Prevent IDM from downloading automatically in web api

Change the mime type to application/octet-stream as a way to work around your problem. Make sure that the file name includes a proper file extension so that it can be recognized by the client system once downloaded.

Another issue is the attachment disposition of the content which typically forces it to save it as a file download. Change it to inline so that the client can consume it without IDM trying to download it as an attachment.

var stream = new FileStream(path, FileMode.Open, FileAccess.Read);var content new StreamContent(stream);content.Headers.ContentDisposition = new ContentDispositionHeaderValue("inline");content.Headers.ContentDisposition.FileName = fileName;content.Headers.ContentType = MediaTypeHeaderValue.Parse("application/octet-stream");var response = Request.CreateResponse(HttpStatusCode.OK);response.Content = content;return response;

I have try to use HttpResponseMessage.

If I use ContentDisposition is inline then response break the file. If use attachment then IDM can detect it.

At the end of the day, I found Accept-Ranges header can make download without IDM but it not valid in HttpResponseMessage.

You can try out my code below to make download file without IDM:

[HttpGet][Route("~/download/{filename}")]public void Download(string filename){    // TODO lookup file path by {filename}    // If you want to have "." in {filename} you need enable in webconfig    string filePath = "<path>"; // your file path here    byte[] fileBytes = File.ReadAllBytes(filePath);    HttpContext.Current.Response.Clear();    HttpContext.Current.Response.AddHeader("Accept-Ranges", "bytes");    HttpContext.Current.Response.ContentType = "application/octet-stream";    HttpContext.Current.Response.AddHeader("ContentDisposition", "attachment, filename=" + filename);    HttpContext.Current.Response.BinaryWrite(fileBytes);    HttpContext.Current.Response.End();}

Note: filename parameter serve for download file name so you can config in webconfig if you want to have file extension (disabled by default).