Add concept of reserved objects

QPDFObjectHandle::{new,is,assert}Reserved, QPDF::replaceReserved
provide a mechanism to add objects to a PDF file when there are
circular references.  This is a prerequisite to copying objects from
one PDF to another.

5 files changed, 96 insertions, 5 deletions

diff --git a/libqpdf/QPDF.cc b/libqpdf/QPDF.cc
index a66b4f15..1c4e5d8d 100644
--- a/libqpdf/QPDF.cc
+++ b/libqpdf/QPDF.cc
@@ -2057,6 +2057,18 @@ QPDF::replaceObject(int objid, int generation, QPDFObjectHandle oh)
 }
 
 void
+QPDF::replaceReserved(QPDFObjectHandle reserved,
+                      QPDFObjectHandle replacement)
+{
+    QTC::TC("qpdf", "QPDF replaceReserved");
+    reserved.assertReserved();
+    replaceObject(reserved.getObjectID(),
+                  reserved.getGeneration(),
+                  replacement);
+}
+
+
+void
 QPDF::swapObjects(int objid1, int generation1, int objid2, int generation2)
 {
     // Force objects to be loaded into cache; then swap them in the
diff --git a/libqpdf/QPDFObjectHandle.cc b/libqpdf/QPDFObjectHandle.cc
index 73d0019c..25298bee 100644
--- a/libqpdf/QPDFObjectHandle.cc
+++ b/libqpdf/QPDFObjectHandle.cc
@@ -10,6 +10,7 @@
 #include <qpdf/QPDF_Array.hh>
 #include <qpdf/QPDF_Dictionary.hh>
 #include <qpdf/QPDF_Stream.hh>
+#include <qpdf/QPDF_Reserved.hh>
 
 #include <qpdf/QTC.hh>
 #include <qpdf/QUtil.hh>
@@ -20,7 +21,8 @@
 QPDFObjectHandle::QPDFObjectHandle() :
     initialized(false),
     objid(0),
-    generation(0)
+    generation(0),
+    reserved(false)
 {
 }
 
@@ -28,7 +30,8 @@ QPDFObjectHandle::QPDFObjectHandle(QPDF* qpdf, int objid, int generation) :
     initialized(true),
     qpdf(qpdf),
     objid(objid),
-    generation(generation)
+    generation(generation),
+    reserved(false)
 {
 }
 
@@ -37,7 +40,8 @@ QPDFObjectHandle::QPDFObjectHandle(QPDFObject* data) :
     qpdf(0),
     objid(0),
     generation(0),
-    obj(data)
+    obj(data),
+    reserved(false)
 {
 }
 
@@ -166,6 +170,14 @@ QPDFObjectHandle::isStream()
 }
 
 bool
+QPDFObjectHandle::isReserved()
+{
+    // dereference will clear reserved if this has been replaced
+    dereference();
+    return this->reserved;
+}
+
+bool
 QPDFObjectHandle::isIndirect()
 {
     assertInitialized();
@@ -568,6 +580,11 @@ QPDFObjectHandle::unparse()
 std::string
 QPDFObjectHandle::unparseResolved()
 {
+    if (this->reserved)
+    {
+        throw std::logic_error(
+            "QPDFObjectHandle: attempting to unparse a reserved object");
+    }
     dereference();
     return this->obj->unparse();
 }
@@ -690,6 +707,19 @@ QPDFObjectHandle::newStream(QPDF* qpdf, std::string const& data)
 }
 
 QPDFObjectHandle
+QPDFObjectHandle::newReserved(QPDF* qpdf)
+{
+    // Reserve a spot for this object by assigning it an object
+    // number, but then return an unresolved handle to the object.
+    QPDFObjectHandle reserved = qpdf->makeIndirectObject(
+	QPDFObjectHandle(new QPDF_Reserved()));
+    QPDFObjectHandle result =
+        newIndirect(qpdf, reserved.objid, reserved.generation);
+    result.reserved = true;
+    return result;
+}
+
+QPDFObjectHandle
 QPDFObjectHandle::shallowCopy()
 {
     assertInitialized();
@@ -746,6 +776,13 @@ QPDFObjectHandle::makeDirectInternal(std::set<int>& visited)
 	visited.insert(cur_objid);
     }
 
+    if (isReserved())
+    {
+        throw std::logic_error(
+            "QPDFObjectHandle: attempting to make a"
+            " reserved object handle direct");
+    }
+
     dereference();
     this->objid = 0;
     this->generation = 0;
@@ -903,6 +940,12 @@ QPDFObjectHandle::assertStream()
 }
 
 void
+QPDFObjectHandle::assertReserved()
+{
+    assertType("Reserved", isReserved());
+}
+
+void
 QPDFObjectHandle::assertScalar()
 {
     assertType("Scalar", isScalar());
@@ -929,12 +972,21 @@ QPDFObjectHandle::dereference()
 {
     if (this->obj.getPointer() == 0)
     {
-	this->obj = QPDF::Resolver::resolve(
+        PointerHolder<QPDFObject> obj = QPDF::Resolver::resolve(
 	    this->qpdf, this->objid, this->generation);
-	if (this->obj.getPointer() == 0)
+	if (obj.getPointer() == 0)
 	{
 	    QTC::TC("qpdf", "QPDFObjectHandle indirect to unknown");
 	    this->obj = new QPDF_Null();
 	}
+        else if (dynamic_cast<QPDF_Reserved*>(obj.getPointer()))
+        {
+            // Do not resolve
+        }
+        else
+        {
+            this->reserved = false;
+            this->obj = obj;
+        }
     }
 }
diff --git a/libqpdf/QPDF_Reserved.cc b/libqpdf/QPDF_Reserved.cc
new file mode 100644
index 00000000..368db3b4
--- /dev/null
+++ b/libqpdf/QPDF_Reserved.cc
@@ -0,0 +1,13 @@
+#include <qpdf/QPDF_Reserved.hh>
+#include <stdexcept>
+
+QPDF_Reserved::~QPDF_Reserved()
+{
+}
+
+std::string
+QPDF_Reserved::unparse()
+{
+    throw std::logic_error("attempt to unparse QPDF_Reserved");
+    return "";
+}
diff --git a/libqpdf/build.mk b/libqpdf/build.mk
index 7efbbd85..422878f2 100644
--- a/libqpdf/build.mk
+++ b/libqpdf/build.mk
@@ -39,6 +39,7 @@ SRCS_libqpdf = \
 	libqpdf/QPDF_Name.cc \
 	libqpdf/QPDF_Null.cc \
 	libqpdf/QPDF_Real.cc \
+	libqpdf/QPDF_Reserved.cc \
 	libqpdf/QPDF_Stream.cc \
 	libqpdf/QPDF_String.cc \
 	libqpdf/QPDF_encryption.cc \
diff --git a/libqpdf/qpdf/QPDF_Reserved.hh b/libqpdf/qpdf/QPDF_Reserved.hh
new file mode 100644
index 00000000..b149f776
--- /dev/null
+++ b/libqpdf/qpdf/QPDF_Reserved.hh
@@ -0,0 +1,13 @@
+#ifndef __QPDF_RESERVED_HH__
+#define __QPDF_RESERVED_HH__
+
+#include <qpdf/QPDFObject.hh>
+
+class QPDF_Reserved: public QPDFObject
+{
+  public:
+    virtual ~QPDF_Reserved();
+    virtual std::string unparse();
+};
+
+#endif // __QPDF_RESERVED_HH__