Not Receiving Data from Route C#

Question

I'm attempting to return an image from a server route, but I'm getting one that is 0 bytes. I suspect it has something to do with how I'm using the MemoryStream. Here's my code:

[HttpGet]
[Route("edit")]
public async Task<HttpResponseMessage> Edit(int pdfFileId)
{
    var pdf = await PdfFileModel.PdfDbOps.QueryAsync((p => p.Id == pdfFileId));

    IEnumerable<Image> pdfPagesAsImages = PdfOperations.PdfToImages(pdf.Data, 500);
    MemoryStream imageMemoryStream = new MemoryStream();
    pdfPagesAsImages.First().Save(imageMemoryStream, ImageFormat.Png);

    HttpResponseMessage response = new HttpResponseMessage();
    response.Content = new StreamContent(imageMemoryStream);
    response.Content.Headers.ContentType = new MediaTypeHeaderValue("image/png");
    response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
    {
        FileName = pdf.Filename,
        DispositionType = "attachment"
    };
    return response;
}

Through debugging I have verified that the PdfToImages method is working and that imageMemoryStream gets filled with data from the line

pdfPagesAsImages.First().Save(imageMemoryStream, ImageFormat.Png);

However in running it, I receive an attachment that is properly named but is 0 bytes. What do I need to change in order to receive the whole file? I think it's something simple but I'm not sure what. Thanks in advance.

Bloodshed

Maybe you have to set stream position to 0? imageMemoryStream.Position = 0; – Claybourne

Answer 1

After writing to the MemoryStream, Flush it then set Position to 0:

imageMemoryStream.Flush();
imageMemoryStream.Position = 0;

Claybourne

Answer 2

You should rewind MemoryStream to beginning before passing it to response. But you'd better use PushStreamContent:

HttpResponseMessage response = new HttpResponseMessage();
response.Content = new PushStreamContent(async (stream, content, context) => 
  {
    var pdf = await PdfFileModel.PdfDbOps.QueryAsync(p => p.Id == pdfFileId);
    content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
    {
      FileName = pdf.Filename,
      DispositionType = "attachment"
    };

    PdfOperations.PdfToImages(pdf.Data, 500).First().Save(stream, ImageFormat.Png);
  }, "image/png");
return response;

Claus

What's the warrant for using PushStreamContent? – Bloodshed

No need to allocate extra memory for MemoryStream. – Claus

In testing your code it comes through inline, not as an attachment. Any ideas as to why? – Bloodshed

Also it seems to hang, with a spinning wheel in the tab header. – Bloodshed

As to content-disposition - check via http capture which headers are sent. About "hanging" - can't really tell without debugging. – Claus