├── .gitignore ├── go.mod ├── go.sum ├── reflink_other.go ├── car.go ├── common.go ├── reflink_linux.go ├── car_test.go ├── README.md ├── archive.go ├── extract.go └── LICENSE /.gitignore: -------------------------------------------------------------------------------- 1 | .idea/ 2 | *.car 3 | *~ 4 | *.swp 5 | *.swo 6 | -------------------------------------------------------------------------------- /go.mod: -------------------------------------------------------------------------------- 1 | module github.com/teknoraver/car 2 | 3 | go 1.21 4 | 5 | require golang.org/x/sys v0.25.0 6 | -------------------------------------------------------------------------------- /go.sum: -------------------------------------------------------------------------------- 1 | golang.org/x/sys v0.25.0 h1:r+8e+loiHxRqhXVl6ML1nO3l1+oFoWbnlu2Ehimmi34= 2 | golang.org/x/sys v0.25.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA= 3 | -------------------------------------------------------------------------------- /reflink_other.go: -------------------------------------------------------------------------------- 1 | //go:build !linux 2 | 3 | package main 4 | 5 | import "os" 6 | 7 | func reflinkToArchive(*os.File, *os.File, uint64) error { 8 | return reflinkError 9 | } 10 | 11 | func reflinkFromArchive(*os.File, *os.File, uint64) error { 12 | return reflinkError 13 | } 14 | -------------------------------------------------------------------------------- /car.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "flag" 5 | "fmt" 6 | "os" 7 | ) 8 | 9 | func b(b bool) int { 10 | if b { 11 | return 1 12 | } 13 | return 0 14 | } 15 | 16 | func main() { 17 | var err error 18 | 19 | t := flag.Bool("t", false, "list") 20 | c := flag.Bool("c", false, "archive") 21 | x := flag.Bool("x", false, "extract") 22 | file := flag.String("f", "", "file") 23 | verbose := flag.Bool("v", false, "verbose") 24 | flag.Parse() 25 | 26 | if b(*t)+b(*c)+b(*x) != 1 { 27 | fmt.Fprintln(os.Stderr, "Exactly one ption -t, -c or -x must be specified") 28 | os.Exit(1) 29 | } 30 | 31 | var a archive = &car{ 32 | verbose: *verbose, 33 | list: *t, 34 | } 35 | 36 | switch { 37 | case *c: 38 | if flag.NArg() == 0 { 39 | fmt.Fprintln(os.Stderr, "Missing path to compress") 40 | os.Exit(1) 41 | } 42 | 43 | err = a.archive(flag.Args(), *file) 44 | 45 | case *t, *x: 46 | err = a.extract(*file) 47 | } 48 | 49 | if err != nil { 50 | fmt.Fprintln(os.Stderr, err) 51 | } 52 | os.Exit(a.(*car).error) 53 | } 54 | -------------------------------------------------------------------------------- /common.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "errors" 5 | "io" 6 | "io/fs" 7 | ) 8 | 9 | const cowAlignment = 4096 10 | const cowMask = cowAlignment - 1 11 | const cowMagic = "CAR!" 12 | const cowEnd = "!RAC" 13 | 14 | const ( 15 | tagHeader uint16 = iota + 1 16 | tagName 17 | tagData 18 | tagLinkTarget 19 | tagDevice 20 | ) 21 | 22 | type fixedData struct { 23 | Mode uint32 24 | Uid uint32 25 | Gid uint32 26 | Mtime int64 27 | } 28 | 29 | type entry struct { 30 | fixedData 31 | name string 32 | size uint64 33 | localName string 34 | link string 35 | dev uint32 36 | } 37 | 38 | /* 39 | Just a TLV (Type, Length, Value) structure, 40 | but "type" is a reserved word in Go 41 | */ 42 | type tag struct { 43 | Tag uint16 44 | Length uint16 45 | } 46 | 47 | type paddedData struct { 48 | Size uint64 49 | Padding uint32 50 | } 51 | 52 | type archive interface { 53 | archive(paths []string, outFile string) error 54 | extract(inFile string) error 55 | } 56 | 57 | type dirMode struct { 58 | name string 59 | mode fs.FileMode 60 | } 61 | 62 | type car struct { 63 | verbose bool 64 | list bool 65 | error int 66 | infoFd io.Writer 67 | superUser bool 68 | dirModes []dirMode 69 | destDir string 70 | seekable bool 71 | } 72 | 73 | var reflinkError = errors.New("reflink not supported") 74 | 75 | func round4k(size uint64) uint64 { 76 | return (size + cowMask) & ^uint64(cowMask) 77 | } 78 | -------------------------------------------------------------------------------- /reflink_linux.go: -------------------------------------------------------------------------------- 1 | //go:build linux 2 | 3 | package main 4 | 5 | import ( 6 | "io" 7 | "os" 8 | 9 | "golang.org/x/sys/unix" 10 | ) 11 | 12 | func reflinkToArchive(inFd *os.File, archive *os.File, size uint64) error { 13 | // The archive can be non seekable (e.g. a pipe), in this case fall back to classic copy 14 | offset, err := archive.Seek(0, io.SeekCurrent) 15 | if err != nil { 16 | return reflinkError 17 | } 18 | 19 | // If the file size is less than the minimum allowed by reflink, give up 20 | if size >= cowAlignment { 21 | fcrange := unix.FileCloneRange{ 22 | Src_fd: int64(inFd.Fd()), 23 | Src_length: size & ^uint64(cowMask), 24 | Dest_offset: uint64(offset), 25 | } 26 | 27 | /* reflink could fail for a lot of reasons (unsupported, different mountpoint etc.) 28 | * fallback to a copy in case of non fatal error */ 29 | err = unix.IoctlFileCloneRange(int(archive.Fd()), &fcrange) 30 | if err != nil { 31 | return reflinkError 32 | } 33 | 34 | // Past this point, errors are fatal 35 | 36 | /* reflink does not move the file pointer, seek the input file 37 | * to the last reflinked block so we can copy the remainder */ 38 | _, err = inFd.Seek(int64(fcrange.Src_length), io.SeekStart) 39 | if err != nil { 40 | return err 41 | } 42 | 43 | // reflink does not move the file pointer, seek to the end 44 | _, err = archive.Seek(0, io.SeekEnd) 45 | } 46 | 47 | return err 48 | 49 | } 50 | 51 | func reflinkFromArchive(archive *os.File, outFd *os.File, size uint64) error { 52 | // The archive can be non seekable (e.g. a pipe), in this case fall back to classic copy 53 | offset, err := archive.Seek(0, io.SeekCurrent) 54 | if err != nil { 55 | return reflinkError 56 | } 57 | 58 | fcrange := unix.FileCloneRange{ 59 | Src_fd: int64(archive.Fd()), 60 | Src_offset: uint64(offset), 61 | Src_length: round4k(size), 62 | } 63 | 64 | /* reflink could fail for a lot of reasons (unsupported, different mountpoint etc.) 65 | * fallback to a copy in case of non fatal error */ 66 | err = unix.IoctlFileCloneRange(int(outFd.Fd()), &fcrange) 67 | if err != nil { 68 | return reflinkError 69 | } 70 | 71 | // Past this point, errors are fatal 72 | 73 | // We rounded up to the block size, truncate the file to remove the excess, if any 74 | if size&cowMask != 0 { 75 | err = outFd.Truncate(int64(size)) 76 | if err != nil { 77 | return err 78 | } 79 | } 80 | 81 | // reflink does not move the file pointer, skip the file content 82 | _, err = archive.Seek(int64(size), io.SeekCurrent) 83 | 84 | return err 85 | } 86 | -------------------------------------------------------------------------------- /car_test.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "bufio" 5 | "io" 6 | "io/fs" 7 | "os" 8 | "testing" 9 | ) 10 | 11 | var testDir string 12 | 13 | type testEntry struct { 14 | name string 15 | mode fs.FileMode 16 | size uint64 17 | link string 18 | content byte 19 | } 20 | 21 | var testEntries = []*testEntry{ 22 | {mode: 0o755 | fs.ModeDir, size: 0, name: "dir1"}, 23 | {mode: 0o644, size: 0, name: "dir1/empty"}, 24 | {mode: 0o755, size: 16, name: "dir1/exe", content: 'x'}, 25 | {mode: 0o600, size: 4300, name: "dir1/private", content: 'p'}, 26 | {mode: 0o444, size: 8300, name: "dir1/readonly", content: 'r'}, 27 | {mode: 0o755 | fs.ModeDir, size: 0, name: "dir2"}, 28 | {mode: 0o644, size: 200, name: "dir2/200", content: '2'}, 29 | {mode: 0o644, size: 4096, name: "dir2/4k", content: '4'}, 30 | {mode: 0o644, size: 4192, name: "dir2/4k1", content: '1'}, 31 | {mode: 0o644, size: 8300, name: "dir2/copy_of_readonly"}, 32 | {mode: 0o755 | fs.ModeDir, size: 0, name: "dir2/subdir"}, 33 | {mode: 0o777 | fs.ModeSymlink, size: 0, name: "dir2/subdir/link", link: "../4k"}, 34 | {mode: 0o644, size: 512, name: "toplevel", content: 't'}, 35 | } 36 | 37 | func fillFile(path string, mode fs.FileMode, c byte, size uint64) error { 38 | f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY, mode) 39 | if err != nil { 40 | return err 41 | } 42 | defer f.Close() 43 | 44 | f2 := bufio.NewWriter(f) 45 | defer f2.Flush() 46 | 47 | for i := uint64(0); i < size; i++ { 48 | if err := f2.WriteByte(c); err != nil { 49 | return err 50 | } 51 | } 52 | 53 | return nil 54 | } 55 | 56 | func makeEntry(e *testEntry) error { 57 | switch { 58 | case e.mode.IsDir(): 59 | if err := os.Mkdir(testDir+"/create/"+e.name, e.mode); err != nil { 60 | return err 61 | } 62 | case e.mode&fs.ModeSymlink != 0: 63 | if err := os.Symlink(e.link, testDir+"/create/"+e.name); err != nil { 64 | return err 65 | } 66 | default: 67 | if err := fillFile(testDir+"/create/"+e.name, e.mode, e.content, e.size); err != nil { 68 | return err 69 | } 70 | } 71 | 72 | return nil 73 | } 74 | 75 | func copyFile(src, dst string) error { 76 | srcFd, err := os.Open(src) 77 | if err != nil { 78 | return err 79 | } 80 | defer srcFd.Close() 81 | 82 | dstFd, err := os.Create(dst) 83 | if err != nil { 84 | return err 85 | } 86 | 87 | _, err = io.Copy(dstFd, srcFd) 88 | 89 | return err 90 | } 91 | 92 | func testSetup(t *testing.T) error { 93 | var err error 94 | 95 | testDir = t.TempDir() 96 | err = os.Mkdir(testDir+"/create", 0o755) 97 | if err != nil { 98 | return err 99 | } 100 | 101 | for _, e := range testEntries { 102 | if err = makeEntry(e); err != nil { 103 | return err 104 | } 105 | } 106 | 107 | err = copyFile(testDir+"/create/dir1/readonly", testDir+"/create/dir2/copy_of_readonly") 108 | 109 | return err 110 | } 111 | 112 | func testCreate(t *testing.T) { 113 | c := car{} 114 | 115 | err := c.archive([]string{testDir + "/create"}, testDir+"/test.car") 116 | if err != nil { 117 | t.Fatal(err) 118 | } 119 | } 120 | 121 | func testList(t *testing.T) { 122 | c := car{ 123 | list: true, 124 | } 125 | 126 | oldStdout := os.Stdout 127 | 128 | os.Stdout, _ = os.Open(os.DevNull) 129 | err := c.extract(testDir + "/test.car") 130 | os.Stdout = oldStdout 131 | 132 | if err != nil { 133 | t.Fatal(err) 134 | } 135 | } 136 | 137 | func testExtract(t *testing.T) { 138 | c := car{} 139 | 140 | err := c.extract(testDir + "/test.car") 141 | if err != nil { 142 | t.Fatal(err) 143 | } 144 | } 145 | 146 | func TestCar(t *testing.T) { 147 | err := testSetup(t) 148 | if err != nil { 149 | t.Fatal(err) 150 | } 151 | 152 | if t.Run("Create", testCreate) { 153 | t.Run("List", testList) 154 | t.Run("Extract", testExtract) 155 | } 156 | } 157 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # CAR - Copy-on-write Archive 2 | `car` is a tool to create and extract archives without copying data. This is possible by using the filesystem capabilities to reflink data from and to the archive. 