mirror of https://github.com/containers/podman.git
104 lines
3.6 KiB
Go
104 lines
3.6 KiB
Go
package archive
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import (
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"errors"
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"fmt"
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"io"
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"os"
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"sync"
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"github.com/containers/image/v5/docker/internal/tarfile"
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"github.com/containers/image/v5/docker/reference"
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"github.com/containers/image/v5/types"
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)
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// Writer manages a single in-progress Docker archive and allows adding images to it.
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type Writer struct {
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path string // The original, user-specified path; not the maintained temporary file, if any
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regularFile bool // path refers to a regular file (e.g. not a pipe)
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archive *tarfile.Writer
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writer io.Closer
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// The following state can only be acccessed with the mutex held.
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mutex sync.Mutex
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hadCommit bool // At least one successful commit has happened
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}
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// NewWriter returns a Writer for path.
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// The caller should call .Close() on the returned object.
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func NewWriter(sys *types.SystemContext, path string) (*Writer, error) {
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// path can be either a pipe or a regular file
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// in the case of a pipe, we require that we can open it for write
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// in the case of a regular file, we don't want to overwrite any pre-existing file
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// so we check for Size() == 0 below (This is racy, but using O_EXCL would also be racy,
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// only in a different way. Either way, it’s up to the user to not have two writers to the same path.)
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fh, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE, 0644)
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if err != nil {
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return nil, fmt.Errorf("opening file %q: %w", path, err)
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}
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succeeded := false
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defer func() {
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if !succeeded {
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fh.Close()
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}
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}()
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fhStat, err := fh.Stat()
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if err != nil {
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return nil, fmt.Errorf("statting file %q: %w", path, err)
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}
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regularFile := fhStat.Mode().IsRegular()
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if regularFile && fhStat.Size() != 0 {
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return nil, errors.New("docker-archive doesn't support modifying existing images")
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}
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archive := tarfile.NewWriter(fh)
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succeeded = true
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return &Writer{
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path: path,
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regularFile: regularFile,
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archive: archive,
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writer: fh,
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hadCommit: false,
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}, nil
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}
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// imageCommitted notifies the Writer that at least one image was successfully committed to the stream.
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func (w *Writer) imageCommitted() {
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w.mutex.Lock()
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defer w.mutex.Unlock()
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w.hadCommit = true
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}
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// Close writes all outstanding data about images to the archive, and
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// releases state associated with the Writer, if any.
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// No more images can be added after this is called.
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func (w *Writer) Close() error {
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err := w.archive.Close()
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if err2 := w.writer.Close(); err2 != nil && err == nil {
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err = err2
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}
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if err == nil && w.regularFile && !w.hadCommit {
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// Writing to the destination never had a success; delete the destination if we created it.
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// This is done primarily because we don’t implement adding another image to a pre-existing image, so if we
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// left a partial archive around (notably because reading from the _source_ has failed), we couldn’t retry without
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// the caller manually deleting the partial archive. So, delete it instead.
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//
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// Archives with at least one successfully created image are left around; they might still be valuable.
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//
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// Note a corner case: If there _originally_ was an empty file (which is not a valid archive anyway), this deletes it.
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// Ideally, if w.regularFile, we should write the full contents to a temporary file and use os.Rename here, only on success.
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if err2 := os.Remove(w.path); err2 != nil {
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err = err2
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}
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}
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return err
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}
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// NewReference returns an ImageReference that allows adding an image to Writer,
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// with an optional reference.
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func (w *Writer) NewReference(destinationRef reference.NamedTagged) (types.ImageReference, error) {
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return newReference(w.path, destinationRef, -1, nil, w)
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}
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