Add writer open helper to handle unavailable refs

Updates blob writer helper to use new open and ensure
unavailable errors are always handled.
Removes duplication of unavailable handling code.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

content/helpers.go

@@ -20,7 +20,9 @@ import (
 	"context"
 	"io"
 	"io/ioutil"
+	"math/rand"
 	"sync"
+	"time"
 
 	"github.com/containerd/containerd/errdefs"
 	"github.com/opencontainers/go-digest"
@@ -64,7 +66,7 @@ func ReadBlob(ctx context.Context, provider Provider, dgst digest.Digest) ([]byt
 //
 // Copy is buffered, so no need to wrap reader in buffered io.
 func WriteBlob(ctx context.Context, cs Ingester, ref string, r io.Reader, size int64, expected digest.Digest, opts ...Opt) error {
-	cw, err := cs.Writer(ctx, ref, size, expected)
+	cw, err := OpenWriter(ctx, cs, ref, size, expected)
 	if err != nil {
 		if !errdefs.IsAlreadyExists(err) {
 			return err
@@ -77,6 +79,43 @@ func WriteBlob(ctx context.Context, cs Ingester, ref string, r io.Reader, size i
 	return Copy(ctx, cw, r, size, expected, opts...)
 }
 
+// OpenWriter opens a new writer for the given reference, retrying if the writer
+// is locked until the reference is available or returns an error.
+func OpenWriter(ctx context.Context, cs Ingester, ref string, size int64, expected digest.Digest) (Writer, error) {
+	var (
+		cw    Writer
+		err   error
+		retry = 16
+	)
+	for {
+		cw, err = cs.Writer(ctx, ref, size, expected)
+		if err != nil {
+			if !errdefs.IsUnavailable(err) {
+				return nil, err
+			}
+
+			// TODO: Check status to determine if the writer is active,
+			// continue waiting while active, otherwise return lock
+			// error or abort. Requires asserting for an ingest manager
+
+			select {
+			case <-time.After(time.Millisecond * time.Duration(rand.Intn(retry))):
+				if retry < 2048 {
+					retry = retry << 1
+				}
+				continue
+			case <-ctx.Done():
+				// Propagate lock error
+				return nil, err
+			}
+
+		}
+		break
+	}
+
+	return cw, err
+}
+
 // Copy copies data with the expected digest from the reader into the
 // provided content store writer. This copy commits the writer.
 //

remotes/docker/schema1/converter.go

@@ -25,7 +25,6 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
-	"math/rand"
 	"strings"
 	"sync"
 	"time"
@@ -258,7 +257,6 @@ func (c *Converter) fetchBlob(ctx context.Context, desc ocispec.Descriptor) erro
 	var (
 		ref  = remotes.MakeRefKey(ctx, desc)
 		calc = newBlobStateCalculator()
-		retry = 16
 		size = desc.Size
 	)
 
@@ -267,20 +265,9 @@ func (c *Converter) fetchBlob(ctx context.Context, desc ocispec.Descriptor) erro
 		size = 0
 	}
 
-tryit:
+	cw, err := content.OpenWriter(ctx, c.contentStore, ref, size, desc.Digest)
-	cw, err := c.contentStore.Writer(ctx, ref, size, desc.Digest)
 	if err != nil {
-		if errdefs.IsUnavailable(err) {
+		if !errdefs.IsAlreadyExists(err) {
-			select {
-			case <-time.After(time.Millisecond * time.Duration(rand.Intn(retry))):
-				if retry < 2048 {
-					retry = retry << 1
-				}
-				goto tryit
-			case <-ctx.Done():
-				return err
-			}
-		} else if !errdefs.IsAlreadyExists(err) {
 			return err
 		}
 

remotes/handlers.go

@@ -20,10 +20,8 @@ import (
 	"context"
 	"fmt"
 	"io"
-	"math/rand"
 	"strings"
 	"sync"
-	"time"
 
 	"github.com/containerd/containerd/content"
 	"github.com/containerd/containerd/errdefs"
@@ -83,38 +81,14 @@ func FetchHandler(ingester content.Ingester, fetcher Fetcher) images.HandlerFunc
 func fetch(ctx context.Context, ingester content.Ingester, fetcher Fetcher, desc ocispec.Descriptor) error {
 	log.G(ctx).Debug("fetch")
 
-	var (
+	cw, err := content.OpenWriter(ctx, ingester, MakeRefKey(ctx, desc), desc.Size, desc.Digest)
-		ref   = MakeRefKey(ctx, desc)
-		cw    content.Writer
-		err   error
-		retry = 16
-	)
-	for {
-		cw, err = ingester.Writer(ctx, ref, desc.Size, desc.Digest)
 	if err != nil {
 		if errdefs.IsAlreadyExists(err) {
 			return nil
-			} else if !errdefs.IsUnavailable(err) {
+		}
 		return err
 	}
-
-			// TODO: On first time locked is encountered, get status
-			// of writer and abort if not updated recently.
-
-			select {
-			case <-time.After(time.Millisecond * time.Duration(rand.Intn(retry))):
-				if retry < 2048 {
-					retry = retry << 1
-				}
-				continue
-			case <-ctx.Done():
-				// Propagate lock error
-				return err
-			}
-		}
 	defer cw.Close()
-		break
-	}
 
 	ws, err := cw.Status()
 	if err != nil {