Error handler cleanup

Cleanup per additional comments in PR #992.

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

metadata/errors.go

@@ -1,5 +1,7 @@
 package metadata
 
+import "github.com/pkg/errors"
+
 type metadataExistsErr struct {
 	desc string
 }
@@ -15,9 +17,9 @@ func ErrExists(msg string) error {
 	if msg == "" {
 		msg = "metadata: exists"
 	}
-	return metadataExistsErr{
+	return errors.WithStack(metadataExistsErr{
 		desc: msg,
-	}
+	})
 }
 
 // ErrNotFound is returned when an item cannot be found in metadata
@@ -25,9 +27,9 @@ func ErrNotFound(msg string) error {
 	if msg == "" {
 		msg = "metadata: not found"
 	}
-	return metadataNotFoundErr{
+	return errors.WithStack(metadataNotFoundErr{
 		desc: msg,
-	}
+	})
 }
 
 // ErrNotEmpty is returned when a metadata item can't be deleted because it is not empty
@@ -35,9 +37,9 @@ func ErrNotEmpty(msg string) error {
 	if msg == "" {
 		msg = "metadata: namespace not empty"
 	}
-	return metadataNotEmptyErr{
+	return errors.WithStack(metadataNotEmptyErr{
 		desc: msg,
-	}
+	})
 }
 
 func (m metadataExistsErr) Error() string {
@@ -64,54 +66,30 @@ func (m metadataNotEmptyErr) NotEmpty() bool {
 
 // IsNotFound returns true if the error is due to a missing metadata item
 func IsNotFound(err error) bool {
-	if err, ok := err.(interface {
+	if err, ok := errors.Cause(err).(interface {
 		NotFound() bool
 	}); ok {
 		return err.NotFound()
 	}
-
-	causal, ok := err.(interface {
-		Cause() error
-	})
-	if !ok {
-		return false
-	}
-
-	return IsNotFound(causal.Cause())
+	return false
 }
 
 // IsExists returns true if the error is due to an already existing metadata item
 func IsExists(err error) bool {
-	if err, ok := err.(interface {
+	if err, ok := errors.Cause(err).(interface {
 		Exists() bool
 	}); ok {
 		return err.Exists()
 	}
-
-	causal, ok := err.(interface {
-		Cause() error
-	})
-	if !ok {
-		return false
-	}
-
-	return IsExists(causal.Cause())
+	return false
 }
 
 // IsNotEmpty returns true if the error is due to delete request of a non-empty metadata item
 func IsNotEmpty(err error) bool {
-	if err, ok := err.(interface {
+	if err, ok := errors.Cause(err).(interface {
 		NotEmpty() bool
 	}); ok {
 		return err.NotEmpty()
 	}
-
-	causal, ok := err.(interface {
-		Cause() error
-	})
-	if !ok {
-		return false
-	}
-
-	return IsNotEmpty(causal.Cause())
+	return false
 }