Fprint(&buf, paxHeader(k+"="+v))
+	}
+
+	ext.Size = int64(len(buf.Bytes()))
+	if err := tw.writeHeader(ext, false); err != nil {
+		return err
+	}
+	if _, err := tw.Write(buf.Bytes()); err != nil {
+		return err
+	}
+	if err := tw.Flush(); err != nil {
+		return err
+	}
+	return nil
+}
+
+// paxHeader formats a single pax record, prefixing it with the appropriate length
+func paxHeader(msg string) string {
+	const padding = 2 // Extra padding for space and newline
+	size := len(msg) + padding
+	size += len(strconv.Itoa(size))
+	record := fmt.Sprintf("%d %s\n", size, msg)
+	if len(record) != size {
+		// Final adjustment if adding size increased
+		// the number of digits in size
+		size = len(record)
+		record = fmt.Sprintf("%d %s\n", size, msg)
+	}
+	return record
+}
+
+// Write writes to the current entry in the tar archive.
+// Write returns the error ErrWriteTooLong if more than
+// hdr.Size bytes are written after WriteHeader.
+func (tw *Writer) Write(b []byte) (n int, err error) {
+	if tw.closed {
+		err = ErrWriteTooLong
+		return
+	}
+	overwrite := false
+	if int64(len(b)) > tw.nb {
+		b = b[0:tw.nb]
+		overwrite = true
+	}
+	n, err = tw.w.Write(b)
+	tw.nb -= int64(n)
+	if err == nil && overwrite {
+		err = ErrWriteTooLong
+		return
+	}
+	tw.err = err
+	return
+}
+
+// Close closes the tar archive, flushing any unwritten
+// data to the underlying writer.
+func (tw *Writer) Close() error {
+	if tw.err != nil || tw.closed {
+		return tw.err
+	}
+	tw.Flush()
+	tw.closed = true
+	if tw.err != nil {
+		return tw.err
+	}
+
+	// trailer: two zero blocks
+	for i := 0; i < 2; i++ {
+		_, tw.err = tw.w.Write(zeroBlock)
+		if tw.err != nil {
+			break
+		}
+	}
+	return tw.err
+}

archive/tar/writer_test.go

@@ -0,0 +1,491 @@
+// 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
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"reflect"
+	"strings"
+	"testing"
+	"testing/iotest"
+	"time"
+)
+
+type writerTestEntry struct {
+	header   *Header
+	contents string
+}
+
+type writerTest struct {
+	file    string // filename of expected output
+	entries []*writerTestEntry
+}
+
+var writerTests = []*writerTest{
+	// The writer test file was produced with this command:
+	// tar (GNU tar) 1.26
+	//   ln -s small.txt link.txt
+	//   tar -b 1 --format=ustar -c -f writer.tar small.txt small2.txt link.txt
+	{
+		file: "testdata/writer.tar",
+		entries: []*writerTestEntry{
+			{
+				header: &Header{
+					Name:     "small.txt",
+					Mode:     0640,
+					Uid:      73025,
+					Gid:      5000,
+					Size:     5,
+					ModTime:  time.Unix(1246508266, 0),
+					Typeflag: '0',
+					Uname:    "dsymonds",
+					Gname:    "eng",
+				},
+				contents: "Kilts",
+			},
+			{
+				header: &Header{
+					Name:     "small2.txt",
+					Mode:     0640,
+					Uid:      73025,
+					Gid:      5000,
+					Size:     11,
+					ModTime:  time.Unix(1245217492, 0),
+					Typeflag: '0',
+					Uname:    "dsymonds",
+					Gname:    "eng",
+				},
+				contents: "Google.com\n",
+			},
+			{
+				header: &Header{
+					Name:     "link.txt",
+					Mode:     0777,
+					Uid:      1000,
+					Gid:      1000,
+					Size:     0,
+					ModTime:  time.Unix(1314603082, 0),
+					Typeflag: '2',
+					Linkname: "small.txt",
+					Uname:    "strings",
+					Gname:    "strings",
+				},
+				// no contents
+			},
+		},
+	},
+	// The truncated test file was produced using these commands:
+	//   dd if=/dev/zero bs=1048576 count=16384 > /tmp/16gig.txt
+	//   tar -b 1 -c -f- /tmp/16gig.txt | dd bs=512 count=8 > writer-big.tar
+	{
+		file: "testdata/writer-big.tar",
+		entries: []*writerTestEntry{
+			{
+				header: &Header{
+					Name:     "tmp/16gig.txt",
