Optimaze SeekAsync to seek directly.

Author: pluskal

Kaitai.Struct.Runtime.Async/KaitaiPipeReaderAsyncStream.cs

@@ -19,10 +19,11 @@ public class KaitaiPipeReaderAsyncStream : KaitaiStreamBase, IKaitaiAsyncStream
 
     public PipeReader PipeReader { get; }
     public ReadResult ReadResult { get; set; }
+    private long RemainingBytesInReadResult => ReadResult.Buffer.Length - _pos;
 
-    #region Constructors
+        #region Constructors
 
-    public KaitaiPipeReaderAsyncStream(PipeReader pipeReader)
+        public KaitaiPipeReaderAsyncStream(PipeReader pipeReader)
     {
       PipeReader = pipeReader;
       //AsyncBinaryReader = new AsyncBinaryReader(BaseStream);
@@ -75,7 +76,22 @@ public virtual async Task SeekAsync(long position)
       }
       else
       {
-        await ReadBytesAsync(position - _pos); //TODO Optimize
+        while (true)
+        {
+          if (ReadResult.IsCompleted)
+          {
+            throw new EndOfStreamException(
+              $"requested {position} bytes, but got only {RemainingBytesInReadResult} bytes");
+          }
+
+          PipeReader.AdvanceTo(ReadResult.Buffer.Start, ReadResult.Buffer.GetPosition(Pos));
+          ReadResult = await PipeReader.ReadAsync();
+          if (ReadResult.Buffer.Length >= position)
+          {
+            _pos = position;
+            return;
+          }
+        }
       }
     }
 
@@ -274,7 +290,7 @@ public async Task<byte[]> ReadBytesAsync(long count)
         if (ReadResult.IsCompleted)
         {
           throw new EndOfStreamException(
-            $"requested {count} bytes, but got only {CountRemainingBytesInReadResult()} bytes");
+            $"requested {count} bytes, but got only {RemainingBytesInReadResult} bytes");
         }
 
         PipeReader.AdvanceTo(ReadResult.Buffer.Start, ReadResult.Buffer.GetPosition(Pos));
@@ -286,7 +302,7 @@ public async Task<byte[]> ReadBytesAsync(long count)
 
       bool TryRead(out byte[] readBytes, long readBytesCount)
       {
-        if (CountRemainingBytesInReadResult() < readBytesCount)
+        if (RemainingBytesInReadResult < readBytesCount)
         {
           readBytes = null;
           return false;
@@ -295,8 +311,6 @@ bool TryRead(out byte[] readBytes, long readBytesCount)
         readBytes = ReadResult.Buffer.Slice(_pos, readBytesCount).ToArray();
         return true;
       }
-
-      long CountRemainingBytesInReadResult() => ReadResult.Buffer.Length - _pos;
     }
 
     public async Task<byte[]> ReadBytesAsync(ulong count)