Calling OpenReadStream of an IFormFile multiple times-CodePudding

I need to have the stream of the file in 2 different locations. In the code the IFormFile is already passed as parameter in the 2 methods. I thought of either modifying the methods and calling the OpenReadStream in the beginning and pass the stream as param or calling OpenReadStream separately.

I inspected the dissasembled code and OpenReadStream does this:

return new ReferenceReadStream(_baseStream, _baseStreamOffset, Length);

and the ReferenceReadStream class does this in the constructor:

public ReferenceReadStream(Stream inner, long offset, long length)
{
    if (inner == null)
    {
        throw new ArgumentNullException("inner");
    }
    _inner = inner;
    _innerOffset = offset;
    _length = length;
    _inner.Position = offset;
}

In my understanding the base stream is the same and it doesn't matter calling OpenReadStream multiple times.

What worries me is if I'll run into problems when I start using Seek method.

Does anyone know what's the correct usage of OpenReadStream in this senario?

CodePudding user response：

Apparently it's not safe to call OpenReadStream multiple times.

When Read method is called, it calls this method:

private void VerifyPosition()
    {
        if (_inner.Position == _innerOffset   _position)
        {
            return;
        }
        throw new InvalidOperationException("The inner stream position has changed unexpectedly.");
    }

I was able to trigger this exception with the following code:

var s = file.OpenReadStream();
s.Seek(10, SeekOrigin.Begin);
var b = new byte[2];
var c = s.Read(b);
var s2 = file.OpenReadStream();
c = s.Read(b);