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https://github.com/vbatts/tar-split.git
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99c8914877
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 <mitr@redhat.com>
57 lines
1.7 KiB
Go
57 lines
1.7 KiB
Go
package asm
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import (
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"bytes"
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"fmt"
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"io"
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"github.com/vbatts/tar-split/archive/tar"
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"github.com/vbatts/tar-split/tar/storage"
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)
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// IterateHeaders calls handler for each tar header provided by Unpacker
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func IterateHeaders(unpacker storage.Unpacker, handler func(hdr *tar.Header) error) error {
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// We assume about NewInputTarStream:
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// - There is a separate SegmentType entry for every tar header, but only one SegmentType entry for the full header incl. any extensions
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// - (There is a FileType entry for every tar header, we ignore it)
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// - Trailing padding of a file, if any, is included in the next SegmentType entry
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// - At the end, there may be SegmentType entries just for the terminating zero blocks.
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var pendingPadding int64 = 0
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for {
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tsEntry, err := unpacker.Next()
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if err != nil {
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if err == io.EOF {
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return nil
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}
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return fmt.Errorf("reading tar-split entries: %w", err)
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}
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switch tsEntry.Type {
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case storage.SegmentType:
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payload := tsEntry.Payload
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if int64(len(payload)) < pendingPadding {
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return fmt.Errorf("expected %d bytes of padding after previous file, but next SegmentType only has %d bytes", pendingPadding, len(payload))
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}
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payload = payload[pendingPadding:]
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pendingPadding = 0
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tr := tar.NewReader(bytes.NewReader(payload))
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hdr, err := tr.Next()
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if err != nil {
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if err == io.EOF { // Probably the last entry, but let’s let the unpacker drive that.
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break
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}
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return fmt.Errorf("decoding a tar header from a tar-split entry: %w", err)
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}
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if err := handler(hdr); err != nil {
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return err
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}
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pendingPadding = tr.ExpectedPadding()
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case storage.FileType:
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// Nothing
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default:
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return fmt.Errorf("unexpected tar-split entry type %q", tsEntry.Type)
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}
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}
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}
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