From 7de0b3f3c083990842523112959f8e27a0d2e5a0 Mon Sep 17 00:00:00 2001
From: Jay Berkenbilt <ejb@ql.org>
Date: Tue, 9 Jan 2024 20:28:28 -0500
Subject: [PATCH] JSONHandler: add fallback handler support

---
 .idea/dictionaries/ejb.xml                   |  1 +
 libqpdf/JSONHandler.cc                       | 13 ++++++++++++-
 libqpdf/qpdf/JSONHandler.hh                  |  3 +++
 libtests/json_handler.cc                     |  6 ++++++
 libtests/qtest/json_handler/json_handler.out |  6 ++++++
 5 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/.idea/dictionaries/ejb.xml b/.idea/dictionaries/ejb.xml
index 0dcc3d1a..a9dcf246 100644
--- a/.idea/dictionaries/ejb.xml
+++ b/.idea/dictionaries/ejb.xml
@@ -1,6 +1,7 @@
 <component name="ProjectDictionaryState">
   <dictionary name="ejb">
     <words>
+      <w>phour</w>
       <w>whoami</w>
     </words>
   </dictionary>
diff --git a/libqpdf/JSONHandler.cc b/libqpdf/JSONHandler.cc
index 4a69fd60..a8116cb0 100644
--- a/libqpdf/JSONHandler.cc
+++ b/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
diff --git a/libqpdf/qpdf/JSONHandler.hh b/libqpdf/qpdf/JSONHandler.hh
index 9b2a0b33..1c53e32d 100644
--- a/libqpdf/qpdf/JSONHandler.hh
+++ b/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);
 
diff --git a/libtests/json_handler.cc b/libtests/json_handler.cc
index 57185c98..2d3f9862 100644
--- a/libtests/json_handler.cc
+++ b/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);
 }
diff --git a/libtests/qtest/json_handler/json_handler.out b/libtests/qtest/json_handler/json_handler.out
index f076d4ee..4f340b85 100644
--- a/libtests/qtest/json_handler/json_handler.out
+++ b/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: {