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archive/tar: properly format GNU base-256 encoding

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Motivation:
* Previous implementation silently failed when an integer overflow
occurred. Now, we report an ErrFieldTooLong.
* Previous implementation did not encode in two's complement format and was
unable to encode negative numbers.

The relevant GNU specification says:
<<<
GNU format uses two's-complement base-256 notation to store values
that do not fit into standard ustar range.
>>>

Fixes #12436

Change-Id: I09c20602eabf8ae3a7e0db35b79440a64bfaf807
Reviewed-on: https://go-review.googlesource.com/17425
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Joe Tsai 2015-12-02 15:48:06 -08:00 committed by Vincent Batts
parent be9ac88117
commit ce5aac17f9
2 changed files with 105 additions and 4 deletions
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26
archive/tar/writer.go
View file

@ -94,13 +94,31 @@ func (f *formatter) formatOctal(b []byte, x int64) {
f.formatString(b, s)
}
// 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 {
var binBits = uint(n-1) * 8
return n >= 9 || (x >= -1<<binBits && x < 1<<binBits)
}
// Write x into b, as binary (GNUtar/star extension).
func (f *formatter) formatNumeric(b []byte, x int64) {
for i := len(b) - 1; x > 0 && i >= 0; i-- {
b[i] = byte(x)
x >>= 8
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
}
b[0] |= 0x80 // highest bit indicates binary format
f.formatOctal(b, 0) // Last resort, just write zero
f.err = ErrFieldTooLong
}
var (

83
archive/tar/writer_test.go
View file

@ -9,6 +9,7 @@ import (
"fmt"
"io"
"io/ioutil"
"math"
"os"
"reflect"
"sort"
@ -637,3 +638,85 @@ func TestFormatPAXRecord(t *testing.T) {
}
}
}
func TestFitsInBase256(t *testing.T) {
var vectors = []struct {
input int64
width int
ok bool
}{
{+1, 8, true},
{0, 8, true},
{-1, 8, true},
{1 << 56, 8, false},
{(1 << 56) - 1, 8, true},
{-1 << 56, 8, true},
{(-1 << 56) - 1, 8, false},
{121654, 8, true},
{-9849849, 8, true},
{math.MaxInt64, 9, true},
{0, 9, true},
{math.MinInt64, 9, true},
{math.MaxInt64, 12, true},
{0, 12, true},
{math.MinInt64, 12, true},
}
for _, v := range vectors {
ok := fitsInBase256(v.width, v.input)
if ok != v.ok {
t.Errorf("checkNumeric(%d, %d): got %v, want %v", v.input, v.width, ok, v.ok)
}
}
}
func TestFormatNumeric(t *testing.T) {
var vectors = []struct {
input int64
output string
ok bool
}{
// Test base-256 (binary) encoded values.
{-1, "\xff", true},
{-1, "\xff\xff", true},
{-1, "\xff\xff\xff", true},
{(1 << 0), "0", false},
{(1 << 8) - 1, "\x80\xff", true},
{(1 << 8), "0\x00", false},
{(1 << 16) - 1, "\x80\xff\xff", true},
{(1 << 16), "00\x00", false},
{-1 * (1 << 0), "\xff", true},
{-1*(1<<0) - 1, "0", false},
{-1 * (1 << 8), "\xff\x00", true},
{-1*(1<<8) - 1, "0\x00", false},
{-1 * (1 << 16), "\xff\x00\x00", true},
{-1*(1<<16) - 1, "00\x00", false},
{537795476381659745, "0000000\x00", false},
{537795476381659745, "\x80\x00\x00\x00\x07\x76\xa2\x22\xeb\x8a\x72\x61", true},
{-615126028225187231, "0000000\x00", false},
{-615126028225187231, "\xff\xff\xff\xff\xf7\x76\xa2\x22\xeb\x8a\x72\x61", true},
{math.MaxInt64, "0000000\x00", false},
{math.MaxInt64, "\x80\x00\x00\x00\x7f\xff\xff\xff\xff\xff\xff\xff", true},
{math.MinInt64, "0000000\x00", false},
{math.MinInt64, "\xff\xff\xff\xff\x80\x00\x00\x00\x00\x00\x00\x00", true},
{math.MaxInt64, "\x80\x7f\xff\xff\xff\xff\xff\xff\xff", true},
{math.MinInt64, "\xff\x80\x00\x00\x00\x00\x00\x00\x00", true},
}
for _, v := range vectors {
var f formatter
output := make([]byte, len(v.output))
f.formatNumeric(output, v.input)
ok := (f.err == nil)
if ok != v.ok {
if v.ok {
t.Errorf("formatNumeric(%d): got formatting failure, want success", v.input)
} else {
t.Errorf("formatNumeric(%d): got formatting success, want failure", v.input)
}
}
if string(output) != v.output {
t.Errorf("formatNumeric(%d): got %q, want %q", v.input, output, v.output)
}
}
}