containerd/content/writer.go

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package content
import (
"os"
"path/filepath"
"github.com/docker/distribution/digest"
"github.com/pkg/errors"
)
// ContentWriter represents a write transaction against the blob store.
//
//
type ContentWriter struct {
cs *ContentStore
fp *os.File // opened data file
path string // path to writer dir
offset int64
digester digest.Digester
}
// Write p to the transaction.
//
// Note that writes are unbuffered to the backing file. When writing, it is
// recommended to wrap in a bufio.Writer or, preferrably, use io.CopyBuffer.
func (cw *ContentWriter) Write(p []byte) (n int, err error) {
n, err = cw.fp.Write(p)
cw.digester.Hash().Write(p[:n])
return n, err
}
func (cw *ContentWriter) Commit(size int64, expected digest.Digest) error {
if err := cw.fp.Sync(); err != nil {
return errors.Wrap(err, "sync failed")
}
fi, err := cw.fp.Stat()
if err != nil {
return errors.Wrap(err, "stat on ingest file failed")
}
// change to readonly, more important for read, but provides _some_
// protection from this point on. We use the existing perms with a mask
// only allowing reads honoring the umask on creation.
//
// This removes write and exec, only allowing read per the creation umask.
if err := cw.fp.Chmod((fi.Mode() & os.ModePerm) &^ 0333); err != nil {
return errors.Wrap(err, "failed to change ingest file permissions")
}
if size != fi.Size() {
return errors.Errorf("failed size validation: %v != %v", fi.Size(), size)
}
dgst := cw.digester.Digest()
if expected != dgst {
return errors.Errorf("unexpected digest: %v != %v", dgst, expected)
}
apath := filepath.Join(cw.cs.root, "blobs", dgst.Algorithm().String())
if err := os.MkdirAll(apath, 0755); err != nil {
return err
}
var (
ingest = filepath.Join(cw.path, "data")
target = filepath.Join(apath, dgst.Hex())
)
// clean up!!
defer os.RemoveAll(cw.path)
if err := os.Rename(ingest, target); err != nil {
if os.IsExist(err) {
// collision with the target file!
return nil
}
return err
}
return nil
}
// Close the writer, flushing any unwritten data and leaving the progress in
// tact.
//
// If one needs to resume the transaction, a new writer can be obtained from
// `ContentStore.Resume` using the same key. The write can then be continued
// from it was left off.
func (cw *ContentWriter) Close() (err error) {
cw.fp.Sync()
return cw.fp.Close()
}