xmlsecurity: pdf incremental updates that are non-commenting are invalid

I.e. it's OK to add incremental updates for annotation/commenting
purposes and that doesn't invalite existing signatures. Everything else
does.

(cherry picked from commit 61834cd574568613f0b0a2ee099a60fa5a8d9804)

Conflicts:
include/vcl/filter/PDFiumLibrary.hxx
vcl/source/pdf/PDFiumLibrary.cxx

Change-Id: I4607c242b3c6f6b01517b02407e9e7a095e2e069
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/102240
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>

1 files changed, 48 insertions, 0 deletions

diff --git a/include/vcl/filter/PDFiumLibrary.hxx b/include/vcl/filter/PDFiumLibrary.hxx
index bc7912c17e81..639c71d61a3d 100644
--- a/include/vcl/filter/PDFiumLibrary.hxx
+++ b/include/vcl/filter/PDFiumLibrary.hxx
@@ -17,9 +17,14 @@
 #include <memory>
 #include <rtl/instance.hxx>
 #include <vcl/dllapi.h>
+#include <vcl/checksum.hxx>
+
+#include <fpdf_doc.h>
 
 namespace vcl::pdf
 {
+class PDFiumDocument;
+
 class VCL_DLLPUBLIC PDFium final
 {
 private:
@@ -31,6 +36,49 @@ public:
     ~PDFium();
 };
 
+class VCL_DLLPUBLIC PDFiumPage final
+{
+private:
+    FPDF_PAGE mpPage;
+
+private:
+    PDFiumPage(const PDFiumPage&) = delete;
+    PDFiumPage& operator=(const PDFiumPage&) = delete;
+
+public:
+    PDFiumPage(FPDF_PAGE pPage)
+        : mpPage(pPage)
+    {
+    }
+
+    ~PDFiumPage()
+    {
+        if (mpPage)
+            FPDF_ClosePage(mpPage);
+    }
+
+    /// Get bitmap checksum of the page, without annotations/commenting.
+    BitmapChecksum getChecksum();
+};
+
+class VCL_DLLPUBLIC PDFiumDocument final
+{
+private:
+    FPDF_DOCUMENT mpPdfDocument;
+
+private:
+    PDFiumDocument(const PDFiumDocument&) = delete;
+    PDFiumDocument& operator=(const PDFiumDocument&) = delete;
+
+public:
+    PDFiumDocument(FPDF_DOCUMENT pPdfDocument);
+    ~PDFiumDocument();
+
+    int getPageCount();
+
+    std::unique_ptr<PDFiumPage> openPage(int nIndex);
+};
+
 struct PDFiumLibrary : public rtl::StaticWithInit<std::shared_ptr<PDFium>, PDFiumLibrary>
 {
     std::shared_ptr<PDFium> operator()() { return std::make_shared<PDFium>(); }