fix: prevent panic on nil intermediate values during Set operations

Add nil checks in setSingleImpl() and traversal loop to handle nil
intermediate values gracefully. Per RFC 6901 Section 7, implementations
must raise error conditions for unresolvable paths instead of panicking.

- Add isNil() check before reflection operations in setSingleImpl()
- Add nil validation in set() method traversal loop
- Return descriptive errors: "cannot set field X on nil value"
- Add comprehensive test cases for nil traversal scenarios

Fixes panic: "reflect: call of reflect.Value.Type on zero Value" when
traversing JSON paths containing nil intermediate values.

Signed-off-by: Matthew F Leader <[email protected]>

Author: mfleader

pointer.go

@@ -179,6 +179,11 @@ func getSingleImpl(node any, decodedToken string, nameProvider *swag.NameProvide
 func setSingleImpl(node, data any, decodedToken string, nameProvider *swag.NameProvider) error {
 	rValue := reflect.Indirect(reflect.ValueOf(node))
 
+	// Check for nil to prevent panic when calling rValue.Type()
+	if isNil(node) {
+		return fmt.Errorf("cannot set field %q on nil value: %w", decodedToken, ErrPointer)
+	}
+
 	if ns, ok := node.(JSONSetable); ok { // pointer impl
 		return ns.JSONSet(decodedToken, data)
 	}
@@ -285,6 +290,11 @@ func (p *Pointer) set(node, data any, nameProvider *swag.NameProvider) error {
 			return setSingleImpl(node, data, decodedToken, nameProvider)
 		}
 
+		// Check for nil during traversal
+		if isNil(node) {
+			return fmt.Errorf("cannot traverse through nil value at %q: %w", decodedToken, ErrPointer)
+		}
+
 		rValue := reflect.Indirect(reflect.ValueOf(node))
 		kind := rValue.Kind()
 

pointer_test.go

@@ -644,6 +644,94 @@ func TestSetNode(t *testing.T) {
 			assert.Equal(t, 999, setDoc.Coll.Items[0].C)
 		})
 	})
+
+	t.Run("with nil traversal panic", func(t *testing.T) {
+		// This test exposes the panic that occurs when trying to set a value
+		// through a path that contains nil intermediate values
+		data := map[string]any{
+			"level1": map[string]any{
+				"level2": map[string]any{
+					"level3": nil, // This nil causes the panic
+				},
+			},
+		}
+
+		ptr, err := New("/level1/level2/level3/value")
+		require.NoError(t, err)
+
+		// This should return an error, not panic
+		_, err = ptr.Set(data, "test-value")
+
+		// The library should handle this gracefully and return an error
+		// instead of panicking
+		require.Error(t, err, "Setting value through nil intermediate path should return an error, not panic")
+	})
+
+	t.Run("with direct nil map value", func(t *testing.T) {
+		// Simpler test case that directly tests nil traversal
+		data := map[string]any{
+			"container": nil,
+		}
+
+		ptr, err := New("/container/nested/value")
+		require.NoError(t, err)
+
+		// Attempting to traverse through nil should return an error, not panic
+		_, err = ptr.Set(data, "test")
+		require.Error(t, err, "Cannot traverse through nil intermediate values")
+	})
+
+	t.Run("with nil in nested structure", func(t *testing.T) {
+		// Test case with multiple nil values in nested structure
+		data := map[string]any{
+			"config": map[string]any{
+				"settings": nil,
+			},
+			"data": map[string]any{
+				"nested": map[string]any{
+					"properties": map[string]any{
+						"attributes": nil, // Nil intermediate value
+					},
+				},
+			},
+		}
+
+		ptr, err := New("/data/nested/properties/attributes/name")
+		require.NoError(t, err)
+
+		// Should return error, not panic
+		_, err = ptr.Set(data, "test-name")
+		require.Error(t, err, "Setting through nil intermediate path should return error")
+	})
+
+	t.Run("with path creation through nil intermediate", func(t *testing.T) {
+		// Test case that simulates path creation functions encountering nil
+		// This happens when tools try to create missing paths but encounter nil intermediate values
+		data := map[string]any{
+			"spec": map[string]any{
+				"template": nil, // This blocks path creation attempts
+			},
+		}
+
+		// Attempting to create a path like /spec/template/metadata/labels should fail gracefully
+		ptr, err := New("/spec/template/metadata")
+		require.NoError(t, err)
+
+		// Should return error when trying to set on nil intermediate during path creation
+		_, err = ptr.Set(data, map[string]any{"labels": map[string]any{}})
+		require.Error(t, err, "Setting on nil intermediate during path creation should return error")
+	})
+
+	t.Run("with SetForToken on nil", func(t *testing.T) {
+		// Test the single-level SetForToken function with nil
+		data := map[string]any{
+			"container": nil,
+		}
+
+		// Should handle nil gracefully at single token level
+		_, err := SetForToken(data["container"], "nested", "value")
+		require.Error(t, err, "SetForToken on nil should return error, not panic")
+	})
 }
 
 func TestOffset(t *testing.T) {