Fast, cross-platform and reliable multipart downloader with asynchronous progress events for .NET applications.
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🚀 Fast, cross-platform and reliable multipart downloader with .Net Core supporting 🚀

Downloader is a modern, fluent, asynchronous, testable and portable library for .NET. This is a multipart downloader with asynchronous progress events. This library can added in your .Net Core v2 and later or .Net Framework v4.5 or later projects.

Downloader is compatible with .NET Standard 2.0 and above, running on Windows, Linux, and macOS, in full .NET Framework or .NET Core.

For a complete example see Downloader.Sample project from this repository.

Sample Console Application


Features at a glance

  • Simple interface to make download request.
  • Download files async and non-blocking.
  • Download any type of files like image, video, pdf, apk and etc.
  • Cross-platform library to download any files with any size.
  • Get real-time progress info of each block.
  • Download file multipart as parallel.
  • Handle all the client-side and server-side exceptions non-stopping.
  • Config your ChunkCount to define the parts count of the download file.
  • Download file multipart as in-memory or on-disk mode.
  • Chunks are saved in parallel on the final file and not on the temp files.
  • The file size is pre-allocated before the download starts.
  • Store download package object to resume the download when you want.
  • Get download speed or progress percentage in each progress event.
  • Get download progress events per chunk downloads.
  • Fast Pause and Resume downloads asynchronously.
  • Stop and Resume downloads whenever you want with the package object.
  • Supports large file download.
  • Set a dynamic speed limit on downloads (changeable speed limitation on the go).
  • Download files without storing on disk and get a memory stream for each downloaded file.
  • Serializable download package (to/from JSON or Binary)
  • Live streaming support, suitable for playing music at the same time as downloading.
  • Ability to download just a certain range of bytes of a large file.
  • Code is tiny, fast and does not depend on external libraries.
  • Control the amount of system memroy (RAM) that the Downloader consumes during downloading.

Installing via NuGet

PM> Install-Package Downloader

Installing via the .NET Core command line interface

dotnet add package Downloader

How to use

Step 1: Create your custom configuration

Simple Configuration

var downloadOpt = new DownloadConfiguration()
    ChunkCount = 8, // file parts to download, default value is 1
    ParallelDownload = true // download parts of file as parallel or not. Default value is false

Complex Configuration

Note: Do not use all of the below options in your applications, just add which one you need.

var downloadOpt = new DownloadConfiguration()
    // usually, hosts support max to 8000 bytes, default values is 8000
    BufferBlockSize = 10240,
    // file parts to download, default value is 1
    ChunkCount = 8,             
    // download speed limited to 2MB/s, default values is zero or unlimited
    MaximumBytesPerSecond = 1024*1024*2, 
    // the maximum number of times to fail
    MaxTryAgainOnFailover = 5,    
    // release memory buffer after each 50 MB
    MaximumMemoryBufferBytes = 1024 * 1024 * 50, 
    // download parts of file as parallel or not. Default value is false
    ParallelDownload = true,
    // number of parallel downloads. The default value is the same as the chunk count
    ParallelCount = 4,    
    // timeout (millisecond) per stream block reader, default values is 1000
    Timeout = 1000,      
    // set true if you want to download just a specific range of bytes of a large file
    RangeDownload = false,
    // floor offset of download range of a large file
    RangeLow = 0,
    // ceiling offset of download range of a large file
    RangeHigh = 0, 
    // clear package chunks data when download completed with failure, default value is false
    ClearPackageOnCompletionWithFailure = true, 
    // minimum size of chunking to download a file in multiple parts, default value is 512
    MinimumSizeOfChunking = 1024, 
    // Before starting the download, reserve the storage space of the file as file size, default value is false
    ReserveStorageSpaceBeforeStartingDownload = true; 
    // config and customize request headers
    RequestConfiguration = 
        Accept = "*/*",
        CookieContainer = cookies,
        Headers = new WebHeaderCollection(), // { your custom headers }
        KeepAlive = true, // default value is false
        ProtocolVersion = HttpVersion.Version11, // default value is HTTP 1.1
        UseDefaultCredentials = false,
        // your custom user agent or your_app_name/app_version.
        UserAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64)",
        Proxy = new WebProxy() {
           Address = new Uri("http://YourProxyServer/proxy.pac"),
           UseDefaultCredentials = false,
           Credentials = System.Net.CredentialCache.DefaultNetworkCredentials,
           BypassProxyOnLocal = true

Step 2: Create download service instance per download and pass your config

var downloader = new DownloadService(downloadOpt);

Step 3: Handle download events

// Provide `FileName` and `TotalBytesToReceive` at the start of each downloads
downloader.DownloadStarted += OnDownloadStarted;

// Provide any information about chunker downloads, 
// like progress percentage per chunk, speed, 
// total received bytes and received bytes array to live streaming.
downloader.ChunkDownloadProgressChanged += OnChunkDownloadProgressChanged;

// Provide any information about download progress, 
// like progress percentage of sum of chunks, total speed, 
// average speed, total received bytes and received bytes array 
// to live streaming.
downloader.DownloadProgressChanged += OnDownloadProgressChanged;

// Download completed event that can include occurred errors or 
// cancelled or download completed successfully.
downloader.DownloadFileCompleted += OnDownloadFileCompleted;

Step 4: Start the download with the url and file name

string file = @"Your_Path\";
string url = @"";
await downloader.DownloadFileTaskAsync(url, file);

Step 4b: Start the download without file name

DirectoryInfo path = new DirectoryInfo("Your_Path");
string url = @"";
// download into "Your_Path\"
await downloader.DownloadFileTaskAsync(url, path); 

Step 4c: Download in MemoryStream

// After download completion, it gets a MemoryStream
Stream destinationStream = await downloader.DownloadFileTaskAsync(url); 

How to pause and resume downloads quickly

When you want to resume a download quickly after pausing a few seconds. You can call the Pause function of the downloader service. This way, streams stay alive and are only suspended by a locker to be released and resumed whenever you want.

