.NET Core Framework

File Upload

The following code example illustrates how to handle file upload on your server using .Net Core Framework as a server-side language. For step by step explanation of the upload flow see file upload concept.

Frontend

The main index page.

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <!-- Include Editor style. -->
  <link href="https://cdn.jsdelivr.net/npm/froala-editor@3.0.0-beta.1/css/froala_editor.pkgd.min.css" rel="stylesheet" type="text/css" />
</head>

<body>
  <!-- Include Editor JS files. -->
  <script type="text/javascript" src="https://cdn.jsdelivr.net/npm/froala-editor@3.0.0-beta.1//js/froala_editor.pkgd.min.js"></script>

  <div class="sample">
    <h2>File upload example.</h2>
    <form>
      <textarea id="edit" name="content"></textarea>
    </form>
  </div>

  <!-- Initialize the editor. -->
  <script>
    new FroalaEditor('#edit', {
      // Set the file upload URL.
      fileUploadURL: '/UploadFiles',

      fileUploadParams: {
        id: 'my_editor'
      }
    })
  </script>
</body>
</html>

Backend

HomeController.cs file is the default controller that will be used in this example to define the upload part. The uploads directory will be automatically created if it does not exist under wwwroot/upload/. The root directory must be write available otherwise the upload directory will not be created.

The HomeController will manage the request and the upload part, so you should define the following functions in this file. After processing the uploaded file, if it passes the validation, the server will respond with a JSON object containing a link to the uploaded file.

E.g.: {"link":"http://server_address/upload/name_of_file"}.

public class HomeController : Controller
{
  private readonly IHostingEnvironment _hostingEnvironment;

  public HomeController(IHostingEnvironment hostingEnvironment)
  {
   _hostingEnvironment = hostingEnvironment;
  }

  [HttpPost("UploadFiles")]
  [Produces("application/json")]
  public async Task<IActionResult> Post(List<IFormFile> files)
  {
    // Get the file from the POST request
    var theFile = HttpContext.Request.Form.Files.GetFile("file");

    // Get the server path, wwwroot
    string webRootPath = _hostingEnvironment.WebRootPath;

    // Building the path to the uploads directory
    var fileRoute = Path.Combine(webRootPath, "uploads");

    // Get the mime type
    var mimeType = HttpContext.Request.Form.Files.GetFile("file").ContentType;

    // Get File Extension
    string extension = System.IO.Path.GetExtension(theFile.FileName);

    // Generate Random name.
    string name = Guid.NewGuid().ToString().Substring(0, 8) + extension;

    // Build the full path inclunding the file name
    string link = Path.Combine(fileRoute, name);

    // Create directory if it dose not exist.
    FileInfo dir = new FileInfo(fileRoute);
    dir.Directory.Create();

    // Basic validation on mime types and file extension
    string[] fileMimetypes = { "text/plain", "application/msword", "application/x-pdf", "application/pdf", "application/json","text/html" };
    string[] fileExt = { ".txt", ".pdf", ".doc",".json",".html"};

    try
    {
      if (Array.IndexOf(fileMimetypes, mimeType) >= 0 && (Array.IndexOf(fileExt, extension) >= 0))
      {
        // Copy contents to memory stream.
        Stream stream;
        stream = new MemoryStream();
        theFile.CopyTo(stream);
        stream.Position = 0;
        String serverPath = link;

        // Save the file
        using (FileStream writerFileStream = System.IO.File.Create(serverPath))
        {
          await stream.CopyToAsync(writerFileStream);
          writerFileStream.Dispose();
        }

        // Return the file path as json
        Hashtable fileUrl = new Hashtable();
        fileUrl.Add("link", "/uploads/" + name);

        return Json(fileUrl);
      }
      throw new ArgumentException("The file did not pass the validation");
    }

    catch (ArgumentException ex)
    {
      return Json(ex.Message);
    }
  }
}