Create a special "destroyed" type rather than using null

When a QPDF is destroyed, changing indirect objects to direct nulls
makes them effectively disappear silently when they sneak into other
places. Instead, we should treat this as an error. Adding a destroyed
object type makes this possible.

1 files changed, 39 insertions, 0 deletions

diff --git a/libqpdf/QPDF_Destroyed.cc b/libqpdf/QPDF_Destroyed.cc
new file mode 100644
index 00000000..55308c9a
--- /dev/null
+++ b/libqpdf/QPDF_Destroyed.cc
@@ -0,0 +1,39 @@
+#include <qpdf/QPDF_Destroyed.hh>
+
+#include <stdexcept>
+
+QPDF_Destroyed::QPDF_Destroyed() :
+    QPDFValue(::ot_destroyed, "destroyed")
+{
+}
+
+std::shared_ptr<QPDFValue>
+QPDF_Destroyed::getInstance()
+{
+    static std::shared_ptr<QPDFValue> instance(new QPDF_Destroyed());
+    return instance;
+}
+
+std::shared_ptr<QPDFValueProxy>
+QPDF_Destroyed::shallowCopy()
+{
+    throw std::logic_error(
+        "attempted to shallow copy QPDFObjectHandle from destroyed QPDF");
+    return nullptr;
+}
+
+std::string
+QPDF_Destroyed::unparse()
+{
+    throw std::logic_error(
+        "attempted to unparse a QPDFObjectHandle from a destroyed QPDF");
+    return "";
+}
+
+JSON
+QPDF_Destroyed::getJSON(int json_version)
+{
+    throw std::logic_error(
+        "attempted to get JSON from a QPDFObjectHandle from a destroyed QPDF");
+    return JSON::makeNull();
+}