Merge branch '10-forward-pipereader-seekasync-on-completed-readresult-ends-with-exception' into 'master'

Resolve "Forward PipeReader.SeekAsync on completed ReadResult ends with exception"

Closes kaitai-io#10

See merge request marta/kaitai_struct_csharp_runtime!20

Author: pluskal

Kaitai.Struct.Runtime.Async.Tests/KaitaiAsyncStreamBaseTests.cs

@@ -1,6 +1,7 @@
 using System;
 using System.IO;
 using System.IO.Pipelines;
+using System.Threading;
 using System.Threading.Tasks;
 using Kaitai.Async;
 using Xunit;
@@ -115,6 +116,24 @@ await EvaluateMaybeCancelled(async () =>
       });
     }
 
+    [Fact]
+    public async Task ForwardSeek_AfterReadToEndAndBackwardSeek_Test()
+    {
+        const int toRead = 1;
+
+      var kaitaiStreamSUT = Create(new byte[2]);
+
+      await EvaluateMaybeCancelled(async () =>
+      { 
+        // Simulates kaitai compiler generated code for multiple fields defined as `instances`
+        await kaitaiStreamSUT.ReadBytesFullAsync(CancellationToken.None);
+        await kaitaiStreamSUT.SeekAsync(0);
+        await kaitaiStreamSUT.SeekAsync(toRead);
+
+        Assert.Equal(toRead, kaitaiStreamSUT.Pos);
+      });
+    }
+
     [Theory]
     [InlineData(0)]
     [InlineData(1)]

Kaitai.Struct.Runtime.Async/ReaderContext/PipeReaderContext.cs

@@ -58,7 +58,7 @@ public virtual async ValueTask SeekAsync(long position, CancellationToken cancel
           ReadResult = await PipeReader.ReadAsync(cancellationToken);
         }
 
-        if (ReadResult.Buffer.Length <= position)
+        if (ReadResult.Buffer.Length >= position)
         {
           Position = position;
           return;