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How to use SignalR to handle large file uploads, providing a better end-user experience



Large file uploads are a common requirement in web applications today, and handling them efficiently can greatly enhance the user experience. Traditional file upload mechanisms can be slow and prone to timeouts, leading to frustration for users. SignalR, a real-time communication library in ASP.NET, can be a game-changer in addressing this issue. In this article, we’ll explore how to leverage SignalR for handling large file uploads in ASP.NET MVC/C# projects or WebAPI, providing a seamless and responsive user experience.

Why SignalR?

SignalR is a technology that enables real-time communication between the server and connected clients. Its ability to push updates from the server to the client makes it an ideal choice for handling large file uploads. With SignalR, you can provide real-time progress updates to users, enhance error handling, and even allow users to cancel uploads if needed.

Setting up SignalR

First, ensure that you have SignalR installed in your project. You can use NuGet Package Manager to add the SignalR library to your project.

Install-Package Microsoft.AspNet.SignalR

Next, create a SignalR hub that will handle the file uploads. Here’s a basic example:

using Microsoft.AspNet.SignalR;

public class FileUploadHub : Hub
    public void UploadFile(string fileName, byte[] fileData)
        // Handle the file upload logic here
        // You can send progress updates to clients using Clients.Caller or Clients.All

Client-Side Implementation

On the client-side, you’ll need JavaScript to interact with the SignalR hub. Here’s a simple example using jQuery:

// Connect to the SignalR hub
var fileUploadHub = $.connection.fileUploadHub;

// Start the SignalR hub connection
$.connection.hub.start().done(function () {
    // Handle file input change event
    $('#fileInput').on('change', function () {
        var file = this.files[0];
        var reader = new FileReader();
        reader.onload = function () {
            var fileData = new Uint8Array(reader.result);
            // Call the hub method to upload the file
            fileUploadHub.server.uploadFile(, fileData);

Handling Large File Uploads

To handle large file uploads efficiently, you can implement chunked uploading. Break the large file into smaller chunks on the client-side and send them to the server using SignalR. On the server-side, reassemble the chunks into the original file.


Using SignalR to handle large file uploads in ASP.NET MVC/C# projects or WebAPI can greatly improve the end-user experience. Real-time progress updates, error handling, and the ability to cancel uploads make for a smoother and more responsive file upload process. With SignalR, you can provide a more enjoyable user experience, even when dealing with large files.

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Anthony Liu

Anthony is a lead technical consultant who is a full-stack developer but loves front-end technologies. Starting from the days of jQuery and Forms, he’s grown and developed with the newest front-end and back-end technologies.

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