| // 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 "strings" |
| |
| // Format represents the tar archive format. |
| // |
| // The original tar format was introduced in Unix V7. |
| // Since then, there have been multiple competing formats attempting to |
| // standardize or extend the V7 format to overcome its limitations. |
| // The most common formats are the USTAR, PAX, and GNU formats, |
| // each with their own advantages and limitations. |
| // |
| // The following table captures the capabilities of each format: |
| // |
| // | USTAR | PAX | GNU |
| // ------------------+--------+-----------+---------- |
| // Name | 256B | unlimited | unlimited |
| // Linkname | 100B | unlimited | unlimited |
| // Size | uint33 | unlimited | uint89 |
| // Mode | uint21 | uint21 | uint57 |
| // Uid/Gid | uint21 | unlimited | uint57 |
| // Uname/Gname | 32B | unlimited | 32B |
| // ModTime | uint33 | unlimited | int89 |
| // AccessTime | n/a | unlimited | int89 |
| // ChangeTime | n/a | unlimited | int89 |
| // Devmajor/Devminor | uint21 | uint21 | uint57 |
| // ------------------+--------+-----------+---------- |
| // string encoding | ASCII | UTF-8 | binary |
| // sub-second times | no | yes | no |
| // sparse files | no | yes | yes |
| // |
| // The table's upper portion shows the Header fields, where each format reports |
| // the maximum number of bytes allowed for each string field and |
| // the integer type used to store each numeric field |
| // (where timestamps are stored as the number of seconds since the Unix epoch). |
| // |
| // The table's lower portion shows specialized features of each format, |
| // such as supported string encodings, support for sub-second timestamps, |
| // or support for sparse files. |
| // |
| // The Writer currently provides no support for sparse files. |
| type Format int |
| |
| // Constants to identify various tar formats. |
| const ( |
| // Deliberately hide the meaning of constants from public API. |
| _ Format = (1 << iota) / 4 // Sequence of 0, 0, 1, 2, 4, 8, etc... |
| |
| // FormatUnknown indicates that the format is unknown. |
| FormatUnknown |
| |
| // The format of the original Unix V7 tar tool prior to standardization. |
| formatV7 |
| |
| // FormatUSTAR represents the USTAR header format defined in POSIX.1-1988. |
| // |
| // While this format is compatible with most tar readers, |
| // the format has several limitations making it unsuitable for some usages. |
| // Most notably, it cannot support sparse files, files larger than 8GiB, |
| // filenames larger than 256 characters, and non-ASCII filenames. |
| // |
| // Reference: |
| // http://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html#tag_20_92_13_06 |
| FormatUSTAR |
| |
| // FormatPAX represents the PAX header format defined in POSIX.1-2001. |
| // |
| // PAX extends USTAR by writing a special file with Typeflag TypeXHeader |
| // preceding the original header. This file contains a set of key-value |
| // records, which are used to overcome USTAR's shortcomings, in addition to |
| // providing the ability to have sub-second resolution for timestamps. |
| // |
| // Some newer formats add their own extensions to PAX by defining their |
| // own keys and assigning certain semantic meaning to the associated values. |
| // For example, sparse file support in PAX is implemented using keys |
| // defined by the GNU manual (e.g., "GNU.sparse.map"). |
| // |
| // Reference: |
| // http://pubs.opengroup.org/onlinepubs/009695399/utilities/pax.html |
| FormatPAX |
| |
| // FormatGNU represents the GNU header format. |
| // |
| // The GNU header format is older than the USTAR and PAX standards and |
| // is not compatible with them. The GNU format supports |
| // arbitrary file sizes, filenames of arbitrary encoding and length, |
| // sparse files, and other features. |
| // |
| // It is recommended that PAX be chosen over GNU unless the target |
| // application can only parse GNU formatted archives. |
