下载文件请求返回 JSON 而不是服务器上 ASP.NET Web API 中的文件

Question

I'm trying to download CSV file in ASP.NET Web API. Here is my code, and it's working in local.

[Route("{name?}")]
public HttpResponseMessage Get(string name = "DownloadFile")
{
    name = name.EndsWith(".csv") ? name : $"{name}.csv";
    var stream = new MemoryStream();
    var writer = new StreamWriter(stream);
    writer.Write("Hello, World!");
    writer.Flush();
    stream.Position = 0;

    var result = new HttpResponseMessage(HttpStatusCode.OK)
    {
        Content = new ByteArrayContent(stream.ToArray())
    };
    result.Content.Headers.Add("x-filename", name);
    result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
    result.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
    {
        FileName = name
    };
    return result;
}

The file is being downloaded in browser in localhost. I deployed the same code on the server and it's returning a JSON in the browser instead of downloading a file.

JSON looks like this:

{
  "version": {
    "major": 1,
    "minor": 1,
    "build": -1,
    "revision": -1,
    "majorRevision": -1,
    "minorRevision": -1
  },
  "content": {
    "headers": [
      {
        "key": "x-filename",
        "value": [
          "test.csv"
        ]
      },
      {
        "key": "Content-Type",
        "value": [
          "application/octet-stream"
        ]
      },
      {
        "key": "Content-Disposition",
        "value": [
          "attachment; filename=test.csv"
        ]
      }
    ]
  },
  "statusCode": 200,
  "reasonPhrase": "OK",
  "headers": [],
  "requestMessage": null,
  "isSuccessStatusCode": true
}

I've checked mime type in IIS and it's there. Am I missing anything ??

Answer 1

This is what usually works for me

        private ActionResult GetFile(string path, string fileName)
        {
            var memory = new MemoryStream();
            using (var stream = new FileStream(path + fileName, FileMode.Open))
            {
                stream.CopyTo(memory);
            }
            memory.Position = 0;
            var file = File(memory, GetContentType(path + fileName), Path.GetFileName(path + fileName));
            file.FileDownloadName = fileName;
            return file;
        }

        private string GetContentType(string path)
        {
            var types = GetMimeTypes();
            var ext = Path.GetExtension(path).ToLowerInvariant();
            return types[ext];
        }
        //find out what .csv is these won't work for you
        private Dictionary<string, string> GetMimeTypes()
        {
            return new Dictionary<string, string>
            {
                //{".pptx", "application/vnd.openxmlformats-officedocument.presentationml.presentation" }
                //{".docx", "application/vnd.ms-word"}
                //{".pdf", "application/pdf"}
            };
        }

Then for the controller call it like this

public FileResult GeneratePoExportDocument(params)
{

    return GetFile(HostingEnvironment.ApplicationPhysicalPath + "Documents", "\\mydoc.docx");
}

After that it should automatically download the file.

Edit: Fix return type for controller method

Try the mimetypes

application/vnd.ms-excel

or

text/csv

Answer 2

I ran into this similar problem using WebApi which worked fine locally when debugging in Visual Studio and when deployed to IIS locally. On my server, I was getting the JSON response as above. After a fresh deploy I was seeing a new error about missing method:

Method not found: 'System.Net.Http.HttpRequestMessage System.Web.Http.Controllers.HttpActionContext.get_Request()'.

The resolution was to add a new binding redirect. Perhaps this is an effective fix for you.

  <dependentAssembly>
    <assemblyIdentity name="System.Net.Http" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
    <bindingRedirect oldVersion="0.0.0.0-4.0.0.0" newVersion="4.2.0.0" />
  </dependentAssembly>

Answer 3

I faced the similar issue and answer here to another SO question helped me with it.

Apparently it was the conflicts in System.Net.Http assemblies causing the HttpResponse to behave abnormally. I uninstalled the System.Net.Http nuget package and installed it back. And then I checked in Binding Redirects generated in the web.config .