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// Copyright 2016 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"
"strconv"
"strings"
"time"
)
// hasNUL reports whether the NUL character exists within s.
func hasNUL(s string) bool {
return strings.IndexByte(s, 0) >= 0
}
// isASCII reports whether the input is an ASCII C-style string.
func isASCII(s string) bool {
for _, c := range s {
if c >= 0x80 || c == 0x00 {
return false
}
}
return true
}
// toASCII converts the input to an ASCII C-style string.
// This a best effort conversion, so invalid characters are dropped.
func toASCII(s string) string {
if isASCII(s) {
return s
}
b := make([]byte, 0, len(s))
for _, c := range s {
if c < 0x80 && c != 0x00 {
b = append(b, byte(c))
}
}
return string(b)
}
type parser struct {
err error // Last error seen
}
type formatter struct {
err error // Last error seen
}
// parseString 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 (*parser) parseString(b []byte) string {
if i := bytes.IndexByte(b, 0); i >= 0 {
return string(b[:i])
}
return string(b)
}
// formatString copies s into b, NUL-terminating if possible.
func (f *formatter) formatString(b []byte, s string) {
if len(s) > len(b) {
f.err = ErrFieldTooLong
}
copy(b, s)
if len(s) < len(b) {
b[len(s)] = 0
}
// Some buggy readers treat regular files with a trailing slash
// in the V7 path field as a directory even though the full path
// recorded elsewhere (e.g., via PAX record) contains no trailing slash.
if len(s) > len(b) && b[len(b)-1] == '/' {
n := len(strings.TrimRight(s[:len(b)], "/"))
b[n] = 0 // Replace trailing slash with NUL terminator
}
}
// fitsInBase256 reports whether x can be encoded into n bytes using base-256
// encoding. Unlike octal encoding, base-256 encoding does not require that the
// string ends with a NUL character. Thus, all n bytes are available for output.
//
// If operating in binary mode, this assumes strict GNU binary mode; which means
// that the first byte can only be either 0x80 or 0xff. Thus, the first byte is
// equivalent to the sign bit in two's complement form.
func fitsInBase256(n int, x int64) bool {
binBits := uint(n-1) * 8
return n >= 9 || (x >= -1<<binBits && x < 1<<binBits)
}
// parseNumeric parses the input as being encoded in either base-256 or octal.
// This function may return negative numbers.
// If parsing fails or an integer overflow occurs, err will be set.
func (p *parser) parseNumeric(b []byte) int64 {
// Check for base-256 (binary) format first.
// If the first bit is set, then all following bits constitute a two's
// complement encoded number in big-endian byte order.
if len(b) > 0 && b[0]&0x80 != 0 {
// Handling negative numbers relies on the following identity:
// -a-1 == ^a
//
// If the number is negative, we use an inversion mask to invert the
// data bytes and treat the value as an unsigned number.
var inv byte // 0x00 if positive or zero, 0xff if negative
if b[0]&0x40 != 0 {
inv = 0xff
}
var x uint64
for i, c := range b {
c ^= inv // Inverts c only if inv is 0xff, otherwise does nothing
if i == 0 {
c &= 0x7f // Ignore signal bit in first byte
}
if (x >> 56) > 0 {
p.err = ErrHeader // Integer overflow
return 0
}
x = x<<8 | uint64(c)
}
if (x >> 63) > 0 {
p.err = ErrHeader // Integer overflow
return 0
}
if inv == 0xff {
return ^int64(x)
}
return int64(x)
}
// Normal case is base-8 (octal) format.
return p.parseOctal(b)
}
// formatNumeric encodes x into b using base-8 (octal) encoding if possible.
// Otherwise it will attempt to use base-256 (binary) encoding.
func (f *formatter) formatNumeric(b []byte, x int64) {
if fitsInOctal(len(b), x) {
f.formatOctal(b, x)
return
}
if fitsInBase256(len(b), x) {
for i := len(b) - 1; i >= 0; i-- {
b[i] = byte(x)
x >>= 8
}
b[0] |= 0x80 // Highest bit indicates binary format
return
}
f.formatOctal(b, 0) // Last resort, just write zero
f.err = ErrFieldTooLong
}
func (p *parser) parseOctal(b []byte) int64 {
// 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, perr := strconv.ParseUint(p.parseString(b), 8, 64)
if perr != nil {
p.err = ErrHeader
}
return int64(x)
}
func (f *formatter) formatOctal(b []byte, x int64) {
if !fitsInOctal(len(b), x) {
x = 0 // Last resort, just write zero
f.err = ErrFieldTooLong
}
s := strconv.FormatInt(x, 8)
// Add leading zeros, but leave room for a NUL.
