Web API download locks file

Question

I'm having a small issue with a WebAPI method that downloads a file when the user calls the route of the method.

The method itself is rather simple:

public HttpResponseMessage Download(string fileId, string extension)
{
    var location = ConfigurationManager.AppSettings["FilesDownloadLocation"];
    var path = HttpContext.Current.Server.MapPath(location) + fileId + "." + extension;

    var result = new HttpResponseMessage(HttpStatusCode.OK);
    var stream = new FileStream(path, FileMode.Open);
    result.Content = new StreamContent(stream);
    result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
    return result;
}

The method works as expected - the first time I call it. The file is transmitted and my browser starts downloading the file.

However - if I call the same URL again from either my own computer or from any other - I get an error saying:

The process cannot access the file 'D:\...\App_Data\pdfs\test-file.pdf' because it is being used by another process.

This error persists for about a minute - and then I can download the file again - but only once - and then I have to wait another minute or so until the file is unlocked.

Please note that my files are rather large (100-800 MB).

Am I missing something in my method? It almost seems like the stream locks the file for some time or something like that?

Thanks :)

Answer 1

It is because your file is locked by the first stream, you must specify a FileShare that allow it to be opened by multiple streams :

public HttpResponseMessage Download(string fileId, string extension)
{
    var location = ConfigurationManager.AppSettings["FilesDownloadLocation"];
    var path = HttpContext.Current.Server.MapPath(location) + fileId + "." + extension;

    var result = new HttpResponseMessage(HttpStatusCode.OK);
    var stream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read);
    result.Content = new StreamContent(stream);
    result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
    return result;
}

Like that you allow multiple stream to open this file for read only.

See the MSDN documentation on that constructor overload.