3 | A filesystem with [reflink](https://man7.org/linux/man-pages/man2/ioctl_ficlone.2.html) support is needed, like [BtrFS](https://docs.kernel.org/filesystems/btrfs.html) or [XFS](https://xfs.wiki.kernel.org/). 4 | ## Usage 5 | `car` mimics the syntax of the glorious `tar` tool, so to create an archive, we do: 6 | ``` 7 | $ car -c -v -f dir.car dir 8 | dir 9 | dir/a_200 10 | dir/b_4k 11 | dir/c_4k10 12 | dir/link 13 | ``` 14 | While to extract it: 15 | ``` 16 | $ car -x -v -f dir.car 17 | dir/a_200 18 | dir/b_4k 19 | dir/c_4k10 20 | dir/link 21 | ``` 22 | ## Benchmark 23 | The following benchmark was done on a BtrFS filesystem with a 6.10 aarch64 kernel. 24 | 25 | Test setup: 26 | ``` 27 | $ ll software/ 28 | total 1.2G 29 | -rw-r--r--. 1 teknoraver teknoraver 631M Aug 31 14:07 debian-12.7.0-amd64-netinst.iso 30 | -rw-r--r--. 1 teknoraver teknoraver 154M Aug 1 10:51 gcc-14.2.0.tar.gz 31 | -rw-r--r--. 1 teknoraver teknoraver 18M Jul 22 13:59 glibc-2.40.tar.xz 32 | -rw-r--r--. 1 teknoraver teknoraver 27M Sep 5 17:20 go1.23.1.src.tar.gz 33 | -rw-r--r--. 1 teknoraver teknoraver 139M Sep 8 08:08 linux-6.10.9.tar.xz 34 | -rw-r--r--. 1 teknoraver teknoraver 207M Sep 5 18:05 rustc-1.81.0-src.tar.xz 35 | ``` 36 | Archive creation: 37 | ``` 38 | $ time tar cf software.tar software/ 39 | 40 | real 0m1.936s 41 | user 0m0.020s 42 | sys 0m0.600s 43 | 44 | $ time car -c -f software.car software/ 45 | 46 | real 0m0.052s 47 | user 0m0.000s 48 | sys 0m0.014s 49 | 50 | $ ll software.* 51 | -rw-r--r--. 1 teknoraver teknoraver 1.2G Sep 8 16:08 software.car 52 | -rw-r--r--. 1 teknoraver teknoraver 1.2G Sep 8 16:08 software.tar 53 | ``` 54 | Archive extraction: 55 | ``` 56 | $ time tar xf software.tar 57 | 58 | real 0m2.394s 59 | user 0m0.026s 60 | sys 0m0.668s 61 | 62 | $ car -x -f software.car 63 | 64 | real 0m0.059s 65 | user 0m0.001s 66 | sys 0m0.015s 67 | ``` 68 | perf stat: 69 | ``` 70 | $ perf stat tar xf software.tar 71 | 72 | Performance counter stats for 'tar xf software.tar': 73 | 74 | 691.06 msec task-clock:u # 0.765 CPUs utilized 75 | 0 context-switches:u # 0.000 /sec 76 | 0 cpu-migrations:u # 0.000 /sec 77 | 187 page-faults:u # 270.599 /sec 78 | cycles:u 79 | instructions:u 80 | branches:u 81 | branch-misses:u 82 | 83 | 0.902759486 seconds time elapsed 84 | 85 | 0.015161000 seconds user 86 | 0.624258000 seconds sys 87 | 88 | $ perf stat car -x -f software.car 89 | 90 | Performance counter stats for 'car -x -f software.car': 91 | 92 | 6.22 msec task-clock:u # 0.248 CPUs utilized 93 | 0 context-switches:u # 0.000 /sec 94 | 0 cpu-migrations:u # 0.000 /sec 95 | 210 page-faults:u # 33.754 K/sec 96 | cycles:u 97 | instructions:u 98 | branches:u 99 | branch-misses:u 100 | 101 | 0.025132295 seconds time elapsed 102 | 103 | 0.001251000 seconds user 104 | 0.004706000 seconds sys 105 | ``` 106 | ## File format 107 | The archive is composed by a list of entries, each one representing a file. 108 | An entry is composed by a list of [TLV (Type-Length-Value)](https://en.wikipedia.org/wiki/Type%E2%80%93length%E2%80%93value) fields, where the type is a 2 byte word, the length is a 2 byte word and the value is a variable length field. 109 | The list of types are: 110 | 1. Header (0x0001) 111 | *Mandatory*, contains the following fields: 112 | * uint32 file mode, which in turn contains the file type in the first bits and the permissions in the lowest 12 bits. 113 | * uint32 User ID 114 | * uint32 Group ID 115 | * uint64 Modification time (nanoseconds since epoch) 116 | 2. Name (0x0002) 117 | *Mandatory*, contains the name of the file, as a string. 118 | 3. Data (0x0003) 119 | *Mandatory*, must be the last field. If the file is not a regular file or is empty, the tag lenght is 0, otherwise it contains the following fields: 120 | * uint64 the file size 121 | * uint32 number of padding bytes between the tag and the file content 122 | 4. Link target (0x0004) 123 | Contains the target of a symlink, as a string. 124 | 5. Device (0x0005) 125 | uint32 contains the major and minor numbers, Mandatory for block and character devices. 126 | 127 | After the last tag, which must be 'Data', there is the padding and the file content. 128 | After the last entry there is the magic written in backwards (`!RAC`) to signal the end of the archive. The archive must be padded with zero bytes so that its length is a multiple of 4k. This is required otherwise the reflink operation will fail when extracting the last entries. 