How to use the same stream twice

[snailcatcher]

Hi there,

I try to send the same stream twice via refit. But when the first request is done, Refit just disposes my stream.
Is there a way to prevent the disposal?

My Refit Interface

using Refit;

namespace CK.Kalypso.BinaryStore.VirusScanner.Services;

public interface IExampleApi
{
   [Multipart]
   [Post("/api/scanFile")]
   Task<MyResult> RequestAsync([AliasAs("file")] MultipartItem stream, CancellationToken cancellationToken);
}

public record MyResult(string text);

My Api Call Code

using Refit;

namespace CK.Kalypso.BinaryStore.VirusScanner.Services;

public class ExampleApi
{
   private readonly IExampleApi _exampleApi;
   
   public ExampleApi(IExampleApi exampleApi)
   {
      _exampleApi = exampleApi;
   }
   
   public async Task<MyResult> RequestAsync(Stream stream, string fileName, CancellationToken cancellationToken)
   {
      if (!stream.CanSeek)
         throw new ArgumentException($"{nameof(stream)} must be seekable!");
      stream.Seek(0, SeekOrigin.Begin);

      var result = await _exampleApi.RequestAsync(new StreamPart(stream, fileName), cancellationToken);
     
      if (!stream.CanSeek)
         throw new ArgumentException($"{nameof(stream)} must be seekable!");
      stream.Seek(0, SeekOrigin.Begin); // Here it fails with an Object Disposed Exception

      var result2 = await _exampleApi.RequestAsync(new StreamPart(stream, fileName), cancellationToken);

      return result ?? result2;
   }
}

When the stream was sent once it get disposed and I don't know why, because it forces me to copy it an load all the contents into memory (files up to 200mb are possible).

Thanks for any help!
Sincerely snailcatcher

[snailcatcher]

I fixed this problem for myself. This is what i came up with:

public class KeepStreamAliveStreamDecorator : Stream
{
   private readonly Stream _original;

   public KeepStreamAliveStreamDecorator(Stream original)
   {
      _original = original ?? throw new ArgumentNullException(nameof(original));
   }
   
   public override bool CanRead => _original.CanRead;
   public override bool CanSeek => _original.CanSeek;
   public override bool CanWrite => _original.CanWrite;
   public override long Length => _original.Length;
   public override long Position { get => _original.Position; set { _original.Position = value; } }
   
   public override void Flush() => _original.Flush();
   public override int Read(byte[] buffer, int offset, int count) => _original.Read(buffer, offset, count);
   public override long Seek(long offset, SeekOrigin origin) => _original.Seek(offset, origin);
   public override void SetLength(long value) => _original.SetLength(value);
   public override void Write(byte[] buffer, int offset, int count) => _original.Write(buffer, offset, count);
}

using Refit;

namespace CK.Kalypso.BinaryStore.VirusScanner.Services;

public class ExampleApi
{
   private readonly IExampleApi _exampleApi;
   
   public ExampleApi(IExampleApi exampleApi)
   {
      _exampleApi = exampleApi;
   }
   
   public async Task<MyResult> RequestAsync(Stream stream, string fileName, CancellationToken cancellationToken)
   {
      if (!stream.CanSeek)
         throw new ArgumentException($"{nameof(stream)} must be seekable!");
      stream.Seek(0, SeekOrigin.Begin);

      await using var streamDecorator = new KeepStreamAliveStreamDecorator(stream);
      var result = await _exampleApi.RequestAsync(new StreamPart(streamDecorator, fileName), cancellationToken);
     
      if (!stream.CanSeek)
         throw new ArgumentException($"{nameof(stream)} must be seekable!");
      stream.Seek(0, SeekOrigin.Begin); // Here it fails with an Object Disposed Exception

      var result2 = await _exampleApi.RequestAsync(new StreamPart(stream, fileName), cancellationToken);

      return result ?? result2;
   }
}

I wrap the stream before the first request in a decorator which prevents it from being disposed. So the underlying framework can throw away the decorator instance without touching the Dispose/Close/Whatever of my passed stream.

Sincerely snailcatcher