| // |
| // Reference: |
| // http://www.gnu.org/software/tar/manual/html_node/Standard.html |
| FormatGNU |
| |
| // Schily's tar format, which is incompatible with USTAR. |
| // This does not cover STAR extensions to the PAX format; these fall under |
| // the PAX format. |
| formatSTAR |
| |
| formatMax |
| ) |
| |
| func (f Format) has(f2 Format) bool { return f&f2 != 0 } |
| func (f *Format) mayBe(f2 Format) { *f |= f2 } |
| func (f *Format) mayOnlyBe(f2 Format) { *f &= f2 } |
| func (f *Format) mustNotBe(f2 Format) { *f &^= f2 } |
| |
| var formatNames = map[Format]string{ |
| formatV7: "V7", FormatUSTAR: "USTAR", FormatPAX: "PAX", FormatGNU: "GNU", formatSTAR: "STAR", |
| } |
| |
| func (f Format) String() string { |
| var ss []string |
| for f2 := Format(1); f2 < formatMax; f2 <<= 1 { |
| if f.has(f2) { |
| ss = append(ss, formatNames[f2]) |
| } |
| } |
| switch len(ss) { |
| case 0: |
| return "<unknown>" |
| case 1: |
| return ss[0] |
| default: |
| return "(" + strings.Join(ss, " | ") + ")" |
| } |
| } |
| |
| // Magics used to identify various formats. |
| const ( |
| magicGNU, versionGNU = "ustar ", " \x00" |
| magicUSTAR, versionUSTAR = "ustar\x00", "00" |
| trailerSTAR = "tar\x00" |
| ) |
| |
| // Size constants from various tar specifications. |
| const ( |
| blockSize = 512 // Size of each block in a tar stream |
| nameSize = 100 // Max length of the name field in USTAR format |
| prefixSize = 155 // Max length of the prefix field in USTAR format |
| ) |
| |
| // blockPadding computes the number of bytes needed to pad offset up to the |
| // nearest block edge where 0 <= n < blockSize. |
| func blockPadding(offset int64) (n int64) { |
| return -offset & (blockSize - 1) |
| } |
| |
| var zeroBlock block |
| |
| type block [blockSize]byte |
| |
| // Convert block to any number of formats. |
| func (b *block) V7() *headerV7 { return (*headerV7)(b) } |
| func (b *block) GNU() *headerGNU { return (*headerGNU)(b) } |
| func (b *block) STAR() *headerSTAR { return (*headerSTAR)(b) } |
| func (b *block) USTAR() *headerUSTAR { return (*headerUSTAR)(b) } |
| func (b *block) Sparse() sparseArray { return (sparseArray)(b[:]) } |
| |
| // GetFormat checks that the block is a valid tar header based on the checksum. |
| // It then attempts to guess the specific format based on magic values. |
| // If the checksum fails, then FormatUnknown is returned. |
| func (b *block) GetFormat() Format { |
| // Verify checksum. |
| var p parser |
| value := p.parseOctal(b.V7().Chksum()) |
| chksum1, chksum2 := b.ComputeChecksum() |
| if p.err != nil || (value != chksum1 && value != chksum2) { |
| return FormatUnknown |
| } |
| |
| // Guess the magic values. |
| magic := string(b.USTAR().Magic()) |
| version := string(b.USTAR().Version()) |
| trailer := string(b.STAR().Trailer()) |
| switch { |
| case magic == magicUSTAR && trailer == trailerSTAR: |
| return formatSTAR |
| case magic == magicUSTAR: |
| return FormatUSTAR | FormatPAX |
| case magic == magicGNU && version == versionGNU: |
| return FormatGNU |
| default: |
| return formatV7 |
| } |
| } |
| |
| // SetFormat writes the magic values necessary for specified format |
| // and then updates the checksum accordingly. |
| func (b *block) SetFormat(format Format) { |
| // Set the magic values. |
| switch { |
| case format.has(formatV7): |
| // Do nothing. |
| case format.has(FormatGNU): |
| copy(b.GNU().Magic(), magicGNU) |
| copy(b.GNU().Version(), versionGNU) |
| case format.has(formatSTAR): |
| copy(b.STAR().Magic(), magicUSTAR) |
| copy(b.STAR().Version(), versionUSTAR) |
| copy(b.STAR().Trailer(), trailerSTAR) |
| case format.has(FormatUSTAR | FormatPAX): |
| copy(b.USTAR().Magic(), magicUSTAR) |
| copy(b.USTAR().Version(), versionUSTAR) |
| default: |
| panic("invalid format") |
| } |
| |
| // Update checksum. |
| // This field is special in that it is terminated by a NULL then space. |
| var f formatter |
