Enable construction of TruncIndex from id array.

Fixes #5166

Current graph.restore is essentially O(n^2 log n) due to how
suffixarray creation works.

Rather than create/append/create new this supports creation from a seed
array of ids.

Functional testing shows this eliminates the hang on Creating image
graph reported on list.

Docker-DCO-1.1-Signed-off-by: Paul Nasrat <pnasrat@gmail.com> (github: pnasrat)

utils/utils.go

@@ -426,12 +426,17 @@ type TruncIndex struct {
 	bytes []byte
 }
 
-func NewTruncIndex() *TruncIndex {
-	return &TruncIndex{
-		index: suffixarray.New([]byte{' '}),
+func NewTruncIndex(ids []string) (idx *TruncIndex) {
+	idx = &TruncIndex{
 		ids:   make(map[string]bool),
 		bytes: []byte{' '},
 	}
+	for _, id := range ids {
+		idx.ids[id] = true
+		idx.bytes = append(idx.bytes, []byte(id+" ")...)
+	}
+	idx.index = suffixarray.New(idx.bytes)
+	return
 }
 
 func (idx *TruncIndex) Add(id string) error {

utils/utils_test.go

@@ -138,7 +138,8 @@ func TestRaceWriteBroadcaster(t *testing.T) {
 
 // Test the behavior of TruncIndex, an index for querying IDs from a non-conflicting prefix.
 func TestTruncIndex(t *testing.T) {
-	index := NewTruncIndex()
+	ids := []string{}
+	index := NewTruncIndex(ids)
 	// Get on an empty index
 	if _, err := index.Get("foobar"); err == nil {
 		t.Fatal("Get on an empty index should return an error")