content: cleanup service and interfaces

After implementing pull, a few changes are required to the content store
interface to make sure that the implementation works smoothly.
Specifically, we work to make sure the predeclaration path for digests
works the same between remote and local writers. Before, we were
hesitent to require the the size and digest up front, but it became
clear that having this provided significant benefit.

There are also several cleanups related to naming. We now call the
expected digest `Expected` consistently across the board and `Total` is
used to mark the expected size.

This whole effort comes together to provide a very smooth status
reporting workflow for image pull and push. This will be more obvious
when the bulk of pull code lands.

There are a few other changes to make `content.WriteBlob` more broadly
useful. In accordance with addition for predeclaring expected size when
getting a `Writer`, `WriteBlob` now supports this fully. It will also
resume downloads if provided an `io.Seeker` or `io.ReaderAt`. Coupled
with the `httpReadSeeker` from `docker/distribution`, we should only be
a lines of code away from resumable downloads.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

content/writer.go

@@ -1,11 +1,11 @@
 package content
 
 import (
-	"log"
 	"os"
 	"path/filepath"
 	"time"
 
+	"github.com/docker/containerd/log"
 	"github.com/nightlyone/lockfile"
 	"github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
@@ -19,6 +19,7 @@ type writer struct {
 	path      string // path to writer dir
 	ref       string // ref key
 	offset    int64
+	total     int64
 	digester  digest.Digester
 	startedAt time.Time
 	updatedAt time.Time
@@ -28,6 +29,7 @@ func (w *writer) Status() (Status, error) {
 	return Status{
 		Ref:       w.ref,
 		Offset:    w.offset,
+		Total:     w.total,
 		StartedAt: w.startedAt,
 		UpdatedAt: w.updatedAt,
 	}, nil
@@ -52,12 +54,12 @@ func (w *writer) Write(p []byte) (n int, err error) {
 	return n, err
 }
 
-func (cw *writer) Commit(size int64, expected digest.Digest) error {
-	if err := cw.fp.Sync(); err != nil {
+func (w *writer) Commit(size int64, expected digest.Digest) error {
+	if err := w.fp.Sync(); err != nil {
 		return errors.Wrap(err, "sync failed")
 	}
 
-	fi, err := cw.fp.Stat()
+	fi, err := w.fp.Stat()
 	if err != nil {
 		return errors.Wrap(err, "stat on ingest file failed")
 	}
@@ -67,7 +69,7 @@ func (cw *writer) Commit(size int64, expected digest.Digest) error {
 	// 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 {
+	if err := w.fp.Chmod((fi.Mode() & os.ModePerm) &^ 0333); err != nil {
 		return errors.Wrap(err, "failed to change ingest file permissions")
 	}
 
@@ -75,18 +77,18 @@ func (cw *writer) Commit(size int64, expected digest.Digest) error {
 		return errors.Errorf("failed size validation: %v != %v", fi.Size(), size)
 	}
 
-	if err := cw.fp.Close(); err != nil {
+	if err := w.fp.Close(); err != nil {
 		return errors.Wrap(err, "failed closing ingest")
 	}
 
-	dgst := cw.digester.Digest()
+	dgst := w.digester.Digest()
 	if expected != "" && expected != dgst {
 		return errors.Errorf("unexpected digest: %v != %v", dgst, expected)
 	}
 
 	var (
-		ingest = filepath.Join(cw.path, "data")
-		target = cw.s.blobPath(dgst)
+		ingest = filepath.Join(w.path, "data")
+		target = w.s.blobPath(dgst)
 	)
 
 	// make sure parent directories of blob exist
@@ -95,18 +97,18 @@ func (cw *writer) Commit(size int64, expected digest.Digest) error {
 	}
 
 	// clean up!!
-	defer os.RemoveAll(cw.path)
+	defer os.RemoveAll(w.path)
 
 	if err := os.Rename(ingest, target); err != nil {
 		if os.IsExist(err) {
 			// collision with the target file!
-			return nil
+			return errExists
 		}
 		return err
 	}
 
-	unlock(cw.lock)
-	cw.fp = nil
+	unlock(w.lock)
+	w.fp = nil
 	return nil
 }
 
@@ -121,7 +123,7 @@ func (cw *writer) Commit(size int64, expected digest.Digest) error {
 // clean up the associated resources.
 func (cw *writer) Close() (err error) {
 	if err := unlock(cw.lock); err != nil {
-		log.Printf("unlock failed: %v", err)
+		log.L.Debug("unlock failed: %v", err)
 	}
 
 	if cw.fp != nil {