warrenbuckley/BlogPost.cshtml

## BlogPost.cshtml
@using Umbraco.Cms.Web.Common.PublishedModels;
@inherits Umbraco.Cms.Web.Common.Views.UmbracoViewPage<ContentModels.BlogPost>
@using ContentModels = Umbraco.Cms.Web.Common.PublishedModels;
@{
    Layout = null;
}

<html>
<head>
    <meta property="og:title" content="@Model.Header" />
    <meta property="og:image" content="/img/og/@(Model.Key).png" />
</head>
<body>
    <h1>@Model.Header</h1>
    @Model.BlogContent
</body>
</html>

## GenerateOpenGraph.cs
using PuppeteerSharp;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
using Umbraco.Cms.Core.Events;
using Umbraco.Cms.Core.Logging;
using Umbraco.Cms.Core.Models.PublishedContent;
using Umbraco.Cms.Core.Notifications;
using Umbraco.Cms.Core.Routing;

namespace Umbraco.OpenGraph.Images
{
    public class GenerateOpenGraph : INotificationAsyncHandler<ContentPublishingNotification>
    {
        private IPublishedUrlProvider _publishedUrlProvider;
        private IProfilingLogger _profilingLogger;

        public GenerateOpenGraph(IPublishedUrlProvider publishedUrlProvider, IProfilingLogger profilingLogger)
        {
            _publishedUrlProvider = publishedUrlProvider;
            _profilingLogger = profilingLogger;
        }

        public async Task HandleAsync(ContentPublishingNotification notification, CancellationToken cancellationToken)
        {
            using (System.Threading.ExecutionContext.SuppressFlow())
            {
                foreach (var node in notification.PublishedEntities)
                {
                    var filename = node.Key.ToString();
                    var pageUrl = _publishedUrlProvider.GetUrl(node.Key, UrlMode.Absolute);
                    var altTemplateUrl = $"{pageUrl}?altTemplate=opengraph";

                    // Fire & forget
                    Task.Run(() => GenerateImagesAsync(filename, altTemplateUrl));
                }
            }
        }

        public async Task GenerateImagesAsync(string filename, string pageUrl)
        {
            // Puppetter - Will fetch Chrome
            // Will reuse Chrome binary once downloaded first time
            using (_profilingLogger.DebugDuration<GenerateOpenGraph>("Downloading Chrome with Puppeteer"))
            {
                // EEK first download is about 22seconds
                // Once downloaded it uses one from on disk to save time
                var browserFetcher = new BrowserFetcher();
                await browserFetcher.DownloadAsync();
            }

            await using var browser = await Puppeteer.LaunchAsync(
                new LaunchOptions { Headless = true }
            );

            using (_profilingLogger.DebugDuration<GenerateOpenGraph>("Generating Open Graph Image for {PageUrl}", pageUrl))
            {
                // Generate an image on disk
                // Use convention and store image URL at /img/og/{key}.png

                // Use puppetter (headless chrome) to view the published page (alternative template)
                // /my-blog-post?altTemplate=opengraph
                // Get Puppetter to take a screenshot of the page and save as PNG

                if(Directory.Exists("img/og") == false)
                    Directory.CreateDirectory("img/og");

                var screenshotFileName = "img/og/" + filename + ".png";

                using var page = await browser.NewPageAsync();
                await page.GoToAsync(pageUrl);
                await page.ScreenshotAsync(screenshotFileName);
            }
        }


    }
}

## OpenGraph.cshtml
@using Umbraco.Cms.Web.Common.PublishedModels;
@inherits Umbraco.Cms.Web.Common.Views.UmbracoViewPage<ContentModels.BlogPost>
@using ContentModels = Umbraco.Cms.Web.Common.PublishedModels;
@{
	Layout = null;
}
<html>
    <head>
        <link rel="preconnect" href="https://fonts.googleapis.com">
        <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
        <link href="https://fonts.googleapis.com/css2?family=Montserrat:wght@100;400;900&display=swap" rel="stylesheet">