+					Mode:     0640,
+					Uid:      73025,
+					Gid:      5000,
+					Size:     16 << 30,
+					ModTime:  time.Unix(1254699560, 0),
+					Typeflag: '0',
+					Uname:    "dsymonds",
+					Gname:    "eng",
+				},
+				// fake contents
+				contents: strings.Repeat("\x00", 4<<10),
+			},
+		},
+	},
+	// The truncated test file was produced using these commands:
+	//   dd if=/dev/zero bs=1048576 count=16384 > (longname/)*15 /16gig.txt
+	//   tar -b 1 -c -f- (longname/)*15 /16gig.txt | dd bs=512 count=8 > writer-big-long.tar
+	{
+		file: "testdata/writer-big-long.tar",
+		entries: []*writerTestEntry{
+			{
+				header: &Header{
+					Name:     strings.Repeat("longname/", 15) + "16gig.txt",
+					Mode:     0644,
+					Uid:      1000,
+					Gid:      1000,
+					Size:     16 << 30,
+					ModTime:  time.Unix(1399583047, 0),
+					Typeflag: '0',
+					Uname:    "guillaume",
+					Gname:    "guillaume",
+				},
+				// fake contents
+				contents: strings.Repeat("\x00", 4<<10),
+			},
+		},
+	},
+	// This file was produced using gnu tar 1.17
+	// gnutar  -b 4 --format=ustar (longname/)*15 + file.txt
+	{
+		file: "testdata/ustar.tar",
+		entries: []*writerTestEntry{
+			{
+				header: &Header{
+					Name:     strings.Repeat("longname/", 15) + "file.txt",
+					Mode:     0644,
+					Uid:      0765,
+					Gid:      024,
+					Size:     06,
+					ModTime:  time.Unix(1360135598, 0),
+					Typeflag: '0',
+					Uname:    "shane",
+					Gname:    "staff",
+				},
+				contents: "hello\n",
+			},
+		},
+	},
+}
+
+// Render byte array in a two-character hexadecimal string, spaced for easy visual inspection.
+func bytestr(offset int, b []byte) string {
+	const rowLen = 32
+	s := fmt.Sprintf("%04x ", offset)
+	for _, ch := range b {
+		switch {
+		case '0' <= ch && ch <= '9', 'A' <= ch && ch <= 'Z', 'a' <= ch && ch <= 'z':
+			s += fmt.Sprintf("  %c", ch)
+		default:
+			s += fmt.Sprintf(" %02x", ch)
+		}
+	}
+	return s
+}
+
+// Render a pseudo-diff between two blocks of bytes.
+func bytediff(a []byte, b []byte) string {
+	const rowLen = 32
+	s := fmt.Sprintf("(%d bytes vs. %d bytes)\n", len(a), len(b))
+	for offset := 0; len(a)+len(b) > 0; offset += rowLen {
+		na, nb := rowLen, rowLen
+		if na > len(a) {
+			na = len(a)
+		}
+		if nb > len(b) {
+			nb = len(b)
+		}
+		sa := bytestr(offset, a[0:na])
+		sb := bytestr(offset, b[0:nb])
+		if sa != sb {
+			s += fmt.Sprintf("-%v\n+%v\n", sa, sb)
+		}
+		a = a[na:]
+		b = b[nb:]
+	}
+	return s
+}
+
+func TestWriter(t *testing.T) {
+testLoop:
+	for i, test := range writerTests {
+		expected, err := ioutil.ReadFile(test.file)
+		if err != nil {
+			t.Errorf("test %d: Unexpected error: %v", i, err)
+			continue
+		}
+
+		buf := new(bytes.Buffer)
+		tw := NewWriter(iotest.TruncateWriter(buf, 4<<10)) // only catch the first 4 KB
+		big := false
+		for j, entry := range test.entries {
+			big = big || entry.header.Size > 1<<10
+			if err := tw.WriteHeader(entry.header); err != nil {
+				t.Errorf("test %d, entry %d: Failed writing header: %v", i, j, err)
+				continue testLoop
+			}
+			if _, err := io.WriteString(tw, entry.contents); err != nil {
+				t.Errorf("test %d, entry %d: Failed writing contents: %v", i, j, err)
+				continue testLoop
+			}
+		}
+		// Only interested in Close failures for the small tests.
+		if err := tw.Close(); err != nil && !big {
+			t.Errorf("test %d: Failed closing archive: %v", i, err)
+			continue testLoop
+		}
+
+		actual := buf.Bytes()
+		if !bytes.Equal(expected, actual) {
+			t.Errorf("test %d: Incorrect result: (-=expected, +=actual)\n%v",
+				i, bytediff(expected, actual))
+		}
+		if testing.Short() { // The second test is expensive.
