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This allows reading the metadata contained in tar-split without expensively recreating the whole tar stream including full contents. We have two use cases for this: - In a situation where tar-split is distributed along with a separate metadata stream, ensuring that the two are exactly consistent - Reading the tar headers allows making a ~cheap check of consistency of on-disk layers, just checking that the files exist in expected sizes, without reading the full contents. This can be implemented outside of this repo, but it's not ideal: - The function necessarily hard-codes some assumptions about how tar-split determines the boundaries of SegmentType/FileType entries (or, indeed, whether it uses FileType entries at all). That's best maintained directly beside the code that creates this. - The ExpectedPadding() value is not currently exported, so the consumer would have to heuristically guess where the padding ends. Signed-off-by: Miloslav Trmač <[email protected]>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,57 @@ | ||
| package asm | ||
|
|
||
| import ( | ||
| "bytes" | ||
| "fmt" | ||
| "io" | ||
|
|
||
| "github.com/vbatts/tar-split/archive/tar" | ||
| "github.com/vbatts/tar-split/tar/storage" | ||
| ) | ||
|
|
||
| // IterateHeaders calls handler for each tar header provided by Unpacker | ||
| func IterateHeaders(unpacker storage.Unpacker, handler func(hdr *tar.Header) error) error { | ||
| // We assume about NewInputTarStream: | ||
| // - There is a separate SegmentType entry for every tar header, but only one SegmentType entry for the full header incl. any extensions | ||
| // - (There is a FileType entry for every tar header, we ignore it) | ||
| // - Trailing padding of a file, if any, is included in the next SegmentType entry | ||
| // - At the end, there may be SegmentType entries just for the terminating zero blocks. | ||
|
|
||
| var pendingPadding int64 = 0 | ||
| for { | ||
| tsEntry, err := unpacker.Next() | ||
| if err != nil { | ||
| if err == io.EOF { | ||
| return nil | ||
| } | ||
| return fmt.Errorf("reading tar-split entries: %w", err) | ||
| } | ||
| switch tsEntry.Type { | ||
| case storage.SegmentType: | ||
| payload := tsEntry.Payload | ||
| if int64(len(payload)) < pendingPadding { | ||
| return fmt.Errorf("expected %d bytes of padding after previous file, but next SegmentType only has %d bytes", pendingPadding, len(payload)) | ||
| } | ||
| payload = payload[pendingPadding:] | ||
| pendingPadding = 0 | ||
|
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||
| tr := tar.NewReader(bytes.NewReader(payload)) | ||
| hdr, err := tr.Next() | ||
| if err != nil { | ||
| if err == io.EOF { // Probably the last entry, but let’s let the unpacker drive that. | ||
| break | ||
| } | ||
| return fmt.Errorf("decoding a tar header from a tar-split entry: %w", err) | ||
| } | ||
| if err := handler(hdr); err != nil { | ||
| return err | ||
| } | ||
| pendingPadding = tr.ExpectedPadding() | ||
|
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||
| case storage.FileType: | ||
| // Nothing | ||
| default: | ||
| return fmt.Errorf("unexpected tar-split entry type %q", tsEntry.Type) | ||
| } | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,119 @@ | ||
| package asm | ||
|
|
||
| import ( | ||
| "bytes" | ||
| "fmt" | ||
| "io" | ||
| "testing" | ||
| "time" | ||
|
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| "github.com/stretchr/testify/assert" | ||
| "github.com/stretchr/testify/require" | ||
| "github.com/vbatts/tar-split/archive/tar" | ||
| "github.com/vbatts/tar-split/tar/storage" | ||
| ) | ||
|
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| func createTestTarheader(index int, typeFlag byte, size int64) tar.Header { | ||
| n := (index + 1) * 100 // Use predictable, but distinct, values for all headers | ||
|
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| res := tar.Header{ | ||
| Typeflag: typeFlag, | ||
