From 8e33527bb968d718cec3542fdbd384a63f695fcb Mon Sep 17 00:00:00 2001
From: Julien R <j.raffray@gmail.com>
Date: Mon, 16 Oct 2023 14:16:10 +0200
Subject: [PATCH] add CheckSum to PdfEmbeddedFileStream

checksum has to be an MD5 hash of the file
---
 .../src/PdfSharp/Pdf.Advanced/PdfEmbeddedFileStream.cs |  7 ++++++-
 .../src/PdfSharp/Pdf.Advanced/PdfNameDictionary.cs     |  4 ++--
 .../src/PDFsharp/src/PdfSharp/Pdf/PdfDocument.cs       | 10 ++++++----
 3 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/src/foundation/src/PDFsharp/src/PdfSharp/Pdf.Advanced/PdfEmbeddedFileStream.cs b/src/foundation/src/PDFsharp/src/PdfSharp/Pdf.Advanced/PdfEmbeddedFileStream.cs
index 04c12d0c..21a37d53 100644
--- a/src/foundation/src/PDFsharp/src/PdfSharp/Pdf.Advanced/PdfEmbeddedFileStream.cs
+++ b/src/foundation/src/PDFsharp/src/PdfSharp/Pdf.Advanced/PdfEmbeddedFileStream.cs
@@ -18,13 +18,15 @@ public class PdfEmbeddedFileStream : PdfDictionary
         /// <summary>
         /// Initializes a new instance of PdfEmbeddedFileStream from a stream.
         /// </summary>
-        public PdfEmbeddedFileStream(PdfDocument document, Stream stream) : base(document)
+        /// <param name="checksum">A 16-byte string which is a MD5 checksum of the bytes of the file</param>
+        public PdfEmbeddedFileStream(PdfDocument document, Stream stream, string? checksum = null) : base(document)
         {
             _data = new byte[stream.Length];
             using (stream)
             {
                 stream.Read(_data, 0, (int)stream.Length);
             }
+            _checksum = checksum;
 
             Initialize();
         }
@@ -39,6 +41,8 @@ void Initialize()
             var now = DateTime.Now;
             objParams.Elements.SetDateTime("/CreationDate", now);
             objParams.Elements.SetDateTime("/ModDate", now);
+            if (!string.IsNullOrEmpty(_checksum))
+                objParams.Elements.SetString("/CheckSum", _checksum);
             Elements.SetObject(Keys.Params, objParams);
 
             Stream = new PdfStream(_data, this);
@@ -53,6 +57,7 @@ public static bool IsEmbeddedFile(PdfDictionary dictionary)
         }
 
         readonly byte[] _data;
+        readonly string? _checksum;
 
         const string TypeValue = "/EmbeddedFile";
 
diff --git a/src/foundation/src/PDFsharp/src/PdfSharp/Pdf.Advanced/PdfNameDictionary.cs b/src/foundation/src/PDFsharp/src/PdfSharp/Pdf.Advanced/PdfNameDictionary.cs
index 6ab77bf4..7c0bd975 100644
--- a/src/foundation/src/PDFsharp/src/PdfSharp/Pdf.Advanced/PdfNameDictionary.cs
+++ b/src/foundation/src/PDFsharp/src/PdfSharp/Pdf.Advanced/PdfNameDictionary.cs
@@ -55,7 +55,7 @@ internal void AddNamedDestination(string destinationName, int destinationPage, P
 
         PdfNameTreeNode? _dests;
 
-        internal void AddEmbeddedFile(string name, Stream stream)
+        internal void AddEmbeddedFile(string name, Stream stream, string? checksum = null)
         {
             if (_embeddedFiles == null)
             {
@@ -64,7 +64,7 @@ internal void AddEmbeddedFile(string name, Stream stream)
                 Elements.SetReference(Keys.EmbeddedFiles, _embeddedFiles.Reference);
             }
 
-            var embeddedFileStream = new PdfEmbeddedFileStream(Owner, stream);
+            var embeddedFileStream = new PdfEmbeddedFileStream(Owner, stream, checksum);
             var fileSpecification = new PdfFileSpecification(Owner, embeddedFileStream, name);
             Owner.Internals.AddObject(fileSpecification);
 
diff --git a/src/foundation/src/PDFsharp/src/PdfSharp/Pdf/PdfDocument.cs b/src/foundation/src/PDFsharp/src/PdfSharp/Pdf/PdfDocument.cs
index c5054814..cb62656c 100644
--- a/src/foundation/src/PDFsharp/src/PdfSharp/Pdf/PdfDocument.cs
+++ b/src/foundation/src/PDFsharp/src/PdfSharp/Pdf/PdfDocument.cs
@@ -770,10 +770,11 @@ public void AddNamedDestination(string destinationName, int destinationPage, Pdf
         /// </summary>
         /// <param name="name">The name used to refer and to entitle the embedded file.</param>
         /// <param name="path">The path of the file to embed.</param>
-        public void AddEmbeddedFile(string name, string path)
+        /// <param name="checksum">A 16-byte string which is a MD5 checksum of the bytes of the file</param>
+        public void AddEmbeddedFile(string name, string path, string? checksum = null)
         {
             var stream = new FileStream(path, FileMode.Open);
-            AddEmbeddedFile(name, stream);
+            AddEmbeddedFile(name, stream, checksum);
         }
 
         /// <summary>
@@ -781,8 +782,9 @@ public void AddEmbeddedFile(string name, string path)
         /// </summary>
         /// <param name="name">The name used to refer and to entitle the embedded file.</param>
         /// <param name="stream">The stream containing the file to embed.</param>
-        public void AddEmbeddedFile(string name, Stream stream)
-            => Internals.Catalog.Names.AddEmbeddedFile(name, stream);
+        /// <param name="checksum">A 16-byte string which is a MD5 checksum of the bytes of the file</param>
+        public void AddEmbeddedFile(string name, Stream stream, string? checksum = null)
+            => Internals.Catalog.Names.AddEmbeddedFile(name, stream, checksum);
 
         /// <summary>
         /// Flattens a document (make the fields non-editable).