[FIXED] More protection against stree being nil (#5662)

There are cases in filestore where errors can leave an stree nil. We
report those errors but do not terminate all executions so this protects
us generally from the stree being nil.

Resolves: #5656 

Signed-off-by: Derek Collison <[email protected]>

Author: derekcollison

server/stree/stree.go

@@ -51,6 +51,10 @@ func (t *SubjectTree[T]) Empty() *SubjectTree[T] {
 
 // Insert a value into the tree. Will return if the value was updated and if so the old value.
 func (t *SubjectTree[T]) Insert(subject []byte, value T) (*T, bool) {
+	if t == nil {
+		return nil, false
+	}
+
 	old, updated := t.insert(&t.root, subject, value, 0)
 	if !updated {
 		t.size++
@@ -60,6 +64,10 @@ func (t *SubjectTree[T]) Insert(subject []byte, value T) (*T, bool) {
 
 // Find will find the value and return it or false if it was not found.
 func (t *SubjectTree[T]) Find(subject []byte) (*T, bool) {
+	if t == nil {
+		return nil, false
+	}
+
 	var si int
 	for n := t.root; n != nil; {
 		if n.isLeaf() {
@@ -88,6 +96,10 @@ func (t *SubjectTree[T]) Find(subject []byte) (*T, bool) {
 
 // Delete will delete the item and return its value, or not found if it did not exist.
 func (t *SubjectTree[T]) Delete(subject []byte) (*T, bool) {
+	if t == nil {
+		return nil, false
+	}
+
 	val, deleted := t.delete(&t.root, subject, 0)
 	if deleted {
 		t.size--
@@ -97,7 +109,7 @@ func (t *SubjectTree[T]) Delete(subject []byte) (*T, bool) {
 
 // Match will match against a subject that can have wildcards and invoke the callback func for each matched value.
 func (t *SubjectTree[T]) Match(filter []byte, cb func(subject []byte, val *T)) {
-	if len(filter) == 0 || cb == nil {
+	if t == nil || t.root == nil || len(filter) == 0 || cb == nil {
 		return
 	}
 	// We need to break this up into chunks based on wildcards, either pwc '*' or fwc '>'.

server/stree/stree_test.go

@@ -764,3 +764,14 @@ func TestSubjectTreeMatchNoCallbackDupe(t *testing.T) {
 		})
 	}
 }
+
+func TestSubjectTreeNilNoPanic(t *testing.T) {
+	var st *SubjectTree[int]
+	st.Match([]byte("foo"), func(_ []byte, _ *int) {})
+	_, found := st.Find([]byte("foo"))
+	require_False(t, found)
+	_, found = st.Delete([]byte("foo"))
+	require_False(t, found)
+	_, found = st.Insert([]byte("foo"), 22)
+	require_False(t, found)
+}