errdefs: centralize error handling

Now that we have most of the services required for use with containerd,
it was found that common patterns were used throughout services. By
defining a central `errdefs` package, we ensure that services will map
errors to and from grpc consistently and cleanly. One can decorate an
error with as much context as necessary, using `pkg/errors` and still
have the error mapped correctly via grpc.

We make a few sacrifices. At this point, the common errors we use across
the repository all map directly to grpc error codes. While this seems
positively crazy, it actually works out quite well. The error conditions
that were specific weren't super necessary and the ones that were
necessary now simply have better context information. We lose the
ability to add new codes, but this constraint may not be a bad thing.

Effectively, as long as one uses the errors defined in `errdefs`, the
error class will be mapped correctly across the grpc boundary and
everything will be good. If you don't use those definitions, the error
maps to "unknown" and the error message is preserved.

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

services/content/helpers.go

@@ -1,33 +0,0 @@
-package content
-
-import (
-	"github.com/containerd/containerd/content"
-	"github.com/pkg/errors"
-	"google.golang.org/grpc"
-	"google.golang.org/grpc/codes"
-)
-
-func rewriteGRPCError(err error) error {
-	switch grpc.Code(errors.Cause(err)) {
-	case codes.AlreadyExists:
-		return content.ErrExists(grpc.ErrorDesc(err))
-	case codes.NotFound:
-		return content.ErrNotFound(grpc.ErrorDesc(err))
-	case codes.Unavailable:
-		return content.ErrLocked(grpc.ErrorDesc(err))
-	}
-	return err
-}
-
-func serverErrorToGRPC(err error, id string) error {
-	switch {
-	case content.IsNotFound(err):
-		return grpc.Errorf(codes.NotFound, "%v: not found", id)
-	case content.IsExists(err):
-		return grpc.Errorf(codes.AlreadyExists, "%v: exists", id)
-	case content.IsLocked(err):
-		return grpc.Errorf(codes.Unavailable, "%v: locked", id)
-	}
-
-	return err
-}

services/content/service.go

@@ -8,6 +8,7 @@ import (
 	api "github.com/containerd/containerd/api/services/content/v1"
 	eventsapi "github.com/containerd/containerd/api/services/events/v1"
 	"github.com/containerd/containerd/content"
+	"github.com/containerd/containerd/errdefs"
 	"github.com/containerd/containerd/events"
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/plugin"
@@ -66,7 +67,7 @@ func (s *Service) Info(ctx context.Context, req *api.InfoRequest) (*api.InfoResp
 
 	bi, err := s.store.Info(ctx, req.Digest)
 	if err != nil {
-		return nil, serverErrorToGRPC(err, req.Digest.String())
+		return nil, errdefs.ToGRPC(err)
 	}
 
 	return &api.InfoResponse{
@@ -125,7 +126,7 @@ func (s *Service) Delete(ctx context.Context, req *api.DeleteContentRequest) (*e
 	}
 
 	if err := s.store.Delete(ctx, req.Digest); err != nil {
-		return nil, serverErrorToGRPC(err, req.Digest.String())
+		return nil, errdefs.ToGRPC(err)
 	}
 
 	if err := s.emit(ctx, "/content/delete", &eventsapi.ContentDelete{
@@ -144,12 +145,12 @@ func (s *Service) Read(req *api.ReadContentRequest, session api.Content_ReadServ
 
 	oi, err := s.store.Info(session.Context(), req.Digest)
 	if err != nil {
-		return serverErrorToGRPC(err, req.Digest.String())
+		return errdefs.ToGRPC(err)
 	}
 
 	rc, err := s.store.Reader(session.Context(), req.Digest)
 	if err != nil {
-		return serverErrorToGRPC(err, req.Digest.String())
+		return errdefs.ToGRPC(err)
 	}
 	defer rc.Close() // TODO(stevvooe): Cache these file descriptors for performance.
 
@@ -217,7 +218,7 @@ func (rw *readResponseWriter) Write(p []byte) (n int, err error) {
 func (s *Service) Status(ctx context.Context, req *api.StatusRequest) (*api.StatusResponse, error) {
 	statuses, err := s.store.Status(ctx, req.Filter)
 	if err != nil {
-		return nil, serverErrorToGRPC(err, req.Filter)
+		return nil, errdefs.ToGRPCf(err, "could not get status for filter %q", req.Filter)
 	}
 
 	var resp api.StatusResponse
@@ -295,7 +296,7 @@ func (s *Service) Write(session api.Content_WriteServer) (err error) {
 	// this action locks the writer for the session.
 	wr, err := s.store.Writer(ctx, ref, total, expected)
 	if err != nil {
-		return serverErrorToGRPC(err, ref)
+		return errdefs.ToGRPC(err)
 	}
 	defer wr.Close()
 
