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110 lines
2.5 KiB
Go
110 lines
2.5 KiB
Go
//go:build windows
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package ociwclayer
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import (
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"archive/tar"
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"context"
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"io"
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"path/filepath"
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"github.com/Microsoft/go-winio/backuptar"
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"github.com/Microsoft/hcsshim/internal/wclayer"
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)
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// ExportLayerToTar writes an OCI layer tar stream from the provided on-disk layer.
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// The caller must specify the parent layers, if any, ordered from lowest to
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// highest layer.
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//
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// The layer will be mounted for this process, so the caller should ensure that
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// it is not currently mounted.
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func ExportLayerToTar(ctx context.Context, w io.Writer, path string, parentLayerPaths []string) error {
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err := wclayer.ActivateLayer(ctx, path)
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if err != nil {
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return err
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}
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defer func() {
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_ = wclayer.DeactivateLayer(ctx, path)
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}()
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// Prepare and unprepare the layer to ensure that it has been initialized.
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err = wclayer.PrepareLayer(ctx, path, parentLayerPaths)
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if err != nil {
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return err
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}
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err = wclayer.UnprepareLayer(ctx, path)
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if err != nil {
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return err
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}
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r, err := wclayer.NewLayerReader(ctx, path, parentLayerPaths)
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if err != nil {
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return err
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}
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err = writeTarFromLayer(ctx, r, w)
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cerr := r.Close()
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if err != nil {
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return err
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}
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return cerr
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}
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func writeTarFromLayer(ctx context.Context, r wclayer.LayerReader, w io.Writer) error {
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linkRecords := make(map[[16]byte]string)
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t := tar.NewWriter(w)
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for {
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select {
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case <-ctx.Done():
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return ctx.Err()
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default:
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}
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name, size, fileInfo, err := r.Next()
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if err == io.EOF {
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break
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}
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if err != nil {
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return err
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}
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if fileInfo == nil {
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// Write a whiteout file.
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hdr := &tar.Header{
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Name: filepath.ToSlash(filepath.Join(filepath.Dir(name), whiteoutPrefix+filepath.Base(name))),
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}
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err := t.WriteHeader(hdr)
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if err != nil {
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return err
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}
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} else {
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numberOfLinks, fileIDInfo, err := r.LinkInfo()
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if err != nil {
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return err
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}
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if numberOfLinks > 1 {
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if linkName, ok := linkRecords[fileIDInfo.FileID]; ok {
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// We've seen this file before, by another name, so put a hardlink in the tar stream.
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hdr := backuptar.BasicInfoHeader(name, 0, fileInfo)
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hdr.Mode = 0644
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hdr.Typeflag = tar.TypeLink
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hdr.Linkname = linkName
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if err := t.WriteHeader(hdr); err != nil {
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return err
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}
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continue
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}
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// All subsequent names for this file will be hard-linked to this name
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linkRecords[fileIDInfo.FileID] = filepath.ToSlash(name)
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}
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err = backuptar.WriteTarFileFromBackupStream(t, r, name, size, fileInfo)
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if err != nil {
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return err
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}
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}
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}
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return t.Close()
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}
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