+			break
+		}
+	}
+}
+
+func TestPax(t *testing.T) {
+	// Create an archive with a large name
+	fileinfo, err := os.Stat("testdata/small.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	hdr, err := FileInfoHeader(fileinfo, "")
+	if err != nil {
+		t.Fatalf("os.Stat: %v", err)
+	}
+	// Force a PAX long name to be written
+	longName := strings.Repeat("ab", 100)
+	contents := strings.Repeat(" ", int(hdr.Size))
+	hdr.Name = longName
+	var buf bytes.Buffer
+	writer := NewWriter(&buf)
+	if err := writer.WriteHeader(hdr); err != nil {
+		t.Fatal(err)
+	}
+	if _, err = writer.Write([]byte(contents)); err != nil {
+		t.Fatal(err)
+	}
+	if err := writer.Close(); err != nil {
+		t.Fatal(err)
+	}
+	// Simple test to make sure PAX extensions are in effect
+	if !bytes.Contains(buf.Bytes(), []byte("PaxHeaders.")) {
+		t.Fatal("Expected at least one PAX header to be written.")
+	}
+	// Test that we can get a long name back out of the archive.
+	reader := NewReader(&buf)
+	hdr, err = reader.Next()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if hdr.Name != longName {
+		t.Fatal("Couldn't recover long file name")
+	}
+}
+
+func TestPaxSymlink(t *testing.T) {
+	// Create an archive with a large linkname
+	fileinfo, err := os.Stat("testdata/small.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	hdr, err := FileInfoHeader(fileinfo, "")
+	hdr.Typeflag = TypeSymlink
+	if err != nil {
+		t.Fatalf("os.Stat:1 %v", err)
+	}
+	// Force a PAX long linkname to be written
+	longLinkname := strings.Repeat("1234567890/1234567890", 10)
+	hdr.Linkname = longLinkname
+
+	hdr.Size = 0
+	var buf bytes.Buffer
+	writer := NewWriter(&buf)
+	if err := writer.WriteHeader(hdr); err != nil {
+		t.Fatal(err)
+	}
+	if err := writer.Close(); err != nil {
+		t.Fatal(err)
+	}
+	// Simple test to make sure PAX extensions are in effect
+	if !bytes.Contains(buf.Bytes(), []byte("PaxHeaders.")) {
+		t.Fatal("Expected at least one PAX header to be written.")
+	}
+	// Test that we can get a long name back out of the archive.
+	reader := NewReader(&buf)
+	hdr, err = reader.Next()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if hdr.Linkname != longLinkname {
+		t.Fatal("Couldn't recover long link name")
+	}
+}
+
+func TestPaxNonAscii(t *testing.T) {
+	// Create an archive with non ascii. These should trigger a pax header
+	// because pax headers have a defined utf-8 encoding.
+	fileinfo, err := os.Stat("testdata/small.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	hdr, err := FileInfoHeader(fileinfo, "")
+	if err != nil {
+		t.Fatalf("os.Stat:1 %v", err)
+	}
+
+	// some sample data
+	chineseFilename := "文件名"
+	chineseGroupname := "組"
+	chineseUsername := "用戶名"
+
+	hdr.Name = chineseFilename
+	hdr.Gname = chineseGroupname
+	hdr.Uname = chineseUsername
+
+	contents := strings.Repeat(" ", int(hdr.Size))
+
+	var buf bytes.Buffer
+	writer := NewWriter(&buf)
+	if err := writer.WriteHeader(hdr); err != nil {
+		t.Fatal(err)
+	}
+	if _, err = writer.Write([]byte(contents)); err != nil {
+		t.Fatal(err)
+	}
+	if err := writer.Close(); err != nil {
+		t.Fatal(err)
+	}
+	// Simple test to make sure PAX extensions are in effect
+	if !bytes.Contains(buf.Bytes(), []byte("PaxHeaders.")) {
+		t.Fatal("Expected at least one PAX header to be written.")
+	}
+	// Test that we can get a long name back out of the archive.
