feat: additional method GetOriginalFileName

Author: millsotron-ibm

application/DotNetMeshClient/NHS.Mesh.Client/Helpers/ContentHelpers/GZIPHelpers.cs

@@ -4,7 +4,7 @@ namespace NHS.MESH.Client.Helpers.ContentHelpers;
 
 public class GZIPHelpers
 {
-    public static byte[] CompressBuffer(byte[]  data)
+    public static byte[] CompressBuffer(byte[] data)
     {
         using (var compressedStream = new MemoryStream())
         using (var zipStream = new GZipStream(compressedStream, CompressionMode.Compress))
@@ -25,4 +25,31 @@ public static byte[] DeCompressBuffer(byte[] byteArray)
         }
     }
 
+    public static string? GetOriginalFileName(byte[] gzipBuffer)
+    {
+        using (var compressedStream = new MemoryStream(gzipBuffer))
+        using (var gzipStream = new GZipStream(compressedStream, CompressionMode.Decompress))
+        {
+            // Read the GZIP header
+            byte[] header = new byte[10];
+            compressedStream.Read(header, 0, 10);
+
+            // Check if the original file name is present
+            if ((header[3] & 0x08) != 0)
+            {
+                using (var reader = new BinaryReader(compressedStream))
+                {
+                    var fileNameBytes = new List<byte>();
+                    byte b;
+                    while ((b = reader.ReadByte()) != 0)
+                    {
+                        fileNameBytes.Add(b);
+                    }
+                    return System.Text.Encoding.UTF8.GetString(fileNameBytes.ToArray());
+                }
+            }
+        }
+        return null;
+    }
+
 }