JSONHandler: add fallback handler support

.idea/dictionaries/ejb.xml

@@ -1,6 +1,7 @@
 <component name="ProjectDictionaryState">
   <dictionary name="ejb">
     <words>
+      <w>phour</w>
       <w>whoami</w>
     </words>
   </dictionary>

libqpdf/JSONHandler.cc

@@ -17,10 +17,10 @@ struct Handlers
     JSONHandler::void_handler_t dict_end_handler{nullptr};
     JSONHandler::json_handler_t array_start_handler{nullptr};
     JSONHandler::void_handler_t array_end_handler{nullptr};
-    JSONHandler::void_handler_t final_handler{nullptr};
     std::map<std::string, std::shared_ptr<JSONHandler>> dict_handlers;
     std::shared_ptr<JSONHandler> fallback_dict_handler;
     std::shared_ptr<JSONHandler> array_item_handler;
+    std::shared_ptr<JSONHandler> fallback_handler;
 };
 
 class JSONHandler::Members
@@ -110,6 +110,12 @@ JSONHandler::addArrayHandlers(
     m->h.array_item_handler = ah;
 }
 
+void
+JSONHandler::addFallbackHandler(std::shared_ptr<JSONHandler> h)
+{
+    m->h.fallback_handler = std::move(h);
+}
+
 void
 JSONHandler::handle(std::string const& path, JSON j)
 {
@@ -169,6 +175,11 @@ JSONHandler::handle(std::string const& path, JSON j)
         return;
     }
 
+    if (m->h.fallback_handler) {
+        m->h.fallback_handler->handle(path, j);
+        return;
+    }
+
     // It would be nice to include information about what type the object was and what types were
     // allowed, but we're relying on schema validation to make sure input is properly structured
     // before calling the handlers. It would be different if this code were trying to be part of a

libqpdf/qpdf/JSONHandler.hh

@@ -45,6 +45,9 @@ class JSONHandler
     void addArrayHandlers(
         json_handler_t start_fn, void_handler_t end_fn, std::shared_ptr<JSONHandler> item_handlers);
 
+    // If no handlers is called, the fallback handler will be used to try to handle the item.
+    void addFallbackHandler(std::shared_ptr<JSONHandler>);
+
     // Apply handlers recursively to a JSON object.
     void handle(std::string const& path, JSON j);
 

libtests/json_handler.cc

@@ -77,6 +77,7 @@ make_all_handler()
     auto h5s = std::make_shared<JSONHandler>();
     h->addDictKeyHandler("five", h5s);
     h5s->addArrayHandlers(print_json, make_print_message("array end"), h5);
+    h5s->addFallbackHandler(h5);
     auto h6 = std::make_shared<JSONHandler>();
     h6->addDictHandlers(print_json, make_print_message("dict end"));
     auto h6a = std::make_shared<JSONHandler>();
@@ -107,6 +108,11 @@ test_all()
    "five": ["x", false, "y", null, true],
    "phour": null,
    "six": {"a": {"b": "quack", "Q": "baaa"}, "b": "moo"}
+})");
+    h->handle(".", j);
+    std::cerr << "-- fallback --" << std::endl;
+    j = JSON::parse(R"({
+   "five": "not-array"
 })");
     h->handle(".", j);
 }

libtests/qtest/json_handler/json_handler.out

@@ -63,6 +63,12 @@
 .three: bool: true
 .two: number: 3.14
 .: json: dict end
+-- fallback --
+.: json: {
+  "five": "not-array"
+}
+.five: string: not-array
+.: json: dict end
 -- errors --
 bad type at top: JSON handler: value at . is not of expected type
 .: json: {