data: add support for unknown keys to treeIterator

While not planned, it's also not completely impossible that a tree node
might get additional top-level fields. As the tree iterator is built
with a strict expectation of the top-level fields, this would result in
a parsing error. Future-proof the code by simply skipping unknown
fields.

internal/data/tree.go

@@ -67,18 +67,37 @@ func NewTreeNodeIterator(rd io.Reader) (TreeNodeIterator, error) {
 }
 
 func (t *treeIterator) init() error {
-	// `{"nodes":[` `]}`
+	// A tree is expected to be encoded as a JSON object with a single key "nodes".
+	// However, for future-proofness, we allow unknown keys before and after the "nodes" key.
+	// The following is the expected format:
+	// `{"nodes":[...]}`
 
 	if err := t.assertToken(json.Delim('{')); err != nil {
 		return err
 	}
-	if err := t.assertToken("nodes"); err != nil {
-		return err
+	// Skip unknown keys until we find "nodes"
+	for {
+		token, err := t.dec.Token()
+		if err != nil {
+			return err
+		}
+		key, ok := token.(string)
+		if !ok {
+			return errors.Errorf("error decoding tree: expected string key, got %v", token)
+		}
+		if key == "nodes" {
+			// Found "nodes", proceed to read the array
+			if err := t.assertToken(json.Delim('[')); err != nil {
+				return err
+			}
+			return nil
+		}
+		// Unknown key, decode its value into RawMessage and discard it
+		var raw json.RawMessage
+		if err := t.dec.Decode(&raw); err != nil {
+			return err
+		}
 	}
-	if err := t.assertToken(json.Delim('[')); err != nil {
-		return err
-	}
-	return nil
 }
 
 func (t *treeIterator) next() (*Node, error) {
@@ -94,10 +113,21 @@ func (t *treeIterator) next() (*Node, error) {
 	if err := t.assertToken(json.Delim(']')); err != nil {
 		return nil, err
 	}
-	if err := t.assertToken(json.Delim('}')); err != nil {
-		return nil, err
+	// Skip unknown keys after the array until we find the closing brace
+	for {
+		token, err := t.dec.Token()
+		if err != nil {
+			return nil, err
+		}
+		if token == json.Delim('}') {
+			return nil, io.EOF
+		}
+		// We have an unknown key, decode its value into RawMessage and discard it
+		var raw json.RawMessage
+		if err := t.dec.Decode(&raw); err != nil {
+			return nil, err
+		}
 	}
-	return nil, io.EOF
 }
 
 func (t *treeIterator) assertToken(token json.Token) error {

internal/data/tree_test.go

@@ -225,6 +225,75 @@ func testLoadTree(t *testing.T, version uint) {
 	}
 }
 
+func TestTreeIteratorUnknownKeys(t *testing.T) {
+	tests := []struct {
+		name      string
+		jsonData  string
+		wantNodes []string
+	}{
+		{
+			name:      "unknown key before nodes",
+			jsonData:  `{"extra": "value", "nodes": [{"name": "test1"}, {"name": "test2"}]}`,
+			wantNodes: []string{"test1", "test2"},
+		},
+		{
+			name:      "unknown key after nodes",
+			jsonData:  `{"nodes": [{"name": "test1"}, {"name": "test2"}], "extra": "value"}`,
+			wantNodes: []string{"test1", "test2"},
+		},
+		{
+			name:      "multiple unknown keys before nodes",
+			jsonData:  `{"key1": "value1", "key2": 42, "nodes": [{"name": "test1"}]}`,
+			wantNodes: []string{"test1"},
+		},
+		{
+			name:      "multiple unknown keys after nodes",
+			jsonData:  `{"nodes": [{"name": "test1"}], "key1": "value1", "key2": 42}`,
+			wantNodes: []string{"test1"},
+		},
+		{
+			name:      "unknown keys before and after nodes",
+			jsonData:  `{"before": "value", "nodes": [{"name": "test1"}], "after": "value"}`,
+			wantNodes: []string{"test1"},
+		},
+		{
+			name:      "nested object as unknown value",
+			jsonData:  `{"extra": {"nested": "value"}, "nodes": [{"name": "test1"}]}`,
+			wantNodes: []string{"test1"},
+		},
+		{
+			name:      "nested array as unknown value",
+			jsonData:  `{"extra": [1, 2, 3], "nodes": [{"name": "test1"}]}`,
+			wantNodes: []string{"test1"},
+		},
+		{
+			name:      "complex nested structure as unknown value",
+			jsonData:  `{"extra": {"obj": {"arr": [1, {"nested": true}]}}, "nodes": [{"name": "test1"}]}`,
+			wantNodes: []string{"test1"},
+		},
+		{
+			name:      "empty nodes array with unknown keys",
+			jsonData:  `{"extra": "value", "nodes": []}`,
+			wantNodes: nil,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			it, err := data.NewTreeNodeIterator(strings.NewReader(tt.jsonData + "\n"))
+			rtest.OK(t, err)
+
+			var gotNodes []string
+			for item := range it {
+				rtest.OK(t, item.Error)
+				gotNodes = append(gotNodes, item.Node.Name)
+			}
+
+			rtest.Equals(t, tt.wantNodes, gotNodes, "nodes mismatch")
+		})
+	}
+}
+
 func BenchmarkLoadTree(t *testing.B) {
 	repository.BenchmarkAllVersions(t, benchmarkLoadTree)
 }