        <style>
            body {
                font-family: 'Montserrat', sans-serif;
                background: #3644B1;
                padding:15px;
            }
            h1 {
                font-size:50px;
                fontw-weight:900;
                color:white;
                margin:0;
            }
            h2 {
                margin:0;
                color:#F1BEBB;
                font-weight:400;
            }
        </style>
    </head>
    <body>

        <div>
            <h1>@Model.Header</h1>
            <h2>5 minute read</h2>
        </div>

    </body>
</html>


## Startup.cs
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System;
using Umbraco.Cms.Core.DependencyInjection;
using Umbraco.Cms.Core.Notifications;
using Umbraco.Extensions;
using Umbraco.OpenGraph.Images;

namespace SocialPuppet
{
    public class Startup
    {
        private readonly IWebHostEnvironment _env;
        private readonly IConfiguration _config;

        /// <summary>
        /// Initializes a new instance of the <see cref="Startup"/> class.
        /// </summary>
        /// <param name="webHostEnvironment">The Web Host Environment</param>
        /// <param name="config">The Configuration</param>
        /// <remarks>
        /// Only a few services are possible to be injected here https://github.com/dotnet/aspnetcore/issues/9337
        /// </remarks>
        public Startup(IWebHostEnvironment webHostEnvironment, IConfiguration config)
        {
            _env = webHostEnvironment ?? throw new ArgumentNullException(nameof(webHostEnvironment));
            _config = config ?? throw new ArgumentNullException(nameof(config));
        }


        /// <summary>
        /// Configures the services
        /// </summary>
        /// <remarks>
        /// This method gets called by the runtime. Use this method to add services to the container.
        /// For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
        /// </remarks>
        public void ConfigureServices(IServiceCollection services)
        {
#pragma warning disable IDE0022 // Use expression body for methods
            services.AddUmbraco(_env, _config)
                .AddBackOffice()
                .AddWebsite()
                .AddComposers()
                .AddNotificationAsyncHandler<ContentPublishingNotification, GenerateOpenGraph>()  // Added this to register this with Umbraco
                .Build();
#pragma warning restore IDE0022 // Use expression body for methods

        }

        /// <summary>
        /// Configures the application
        /// </summary>
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseUmbraco()
                .WithMiddleware(u =>
                {
                    u.WithBackOffice();
                    u.WithWebsite();
                })
                .WithEndpoints(u =>
                {
                    u.UseInstallerEndpoints();
                    u.UseBackOfficeEndpoints();
                    u.UseWebsiteEndpoints();
                });
        }
    }
}
	@using Umbraco.Cms.Web.Common.PublishedModels;
	@inherits Umbraco.Cms.Web.Common.Views.UmbracoViewPage<ContentModels.BlogPost>
	@using ContentModels = Umbraco.Cms.Web.Common.PublishedModels;
	@{
	Layout = null;
	}

	<html>
	<head>
	<meta property="og:title" content="@Model.Header" />
	<meta property="og:image" content="/img/og/@(Model.Key).png" />
	</head>
	<body>
	<h1>@Model.Header</h1>
	@Model.BlogContent
	</body>
	</html>
	using PuppeteerSharp;
	using System.IO;
	using System.Threading;
	using System.Threading.Tasks;
	using Umbraco.Cms.Core.Events;
	using Umbraco.Cms.Core.Logging;
	using Umbraco.Cms.Core.Models.PublishedContent;
	using Umbraco.Cms.Core.Notifications;
	using Umbraco.Cms.Core.Routing;

	namespace Umbraco.OpenGraph.Images
	{
	public class GenerateOpenGraph : INotificationAsyncHandler<ContentPublishingNotification>
	{
	private IPublishedUrlProvider _publishedUrlProvider;
	private IProfilingLogger _profilingLogger;

	public GenerateOpenGraph(IPublishedUrlProvider publishedUrlProvider, IProfilingLogger profilingLogger)
	{
	_publishedUrlProvider = publishedUrlProvider;
	_profilingLogger = profilingLogger;
	}

	public async Task HandleAsync(ContentPublishingNotification notification, CancellationToken cancellationToken)
	{
	using (System.Threading.ExecutionContext.SuppressFlow())
	{
	foreach (var node in notification.PublishedEntities)
	{
	var filename = node.Key.ToString();
	var pageUrl = _publishedUrlProvider.GetUrl(node.Key, UrlMode.Absolute);
	var altTemplateUrl = $"{pageUrl}?altTemplate=opengraph";

