Web Api - How to detect when a response has finished being sent - asp.net

Question

In a web api method I am generating a file and then streaming it to the response like so
public async Task<HttpResponseMessage> GetFile() {
FileInfo file = generateFile();
var msg = Request.CreateResponse(HttpStatusCode.OK);
msg.Content = new StreamContent(file.OpenRead());
msg.Content.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");
msg.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment") {FileName = file.Name};
return msg;
}
because this a generated file I want to delete it after the response has finished streaming but I can't seem to find a hook in the pipeline for this.
I suppose that I can put a reference to the file in a static and set up a custom MessageHandler that pulls values out of this same static variable and deletes. However, this seems like it can't possibly be right both because of the use of a static (when this should all be per-request) and because I'd have to register a separate route.
I've seen this question but it seems to not really have much of a useful response.

Answer 1

Nice scenario!...the problem with using message handlers is that response writing happens at the host layers and below message handlers layer, so they are not ideal...
Following is an example of how you could do it:
msg.Content = new CustomStreamContent(generatedFilePath);
public class CustomStreamContent : StreamContent
{
string filePath;
public CustomStreamContent(string filePath)
: this(File.OpenRead(filePath))
{
this.filePath = filePath;
}
private CustomStreamContent(Stream fileStream)
: base(content: fileStream)
{
}
protected override void Dispose(bool disposing)
{
//close the file stream
base.Dispose(disposing);
try
{
File.Delete(this.filePath);
}
catch (Exception ex)
{
//log this exception somewhere so that you know something bad happened
}
}
}
By the way, are you generating this file because you are converting some data into PDF. If yes, then I think you could use PushStreamContent for this purpose by directly writing the converted data into the response stream. This way you need not generate a file first and then worry about deleting it later.

Answer 2

We performed same action in WebAPI. I needed to delete file just after it downloaded form server.
We can create custom response message class. It takes file path as parameter and delete it once its transmitted.
public class FileResponseMessage : HttpResponseMessage
{
private readonly string _filePath;
public FileHttpResponseMessage(string filePath)
{
this._filePath= filePath;
}
protected override void Dispose(bool disposing)
{
base.Dispose(disposing);
Content.Dispose();
File.Delete(_filePath);
}
}
Use this class as below code and it will delete your file once it will be written on response stream.
var response = new FileResponseMessage(filePath);
response.StatusCode = HttpStatusCode.OK;
response.Content = new StreamContent(new FileStream(filePath, FileMode.Open, FileAccess.Read));
response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
{
FileName = "MyReport.pdf"
};
return response;