| field := b.V7().Chksum() |
| chksum, _ := b.ComputeChecksum() // Possible values are 256..128776 |
| f.formatOctal(field[:7], chksum) // Never fails since 128776 < 262143 |
| field[7] = ' ' |
| } |
| |
| // ComputeChecksum computes the checksum for the header block. |
| // POSIX specifies a sum of the unsigned byte values, but the Sun tar used |
| // signed byte values. |
| // We compute and return both. |
| func (b *block) ComputeChecksum() (unsigned, signed int64) { |
| for i, c := range b { |
| if 148 <= i && i < 156 { |
| c = ' ' // Treat the checksum field itself as all spaces. |
| } |
| unsigned += int64(c) |
| signed += int64(int8(c)) |
| } |
| return unsigned, signed |
| } |
| |
| // Reset clears the block with all zeros. |
| func (b *block) Reset() { |
| *b = block{} |
| } |
| |
| type headerV7 [blockSize]byte |
| |
| func (h *headerV7) Name() []byte { return h[000:][:100] } |
| func (h *headerV7) Mode() []byte { return h[100:][:8] } |
| func (h *headerV7) UID() []byte { return h[108:][:8] } |
| func (h *headerV7) GID() []byte { return h[116:][:8] } |
| func (h *headerV7) Size() []byte { return h[124:][:12] } |
| func (h *headerV7) ModTime() []byte { return h[136:][:12] } |
| func (h *headerV7) Chksum() []byte { return h[148:][:8] } |
| func (h *headerV7) TypeFlag() []byte { return h[156:][:1] } |
| func (h *headerV7) LinkName() []byte { return h[157:][:100] } |
| |
| type headerGNU [blockSize]byte |
| |
| func (h *headerGNU) V7() *headerV7 { return (*headerV7)(h) } |
| func (h *headerGNU) Magic() []byte { return h[257:][:6] } |
| func (h *headerGNU) Version() []byte { return h[263:][:2] } |
| func (h *headerGNU) UserName() []byte { return h[265:][:32] } |
| func (h *headerGNU) GroupName() []byte { return h[297:][:32] } |
| func (h *headerGNU) DevMajor() []byte { return h[329:][:8] } |
| func (h *headerGNU) DevMinor() []byte { return h[337:][:8] } |
| func (h *headerGNU) AccessTime() []byte { return h[345:][:12] } |
| func (h *headerGNU) ChangeTime() []byte { return h[357:][:12] } |
| func (h *headerGNU) Sparse() sparseArray { return (sparseArray)(h[386:][:24*4+1]) } |
| func (h *headerGNU) RealSize() []byte { return h[483:][:12] } |
| |
| type headerSTAR [blockSize]byte |
| |
| func (h *headerSTAR) V7() *headerV7 { return (*headerV7)(h) } |
| func (h *headerSTAR) Magic() []byte { return h[257:][:6] } |
| func (h *headerSTAR) Version() []byte { return h[263:][:2] } |
| func (h *headerSTAR) UserName() []byte { return h[265:][:32] } |
| func (h *headerSTAR) GroupName() []byte { return h[297:][:32] } |
| func (h *headerSTAR) DevMajor() []byte { return h[329:][:8] } |
| func (h *headerSTAR) DevMinor() []byte { return h[337:][:8] } |
| func (h *headerSTAR) Prefix() []byte { return h[345:][:131] } |
| func (h *headerSTAR) AccessTime() []byte { return h[476:][:12] } |
| func (h *headerSTAR) ChangeTime() []byte { return h[488:][:12] } |
| func (h *headerSTAR) Trailer() []byte { return h[508:][:4] } |
| |
| type headerUSTAR [blockSize]byte |
| |
| func (h *headerUSTAR) V7() *headerV7 { return (*headerV7)(h) } |
| func (h *headerUSTAR) Magic() []byte { return h[257:][:6] } |
| func (h *headerUSTAR) Version() []byte { return h[263:][:2] } |
| func (h *headerUSTAR) UserName() []byte { return h[265:][:32] } |
| func (h *headerUSTAR) GroupName() []byte { return h[297:][:32] } |
| func (h *headerUSTAR) DevMajor() []byte { return h[329:][:8] } |
| func (h *headerUSTAR) DevMinor() []byte { return h[337:][:8] } |
| func (h *headerUSTAR) Prefix() []byte { return h[345:][:155] } |
| |
| type sparseArray []byte |
| |
| func (s sparseArray) Entry(i int) sparseElem { return (sparseElem)(s[i*24:]) } |
| func (s sparseArray) IsExtended() []byte { return s[24*s.MaxEntries():][:1] } |
| func (s sparseArray) MaxEntries() int { return len(s) / 24 } |
| |
| type sparseElem []byte |
| |
| func (s sparseElem) Offset() []byte { return s[00:][:12] } |
| func (s sparseElem) Length() []byte { return s[12:][:12] } |