Access FastImage once it is fetched from url and convert to base64 in react native

Question

I have standard fastimage code:

<FastImage
    source={{
        uri: imageUrl,
        priority: FastImage.priority.normal,
    }}
/>

The issue I am having is that I need to convert this image to base64. I cannot figure how to access the image file once it is fetched from the server without fetching from the server a second time, which I don't want to do.