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https://github.com/wader/fq.git
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9b81d4d3ab
Preparation to make decoder use less memory and API more type safe. Now each scalar type has it's own struct type so it can store different things and enables to have a scalar interface. Also own types will enable experimenting with decode DLS designs like using chained methods that are type aware.
110 lines
3.4 KiB
Go
110 lines
3.4 KiB
Go
package tar
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// https://www.gnu.org/software/tar/manual/html_node/Standard.html
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// TODO: extensions?
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import (
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"bytes"
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"time"
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"github.com/wader/fq/format"
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"github.com/wader/fq/pkg/decode"
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"github.com/wader/fq/pkg/interp"
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"github.com/wader/fq/pkg/scalar"
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)
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var probeFormat decode.Group
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func init() {
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interp.RegisterFormat(decode.Format{
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Name: format.TAR,
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Description: "Tar archive",
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Groups: []string{format.PROBE},
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DecodeFn: tarDecode,
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Dependencies: []decode.Dependency{
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{Names: []string{format.PROBE}, Group: &probeFormat},
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},
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})
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}
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var unixTimeEpochDate = time.Date(1970, time.January, 1, 0, 0, 0, 0, time.UTC)
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func tarDecode(d *decode.D, _ any) any {
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const blockBytes = 512
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const blockBits = blockBytes * 8
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mapTrimSpaceNull := scalar.StrActualTrim(" \x00")
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blockPadding := func(d *decode.D) int64 {
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return (blockBits - (d.Pos() % blockBits)) % blockBits
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}
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// end marker is 512*2 zero bytes
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endMarker := [blockBytes * 2]byte{}
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var endMarkerStart int64
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var endMarkerEnd int64
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filesCount := 0
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d.FieldArray("files", func(d *decode.D) {
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for !d.End() {
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d.FieldStruct("file", func(d *decode.D) {
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d.FieldUTF8("name", 100, mapTrimSpaceNull)
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d.FieldUTF8NullFixedLen("mode", 8, scalar.TryStrSymParseUint(8))
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d.FieldUTF8NullFixedLen("uid", 8, scalar.TryStrSymParseUint(8))
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d.FieldUTF8NullFixedLen("gid", 8, scalar.TryStrSymParseUint(8))
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size, sizeOk := d.FieldScalarUTF8NullFixedLen("size", 12, scalar.TryStrSymParseUint(8)).TrySymUint()
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if !sizeOk {
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d.Fatalf("could not decode size")
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}
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size *= 8
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d.FieldUTF8NullFixedLen("mtime", 12, scalar.TryStrSymParseUint(8), scalar.StrFn(func(s scalar.Str) (scalar.Str, error) {
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// TODO: string might not be a number, move to scalar?
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if v, ok := s.TrySymUint(); ok {
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s.Description = unixTimeEpochDate.Add(time.Duration(v) * time.Second).Format(time.RFC3339)
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}
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return s, nil
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}))
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d.FieldUTF8NullFixedLen("chksum", 8, scalar.TryStrSymParseUint(8))
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d.FieldUTF8("typeflag", 1, mapTrimSpaceNull)
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d.FieldUTF8("linkname", 100, mapTrimSpaceNull)
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d.FieldUTF8("magic", 6, mapTrimSpaceNull, d.StrAssert("ustar"))
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d.FieldUTF8NullFixedLen("version", 2, scalar.TryStrSymParseUint(8))
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d.FieldUTF8("uname", 32, mapTrimSpaceNull)
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d.FieldUTF8("gname", 32, mapTrimSpaceNull)
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d.FieldUTF8NullFixedLen("devmajor", 8, scalar.TryStrSymParseUint(8))
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d.FieldUTF8NullFixedLen("devminor", 8, scalar.TryStrSymParseUint(8))
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d.FieldUTF8("prefix", 155, mapTrimSpaceNull)
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d.FieldRawLen("header_block_padding", blockPadding(d), d.BitBufIsZero())
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d.FieldFormatOrRawLen("data", int64(size), probeFormat, nil)
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d.FieldRawLen("data_block_padding", blockPadding(d), d.BitBufIsZero())
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})
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filesCount++
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if d.BitsLeft() >= int64(len(endMarker))*8 && bytes.Equal(d.PeekBytes(len(endMarker)), endMarker[:]) {
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endMarkerStart = d.Pos()
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// consensus seems to be to allow more than 2 zero blocks at end
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d.SeekRel(int64(len(endMarker)) * 8)
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zeroBlock := [blockBytes]byte{}
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for d.BitsLeft() >= blockBytes*8 && bytes.Equal(d.PeekBytes(blockBytes), zeroBlock[:]) {
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d.SeekRel(int64(len(zeroBlock)) * 8)
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}
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endMarkerEnd = d.Pos()
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break
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}
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}
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})
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endMarkerSize := endMarkerEnd - endMarkerStart
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if endMarkerSize > 0 {
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d.RangeFn(endMarkerStart, endMarkerSize, func(d *decode.D) {
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d.FieldRawLen("end_marker", d.BitsLeft())
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})
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}
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if filesCount == 0 {
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d.Errorf("no files found")
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}
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return nil
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}
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