Push/pull errors improvement and cleanup

Several improvements to error handling:

- Introduce ImageConfigPullError type, wrapping errors related to
  downloading the image configuration blob in schema2. This allows for a
  more descriptive error message to be seen by the end user.

- Change some logrus.Debugf calls that display errors to logrus.Errorf.
  Add log lines in the push/pull fallback cases to make sure the errors
  leading to the fallback are shown.

- Move error-related types and functions which are only used by the
  distribution package out of the registry package.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

1 files changed, 102 insertions, 0 deletions

diff --git a/distribution/errors.go b/distribution/errors.go
new file mode 100644
index 0000000000..9f9dcf6978
--- /dev/null
+++ b/distribution/errors.go
@@ -0,0 +1,102 @@
+package distribution
+
+import (
+	"net/url"
+	"strings"
+	"syscall"
+
+	"github.com/docker/distribution/registry/api/errcode"
+	"github.com/docker/distribution/registry/api/v2"
+	"github.com/docker/distribution/registry/client"
+	"github.com/docker/docker/distribution/xfer"
+)
+
+// ErrNoSupport is an error type used for errors indicating that an operation
+// is not supported. It encapsulates a more specific error.
+type ErrNoSupport struct{ Err error }
+
+func (e ErrNoSupport) Error() string {
+	if e.Err == nil {
+		return "not supported"
+	}
+	return e.Err.Error()
+}
+
+// fallbackError wraps an error that can possibly allow fallback to a different
+// endpoint.
+type fallbackError struct {
+	// err is the error being wrapped.
+	err error
+	// confirmedV2 is set to true if it was confirmed that the registry
+	// supports the v2 protocol. This is used to limit fallbacks to the v1
+	// protocol.
+	confirmedV2 bool
+}
+
+// Error renders the FallbackError as a string.
+func (f fallbackError) Error() string {
+	return f.err.Error()
+}
+
+// shouldV2Fallback returns true if this error is a reason to fall back to v1.
+func shouldV2Fallback(err errcode.Error) bool {
+	switch err.Code {
+	case errcode.ErrorCodeUnauthorized, v2.ErrorCodeManifestUnknown, v2.ErrorCodeNameUnknown:
+		return true
+	}
+	return false
+}
+
+// continueOnError returns true if we should fallback to the next endpoint
+// as a result of this error.
+func continueOnError(err error) bool {
+	switch v := err.(type) {
+	case errcode.Errors:
+		if len(v) == 0 {
+			return true
+		}
+		return continueOnError(v[0])
+	case ErrNoSupport:
+		return continueOnError(v.Err)
+	case errcode.Error:
+		return shouldV2Fallback(v)
+	case *client.UnexpectedHTTPResponseError:
+		return true
+	case ImageConfigPullError:
+		return false
+	case error:
+		return !strings.Contains(err.Error(), strings.ToLower(syscall.ENOSPC.Error()))
+	}
+	// let's be nice and fallback if the error is a completely
+	// unexpected one.
+	// If new errors have to be handled in some way, please
+	// add them to the switch above.
+	return true
+}
+
+// retryOnError wraps the error in xfer.DoNotRetry if we should not retry the
+// operation after this error.
+func retryOnError(err error) error {
+	switch v := err.(type) {
+	case errcode.Errors:
+		return retryOnError(v[0])
+	case errcode.Error:
+		switch v.Code {
+		case errcode.ErrorCodeUnauthorized, errcode.ErrorCodeUnsupported, errcode.ErrorCodeDenied:
+			return xfer.DoNotRetry{Err: err}
+		}
+	case *url.Error:
+		return retryOnError(v.Err)
+	case *client.UnexpectedHTTPResponseError:
+		return xfer.DoNotRetry{Err: err}
+	case error:
+		if strings.Contains(err.Error(), strings.ToLower(syscall.ENOSPC.Error())) {
+			return xfer.DoNotRetry{Err: err}
+		}
+	}
+	// let's be nice and fallback if the error is a completely
+	// unexpected one.
+	// If new errors have to be handled in some way, please
+	// add them to the switch above.
+	return err
+}