I love emojis. Recently, I had the fun task to add emoji auto completion to the latest GitHub for Windows release, among other contributions.

In this post, I want to walk through how to use Octokit.NET to download all the emojis that GitHub supports.

The process is pretty simple, we’re going to make a request to the Emojis API to get the list of emojis, and then download each image.

The first example uses the vanilla Octokit package. The second example uses the Octokit.Reactive package. Both examples pretty much accomplish the same thing, but the Rx version downloads emojis four at a time in parallel instead of one by one.

All the code for this example is available in the haacked/EmojiDownloader repository on GitHub.

The Code

To get started, create a console project and install the Octokit.NET package:

Install-Package Octokit

The first step is to create an instance of the GitHubClient. We don’t have to provide any credentials to call the Emojis API.

var githubClient = new GitHubClient(
    new ProductHeaderValue("Haack-Emoji-Downloader"));

The string in the ProductHeaderValue is used to form a User Agent for the request. The GitHub API requires a valid user agent.

Now we can request the list of emojis.

var emojis = await githubClient.Miscellaneous.GetEmojis();

This returns a IReadOnlyList<Emoji>.

Now we can iterate through each one and use an HttpClient to download each image. We’ll use the following code to download the image.

public static async Task DownloadImage(Uri url, string filePath)
{
    Console.WriteLine("Downloading " + filePath);

    using (var httpClient = new HttpClient())
    {
        using (var request = new HttpRequestMessage(HttpMethod.Get, url))
        {
            var response = await httpClient.SendAsync(request);

            using (var responseStream = await response.Content.ReadAsStreamAsync())
            using (var writeStream = new FileStream(filePath, System.IO.FileMode.Create))
            {
                await responseStream.CopyToAsync(writeStream);
            }     
        }
    }
}

Here’s the code of the Console’s Main method that puts all this together. Note that I wrap everything in a Task.Run so I can use the async and await keywords.

static void Main(string[] args)
{
    string outputDirectory = args.Any()
        ? String.Join("", args)
        : Path.GetDirectoryName(Assembly.GetExecutingAssembly().CodeBase);

    Debug.Assert(outputDirectory != null, "The output directory should not be null.`");

    Task.Run(async () =>
    {
        var githubClient = new GitHubClient(new ProductHeaderValue("Haack-Emoji-Downloader"));
        var emojis = await githubClient.Miscellaneous.GetEmojis();
        foreach (var emoji in emojis)
        {
            string emojiFileName = Path.Combine(outputDirectory, emoji.Name + ".png");
            await DownloadImage(emoji.Url, emojiFileName);
        }

    }).Wait();
}

The first part of the method sets up the output directory. By default, it will create the emojis wherever the program EXE is located. But you can also specify a path as the sole argument to the program.

Let’s get Reactive!

If you prefer to use the Reactive version of Octokit.NET, the following example will get you started.

Install-Package Octokit.Reactive

Instead of the GitHubClient we’ll create an ObservableGitHubClient.

var githubClient = new ObservableGitHubClient(
    new ProductHeaderValue("Haack-Reactive-Emoji-Downloader"));

Now we can call the equivalent method, but we have the benefit of using the Buffer method.

githubClient.Miscellaneous.GetEmojis()
    .Buffer(4) // Downloads 4 at a time.
    .Do(group => Task.WaitAll(group
        .Select(emoji => new
        {
            emoji.Url,
            FilePath = Path.Combine(outputDirectory, emoji.Name + ".png")
        })
        .Select(download => DownloadImage(download.Url, download.FilePath)).ToArray()))
    .Wait();

The buffer method groups the sequence of emojis into groups of four so we can then kick off the download for four emojis at a time and then wait for the group to finish before requesting the next four.

The reason we don’t just request them all at the same time is we don’t want to flood the network card or local network.

UPDATE: My buddy Paul Betts suggests an even better more Rx-y approach in the comments.

githubClient.Miscellaneous.GetEmojis()
    .Select(emoji => Observable.FromAsync(async () =>
    {
        var path = Path.Combine(outputDirectory, emoji.Name + ".png");
        await DownloadImage(emoji.Url, path);
        return path;
    }))
    .Merge(4)
    .ToArray()
    .Wait();

We’ll use the Merge method instead of Buffer to throttle requests to four at a time.

And with that, you’ll have 887 (as of right now) emoji png files downloaded to disk.

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