if n := len(b) - len(s) - 1; n > 0 {
s = strings.Repeat("0", n) + s
}
f.formatString(b, s)
}
// fitsInOctal reports whether the integer x fits in a field n-bytes long
// using octal encoding with the appropriate NUL terminator.
func fitsInOctal(n int, x int64) bool {
octBits := uint(n-1) * 3
return x >= 0 && (n >= 22 || x < 1<<octBits)
}
// parsePAXTime takes a string of the form %d.%d as described in the PAX
// specification. Note that this implementation allows for negative timestamps,
// which is allowed for by the PAX specification, but not always portable.
func parsePAXTime(s string) (time.Time, error) {
const maxNanoSecondDigits = 9
// Split string into seconds and sub-seconds parts.
ss, sn := s, ""
if pos := strings.IndexByte(s, '.'); pos >= 0 {
ss, sn = s[:pos], s[pos+1:]
}
// Parse the seconds.
secs, err := strconv.ParseInt(ss, 10, 64)
if err != nil {
return time.Time{}, ErrHeader
}
if len(sn) == 0 {
return time.Unix(secs, 0), nil // No sub-second values
}
// Parse the nanoseconds.
if strings.Trim(sn, "0123456789") != "" {
return time.Time{}, ErrHeader
}
if len(sn) < maxNanoSecondDigits {
sn += strings.Repeat("0", maxNanoSecondDigits-len(sn)) // Right pad
} else {
sn = sn[:maxNanoSecondDigits] // Right truncate
}
nsecs, _ := strconv.ParseInt(sn, 10, 64) // Must succeed
if len(ss) > 0 && ss[0] == '-' {
return time.Unix(secs, -1*nsecs), nil // Negative correction
}
return time.Unix(secs, nsecs), nil
}
// formatPAXTime converts ts into a time of the form %d.%d as described in the
// PAX specification. This function is capable of negative timestamps.
func formatPAXTime(ts time.Time) (s string) {
secs, nsecs := ts.Unix(), ts.Nanosecond()
if nsecs == 0 {
return strconv.FormatInt(secs, 10)
}
// If seconds is negative, then perform correction.
sign := ""
if secs < 0 {
sign = "-" // Remember sign
secs = -(secs + 1) // Add a second to secs
nsecs = -(nsecs - 1E9) // Take that second away from nsecs
}
return strings.TrimRight(fmt.Sprintf("%s%d.%09d", sign, secs, nsecs), "0")
}
// parsePAXRecord parses the input PAX record string into a key-value pair.
// If parsing is successful, it will slice off the currently read record and
// return the remainder as r.
func parsePAXRecord(s string) (k, v, r string, err error) {
// The size field ends at the first space.
sp := strings.IndexByte(s, ' ')
if sp == -1 {
return "", "", s, ErrHeader
}
// Parse the first token as a decimal integer.
n, perr := strconv.ParseInt(s[:sp], 10, 0) // Intentionally parse as native int
if perr != nil || n < 5 || int64(len(s)) < n {
return "", "", s, ErrHeader
}
// Extract everything between the space and the final newline.
rec, nl, rem := s[sp+1:n-1], s[n-1:n], s[n:]
if nl != "\n" {
return "", "", s, ErrHeader
}
// The first equals separates the key from the value.
eq := strings.IndexByte(rec, '=')
if eq == -1 {
return "", "", s, ErrHeader
}
k, v = rec[:eq], rec[eq+1:]
if !validPAXRecord(k, v) {
return "", "", s, ErrHeader
}
return k, v, rem, nil
}
// formatPAXRecord formats a single PAX record, prefixing it with the
// appropriate length.
func formatPAXRecord(k, v string) (string, error) {
if !validPAXRecord(k, v) {
return "", ErrHeader
}
const padding = 3 // Extra padding for ' ', '=', and '\n'
size := len(k) + len(v) + padding
size += len(strconv.Itoa(size))
record := strconv.Itoa(size) + " " + k + "=" + v + "\n"
// Final adjustment if adding size field increased the record size.
if len(record) != size {
size = len(record)
record = strconv.Itoa(size) + " " + k + "=" + v + "\n"
}
return record, nil
}
// validPAXRecord reports whether the key-value pair is valid where each
// record is formatted as:
// "%d %s=%s\n" % (size, key, value)
//
// Keys and values should be UTF-8, but the number of bad writers out there
// forces us to be a more liberal.
// Thus, we only reject all keys with NUL, and only reject NULs in values
// for the PAX version of the USTAR string fields.
// The key must not contain an '=' character.
func validPAXRecord(k, v string) bool {
if k == "" || strings.IndexByte(k, '=') >= 0 {
return false
}
switch k {
case paxPath, paxLinkpath, paxUname, paxGname:
return !hasNUL(v)
default:
return !hasNUL(k)
}
}