129 | -------------------------------------------------------------------------------- /archive.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "encoding/binary" 5 | "errors" 6 | "fmt" 7 | "io" 8 | "io/fs" 9 | "os" 10 | "path/filepath" 11 | "syscall" 12 | 13 | "golang.org/x/sys/unix" 14 | ) 15 | 16 | var zeroes = make([]byte, cowAlignment) 17 | 18 | func (c *car) writeTag(tagType, length uint16, out *os.File, data any) error { 19 | t := tag{ 20 | Tag: tagType, 21 | Length: length, 22 | } 23 | 24 | err := binary.Write(out, binary.BigEndian, &t) 25 | if err != nil { 26 | return err 27 | } 28 | 29 | if data != nil { 30 | return binary.Write(out, binary.BigEndian, data) 31 | } 32 | 33 | return nil 34 | } 35 | 36 | func (c *car) writeData(out *os.File, e entry) error { 37 | if e.size == 0 || e.Mode&unix.S_IFMT != unix.S_IFREG { 38 | return c.writeTag(tagData, 0, out, nil) 39 | } 40 | 41 | pd := paddedData{ 42 | Size: e.size, 43 | } 44 | 45 | // To add padding, we need to know the current offset, so the file must be seekable 46 | if offset, err := out.Seek(0, io.SeekCurrent); err == nil { 47 | // tag + paddedData 48 | const overhead = 4 + 12 49 | newDataOffset := round4k(uint64(offset + overhead)) 50 | padding := newDataOffset - uint64(offset+overhead) 51 | 52 | pd.Padding = uint32(padding) 53 | 54 | err = c.writeTag(tagData, 12, out, &pd) 55 | if err != nil { 56 | return err 57 | } 58 | 59 | _, err = out.Seek(int64(padding), io.SeekCurrent) 60 | if err != nil { 61 | return err 62 | } 63 | } else { 64 | err = c.writeTag(tagData, 12, out, &pd) 65 | if err != nil { 66 | return err 67 | } 68 | } 69 | 70 | in, err := os.Open(e.localName) 71 | if err != nil { 72 | return err 73 | } 74 | defer in.Close() 75 | 76 | err = reflinkToArchive(in, out, e.size) 77 | if err != nil && !errors.Is(err, reflinkError) { 78 | return err 79 | } 80 | 81 | _, err = io.Copy(out, in) 82 | 83 | return err 84 | } 85 | 86 | func (c *car) writeHeader(out *os.File, e entry) error { 87 | _, err := out.Write([]byte(cowMagic)) 88 | if err != nil { 89 | fmt.Fprintln(os.Stderr, "Write error:", err) 90 | return err 91 | } 92 | 93 | err = c.writeTag(tagHeader, uint16(binary.Size(e.fixedData)), out, &e.fixedData) 94 | if err != nil { 95 | return err 96 | } 97 | 98 | err = c.writeTag(tagName, uint16(len(e.name)), out, []byte(e.name)) 99 | if err != nil { 100 | fmt.Fprintln(os.Stderr, "Write error:", err) 101 | return err 102 | } 103 | 104 | if e.Mode&unix.S_IFMT == unix.S_IFLNK { 105 | err = c.writeTag(tagLinkTarget, uint16(len(e.link)), out, []byte(e.link)) 106 | if err != nil { 107 | return err 108 | } 109 | } 110 | 111 | if e.Mode&unix.S_IFMT == unix.S_IFCHR || e.Mode&unix.S_IFMT == unix.S_IFBLK { 112 | err = c.writeTag(tagDevice, 4, out, e.dev) 113 | if err != nil { 114 | return err 115 | } 116 | } 117 | 118 | return c.writeData(out, e) 119 | } 120 | 121 | func unixMode(mode fs.FileMode) uint32 { 122 | var unixMode uint32 123 | 124 | switch { 125 | case mode.IsRegular(): 126 | unixMode = unix.S_IFREG 127 | case mode.IsDir(): 128 | unixMode = unix.S_IFDIR 129 | case mode&fs.ModeSymlink != 0: 130 | unixMode = unix.S_IFLNK 131 | case mode&fs.ModeNamedPipe != 0: 132 | unixMode = unix.S_IFIFO 133 | /* fs.ModeCharDevice bit is contained also in fs.ModeDevice, so order is important */ 134 | case mode&fs.ModeCharDevice != 0: 135 | unixMode = unix.S_IFCHR 136 | case mode&fs.ModeDevice != 0: 137 | unixMode = unix.S_IFBLK 138 | case mode&fs.ModeSocket != 0: 139 | unixMode = unix.S_IFSOCK 140 | } 141 | 142 | if mode&fs.ModeSetuid != 0 { 143 | unixMode |= unix.S_ISUID 144 | } 145 | if mode&fs.ModeSetgid != 0 { 146 | unixMode |= unix.S_ISGID 147 | } 148 | if mode&fs.ModeSticky != 0 { 149 | unixMode |= unix.S_ISVTX 150 | } 151 | 152 | return unixMode | uint32(mode.Perm()) 153 | } 154 | 155 | func (c *car) walker(strip int, p string, statinfo fs.FileInfo, err error, outFd *os.File) error { 156 | if c.verbose { 157 | fmt.Fprintln(c.infoFd, p) 158 | } 159 | 160 | if err != nil { 161 | fmt.Fprintln(os.Stderr, "Error walking", p, err) 162 | return err 163 | } 164 | 165 | info := statinfo.Mode() 166 | 167 | switch { 168 | case info&fs.ModeSocket != 0: 169 | fallthrough 170 | case info&fs.ModeIrregular != 0: 171 | fmt.Fprintln(os.Stderr, "Skipping", p) 172 | return nil 173 | } 174 | 175 | storedName := p[strip:] 176 | if storedName[0] == '/' { 177 | storedName = storedName[1:] 178 | } 179 | 180 | entry := entry{ 181 | fixedData: fixedData{ 182 | Mode: unixMode(info), 183 | Mtime: statinfo.ModTime().UnixNano(), 184 | }, 185 | name: storedName, 186 | localName: p, 187 | } 188 | 189 | if sys, ok := statinfo.Sys().