Refactor Resource.TryGetLength and TryOpenStream.

ICSharpCode.Decompiler/Metadata/Resource.cs

@@ -110,48 +110,39 @@ namespace ICSharpCode.Decompiler.Metadata
 			return ResourceType.Linked;
 		}
 
-		public override unsafe Stream? TryOpenStream()
+		unsafe bool TryReadResource(out byte* ptr, out long length)
 		{
+			ptr = null;
+			length = 0;
 			if (ResourceType != ResourceType.Embedded)
-				return null;
+				return false;
 			var headers = Module.Reader.PEHeaders;
 			if (headers.CorHeader == null)
-				return null;
+				return false;
 			var resources = headers.CorHeader.ResourcesDirectory;
 			if (resources.RelativeVirtualAddress == 0)
-				return null;
+				return false;
 			var sectionData = Module.Reader.GetSectionData(resources.RelativeVirtualAddress);
 			if (sectionData.Length == 0)
-				return null;
+				return false;
 			var resource = Module.Metadata.GetManifestResource(Handle);
-			if (resource.Offset > sectionData.Length)
-				return null;
-			byte* ptr = sectionData.Pointer + resource.Offset;
-			int length = ptr[0] + (ptr[1] << 8) + (ptr[2] << 16) + (ptr[3] << 24);
-			if (length < 0 || length > sectionData.Length)
+			if (resource.Offset + 4 > sectionData.Length)
+				return false;
+			ptr = sectionData.Pointer + resource.Offset;
+			length = ptr[0] + (ptr[1] << 8) + (ptr[2] << 16) + (ptr[3] << 24);
+			return length >= 0 && length <= sectionData.Length;
+		}
+
+		public override unsafe Stream? TryOpenStream()
+		{
+			if (!TryReadResource(out var ptr, out var length))
 				return null;
 			return new ResourceMemoryStream(Module.Reader, ptr + sizeof(int), length);
 		}
 
 		public unsafe override long? TryGetLength()
 		{
-			if (ResourceType != ResourceType.Embedded)
-				return null;
-			var headers = Module.Reader.PEHeaders;
-			if (headers.CorHeader == null)
-				return null;
-			var resources = headers.CorHeader.ResourcesDirectory;
-			if (resources.RelativeVirtualAddress == 0)
-				return null;
-			var sectionData = Module.Reader.GetSectionData(resources.RelativeVirtualAddress);
-			if (sectionData.Length == 0)
-				return null;
-			var resource = Module.Metadata.GetManifestResource(Handle);
-			if (resource.Offset > sectionData.Length)
-				return null;
-			byte* ptr = sectionData.Pointer + resource.Offset;
-			int length = ptr[0] + (ptr[1] << 8) + (ptr[2] << 16) + (ptr[3] << 24);
-			if (length < 0 || length > sectionData.Length)
+			if (!TryReadResource(out _, out var length))
 				return null;
 			return length;
 		}