The recommended/official way for signing a PDF document is by
registering a callback function.
This "mixes" the process of preparing the document and generating the
signature to embed.
In my use case it is "necessary" to split the signing process in
multiple parts:
1) preparing the document (hashing the content in this step is fine)
2) sign the document/the calculated hash
3) put the signature in the document
This is possible, but not so practical.
In the callback it is obviously possible not to generate any signature
(and eventually just hash the content and save the hash somewhere), but
as a user of PoDoFo I have no idea what is the ByteRange I just
hashed/where I have to place the signature.
Of course it is possible to parse the document and search for the last
signature... but the signing process is split in multiple parts also
because of performance reasons...
Another "trick" is putting a dummy signature with some well-known value
in the document and "grep" for it afterwards... but in some scenarios it
can cause problem/get more complicated...
Fortunately the fix is easy, as AdjustByteRange is a void function.
As it's role is to "adjust the ByteRange" it seems like a sensible
operation to return the calculated value for those interested.
Users can ignore the return value, and use only the callback approach as
before (thus the API for those users is unchanged), and for those that
needs to split the creation of the resulting document and signing as
much as possible can reliably know where to put the signature.
Federico
Index: src/podofo/doc/PdfSignOutputDevice.cpp
===================================================================
--- src/podofo/doc/PdfSignOutputDevice.cpp (revision 2029)
+++ src/podofo/doc/PdfSignOutputDevice.cpp (working copy)
@@ -137,7 +137,7 @@
}
}
-void PdfSignOutputDevice::AdjustByteRange()
+PdfArray PdfSignOutputDevice::AdjustByteRange()
{
if(!m_bBeaconFound) {
PODOFO_RAISE_ERROR( ePdfError_InternalLogic );
@@ -185,6 +185,7 @@
m_pRealDevice->Seek(offset);
m_pRealDevice->Write(sPosition.c_str(), sPosition.size());
+ return arr;
}
size_t PdfSignOutputDevice::ReadForSignature(char* pBuffer, size_t lLen)
Index: src/podofo/doc/PdfSignOutputDevice.h
===================================================================
--- src/podofo/doc/PdfSignOutputDevice.h (revision 2029)
+++ src/podofo/doc/PdfSignOutputDevice.h (working copy)
@@ -38,6 +38,7 @@
#include "../base/PdfOutputDevice.h"
#include "../base/PdfData.h"
#include "../base/PdfString.h"
+#include "../base/PdfArray.h"
namespace PoDoFo
{
@@ -83,7 +84,7 @@
/** Modify ByteRange entry according to signature position
*
*/
- virtual void AdjustByteRange();
+ virtual PdfArray AdjustByteRange();
/** Read data for signature
*/
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