(*syscall.Stat_t); ok { 190 | entry.Uid = sys.Uid 191 | entry.Gid = sys.Gid 192 | entry.dev = uint32(sys.Rdev) 193 | } 194 | 195 | switch { 196 | case info&fs.ModeNamedPipe != 0: 197 | break 198 | case info&fs.ModeDevice != 0: 199 | fallthrough 200 | case info&fs.ModeCharDevice != 0: 201 | break 202 | case info.IsRegular(): 203 | entry.size = uint64(statinfo.Size()) 204 | case info.IsDir(): 205 | case info&fs.ModeSymlink != 0: 206 | entry.link, err = os.Readlink(p) 207 | if err != nil { 208 | fmt.Fprintln(os.Stderr, "Error reading symlink", p, err) 209 | return nil 210 | } 211 | } 212 | 213 | err = c.writeHeader(outFd, entry) 214 | if err != nil { 215 | return err 216 | } 217 | 218 | return nil 219 | } 220 | 221 | func (c *car) walkPaths(paths []string, outFd *os.File) error { 222 | for _, dir := range paths { 223 | dir = filepath.Clean(dir) 224 | err := filepath.Walk(dir, func(p string, i fs.FileInfo, err error) error { 225 | topdir := filepath.Dir(dir) 226 | if topdir == "." { 227 | topdir = "" 228 | } 229 | return c.walker(len(topdir), p, i, err, outFd) 230 | }) 231 | if err != nil { 232 | return err 233 | } 234 | } 235 | 236 | return nil 237 | } 238 | 239 | func (c *car) archive(paths []string, outFile string) error { 240 | var err error 241 | outFd := os.Stdout 242 | c.infoFd = os.Stderr 243 | 244 | if outFile != "" { 245 | outFd, err = os.Create(outFile) 246 | if err != nil { 247 | fmt.Fprintln(os.Stderr, "Error creating output file", outFile, err) 248 | return err 249 | } 250 | defer outFd.Close() 251 | 252 | c.infoFd = os.Stdout 253 | } 254 | 255 | _, err = outFd.Seek(0, io.SeekCurrent) 256 | if err == nil { 257 | c.seekable = true 258 | } else { 259 | fmt.Fprintln(os.Stderr, "Warning: archive is not seekable, padding will be disabled") 260 | } 261 | 262 | err = c.walkPaths(paths, outFd) 263 | if err != nil { 264 | return err 265 | } 266 | 267 | _, err = outFd.Write([]byte(cowEnd)) 268 | if err != nil { 269 | return err 270 | } 271 | 272 | if c.seekable { 273 | offset, err := outFd.Seek(0, io.SeekEnd) 274 | if err != nil { 275 | return err 276 | } 277 | err = outFd.Truncate(int64(round4k(uint64(offset)))) 278 | } else { 279 | // As we don't know the cursor position, write the maximum alignment 280 | buf := make([]byte, cowAlignment) 281 | _, err = outFd.Write(buf) 282 | } 283 | 284 | return err 285 | } 286 | -------------------------------------------------------------------------------- /extract.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "encoding/binary" 5 | "errors" 6 | "fmt" 7 | "io" 8 | "io/fs" 9 | "os" 10 | "os/user" 11 | "path/filepath" 12 | "strconv" 13 | "strings" 14 | "syscall" 15 | "time" 16 | 17 | "golang.org/x/sys/unix" 18 | ) 19 | 20 | func (c *car) safeRSeek(file *os.File, offset int64) error { 21 | var err error 22 | if c.seekable { 23 | _, err = file.Seek(offset, io.SeekCurrent) 24 | } else { 25 | buf := make([]byte, 64*1024) 26 | var n int 27 | for offset > 0 { 28 | n, err = file.Read(buf[:min(len(buf), int(offset))]) 29 | if err != nil { 30 | break 31 | } 32 | offset -= int64(n) 33 | } 34 | } 35 | return err 36 | } 37 | 38 | func prettySize(size uint64) string { 39 | units := "KMGTPE" 40 | const unit = 1024 41 | if size < unit { 42 | return fmt.Sprintf("%7d", size) 43 | } 44 | div := int64(unit) 45 | for n := size / unit; n >= unit; n /= unit { 46 | div *= unit 47 | units = units[1:] 48 | } 49 | 50 | if fsize := float64(size) / float64(div); fsize < 100 { 51 | return fmt.Sprintf("%6.1f%c", fsize, units[0]) 52 | } else { 53 | return fmt.Sprintf("%6.0f%c", fsize, units[0]) 54 | } 55 | } 56 | 57 | func verbosePrint(e entry) { 58 | // fs.FileMode.String() doesn't print the setuid or sticky bit 59 | buf := []byte("?rwxrwxrwx") 60 | extra := []byte("sst") 61 | var link string 62 | 63 | switch e.Mode & unix.S_IFMT { 64 | case unix.S_IFREG: 65 | buf[0] = '-' 66 | case unix.S_IFDIR: 67 | buf[0] = 'd' 68 | case unix.S_IFLNK: 69 | buf[0] = 'l' 70 | link = " -> " + e.link 71 | /* S_IFCHR is a subset of S_IFBLK, so order is important */ 72 | case unix.S_IFBLK: 73 | buf[0] = 'b' 74 | case unix.S_IFCHR: 75 | buf[0] = 'c' 76 | case unix.S_IFIFO: 77 | buf[0] = 'p' 78 | case unix.S_IFSOCK: 79 | buf[0] = 's' 80 | } 81 | 82 | for i := range buf[1:] { 83 | if e.Mode&(1<<(9-i-1)) == 0 { 84 | buf[i+1] = '-' 85 | } 86 | if group := i / 3; i%3 == 2 { 87 | if e.Mode&(1<<(9-group+2)) != 0 { 88 | buf[i+1] = extra[group] 89 | if e.Mode&(1<<(9-i-1)) == 0 { 90 | buf[i+1] -= 'a' - 'A' 91 | } 92 | } 93 | } 94 | } 95 | 96 | var size string 97 | perm := string(buf) 98 | mtime := time.Unix(e.Mtime/1e9, e.Mtime%1e9).Format("2006-01-02 15:04") 99 | uid := strconv.FormatUint(uint64(e.Uid), 10) 100 | gid := strconv.FormatUint(uint64(e.Gid), 10) 101 | 102 | if e.Mode&unix.S_IFMT == unix.S_IFBLK || e.Mode&unix.S_IFMT == unix.S_IFCHR { 103 | size = fmt.Sprintf("%3d,%3d", unix.Major(uint64(e.dev)), unix.Minor(uint64(e.dev))) 104 | } else { 105 | size = prettySize(e.size) 106 | } 107 | 108 | if user, err := user.LookupId(uid); err == nil { 109 | uid = user.Username 110 | } 111 | if group, err := user.LookupGroupId(gid); err == nil { 112 | gid = group.Name 113 | } 114 | 115 | fmt.Printf("%s %12s %12s %s %s %s%s\n", perm, uid, gid, size, mtime, e.name, link) 116 | } 117 | 118 | func (c *car) extractFile(archive *os.File, e entry, mode fs.FileMode) error { 119 | f, err := os.OpenFile(e.name, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, mode) 120 | if err != nil { 121 | return err 122 | } 123 | defer f.Close() 124 | 125 | if e.size == 0 { 126 | return nil 127 | } 128 | 129 | err = reflinkFromArchive(archive, f, e.size) 130 | if err != nil && errors.Is(err, reflinkError) { 131 | _, err = io.CopyN(f, archive, int64(e.size)) 132 | } 133 | 134 | return err 135 | } 136 | 137 | func (c *car) extractEntry(archive *os.File, e entry) error { 138 | var err, reterr error 139 | 140 | realPath, err := filepath.EvalSymlinks(filepath.Dir(c.destDir + "/" + e.name)) 141 | if err != nil { 142 | return err 143 | } 144 | 145 | if !strings.HasPrefix(realPath, c.destDir) { 146 | fmt.Fprintf(os.Stderr, "skipping '%s' because its real path '%s' is outside target directory\n", e.name, realPath) 147 | return c.safeRSeek(archive, int64(e.size)) 148 | } 149 | 150 | mode := uint32(e.Mode & 0o777) 151 | fsFileMode := fs.FileMode(mode) 152 | 153 | // File could already exist and have no write permission, delete it 154 | if e.Mode&unix.S_IFMT != unix.S_IFDIR { 155 | os.Remove(e.name) 156 | } 157 | 158 | switch e.Mode & unix.S_IFMT { 159 | case unix.S_IFREG: 160 | err = c.extractFile(archive, e, fsFileMode) 161 | case unix.S_IFDIR: 162 | modeSet := fs.FileMode(e.Mode & 0o7777) 163 | if modeSet&0o300 != 0o300 { 164 | /* A directory can have no write or execute permissions, yet contain files. To correctly 165 | * extract files inside, set permissions to 0300 now and defer the real permission set. */ 166 | c.dirModes = append(c.dirModes, dirMode{e.name, modeSet}) 167 | modeSet = 0o300 168 | } 169 | /* os.MkdirAll() never returns error on exist. If directory 170 | * already exists, ignore it and just change permission later */ 171 | err = os.Mkdir(e.name, fsFileMode|modeSet) 172 | if errors.Is(err, os.ErrExist) { 173 | err = nil 174 | } 175 | case unix.S_IFLNK: 176 | err = os.Symlink(e.link, e.name) 177 | case unix.S_IFBLK, unix.S_IFCHR: 178 | err = syscall.Mknod(e.name, e.Mode, int(e.dev)) 179 | case unix.S_IFIFO: 180 | err = syscall.Mkfifo(e.name, mode) 181 | } 182 | 183 | if err != nil { 184 | return err 185 | } 186 | 187 | /* Errors past this point are not fatal, but will printed 188 | * on stderr and led to error exit status */ 189 | 190 | if c.superUser { 191 | /* chmod() clears the SetUID bit and xattrs, so order is important */ 192 | err = os.Lchown(e.name, int(e.Uid), int(e.Gid)) 193 | if err != nil { 194 | c.error = 1 195 | fmt.Fprintf(os.Stderr, "can't set owner: %v\n", err) 196 | /* Save the first error */ 197 | reterr = err 198 | } 199 | } 200 | 201 | if e.Mode&0o7000 != 0 { 202 | if e.Mode&unix.S_ISUID != 0 { 203 | fsFileMode |= fs.ModeSetuid 204 | } 205 | if e.Mode&unix.S_ISGID != 0 { 206 | fsFileMode |= fs.ModeSetgid 207 | } 208 | if e.Mode&unix.S_ISVTX != 0 { 209 | fsFileMode |= fs.ModeSticky 210 | } 211 | err = os.Chmod(e.name, fsFileMode) 212 | if err != nil { 213 | c.error = 1 214 | fmt.Fprintf(os.Stderr, "can't set permissions: %v\n", err) 215 | if reterr == nil { 216 | /* Having to choose, report only the first error */ 217 | reterr = err 218 | } 219 | } 220 | } 221 | 222 | return reterr 223 | } 224 | 225 | func (c *car) parseEntry(archive *os.File) (*entry, error) { 226 | buf := make([]byte, 4) 227 | 228 | _, err := archive.Read(buf[:4]) 229 | if err != nil { 230 | return nil, err 231 | } 232 | 233 | if string(buf[:4]) == cowEnd { 234 | return nil, io.EOF 235 | } else if string(buf[:4]) != cowMagic { 236 | return nil, errors.New("bad entry") 237 | } 238 | 239 | var e entry 240 | 241 | tagLoop: 242 | for { 243 | var tag tag 244 | 245 | err := binary.Read(archive, binary.BigEndian, &tag) 246 | if err != nil { 247 | return nil, err 248 | } 249 | 250 | switch tag.Tag { 251 | case tagHeader: 252 | err = binary.Read(archive, binary.BigEndian, &e.fixedData) 253 | if err != nil { 254 | return nil, err 255 | } 256 | case tagName: 257 | buf := make([]byte, tag.Length) 258 | _, err := archive.Read(buf) 259 | if err != nil { 260 | return nil, err 261 | } 262 | e.name = string(buf) 263 | 264 | case tagLinkTarget: 265 | buf := make([]byte, tag.Length) 266 | _, err := archive.Read(buf) 267 | if err != nil { 268 | return nil, err 269 | } 270 | e.link = string(buf) 271 | case tagDevice: 272 | err = binary.Read(archive, binary.BigEndian, &e.dev) 273 | if err != nil { 274 | return nil, err 275 | } 276 | case tagData: 277 | if tag.Length == 12 { 278 | var pd paddedData 279 | err = binary.Read(archive, binary.BigEndian, &pd) 280 | if err != nil { 281 | return nil, err 282 | } 283 | e.size = pd.Size 284 | err = c.safeRSeek(archive, int64(pd.Padding)) 285 | if err != nil { 286 | return nil, err 287 | } 288 | } else if tag.Length != 0 { 289 | return nil, errors.New("bad file size field width") 290 | } 291 | break tagLoop 292 | default: 293 | fmt.Fprintf(os.Stderr, "unknown tag: 0x%x\n", tag.Tag) 294 | } 295 | } 296 | 297 | if c.list && c.verbose { 298 | verbosePrint(e) 299 | } else if c.list || c.verbose { 300 | fmt.Println(e.name) 301 | } 302 | 303 | if c.list { 304 | if e.size > 0 { 305 | err = c.safeRSeek(archive, int64(e.size)) 306 | if err != nil { 307 | return nil, err 308 | } 309 | } 