| Name: fmt.Sprintf("name%d", n), | ||
| Size: size, | ||
| Mode: int64(n + 1), | ||
| Uid: n + 2, | ||
| Gid: n + 3, | ||
| Uname: fmt.Sprintf("user%d", n), | ||
| Gname: fmt.Sprintf("group%d", n), | ||
| ModTime: time.Unix(int64(n+4), 0), | ||
| AccessTime: time.Unix(int64(n+5), 0), | ||
| ChangeTime: time.Unix(int64(n+6), 0), | ||
| PAXRecords: map[string]string{fmt.Sprintf("key%d", n): fmt.Sprintf("value%d", n)}, | ||
| Format: tar.FormatPAX, // We must set a format, in the default one AccessTime and ChangeTime are discarded. | ||
| } | ||
| switch res.Typeflag { | ||
| case tar.TypeLink, tar.TypeSymlink: | ||
| res.Linkname = fmt.Sprintf("link%d", n) | ||
| case tar.TypeChar, tar.TypeBlock: | ||
| res.Devmajor = int64(n + 7) | ||
| res.Devminor = int64(n + 8) | ||
| } | ||
| return res | ||
| } | ||
|
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| func TestIterateHeaders(t *testing.T) { | ||
| entries := []struct { | ||
| typeFlag byte | ||
| size int64 | ||
| }{ | ||
| {tar.TypeReg, 0}, | ||
| {tar.TypeReg, 1}, | ||
| {tar.TypeReg, 511}, | ||
| {tar.TypeReg, 512}, | ||
| {tar.TypeReg, 513}, | ||
| {tar.TypeLink, 0}, | ||
| {tar.TypeSymlink, 0}, | ||
| {tar.TypeChar, 0}, | ||
| {tar.TypeBlock, 0}, | ||
| {tar.TypeDir, 0}, | ||
| {tar.TypeFifo, 0}, | ||
| } | ||
|
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| var tarball bytes.Buffer | ||
| var expected []tar.Header | ||
| w := tar.NewWriter(&tarball) | ||
| for i, e := range entries { | ||
| hdr := createTestTarheader(i, e.typeFlag, e.size) | ||
| err := w.WriteHeader(&hdr) | ||
| require.NoError(t, err) | ||
| data := make([]byte, e.size) | ||
| _, err = w.Write(data) | ||
| require.NoError(t, err) | ||
| expected = append(expected, hdr) | ||
| } | ||
| err := w.Close() | ||
| require.NoError(t, err) | ||
|
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| var tarSplit bytes.Buffer | ||
| tsReader, err := NewInputTarStream(&tarball, storage.NewJSONPacker(&tarSplit), storage.NewDiscardFilePutter()) | ||
| require.NoError(t, err) | ||
| _, err = io.Copy(io.Discard, tsReader) | ||
| require.NoError(t, err) | ||
|
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| unpacker := storage.NewJSONUnpacker(&tarSplit) | ||
| var actual []tar.Header | ||
| err = IterateHeaders(unpacker, func(hdr *tar.Header) error { | ||
| actual = append(actual, *hdr) | ||
| return nil | ||
| }) | ||
| require.NoError(t, err) | ||
|
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| assert.Equal(t, len(expected), len(actual)) | ||
| for i := range expected { | ||
| expected := &expected[i] | ||
| actual := &actual[i] | ||
|
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| assert.Equal(t, expected.Typeflag, actual.Typeflag) | ||
| assert.Equal(t, expected.Name, actual.Name) | ||
| assert.Equal(t, expected.Linkname, actual.Linkname) | ||
| assert.Equal(t, expected.Size, actual.Size) | ||
| assert.Equal(t, expected.Mode, actual.Mode) | ||
| assert.Equal(t, expected.Uid, actual.Uid) | ||
| assert.Equal(t, expected.Gid, actual.Gid) | ||
| assert.Equal(t, expected.Uname, actual.Uname) | ||
| assert.Equal(t, expected.Gname, actual.Gname) | ||
| assert.True(t, actual.ModTime.Equal(expected.ModTime)) | ||
| assert.True(t, actual.AccessTime.Equal(expected.AccessTime)) | ||
| assert.True(t, actual.ChangeTime.Equal(expected.ChangeTime)) | ||
| assert.Equal(t, expected.Devmajor, actual.Devmajor) | ||
| assert.Equal(t, expected.Devminor, actual.Devminor) | ||
| assert.Equal(t, expected.Xattrs, actual.Xattrs) //nolint:staticcheck // We do want a comprehensive coverage in this test. | ||
| // We can’t compare PAXRecords for complete equality, because tar.Writer adds atime and ctime entries. So ensure all expected records are present. | ||
| for k, v := range expected.PAXRecords { | ||
| v2, ok := actual.PAXRecords[k] | ||
| assert.True(t, ok, k) | ||
| assert.Equal(t, v, v2) | ||
| } | ||
| assert.Equal(t, expected.Format, actual.Format) | ||
| } | ||
| } |