为什么Web Api HttpResponseMessage没有下载文件？(Why Web Api HttpResponseMessage not download the file?)

 我目前正在对Web Api方法进行GET ，并将文件名作为参数传递。 当我到达方法时，我的参数被正确解析，文件内容正在写入HttpResponseMessage对象中的响应内容。 
 
    public HttpResponseMessage Get ([FromUri]string filen)
    {
        string downloadPath = WebConfigurationManager.AppSettings["DownloadLocation"];

        var fileName = string.Format("{0}{1}", downloadPath, filen);
        var response = Request.CreateResponse();

        if (!File.Exists(fileName))
        {
            response.StatusCode = HttpStatusCode.NotFound;
            response.ReasonPhrase = string.Format("The file [{0}] does not exist.", filen);

            throw new HttpResponseException(response);
        }

        response.Content = new PushStreamContent(async (outputStream, httpContent, transportContext) =>
        {
            try
            {
                var buffer = new byte[65536];

                using (var file = File.Open(fileName, FileMode.Open, FileAccess.Read))
                {
                    var length = (int)file.Length;
                    var bytesRead = 1;

                    while (length > 0 && bytesRead > 0)
                    {
                        bytesRead = file.Read(buffer, 0, Math.Min(length, buffer.Length));
                        await outputStream.WriteAsync(buffer, 0, bytesRead);
                        length -= bytesRead;
                    }
                }

            }
            finally
            {
                outputStream.Close();
            }

        });

        response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
        response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
        {
            FileName = filen
        };

        return response;
    }
 
 似乎没有任何事情发生，而不是看到文件被下载。 似乎文件在任何地方都丢失了。 我想让浏览器自动下载该文件。 我确实在fiddler中看到了响应中的内容。 所以发生了什么事？ 任何指针将不胜感激！ 
 
HTTP/1.1 200 OK
Cache-Control: no-cache
Pragma: no-cache
Transfer-Encoding: chunked
Content-Type: application/octet-stream
Expires: -1
Server: Microsoft-IIS/8.0
Content-Disposition: attachment; filename=w-brand.png
X-AspNet-Version: 4.0.30319
X-SourceFiles: =?UTF-8?B?RDpcSnVubGlcQXN5bmNGaWxlVXBsb2FkV2ViQVBJRGVtb1xBc3luY0ZpbGVVcGxvYWRXZWJBUElEZW1vXGFwaVxGaWxlRG93bmxvYWQ=?=
X-Powered-By: ASP.NET
Date: Thu, 12 Feb 2015 19:32:33 GMT
27b5
PNG
...

I am currently doing a GET to a Web Api method and am passing the file name as parameter. When I get to the method, my parameters are resolved properly, and the file content is writing to the response content in the HttpResponseMessage object. 
 
    public HttpResponseMessage Get ([FromUri]string filen)
    {
        string downloadPath = WebConfigurationManager.AppSettings["DownloadLocation"];

        var fileName = string.Format("{0}{1}", downloadPath, filen);
        var response = Request.CreateResponse();

        if (!File.Exists(fileName))
        {
            response.StatusCode = HttpStatusCode.NotFound;
            response.ReasonPhrase = string.Format("The file [{0}] does not exist.", filen);

            throw new HttpResponseException(response);
        }

        response.Content = new PushStreamContent(async (outputStream, httpContent, transportContext) =>
        {
            try
            {
                var buffer = new byte[65536];

                using (var file = File.Open(fileName, FileMode.Open, FileAccess.Read))
                {
                    var length = (int)file.Length;
                    var bytesRead = 1;

                    while (length > 0 && bytesRead > 0)
                    {
                        bytesRead = file.Read(buffer, 0, Math.Min(length, buffer.Length));
                        await outputStream.WriteAsync(buffer, 0, bytesRead);
                        length -= bytesRead;
                    }
                }

            }
            finally
            {
                outputStream.Close();
            }

        });

        response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
        response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
        {
            FileName = filen
        };

        return response;
    }
 
Instead of seeing the file being downloaded, nothing seems to happen. It seems the file just get lost anywhere. I would like to have the browser to auto download the file. I do see the content in the response in fiddler. So what happened? Any pointers would be appreciated!
 
HTTP/1.1 200 OK
Cache-Control: no-cache
Pragma: no-cache
Transfer-Encoding: chunked
Content-Type: application/octet-stream
Expires: -1
Server: Microsoft-IIS/8.0
Content-Disposition: attachment; filename=w-brand.png
X-AspNet-Version: 4.0.30319
X-SourceFiles: =?UTF-8?B?RDpcSnVubGlcQXN5bmNGaWxlVXBsb2FkV2ViQVBJRGVtb1xBc3luY0ZpbGVVcGxvYWRXZWJBUElEZW1vXGFwaVxGaWxlRG93bmxvYWQ=?=
X-Powered-By: ASP.NET
Date: Thu, 12 Feb 2015 19:32:33 GMT
27b5
PNG
...

原文：https://stackoverflow.com/questions/28486579