310 | } else { 311 | err = c.extractEntry(archive, e) 312 | if err != nil { 313 | c.error = 1 314 | fmt.Fprintf(os.Stderr, "cannot create %s: %v\n", e.name, err) 315 | } 316 | } 317 | 318 | return &e, nil 319 | } 320 | 321 | func (c *car) deferredPermissions() error { 322 | for i := len(c.dirModes) - 1; i >= 0; i-- { 323 | err := os.Chmod(c.dirModes[i].name, c.dirModes[i].mode) 324 | if err != nil { 325 | return err 326 | } 327 | } 328 | return nil 329 | } 330 | 331 | func (c *car) extract(file string) error { 332 | var err error 333 | archive := os.Stdin 334 | c.infoFd = os.Stderr 335 | 336 | if os.Getuid() == 0 { 337 | c.superUser = true 338 | } 339 | 340 | if file != "" { 341 | archive, err = os.Open(file) 342 | if err != nil { 343 | return err 344 | } 345 | defer archive.Close() 346 | 347 | c.infoFd = os.Stdout 348 | } 349 | 350 | c.destDir, err = os.Getwd() 351 | if err != nil { 352 | return err 353 | } 354 | 355 | c.destDir, err = filepath.EvalSymlinks(c.destDir) 356 | if err != nil { 357 | return err 358 | } 359 | 360 | _, err = archive.Seek(0, io.SeekCurrent) 361 | if err == nil { 362 | c.seekable = true 363 | } else { 364 | fmt.Fprintln(os.Stderr, "Warning: archive is not seekable") 365 | } 366 | 367 | for { 368 | _, err = c.parseEntry(archive) 369 | if err == io.EOF { 370 | break 371 | } 372 | if err != nil { 373 | return err 374 | } 375 | } 376 | 377 | return c.deferredPermissions() 378 | 379 | } 380 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | GNU GENERAL PUBLIC LICENSE 2 | Version 3, 29 June 2007 3 | 4 | Copyright (C) 2007 Free Software Foundation, Inc. 5 | Everyone is permitted to copy and distribute verbatim copies 6 | of this license document, but changing it is not allowed. 7 | 8 | Preamble 9 | 10 | The GNU General Public License is a free, copyleft license for 11 | software and other kinds of works. 12 | 13 | The licenses for most software and other practical works are designed 14 | to take away your freedom to share and change the works. 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You may not convey a covered 525 | work if you are a party to an arrangement with a third party that is 526 | in the business of distributing software, under which you make payment 527 | to the third party based on the extent of your activity of conveying 528 | the work, and under which the third party grants, to any of the 529 | parties who would receive the covered work from you, a discriminatory 530 | patent license (a) in connection with copies of the covered work 531 | conveyed by you (or copies made from those copies), or (b) primarily 532 | for and in connection with specific products or compilations that 533 | contain the covered work, unless you entered into that arrangement, 534 | or that patent license was granted, prior to 28 March 2007. 535 | 536 | Nothing in this License shall be construed as excluding or limiting 537 | any implied license or other defenses to infringement that may 538 | otherwise be available to you under applicable patent law. 539 | 540 | 12. No Surrender of Others' Freedom. 541 | 542 | If conditions are imposed on you (whether by court order, agreement or 543 | otherwise) that contradict the conditions of this License, they do not 544 | excuse you from the conditions of this License. If you cannot convey a 545 | covered work so as to satisfy simultaneously your obligations under this 546 | License and any other pertinent obligations, then as a consequence you may 547 | not convey it at all. For example, if you agree to terms that obligate you 548 | to collect a royalty for further conveying from those to whom you convey 549 | the Program, the only way you could satisfy both those terms and this 550 | License would be to refrain entirely from conveying the Program. 551 | 552 | 13. Use with the GNU Affero General Public License. 553 | 554 | Notwithstanding any other provision of this License, you have 555 | permission to link or combine any covered work with a work licensed 556 | under version 3 of the GNU Affero General Public License into a single 557 | combined work, and to convey the resulting work. The terms of this 558 | License will continue to apply to the part which is the covered work, 559 | but the special requirements of the GNU Affero General Public License, 560 | section 13, concerning interaction through a network will apply to the 561 | combination as such. 562 | 563 | 14. Revised Versions of this License. 564 | 565 | The Free Software Foundation may publish revised and/or new versions of 566 | the GNU General Public License from time to time. Such new versions will 567 | be similar in spirit to the present version, but may differ in detail to 568 | address new problems or concerns. 569 | 570 | Each version is given a distinguishing version number. If the 571 | Program specifies that a certain numbered version of the GNU General 572 | Public License "or any later version" applies to it, you have the 573 | option of following the terms and conditions either of that numbered 574 | version or of any later version published by the Free Software 575 | Foundation. If the Program does not specify a version number of the 576 | GNU General Public License, you may choose any version ever published 577 | by the Free Software Foundation. 