Download a file through API controller of Word365 addin

Question

I'm developing a Word 365 addin. The diagram above shows one of a functional flow.

Step 1 - User will click on a ribbon bar button in addin and javascript will call .NET web API controller with relevant details(file id)

Step 2 - controller will send a GET request to outside REST API to fetch file data

Step 3 - controller will have file data response (byte array)

Strp 4 - need to create a file and download it to the client machine. If possible, need to open file browser in client machine to choose a folder to download

So, I'm having problems with downloading the file to the client machine. How to download the file created inside API controller to client machine?

Answer 1

I tried these codes in winform as your addin client:

private void button1_Click(object sender, EventArgs e)
        {
            OpenFileDialog ofd = new OpenFileDialog();
            if (ofd.ShowDialog() == DialogResult.OK)
            {
                string filePath = ofd.FileName;
                var filecontent = new ByteArrayContent(File.ReadAllBytes(filePath));
                var httpclient = new HttpClient();
                var requestContent = new MultipartFormDataContent();
                requestContent.Add(filecontent, "file","x.txt");
                var response = httpclient.PostAsync("https://localhost:44353/WeatherForecast", requestContent).Result;
               

                //Get the filecontent
                var responsebody = response.Content.ReadAsStringAsync().Result;
                byte[] array = Encoding.UTF8.GetBytes(responsebody);
                //Savefiledialog
                SaveFileDialog sfd = new SaveFileDialog();
                //Set file types
                sfd.Filter = "DOC?*.doc?|*.doc|Txt?*.txt?|*.txt";
                sfd.FilterIndex = 1;
                //Set the last path
                sfd.RestoreDirectory = true;
                //Set default filename
                sfd.FileName = "Hellow2";
                if (sfd.ShowDialog() == DialogResult.OK)
                {
                    //Get the filepath you selected
                    string localFilePath = sfd.FileName.ToString();
                    //Get the filename withoutpath
                    string fileNameExt = localFilePath.Substring(localFilePath.LastIndexOf("\\") + 1);
                    //Save file
                    FileStream fs;
                    if (System.IO.File.Exists(localFilePath))
                    {
                        fs = new FileStream(localFilePath, FileMode.Truncate);
                    }
                    else
                    {
                        fs = new FileStream(localFilePath, FileMode.CreateNew);
                    }
                    var br = new BinaryWriter(fs);
                    br.Write(array, 0, array.Length);
                    br.Close();
                    fs.Close();
                }
            }
        }

The codes in webapi:

[HttpPost]
        public FileResult txt([FromForm]IFormFile file)
        {
            var stream=file.OpenReadStream();
            byte[] bytes = new byte[stream.Length];
            stream.Read(bytes, 0, bytes.Length);
            stream.Seek(0, SeekOrigin.Begin);
            byte[] filecontent = bytes;
            return File(filecontent, "text/plain");
        }

The codes need more logical codes to be accomplished . also,with different file types, some other packages are required(for example, npoi for office). the length of filecontent was not considered as well.