return data progressively from ServiceStack API

Question

Currently my app returns data by MemoryStream, the problem is the size of data could be large than 500MB, and that takes up much memory before return.

I am seeking for a way to return the data progressively. For example, flush the output for every 1MB.

First I tried IPartialWriter

public class ViewRenderResult : IPartialWriter
{
    public void WritePartialTo(IResponse response)
    {
        response.Write("XXX");

    }

    public bool IsPartialRequest { get { return true; } }
}

response.Write can only be called for one time.

Then I found IStreamWriter

public interface IStreamWriter
{
    void WriteTo(Stream responseStream);
}

I doubt it caches all data before returining.

Please can anyone clarify it?

score 2 · Accepted Answer · edited May 23 '17 at 10:24

This previous answer shows different response types ServiceStack supports, e.g. you can just return a Stream or write to the base.Response.OutputStream directly from within your Service.

These ImageServices also shows the different ways you can write a binary response like an Image to the response stream, e.g. here's an example of using a custom IStreamWriter which lets you control how to write to the Response OutputStream:

//Your own Custom Result, writes directly to response stream
public class ImageResult : IDisposable, IStreamWriter, IHasOptions
{
    private readonly Image image;
    private readonly ImageFormat imgFormat;

    public ImageResult(Image image, ImageFormat imgFormat = null)
    {
        this.image = image;
        this.imgFormat = imgFormat ?? ImageFormat.Png;
        this.Options = new Dictionary<string, string> {
            { HttpHeaders.ContentType, this.imgFormat.ToImageMimeType() }
        };
    }

    public void WriteTo(Stream responseStream)
    {
        using (var ms = new MemoryStream())
        {
            image.Save(ms, imgFormat);
            ms.WriteTo(responseStream);
        } 
    }

    public void Dispose()
    {
        this.image.Dispose();
    }

    public IDictionary<string, string> Options { get; set; }
}

Which you can return in your Service with:

public object Any(ImageAsCustomResult request)
{
    var image = new Bitmap(100, 100);
    using (var g = Graphics.FromImage(image))
    {
        g.Clear(request.Format.ToImageColor());

        return new ImageResult(image, request.Format.ToImageFormat()); 
    }
}

return data progressively from ServiceStack API

1 Answers1