578 | 579 | If the Program specifies that a proxy can decide which future 580 | versions of the GNU General Public License can be used, that proxy's 581 | public statement of acceptance of a version permanently authorizes you 582 | to choose that version for the Program. 583 | 584 | Later license versions may give you additional or different 585 | permissions. However, no additional obligations are imposed on any 586 | author or copyright holder as a result of your choosing to follow a 587 | later version. 588 | 589 | 15. Disclaimer of Warranty. 590 | 591 | THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY 592 | APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT 593 | HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY 594 | OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, 595 | THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 596 | PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM 597 | IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF 598 | ALL NECESSARY SERVICING, REPAIR OR CORRECTION. 599 | 600 | 16. Limitation of Liability. 601 | 602 | IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING 603 | WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS 604 | THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY 605 | GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE 606 | USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF 607 | DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD 608 | PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), 609 | EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF 610 | SUCH DAMAGES. 611 | 612 | 17. Interpretation of Sections 15 and 16. 613 | 614 | If the disclaimer of warranty and limitation of liability provided 615 | above cannot be given local legal effect according to their terms, 616 | reviewing courts shall apply local law that most closely approximates 617 | an absolute waiver of all civil liability in connection with the 618 | Program, unless a warranty or assumption of liability accompanies a 619 | copy of the Program in return for a fee. 620 | 621 | END OF TERMS AND CONDITIONS 622 | 623 | How to Apply These Terms to Your New Programs 624 | 625 | If you develop a new program, and you want it to be of the greatest 626 | possible use to the public, the best way to achieve this is to make it 627 | free software which everyone can redistribute and change under these terms. 628 | 629 | To do so, attach the following notices to the program. It is safest 630 | to attach them to the start of each source file to most effectively 631 | state the exclusion of warranty; and each file should have at least 632 | the "copyright" line and a pointer to where the full notice is found. 633 | 634 | 635 | Copyright (C) 636 | 637 | This program is free software: you can redistribute it and/or modify 638 | it under the terms of the GNU General Public License as published by 639 | the Free Software Foundation, either version 3 of the License, or 640 | (at your option) any later version. 641 | 642 | This program is distributed in the hope that it will be useful, 643 | but WITHOUT ANY WARRANTY; without even the implied warranty of 644 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 645 | GNU General Public License for more details. 646 | 647 | You should have received a copy of the GNU General Public License 648 | along with this program. If not, see . 649 | 650 | Also add information on how to contact you by electronic and paper mail. 651 | 652 | If the program does terminal interaction, make it output a short 653 | notice like this when it starts in an interactive mode: 654 | 655 | Copyright (C) 656 | This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. 657 | This is free software, and you are welcome to redistribute it 658 | under certain conditions; type `show c' for details. 659 | 660 | The hypothetical commands `show w' and `show c' should show the appropriate 661 | parts of the General Public License. Of course, your program's commands 662 | might be different; for a GUI interface, you would use an "about box". 663 | 664 | You should also get your employer (if you work as a programmer) or school, 665 | if any, to sign a "copyright disclaimer" for the program, if necessary. 666 | For more information on this, and how to apply and follow the GNU GPL, see 667 | . 668 | 669 | The GNU General Public License does not permit incorporating your program 670 | into proprietary programs. If your program is a subroutine library, you 671 | may consider it more useful to permit linking proprietary applications with 672 | the library. If this is what you want to do, use the GNU Lesser General 673 | Public License instead of this License. But first, please read 674 | . 675 | --------------------------------------------------------------------------------