Rework the writing of DictionaryProperty

sources/OpenMcdf.Extensions/OLEProperties/Common.cs

@@ -36,4 +36,9 @@ public enum PropertyType
     {
         TypedPropertyValue = 0, DictionaryProperty = 1
     }
+
+    internal static class CodePages
+    {
+        public const int CP_WINUNICODE = 0x04B0;
+    }
 }

sources/OpenMcdf.Extensions/OLEProperties/DictionaryEntry.cs

@@ -7,8 +7,6 @@ namespace OpenMcdf.Extensions.OLEProperties
 {
     public class DictionaryEntry
     {
-        private const int CP_WINUNICODE = 0x04B0;
-
         int codePage;
 
         public DictionaryEntry(int codePage)
@@ -27,7 +25,7 @@ public void Read(BinaryReader br)
             PropertyIdentifier = br.ReadUInt32();
             Length = br.ReadInt32();
 
-            if (codePage != CP_WINUNICODE)
+            if (codePage != CodePages.CP_WINUNICODE)
             {
                 nameBytes = br.ReadBytes(Length);
             }

sources/OpenMcdf.Extensions/OLEProperties/DictionaryProperty.cs

@@ -59,19 +59,85 @@ public void Read(BinaryReader br)
 
         }
 
+        /// <summary>
+        /// Write the dictionary and all its values into the specified <see cref="BinaryWriter"/>.
+        /// </summary>
+        /// <remarks>
+        /// Based on the Microsoft specifications at https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-oleps/99127b7f-c440-4697-91a4-c853086d6b33
+        /// </remarks>
+        /// <param name="bw">A writer to write the dictionary into.</param>
         public void Write(BinaryWriter bw)
         {
+            long curPos = bw.BaseStream.Position;
+
             bw.Write(entries.Count);
 
             foreach (KeyValuePair<uint, string> kv in entries)
             {
-                bw.Write(kv.Key);
-                string s = kv.Value;
-                if (!s.EndsWith("\0"))
-                    s += "\0";
-                bw.Write(Encoding.GetEncoding(this.codePage).GetBytes(s));
+                WriteEntry(bw, kv.Key, kv.Value);
             }
 
+            var size = (int)(bw.BaseStream.Position - curPos);
+            WritePaddingIfNeeded(bw, size);
+        }
+
+        // Write a single entry to the dictionary, and handle and required null termination and padding.
+        private void WriteEntry(BinaryWriter bw, uint propertyIdentifier, string name)
+        {
+            // Write the PropertyIdentifier
+            bw.Write(propertyIdentifier);
+
+            // Encode string data with the current codepage
+            var nameBytes = Encoding.GetEncoding(this.codePage).GetBytes(name);
+            uint byteLength = (uint)nameBytes.Length;
+
+            // If the code page is WINUNICODE, write the length as the number of characters and pad the length to a multiple of 4 bytes
+            // Otherwise, write the length as the number of bytes and don't pad.
+            // In either case, the string must be null terminated
+            if (codePage == CodePages.CP_WINUNICODE)
+            {
+                bool addNullTerminator =
+                    byteLength == 0 || nameBytes[byteLength - 1] != '\0' || nameBytes[byteLength - 2] != '\0';
+
+                if (addNullTerminator)
+                    byteLength += 2;
+
+                bw.Write((uint)byteLength / 2);
+                bw.Write(nameBytes);
+
+                if (addNullTerminator)
+                {
+                    bw.Write((byte)0);
+                    bw.Write((byte)0);
+                }
+
+                WritePaddingIfNeeded(bw, (int)byteLength);
+            }
+            else
+            {
+                bool addNullTerminator =
+                    byteLength == 0 || nameBytes[byteLength - 1] != '\0';
+
+                if (addNullTerminator)
+                    byteLength += 1;
+
+                bw.Write(byteLength);
+                bw.Write(nameBytes);
+
+                if (addNullTerminator)
+                    bw.Write((byte)0);
+            }
+        }
+
+        // Write as much padding as needed to pad fieldLength to a multiple of 4 bytes
+        private void WritePaddingIfNeeded(BinaryWriter bw, int fieldLength)
+        {
+            var m = fieldLength % 4;
+
+            if (m > 0)
+                for (int i = 0; i < 4 - m; i++)  // padding
+                    bw.Write((byte)0);
         }
     }
 }
+