From 9b0801721710093102c64068b6c643c8fcd7f5db Mon Sep 17 00:00:00 2001
From: m-holger <m-holger@kubitscheck.org>
Date: Thu, 5 Jan 2023 11:09:44 +0000
Subject: [PATCH] Add new convenience class QPDFObjGen::set

---
 include/qpdf/QPDFObjGen.hh | 69 ++++++++++++++++++++++++++++++++++++--
 libqpdf/QPDFObjGen.cc      | 56 +++++++++++++++++++++++++++++--
 2 files changed, 121 insertions(+), 4 deletions(-)

diff --git a/include/qpdf/QPDFObjGen.hh b/include/qpdf/QPDFObjGen.hh
index ccab4ba2..0d14efaf 100644
--- a/include/qpdf/QPDFObjGen.hh
+++ b/include/qpdf/QPDFObjGen.hh
@@ -24,6 +24,10 @@
 
 #include <qpdf/DLL.h>
 #include <iostream>
+#include <set>
+
+class QPDFObjectHandle;
+class QPDFObjectHelper;
 
 // This class represents an object ID and generation pair.  It is
 // suitable to use as a key in a map or set.
@@ -31,6 +35,7 @@
 class QPDFObjGen
 {
   public:
+    // ABI: change to default.
     QPDF_DLL
     QPDFObjGen() :
         obj(0),
@@ -84,12 +89,72 @@ class QPDFObjGen
     QPDF_DLL
     friend std::ostream& operator<<(std::ostream& os, const QPDFObjGen& og);
 
+    // Convenience class for loop detection when processing objects.
+    //
+    // The class adds 'add' methods to a std::set<QPDFObjGen> which allows
+    // to test whether an QPDFObjGen is present in the set and to insert it in
+    // a single operation. The 'add' method is overloaded to take a QPDFObjGen,
+    // QPDFObjectHandle or an QPDFObjectHelper as parameter.
+    //
+    // The erase method is modified to ignore requests to erase
+    // QPDFObjGen(0, 0).
+    //
+    // Usage example:
+    //
+    // void process_object(QPDFObjectHandle oh, QPDFObjGen::Tracker& seen)
+    // {
+    //     if (seen.add(oh)) {
+    //         // handle first encounter of oh
+    //     } else {
+    //         // handle loop / subsequent encounter of oh
+    //     }
+    // }
+    class QPDF_DLL_CLASS set: public std::set<QPDFObjGen>
+    {
+      public:
+        // Add 'og' to the set. Return false if 'og' is already present in
+        // the set. Attempts to insert QPDFObjGen(0, 0) are ignored.
+        QPDF_DLL
+        bool
+        add(QPDFObjGen og)
+        {
+            if (og.isIndirect()) {
+                if (count(og) > 0) {
+                    return false;
+                }
+                emplace(og);
+            }
+            return true;
+        }
+
+        QPDF_DLL
+        bool add(QPDFObjectHandle const& oh);
+
+        QPDF_DLL
+        bool add(QPDFObjectHelper const& oh);
+
+        QPDF_DLL
+        void
+        erase(QPDFObjGen og)
+        {
+            if (og.isIndirect()) {
+                std::set<QPDFObjGen>::erase(og);
+            }
+        }
+
+        QPDF_DLL
+        void erase(QPDFObjectHandle const& oh);
+
+        QPDF_DLL
+        void erase(QPDFObjectHelper const& oh);
+    };
+
   private:
     // This class does not use the Members pattern to avoid a memory
     // allocation for every one of these. A lot of these get created
     // and destroyed.
-    int obj;
-    int gen;
+    int obj{0};
+    int gen{0};
 };
 
 #endif // QPDFOBJGEN_HH
diff --git a/libqpdf/QPDFObjGen.cc b/libqpdf/QPDFObjGen.cc
index 7cce84d8..8e5bd178 100644
--- a/libqpdf/QPDFObjGen.cc
+++ b/libqpdf/QPDFObjGen.cc
@@ -1,7 +1,12 @@
 #include <qpdf/QPDFObjGen.hh>
 
-#include <qpdf/QUtil.hh>
+#include <qpdf/QPDFObjectHandle.hh>
+#include <qpdf/QPDFObjectHelper.hh>
+#include <qpdf/QPDFObject_private.hh>
 
+#include <stdexcept>
+
+// ABI: inline and pass og by value
 std::ostream&
 operator<<(std::ostream& os, const QPDFObjGen& og)
 {
@@ -9,8 +14,55 @@ operator<<(std::ostream& os, const QPDFObjGen& og)
     return os;
 }
 
+// ABI: inline
 std::string
 QPDFObjGen::unparse(char separator) const
 {
-    return std::to_string(this->obj) + separator + std::to_string(this->gen);
+    return std::to_string(obj) + separator + std::to_string(gen);
+}
+
+bool
+QPDFObjGen::set::add(QPDFObjectHandle const& oh)
+{
+    if (auto* ptr = oh.getObjectPtr()) {
+        return add(ptr->getObjGen());
+    } else {
+        throw std::logic_error("attempt to retrieve QPDFObjGen from "
+                               "uninitialized QPDFObjectHandle");
+        return false;
+    }
+}
+
+bool
+QPDFObjGen::set::add(QPDFObjectHelper const& helper)
+{
+    if (auto* ptr = helper.getObjectHandle().getObjectPtr()) {
+        return add(ptr->getObjGen());
+    } else {
+        throw std::logic_error("attempt to retrieve QPDFObjGen from "
+                               "uninitialized QPDFObjectHandle");
+        return false;
+    }
+}
+
+void
+QPDFObjGen::set::erase(QPDFObjectHandle const& oh)
+{
+    if (auto* ptr = oh.getObjectPtr()) {
+        erase(ptr->getObjGen());
+    } else {
+        throw std::logic_error("attempt to retrieve QPDFObjGen from "
+                               "uninitialized QPDFObjectHandle");
+    }
+}
+
+void
+QPDFObjGen::set::erase(QPDFObjectHelper const& helper)
+{
+    if (auto* ptr = helper.getObjectHandle().getObjectPtr()) {
+        erase(ptr->getObjGen());
+    } else {
+        throw std::logic_error("attempt to retrieve QPDFObjGen from "
+                               "uninitialized QPDFObjectHandle");
+    }
 }