@@ -303,7 +304,7 @@ func (s *Service) Write(session api.Content_WriteServer) (err error) {
 		msg.Action = req.Action
 		ws, err := wr.Status()
 		if err != nil {
-			return serverErrorToGRPC(err, ref)
+			return errdefs.ToGRPC(err)
 		}
 
 		msg.Offset = ws.Offset // always set the offset.
@@ -414,7 +415,7 @@ func (s *Service) Write(session api.Content_WriteServer) (err error) {
 
 func (s *Service) Abort(ctx context.Context, req *api.AbortRequest) (*empty.Empty, error) {
 	if err := s.store.Abort(ctx, req.Ref); err != nil {
-		return nil, serverErrorToGRPC(err, req.Ref)
+		return nil, errdefs.ToGRPC(err)
 	}
 
 	return &empty.Empty{}, nil

services/content/store.go

@@ -6,6 +6,7 @@ import (
 
 	contentapi "github.com/containerd/containerd/api/services/content/v1"
 	"github.com/containerd/containerd/content"
+	"github.com/containerd/containerd/errdefs"
 	digest "github.com/opencontainers/go-digest"
 )
 
@@ -24,7 +25,7 @@ func (rs *remoteStore) Info(ctx context.Context, dgst digest.Digest) (content.In
 		Digest: dgst,
 	})
 	if err != nil {
-		return content.Info{}, rewriteGRPCError(err)
+		return content.Info{}, errdefs.FromGRPC(err)
 	}
 
 	return content.Info{
@@ -37,14 +38,14 @@ func (rs *remoteStore) Info(ctx context.Context, dgst digest.Digest) (content.In
 func (rs *remoteStore) Walk(ctx context.Context, fn content.WalkFunc) error {
 	session, err := rs.client.List(ctx, &contentapi.ListContentRequest{})
 	if err != nil {
-		return rewriteGRPCError(err)
+		return errdefs.FromGRPC(err)
 	}
 
 	for {
 		msg, err := session.Recv()
 		if err != nil {
 			if err != io.EOF {
-				return rewriteGRPCError(err)
+				return errdefs.FromGRPC(err)
 			}
 
 			break
@@ -68,7 +69,7 @@ func (rs *remoteStore) Delete(ctx context.Context, dgst digest.Digest) error {
 	if _, err := rs.client.Delete(ctx, &contentapi.DeleteContentRequest{
 		Digest: dgst,
 	}); err != nil {
-		return rewriteGRPCError(err)
+		return errdefs.FromGRPC(err)
 	}
 
 	return nil
@@ -98,7 +99,7 @@ func (rs *remoteStore) Status(ctx context.Context, filter string) ([]content.Sta
 		Filter: filter,
 	})
 	if err != nil {
-		return nil, rewriteGRPCError(err)
+		return nil, errdefs.FromGRPC(err)
 	}
 
 	var statuses []content.Status
@@ -119,7 +120,7 @@ func (rs *remoteStore) Status(ctx context.Context, filter string) ([]content.Sta
 func (rs *remoteStore) Writer(ctx context.Context, ref string, size int64, expected digest.Digest) (content.Writer, error) {
 	wrclient, offset, err := rs.negotiate(ctx, ref, size, expected)
 	if err != nil {
-		return nil, rewriteGRPCError(err)
+		return nil, errdefs.FromGRPC(err)
 	}
 
 	return &remoteWriter{
@@ -134,7 +135,7 @@ func (rs *remoteStore) Abort(ctx context.Context, ref string) error {
 	if _, err := rs.client.Abort(ctx, &contentapi.AbortRequest{
 		Ref: ref,
 	}); err != nil {
-		return rewriteGRPCError(err)
+		return errdefs.FromGRPC(err)
 	}
 
 	return nil

services/content/writer.go

@@ -5,6 +5,7 @@ import (
 
 	contentapi "github.com/containerd/containerd/api/services/content/v1"
 	"github.com/containerd/containerd/content"
+	"github.com/containerd/containerd/errdefs"
 	digest "github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
 )
@@ -86,7 +87,7 @@ func (rw *remoteWriter) Commit(size int64, expected digest.Digest) error {
 		Expected: expected,
 	})
 	if err != nil {
-		return rewriteGRPCError(err)
+		return errdefs.FromGRPC(err)
 	}
 
 	if size != 0 && resp.Offset != size {