+	reader := NewReader(&buf)
+	hdr, err = reader.Next()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if hdr.Name != chineseFilename {
+		t.Fatal("Couldn't recover unicode name")
+	}
+	if hdr.Gname != chineseGroupname {
+		t.Fatal("Couldn't recover unicode group")
+	}
+	if hdr.Uname != chineseUsername {
+		t.Fatal("Couldn't recover unicode user")
+	}
+}
+
+func TestPaxXattrs(t *testing.T) {
+	xattrs := map[string]string{
+		"user.key": "value",
+	}
+
+	// Create an archive with an xattr
+	fileinfo, err := os.Stat("testdata/small.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	hdr, err := FileInfoHeader(fileinfo, "")
+	if err != nil {
+		t.Fatalf("os.Stat: %v", err)
+	}
+	contents := "Kilts"
+	hdr.Xattrs = xattrs
+	var buf bytes.Buffer
+	writer := NewWriter(&buf)
+	if err := writer.WriteHeader(hdr); err != nil {
+		t.Fatal(err)
+	}
+	if _, err = writer.Write([]byte(contents)); err != nil {
+		t.Fatal(err)
+	}
+	if err := writer.Close(); err != nil {
+		t.Fatal(err)
+	}
+	// Test that we can get the xattrs back out of the archive.
+	reader := NewReader(&buf)
+	hdr, err = reader.Next()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !reflect.DeepEqual(hdr.Xattrs, xattrs) {
+		t.Fatalf("xattrs did not survive round trip: got %+v, want %+v",
+			hdr.Xattrs, xattrs)
+	}
+}
+
+func TestPAXHeader(t *testing.T) {
+	medName := strings.Repeat("CD", 50)
+	longName := strings.Repeat("AB", 100)
+	paxTests := [][2]string{
+		{paxPath + "=/etc/hosts", "19 path=/etc/hosts\n"},
+		{"a=b", "6 a=b\n"},          // Single digit length
+		{"a=names", "11 a=names\n"}, // Test case involving carries
+		{paxPath + "=" + longName, fmt.Sprintf("210 path=%s\n", longName)},
+		{paxPath + "=" + medName, fmt.Sprintf("110 path=%s\n", medName)}}
+
+	for _, test := range paxTests {
+		key, expected := test[0], test[1]
+		if result := paxHeader(key); result != expected {
+			t.Fatalf("paxHeader: got %s, expected %s", result, expected)
+		}
+	}
+}
+
+func TestUSTARLongName(t *testing.T) {
+	// Create an archive with a path that failed to split with USTAR extension in previous versions.
+	fileinfo, err := os.Stat("testdata/small.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	hdr, err := FileInfoHeader(fileinfo, "")
+	hdr.Typeflag = TypeDir
+	if err != nil {
+		t.Fatalf("os.Stat:1 %v", err)
+	}
+	// Force a PAX long name to be written. The name was taken from a practical example
+	// that fails and replaced ever char through numbers to anonymize the sample.
+	longName := "/0000_0000000/00000-000000000/0000_0000000/00000-0000000000000/0000_0000000/00000-0000000-00000000/0000_0000000/00000000/0000_0000000/000/0000_0000000/00000000v00/0000_0000000/000000/0000_0000000/0000000/0000_0000000/00000y-00/0000/0000/00000000/0x000000/"
+	hdr.Name = longName
+
+	hdr.Size = 0
+	var buf bytes.Buffer
+	writer := NewWriter(&buf)
+	if err := writer.WriteHeader(hdr); err != nil {
+		t.Fatal(err)
+	}
+	if err := writer.Close(); err != nil {
+		t.Fatal(err)
+	}
+	// Test that we can get a long name back out of the archive.
+	reader := NewReader(&buf)
+	hdr, err = reader.Next()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if hdr.Name != longName {
+		t.Fatal("Couldn't recover long name")
+	}
+}
+
+func TestValidTypeflagWithPAXHeader(t *testing.T) {
+	var buffer bytes.Buffer
+	tw := NewWriter(&buffer)
+
+	fileName := strings.Repeat("ab", 100)
+
+	hdr := &Header{
+		Name:     fileName,
+		Size:     4,
+		Typeflag: 0,
+	}
+	if err := tw.WriteHeader(hdr); err != nil {
+		t.Fatalf("Failed to write header: %s", err)
+	}
+	if _, err := tw.Write([]byte("fooo")); err != nil {
+		t.Fatalf("Failed to write the file's data: %s", err)
+	}
+	tw.Close()
+
+	tr := NewReader(&buffer)
+
+	for {
+		header, err := tr.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			t.Fatalf("Failed to read header: %s", err)
+		}
+		if header.Typeflag != 0 {
+			t.Fatalf("Typeflag should've been 0, found %d", header.Typeflag)
+		}
+	}
+}