feat: read the retained data of proxy entities and objects

src/ACadSharp/Entities/ProxyEntity.cs

@@ -1,6 +1,7 @@
 using ACadSharp.Attributes;
 using ACadSharp.Classes;
 using CSMath;
+using System.IO;
 
 namespace ACadSharp.Entities
 {
@@ -64,6 +65,10 @@ public class ProxyEntity : Entity, IProxy
 		//An object ID(multiple entries can appear) (optional)
 
 		//94 0 (indicates end of object ID section)
+		/// <inheritdoc/>
+		/// <remarks>No <c>DxfCodeValue</c>: the DXF reader has no handler for code 311 on an entity.</remarks>
+		public Stream Data { get; set; }
+
 		/// <inheritdoc/>
 		public ACadVersion Version { get; set; }
 

src/ACadSharp/IO/DWG/DwgStreamReaders/DwgObjectReader.cs

@@ -72,6 +72,8 @@ internal partial class DwgObjectReader : DwgSectionIO
 		/// </summary>
 		private IDwgStreamReader _handlesReader;
 
+		private long _handleSectionOffset = -1;
+
 		private IDwgStreamReader _mergedReaders;
 
 		private long _objectInitialPos = 0;
@@ -234,7 +236,7 @@ private ObjectType getEntityType(long offset)
 				ulong handleSize = this._crcReader.ReadModularChar();
 
 				//Find the handles offset
-				ulong handleSectionOffset = (ulong)this._crcReader.PositionInBits() + sizeInBits - handleSize;
+				this._handleSectionOffset = (long)((ulong)this._crcReader.PositionInBits() + sizeInBits - handleSize);
 
 				//Create a handler section reader
 				this._objectReader = DwgStreamReaderBase.GetStreamHandler(this._version, HugeMemoryStream.Clone(this._memoryStream), this._reader.Encoding);
@@ -246,11 +248,11 @@ private ObjectType getEntityType(long offset)
 
 				//Create a handler section reader
 				this._handlesReader = DwgStreamReaderBase.GetStreamHandler(this._version, HugeMemoryStream.Clone(this._memoryStream), this._reader.Encoding);
-				this._handlesReader.SetPositionInBits((long)handleSectionOffset);
+				this._handlesReader.SetPositionInBits(this._handleSectionOffset);
 
 				//Create a text section reader
 				this._textReader = DwgStreamReaderBase.GetStreamHandler(this._version, HugeMemoryStream.Clone(this._memoryStream), this._reader.Encoding);
-				this._textReader.SetPositionByFlag((long)handleSectionOffset - 1);
+				this._textReader.SetPositionByFlag(this._handleSectionOffset - 1);
 
 				this._mergedReaders = new DwgMergedReader(this._objectReader, this._textReader, this._handlesReader);
 			}
@@ -1181,8 +1183,18 @@ private void readCommonProxyData(IProxy proxy)
 
 			//Common:
 			//Databits X databits, however many there are to the handles
+			//The retained data has no length of its own, it runs up to the handle section
+			if (this._handleSectionOffset > 0)
+			{
+				long dataBits = this._handleSectionOffset - this._objectReader.PositionInBits();
+				if (dataBits > 0)
+				{
+					int dataBytes = (int)((dataBits + 7L) / 8L);
+					byte[] data = this._objectReader.ReadBytes(dataBytes);
 
-			//TODO: Investigate how to read the data in proxies, it can contain data, strings and handles
+					proxy.Data = new MemoryStream(data, writable: false);
+				}
+			}
 		}
 
 		private CadTemplate readDbColor()

src/ACadSharp/IProxy.cs

@@ -1,4 +1,5 @@
 using ACadSharp.Classes;
+using System.IO;
 
 namespace ACadSharp;
 
@@ -29,5 +30,10 @@ public interface IProxy
 	/// </summary>
 	int ProxyClassId { get; }
 
+	/// <summary>
+	/// Gets or sets the retained data of the original object.
+	/// </summary>
+	Stream Data { get; set; }
+
 	ACadVersion Version { get; set; }
 }

src/ACadSharp/Objects/ProxyObject.cs

@@ -53,6 +53,7 @@ public class ProxyObject : NonGraphicalObject, IProxy
 		[DxfCodeValue(310)]
 		public Stream BinaryData { get; set; }
 
+		/// <inheritdoc/>
 		[DxfCodeValue(311)]
 		public Stream Data { get; set; }