Use error interfaces for content/metadata

These interfaces allow us to preserve both the checking of error "cause"
as well as messages returned from the gRPC API so that the client gets
full error reason instead of a default "metadata: not found" in the case
of a missing image.

Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com>

content/content.go

@@ -7,26 +7,9 @@ import (
 	"time"
 
 	"github.com/opencontainers/go-digest"
-	"github.com/pkg/errors"
 )
 
 var (
-	// ErrNotFound is returned when an item is not found.
-	//
-	// Use IsNotFound(err) to detect this condition.
-	ErrNotFound = errors.New("content: not found")
-
-	// ErrExists is returned when something exists when it may not be expected.
-	//
-	// Use IsExists(err) to detect this condition.
-	ErrExists = errors.New("content: exists")
-
-	// ErrLocked is returned when content is actively being uploaded, this
-	// indicates that another process is attempting to upload the same content.
-	//
-	// Use IsLocked(err) to detect this condition.
-	ErrLocked = errors.New("content: locked")
-
 	bufPool = sync.Pool{
 		New: func() interface{} {
 			return make([]byte, 1<<20)
@@ -106,15 +89,3 @@ type Store interface {
 	Ingester
 	Provider
 }
-
-func IsNotFound(err error) bool {
-	return errors.Cause(err) == ErrNotFound
-}
-
-func IsExists(err error) bool {
-	return errors.Cause(err) == ErrExists
-}
-
-func IsLocked(err error) bool {
-	return errors.Cause(err) == ErrLocked
-}

content/errors.go

@@ -0,0 +1,120 @@
+package content
+
+type contentExistsErr struct {
+	desc string
+}
+
+type contentNotFoundErr struct {
+	desc string
+}
+
+type contentLockedErr struct {
+	desc string
+}
+
+// ErrExists is returned when something exists when it may not be expected.
+func ErrExists(msg string) error {
+	if msg == "" {
+		msg = "content: exists"
+	}
+	return contentExistsErr{
+		desc: msg,
+	}
+}
+
+// ErrNotFound is returned when an item is not found.
+func ErrNotFound(msg string) error {
+	if msg == "" {
+		msg = "content: not found"
+	}
+	return contentNotFoundErr{
+		desc: msg,
+	}
+}
+
+// ErrLocked is returned when content is actively being uploaded, this
+// indicates that another process is attempting to upload the same content.
+func ErrLocked(msg string) error {
+	if msg == "" {
+		msg = "content: locked"
+	}
+	return contentLockedErr{
+		desc: msg,
+	}
+}
+
+func (c contentExistsErr) Error() string {
+	return c.desc
+}
+func (c contentNotFoundErr) Error() string {
+	return c.desc
+}
+func (c contentLockedErr) Error() string {
+	return c.desc
+}
+
+func (c contentExistsErr) Exists() bool {
+	return true
+}
+
+func (c contentNotFoundErr) NotFound() bool {
+	return true
+}
+
+func (c contentLockedErr) Locked() bool {
+	return true
+}
+
+// IsNotFound returns true if the error is due to a not found content item
+func IsNotFound(err error) bool {
+	if err, ok := err.(interface {
+		NotFound() bool
+	}); ok {
+		return err.NotFound()
+	}
+
+	causal, ok := err.(interface {
+		Cause() error
+	})
+	if !ok {
+		return false
+	}
+
+	return IsNotFound(causal.Cause())
+}
+
+// IsExists returns true if the error is due to an already existing content item
+func IsExists(err error) bool {
+	if err, ok := err.(interface {
+		Exists() bool
+	}); ok {
+		return err.Exists()
+	}
+
+	causal, ok := err.(interface {
+		Cause() error
+	})
+	if !ok {
+		return false
+	}
+
+	return IsExists(causal.Cause())
+}
+
+// IsLocked returns true if the error is due to a currently locked content item
+func IsLocked(err error) bool {
+	if err, ok := err.(interface {
+		Locked() bool
+	}); ok {
+		return err.Locked()
+	}
+
+	causal, ok := err.(interface {
+		Cause() error
+	})
+	if !ok {
+		return false
+	}
+
+	return IsLocked(causal.Cause())
+}

content/locks.go

@@ -1,9 +1,8 @@
 package content
 
 import (
+	"fmt"
 	"sync"
-
-	"github.com/pkg/errors"
 )
 
 // Handles locking references
@@ -20,7 +19,7 @@ func tryLock(ref string) error {
 	defer locksMu.Unlock()
 
 	if _, ok := locks[ref]; ok {
-		return errors.Wrapf(ErrLocked, "key %s is locked", ref)
+		return ErrLocked(fmt.Sprintf("key %s is locked", ref))
 	}
 
 	locks[ref] = struct{}{}

content/store.go

@@ -40,7 +40,7 @@ func (s *store) Info(ctx context.Context, dgst digest.Digest) (Info, error) {
 	fi, err := os.Stat(p)
 	if err != nil {
 		if os.IsNotExist(err) {
-			err = ErrNotFound
+			err = ErrNotFound("")
 		}
 
 		return Info{}, err
@@ -62,7 +62,7 @@ func (s *store) Reader(ctx context.Context, dgst digest.Digest) (io.ReadCloser,
 	fp, err := os.Open(s.blobPath(dgst))
 	if err != nil {
 		if os.IsNotExist(err) {
-			err = ErrNotFound
+			err = ErrNotFound("")
 		}
 		return nil, err
 	}
@@ -85,7 +85,7 @@ func (cs *store) Delete(ctx context.Context, dgst digest.Digest) error {
 			return err
 		}
 
-		return ErrNotFound
+		return ErrNotFound("")
 	}
 
 	return nil
@@ -323,7 +323,7 @@ func (s *store) Abort(ctx context.Context, ref string) error {
 	root := s.ingestRoot(ref)
 	if err := os.RemoveAll(root); err != nil {
 		if os.IsNotExist(err) {
-			return ErrNotFound
+			return ErrNotFound("")
 		}
 
 		return err

content/writer.go

@@ -99,7 +99,7 @@ func (w *writer) Commit(size int64, expected digest.Digest) error {
 	if err := os.Rename(ingest, target); err != nil {
 		if os.IsExist(err) {
 			// collision with the target file!
-			return ErrExists
+			return ErrExists("")
 		}
 		return err
 	}