X Fix xcontext.Canceled to verify cancellation for error chains

previously

- we were explicitly calling it on errors.Cause(err)
- and not in every place.

go/internal/xcontext/xcontext.go

-// Copyright (C) 2017-2018  Nexedi SA and Contributors.
+// Copyright (C) 2017-2020  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -26,6 +26,7 @@ package xcontext
 
 import (
 	"context"
+	"errors"
 )
 
 // Cancelled reports whether an error is due to a canceled context.
@@ -35,11 +36,14 @@ import (
 // Canceled treats both context.Canceled and context.DeadlineExceeded as errors
 // indicating context cancellation.
 func Canceled(err error) bool {
-	switch err {
-	case context.Canceled, context.DeadlineExceeded:
+	switch {
+	case err == nil:
+		return false
+	case errors.Is(err, context.Canceled):
+		return true
+	case errors.Is(err, context.DeadlineExceeded):
 		return true
 	}
-
 	return false
 }
 

go/neo/client.go

@@ -701,7 +701,7 @@ func openClientByURL(ctx context.Context, u *url.URL, opt *zodb.DriverOptions) (
 		err := c.Run(context.Background()) // NOTE not ctx
 		// Client.Close cancels talkMaster which makes Run to return
 		// `client: talk master(M): context canceled`
-		// do not propagate this error ZODB-level user.
+		// do not propagate this error to ZODB-level user.
 		if errors.Is(err, context.Canceled) {
 			err = nil
 		}

go/neo/master.go

@@ -29,8 +29,6 @@ import (
 
 	"golang.org/x/sync/errgroup"
 
-	"github.com/pkg/errors"
-
 	"lab.nexedi.com/kirr/go123/xnet"
 
 	"lab.nexedi.com/kirr/neo/go/neo/neonet"
@@ -349,7 +347,7 @@ loop:
 			if r.err != nil {
 				log.Error(ctx, r.err)
 
-				if !xcontext.Canceled(errors.Cause(r.err)) {
+				if !xcontext.Canceled(r.err) {
 					r.stor.CloseLink(ctx)
 					r.stor.SetState(proto.DOWN)
 				}
@@ -433,7 +431,7 @@ loop2:
 			// XXX dup wrt <-recovery handler above
 			log.Error(ctx, r.err)
 
-			if !xcontext.Canceled(errors.Cause(r.err)) {
+			if !xcontext.Canceled(r.err) {
 				r.stor.CloseLink(ctx)
 				r.stor.SetState(proto.DOWN)
 			}
@@ -608,7 +606,7 @@ loop:
 			if v.err != nil {
 				log.Error(ctx, v.err)
 
-				if !xcontext.Canceled(errors.Cause(v.err)) {
+				if !xcontext.Canceled(v.err) {
 					v.stor.CloseLink(ctx)
 					v.stor.SetState(proto.DOWN)
 				}
@@ -657,7 +655,7 @@ loop2:
 			// XXX dup wrt <-verify handler above
 			log.Error(ctx, v.err)
 
-			if !xcontext.Canceled(errors.Cause(v.err)) {
+			if !xcontext.Canceled(v.err) {
 				v.stor.CloseLink(ctx)
 				v.stor.SetState(proto.DOWN)
 			}