ErrNotFound: Make struct. Expose Cid field. Implement NotFound()

batch_test.go

@@ -26,7 +26,7 @@ func (d *testDag) Get(ctx context.Context, cid cid.Cid) (Node, error) {
 	if n, ok := d.nodes[cid.KeyString()]; ok {
 		return n, nil
 	}
-	return nil, ErrNotFoundCid{cid}
+	return nil, ErrNotFound{cid}
 }
 
 func (d *testDag) GetMany(ctx context.Context, cids []cid.Cid) <-chan *NodeOption {
@@ -37,7 +37,7 @@ func (d *testDag) GetMany(ctx context.Context, cids []cid.Cid) <-chan *NodeOptio
 		if n, ok := d.nodes[c.KeyString()]; ok {
 			out <- &NodeOption{Node: n}
 		} else {
-			out <- &NodeOption{Err: ErrNotFoundCid{c}}
+			out <- &NodeOption{Err: ErrNotFound{c}}
 		}
 	}
 	close(out)
@@ -157,11 +157,11 @@ func TestErrorTypes(t *testing.T) {
 
 	err2 := fmt.Errorf("could not read: %w", err)
 
-	if !errors.Is(err, ErrNotFound) {
+	if !errors.Is(err, ErrNotFound{}) {
 		t.Fatal("should be an ErrNotFound")
 	}
 
-	if !errors.Is(err2, ErrNotFound) {
+	if !errors.Is(err2, ErrNotFound{}) {
 		t.Fatal("should be an ErrNotFound")
 	}
 }

daghelpers.go

@@ -61,7 +61,7 @@ func GetNodes(ctx context.Context, ds NodeGetter, keys []cid.Cid) []*NodePromise
 			case opt, ok := <-nodechan:
 				if !ok {
 					for _, p := range promises {
-						p.Fail(ErrNotFound)
+						p.Fail(ErrNotFound{})
 					}
 					return
 				}

merkledag.go

@@ -10,35 +10,37 @@ import (
 // ErrNotFound is used to signal when a Node could not be found. The specific
 // meaning will depend on the DAGService implementation, which may be trying
 // to read nodes locally but also, trying to find them remotely.
-var ErrNotFound = ErrNotFoundCid{}
-
-// ErrNotFoundCid can be use to provide specific CID information in a NotFound
-// error.
-type ErrNotFoundCid struct {
-	c cid.Cid
+//
+// The Cid field can be filled in to provide additional context.
+type ErrNotFound struct {
+	Cid cid.Cid
 }
 
 // Error implements the error interface and returns a human-readable
 // message for this error.
-func (e ErrNotFoundCid) Error() string {
-	if e.c == cid.Undef {
+func (e ErrNotFound) Error() string {
+	if e.Cid == cid.Undef {
 		return "ipld: node not found"
 	}
 
-	return fmt.Sprintf("ipld: %s not found", e.c)
+	return fmt.Sprintf("ipld: %s not found", e.Cid)
 }
 
-// Is allows to check whether any error is of this ErrNotFoundCid type.
+// Is allows to check whether any error is of this ErrNotFound type.
 // Do not use this directly, but rather errors.Is(yourError, ErrNotFound).
-func (e ErrNotFoundCid) Is(err error) bool {
+func (e ErrNotFound) Is(err error) bool {
 	switch err.(type) {
-	case ErrNotFoundCid:
+	case ErrNotFound:
 		return true
 	default:
 		return false
 	}
 }
 
+func (e ErrNotFound) NotFound() bool {
+	return true
+}
+
 // Either a node or an error.
 type NodeOption struct {
 	Node Node