Web API 返回文件, 参见http://stackoverflow.com/questions/9541351/returning-binary-file-from-controller-in-asp-net-web-api

FileController.cs

public HttpResponseMessage Post(string version, string environment, string filetype)
{
    var path = @"C:\Temp\test.exe";
    HttpResponseMessage 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;
}