In-Memory FileStream

In my current project, I wanted to ‘fake out’ the filesystem for integration tests. In several places in my code, I would first write some data to a temporary file, then later, open the file again for background processing. Now my integration tests run fine using the real filesystem, but just to make sure my tests could run in parallel, I wanted to switch to a faked filesystem.

So, my first attempt used memory streams. But then I found a crucial difference between filestreams and memorystreams. If you dispose a filestream.. the actual file is still there! Not so much with a memorystream.

So here’s an in memory filestream. If you close / dispose it.. it will still be there. Note.. it will only be cleaned up by the garbage collector. So don’t hang on to them in definetly and don’t use this in production.

   1: public class InMemoryFileStream : Stream

   2: {

   3:     private MemoryStream _memoryStream = new MemoryStream();

   4:  

   5:  

   6:     public override void Flush()

   7:     {

   8:         _memoryStream.Flush();

   9:     }

  10:  

  11:     public override long Seek(long offset, SeekOrigin origin)

  12:     {

  13:         return _memoryStream.Seek(offset, origin);

  14:     }

  15:  

  16:     public override void SetLength(long value)

  17:     {

  18:         _memoryStream.SetLength(value);

  19:     }

  20:  

  21:     public override int Read(byte[] buffer, int offset, int count)

  22:     {

  23:         return _memoryStream.Read(buffer, offset, count);

  24:     }

  25:  

  26:     public override void Write(byte[] buffer, int offset, int count)

  27:     {

  28:         _memoryStream.Write(buffer, offset, count);

  29:     }

  30:  

  31:     public override bool CanRead

  32:     {

  33:         get { return _memoryStream.CanRead; }

  34:     }

  35:  

  36:     public override bool CanSeek

  37:     {

  38:         get { return _memoryStream.CanSeek; }

  39:     }

  40:  

  41:     public override bool CanWrite

  42:     {

  43:         get { return _memoryStream.CanWrite; }

  44:     }

  45:  

  46:     public override long Length

  47:     {

  48:         get { return _memoryStream.Length; }

  49:     }

  50:  

  51:     public override long Position

  52:     {

  53:         get { return _memoryStream.Position; }

  54:         set { _memoryStream.Position = value; }

  55:     }

  56:  

  57:     protected override void Dispose(bool disposing)

  58:     {

  59:         if (disposing)

  60:         {

  61:             _memoryStream.Position = 0;

  62:             base.Dispose(disposing);

  63:         }

  64:     }

  65: }