// Pause the download

// Resume the download

How to stop and resume downloads other time

The ‍DownloadService class has a property called Package that stores each step of the download. To stopping the download you must call the CancelAsync method. Now, if you want to continue again, you must call the same DownloadFileTaskAsync function with the Package parameter to resume your download. For example:

// At first, keep and store the Package file to resume 
// your download from the last download position:
DownloadPackage pack = downloader.Package;

Stop or cancel download:

// This function breaks your stream and cancels progress.

Resuming download after cancelation:

await downloader.DownloadFileTaskAsync(pack);

So that you can even save your large downloads with a very small amount in the Package and after restarting the program, restore it again and start continuing your download. The packages are your snapshot of the download instance. Only the downloaded file addresses will be included in the package and you can resume it whenever you want. For more detail see StopResumeDownloadTest method

Note: Sometimes a server does not support downloading in a specific range. That time, we can't resume downloads after canceling. So, the downloader starts from the beginning.

Fluent download builder usage

For easy and fluent use of the downloader, you can use the DownloadBuilder class. Consider the following examples:

Simple usage:

await DownloadBuilder.New()

Complex usage:

IDownload download = DownloadBuilder.New()
    .WithConfiguration(new DownloadConfiguration())

download.DownloadProgressChanged += DownloadProgressChanged;
download.DownloadFileCompleted += DownloadFileCompleted;
download.DownloadStarted += DownloadStarted;
download.ChunkDownloadProgressChanged += ChunkDownloadProgressChanged;

await download.StartAsync();

download.Stop(); // cancel current download

Resume the existing download package:

await DownloadBuilder.Build(package).StartAsync();

Resume the existing download package with a new configuration:

await DownloadBuilder.Build(package, config).StartAsync();

Pause and Resume quickly:

var download = DownloadBuilder.New()
await download.StartAsync();

download.Pause(); // pause current download quickly

download.Resume(); // continue current download quickly

When does Downloader fail to download in multiple chunks?


If your URL server does not provide the file size in the response header (Content-Length). The Downloader cannot split the file into multiple parts and continues its work with one chunk.


If the server return Accept-Ranges: none in the responses header then that means the server does not support download in range and the Downloader cannot use multiple chunking and continues its work with one chunk.


At first, the Downloader sends a GET request to the server to fetch the file's size in the range. If the server does not provide Content-Range in the header then that means the server does not support download in range. Therefore, the Downloader has to continue its work with one chunk.

How to serialize and deserialize downloader package

What is Serialization?

Serialization is the process of converting an object's state into information that can be stored for later retrieval or that can be sent to another system. For example, you may have an object that represents a document that you wish to save. This object could be serialized to a stream of binary information and stored as a file on disk. Later the binary data can be retrieved from the file and deserialized into objects that are exact copies of the original information. As a second example, you may have an object containing the details of a transaction that you wish to send to a non-.NET system. This information could be serialised to XML before being transmitted. The receiving system would convert the XML into a format that it could understand.

In this section, we want to show how to serialize download packages to JSON text or Binary, after stopping download to keep download data and resuming that every time you want. You can serialize packages even using memory storage for caching download data which is used MemoryStream.

JSON Serialization

Serializing the package to JSON is very simple like this:

var packageJson = JsonConvert.SerializeObject(package);

Deserializing into the new package:

var newPack = JsonConvert.DeserializeObject<DownloadPackage>(packageJson);

For more detail see PackageSerializationTest method

Binary Serialization

To serialize or deserialize the package into a binary file, first you need serialize to JSON and next save it with BinaryWriter.

NOTE: The BinaryFormatter type is dangerous and is not recommended for data processing. Applications should stop using BinaryFormatter as soon as possible, even if they believe the data they're processing to be trustworthy. BinaryFormatter is insecure and can't be made secure. So, BinaryFormatter is deprecated and we can no longer support it. Reference

Instructions for Contributing

Welcome to contribute, feel free to change and open a PullRequest to develop branch. You can use either the latest version of Visual Studio or Visual Studio Code and .NET CLI for Windows, Mac and Linux.

For GitHub workflow, check out our Git workflow below this paragraph. We are following the excellent GitHub Flow process, and would like to make sure you have all of the information needed to be a world-class contributor!

Git Workflow

The general process for working with Downloader is:

  1. Fork on GitHub
  2. Make sure your line endings are correctly configured and fix your line endings!
  3. Clone your fork locally
  4. Configure the upstream repo (git remote add upstream git://
  5. Switch to the latest development branch (eg vX.Y.Z, using git checkout vX.Y.Z)
  6. Create a local branch from that (git checkout -b myBranch).
  7. Work on your feature
  8. Rebase if required
  9. Push the branch up to GitHub (git push origin myBranch)
  10. Send a Pull Request on GitHub - the PR should target (have as base branch) the latest development branch (eg vX.Y.Z) rather than master.

We accept pull requests from the community. But, you should never work on a clone of master, and you should never send a pull request from master - always from a branch. Please be sure to branch from the head of the latest vX.Y.Z develop branch (rather than master) when developing contributions.


Licensed under the terms of the MIT License

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