How do I write an image's MemoryStream to the page body? - asp.net

Question

I'm converting ASP.NET WebForms code to ASP.NET Core Razor pages which is new to me. I'm trying to retrieve an image MemoryStream from a business class (based on SixLabors awesome ImageSharp) and have the page render the JPEG -- no HTML, just the image. I intend to use this page elsewhere as an <img> src, like <img src="Render?imageID=42&mode=invert" />
In Render.cshtml.cs:
public class RenderModel : PageModel
{
public void OnGet()
{
//snip
Stream stream = new MemoryStream();
using (Image image1 = Image.Load(imagePath))
{
SixLabors.ImageSharp.Formats.Jpeg.JpegEncoder encoder = new SixLabors.ImageSharp.Formats.Jpeg.JpegEncoder();
encoder.Quality = 75;
image1.Save(stream, encoder);
//image.Save("/temp/xxx.jpg", encoder); //test to see image. it works
}
Response.Clear();
//Response.Headers.ContentLength = stream.Length;
Response.ContentType = "image/jpeg";
Response.Body = stream;
}
}
...but this is not working, I get:
System.InvalidOperationException: Response Content-Length mismatch: too few bytes written (0 of 135408).
135408 is the stream.Length.
I'm probably not doing this correctly in the ASP.NET Core/Razor way. Can anyone set me straight as to how to do this? Thanks!
EDIT: commenting out the Headers.ContentLength fixes the error. But now I get a broken-image icon in the browser. Closer...

Answer 1

You need to write to the Response.Body isntead of replacing it.
stream.Seek(0, SeekOrigin.Begin);
await stream.CopyToAsync(Response.Body);
await Response.Body.FlushAsync();

Answer 2

I think Razor pages are intented to return html content.
However it seems to be possible to return different types of result in OnGet e.g. you could return a new FileContentReset (FileStreamResult seems to have issues with contentlength)
// read as bytes
public FileContentResult OnGet()
{
var image = System.IO.File.ReadAllBytes(#"c:\temp\myimage.jpeg");
return new FileContentResult(image.ToArray(), "image/jpeg");
}
// example if image comes from stream
public FileContentResult OnGet()
{
using var imageStr = System.IO.File.Open(#"c:\temp\myimage.jpeg", FileMode.Open);
using var memStr = new MemoryStream();
imageStr.CopyTo(memStr);
return new FileContentResult(memStr.ToArray(), "image/jpeg");
}
Even better maybe it to not use a Razor page and to add a MVC controller to return the result.