	// Fire & forget
	Task.Run(() => GenerateImagesAsync(filename, altTemplateUrl));
	}
	}
	}

	public async Task GenerateImagesAsync(string filename, string pageUrl)
	{
	// Puppetter - Will fetch Chrome
	// Will reuse Chrome binary once downloaded first time
	using (_profilingLogger.DebugDuration<GenerateOpenGraph>("Downloading Chrome with Puppeteer"))
	{
	// EEK first download is about 22seconds
	// Once downloaded it uses one from on disk to save time
	var browserFetcher = new BrowserFetcher();
	await browserFetcher.DownloadAsync();
	}

	await using var browser = await Puppeteer.LaunchAsync(
	new LaunchOptions { Headless = true }
	);

	using (_profilingLogger.DebugDuration<GenerateOpenGraph>("Generating Open Graph Image for {PageUrl}", pageUrl))
	{
	// Generate an image on disk
	// Use convention and store image URL at /img/og/{key}.png

	// Use puppetter (headless chrome) to view the published page (alternative template)
	// /my-blog-post?altTemplate=opengraph
	// Get Puppetter to take a screenshot of the page and save as PNG

	if(Directory.Exists("img/og") == false)
	Directory.CreateDirectory("img/og");

	var screenshotFileName = "img/og/" + filename + ".png";

	using var page = await browser.NewPageAsync();
	await page.GoToAsync(pageUrl);
	await page.ScreenshotAsync(screenshotFileName);
	}
	}


	}
	}
	using Microsoft.AspNetCore.Builder;
	using Microsoft.AspNetCore.Hosting;
	using Microsoft.Extensions.Configuration;
	using Microsoft.Extensions.DependencyInjection;
	using Microsoft.Extensions.Hosting;
	using System;
	using Umbraco.Cms.Core.DependencyInjection;
	using Umbraco.Cms.Core.Notifications;
	using Umbraco.Extensions;
	using Umbraco.OpenGraph.Images;

	namespace SocialPuppet
	{
	public class Startup
	{
	private readonly IWebHostEnvironment _env;
	private readonly IConfiguration _config;

	/// <summary>
	/// Initializes a new instance of the <see cref="Startup"/> class.
	/// </summary>
	/// <param name="webHostEnvironment">The Web Host Environment</param>
	/// <param name="config">The Configuration</param>
	/// <remarks>
	/// Only a few services are possible to be injected here https://github.com/dotnet/aspnetcore/issues/9337
	/// </remarks>
	public Startup(IWebHostEnvironment webHostEnvironment, IConfiguration config)
	{
	_env = webHostEnvironment ?? throw new ArgumentNullException(nameof(webHostEnvironment));
	_config = config ?? throw new ArgumentNullException(nameof(config));
	}



	/// <summary>
	/// Configures the services
	/// </summary>
	/// <remarks>
	/// This method gets called by the runtime. Use this method to add services to the container.
	/// For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
	/// </remarks>
	public void ConfigureServices(IServiceCollection services)
	{
	#pragma warning disable IDE0022 // Use expression body for methods
	services.AddUmbraco(_env, _config)
	.AddBackOffice()
	.AddWebsite()
	.AddComposers()
	.AddNotificationAsyncHandler<ContentPublishingNotification, GenerateOpenGraph>() // Added this to register this with Umbraco
	.Build();
	#pragma warning restore IDE0022 // Use expression body for methods

	}

	/// <summary>
	/// Configures the application
	/// </summary>
	public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
	{
	if (env.IsDevelopment())
	{
	app.UseDeveloperExceptionPage();
	}

	app.UseUmbraco()
	.WithMiddleware(u =>
	{
	u.WithBackOffice();
	u.WithWebsite();
	})
	.WithEndpoints(u =>
	{
	u.UseInstallerEndpoints();
	u.UseBackOfficeEndpoints();
	u.UseWebsiteEndpoints();
	});
	}
	}
	}