Be explicit about how we ignore errors using trucindex.TruncIndex

This does not change behavior, it just makes it clearer
what is going on.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

containers.go

@@ -221,7 +221,7 @@ func (r *containerStore) Load() error {
 		}
 	}
 	r.containers = containers
-	r.idindex = truncindex.NewTruncIndex(idlist)
+	r.idindex = truncindex.NewTruncIndex(idlist) // Invalid values in idlist are ignored: they are not a reason to refuse processing the whole store.
 	r.byid = ids
 	r.bylayer = layers
 	r.byname = names
@@ -354,7 +354,9 @@ func (r *containerStore) Create(id string, names []string, image, layer, metadat
 		}
 		r.containers = append(r.containers, container)
 		r.byid[id] = container
-		r.idindex.Add(id)
+		// This can only fail on duplicate IDs, which shouldn’t happen — and in that case the index is already in the desired state anyway.
+		// Implementing recovery from an unlikely and unimportant failure here would be too risky.
+		_ = r.idindex.Add(id)
 		r.bylayer[layer] = container
 		for _, name := range names {
 			r.byname[name] = container
@@ -434,7 +436,9 @@ func (r *containerStore) Delete(id string) error {
 		}
 	}
 	delete(r.byid, id)
-	r.idindex.Delete(id)
+	// This can only fail if the ID is already missing, which shouldn’t happen — and in that case the index is already in the desired state anyway.
+	// The store’s Delete method is used on various paths to recover from failures, so this should be robust against partially missing data.
+	_ = r.idindex.Delete(id)
 	delete(r.bylayer, container.LayerID)
 	for _, name := range container.Names {
 		delete(r.byname, name)

images.go

@@ -299,7 +299,7 @@ func (r *imageStore) Load() error {
 		return ErrDuplicateImageNames
 	}
 	r.images = images
-	r.idindex = truncindex.NewTruncIndex(idlist)
+	r.idindex = truncindex.NewTruncIndex(idlist) // Invalid values in idlist are ignored: they are not a reason to refuse processing the whole store.
 	r.byid = ids
 	r.byname = names
 	r.bydigest = digests
@@ -455,7 +455,9 @@ func (r *imageStore) Create(id string, names []string, layer, metadata string, c
 		return nil, fmt.Errorf("validating digests for new image: %w", err)
 	}
 	r.images = append(r.images, image)
-	r.idindex.Add(id)
+	// This can only fail on duplicate IDs, which shouldn’t happen — and in that case the index is already in the desired state anyway.
+	// Implementing recovery from an unlikely and unimportant failure here would be too risky.
+	_ = r.idindex.Add(id)
 	r.byid[id] = image
 	for _, name := range names {
 		r.byname[name] = image
@@ -572,7 +574,9 @@ func (r *imageStore) Delete(id string) error {
 		}
 	}
 	delete(r.byid, id)
-	r.idindex.Delete(id)
+	// This can only fail if the ID is already missing, which shouldn’t happen — and in that case the index is already in the desired state anyway.
+	// The store’s Delete method is used on various paths to recover from failures, so this should be robust against partially missing data.
+	_ = r.idindex.Delete(id)
 	for _, name := range image.Names {
 		delete(r.byname, name)
 	}

layers.go

@@ -393,7 +393,7 @@ func (r *layerStore) Load() error {
 		return ErrDuplicateLayerNames
 	}
 	r.layers = layers
-	r.idindex = truncindex.NewTruncIndex(idlist)
+	r.idindex = truncindex.NewTruncIndex(idlist) // Invalid values in idlist are ignored: they are not a reason to refuse processing the whole store.
 	r.byid = ids
 	r.byname = names
 	r.bycompressedsum = compressedsums
@@ -685,7 +685,9 @@ func (r *layerStore) PutAdditionalLayer(id string, parentLayer *Layer, names []s
 
 	// TODO: check if necessary fields are filled
 	r.layers = append(r.layers, layer)
-	r.idindex.Add(id)
+	// This can only fail on duplicate IDs, which shouldn’t happen — and in that case the index is already in the desired state anyway.
+	// Implementing recovery from an unlikely and unimportant failure here would be too risky.
+	_ = r.idindex.Add(id)
 	r.byid[id] = layer
 	for _, name := range names { // names got from the additional layer store won't be used
 		r.byname[name] = layer
@@ -795,7 +797,9 @@ func (r *layerStore) Put(id string, parentLayer *Layer, names []string, mountLab
 		BigDataNames:       []string{},
 	}
 	r.layers = append(r.layers, layer)
-	r.idindex.Add(id)
+	// This can only fail if the ID is already missing, which shouldn’t happen — and in that case the index is already in the desired state anyway.
+	// This is on various paths to recover from failures, so this should be robust against partially missing data.
+	_ = r.idindex.Add(id)
 	r.byid[id] = layer
 	for _, name := range names {
 		r.byname[name] = layer
@@ -1279,7 +1283,9 @@ func (r *layerStore) deleteInternal(id string) error {
 	for _, name := range layer.Names {
 		delete(r.byname, name)
 	}
-	r.idindex.Delete(id)
+	// This can only fail if the ID is already missing, which shouldn’t happen — and in that case the index is already in the desired state anyway.
+	// The store’s Delete method is used on various paths to recover from failures, so this should be robust against partially missing data.
+	_ = r.idindex.Delete(id)
 	mountLabel := layer.MountLabel
 	if layer.MountPoint != "" {
 		delete(r.bymount, layer.MountPoint)

pkg/truncindex/truncindex.go

@@ -42,6 +42,7 @@ type TruncIndex struct {
 }
 
 // NewTruncIndex creates a new TruncIndex and initializes with a list of IDs.
+// Invalid IDs are _silently_ ignored.
 func NewTruncIndex(ids []string) (idx *TruncIndex) {
 	idx = &TruncIndex{
 		ids: make(map[string]struct{}),
@@ -51,7 +52,7 @@ func NewTruncIndex(ids []string) (idx *TruncIndex) {
 		trie: patricia.NewTrie(patricia.MaxPrefixPerNode(64)),
 	}
 	for _, id := range ids {
-		idx.addID(id)
+		_ = idx.addID(id) // Ignore invalid IDs. Duplicate IDs are not a problem.
 	}
 	return
 }
@@ -132,7 +133,8 @@ func (idx *TruncIndex) Get(s string) (string, error) {
 func (idx *TruncIndex) Iterate(handler func(id string)) {
 	idx.Lock()
 	defer idx.Unlock()
-	idx.trie.Visit(func(prefix patricia.Prefix, item patricia.Item) error {
+	// Ignore the error from Visit: it can only fail if the provided visitor fails, and ours never does.
+	_ = idx.trie.Visit(func(prefix patricia.Prefix, item patricia.Item) error {
 		handler(string(prefix))
 		return nil
 	})