Introduce an Atom feed for packages (#6891)

* copied from the old PR in panic, but should be "cleaner" (at least with the latest master changes)

* copied from the old PR in panic, but should be "cleaner" (at least with the latest master changes)

* revert applicationhost.config to clean state

* avoid using title and published, instead use id and created and

* copied from the old PR in panic, but should be "cleaner" (at least with the latest master changes)

* copied from the old PR in panic, but should be "cleaner" (at least with the latest master changes)

* avoid using title and published, instead use id and created and

* unwanted merge change

* Resolve #2992

Author: robertmuehsig

src/NuGetGallery/App_Start/Routes.cs

@@ -199,6 +199,15 @@ public static void RegisterUIRoutes(RouteCollection routes)
                 },
                 new { version = new VersionRouteConstraint() });
 
+            routes.MapRoute(
+                RouteName.DisplayPackageFeed,
+                "packages/{id}/atom.xml",
+                new
+                {
+                    controller = "Packages",
+                    action = nameof(PackagesController.AtomFeed)
+                });
+
             routes.MapRoute(
                 RouteName.PackageEnableLicenseReport,
                 "packages/{id}/{version}/EnableLicenseReport",

src/NuGetGallery/Content/gallery/img/rss-24x24.png

@@ -9,6 +9,7 @@
 using System.Linq;
 using System.Net;
 using System.Net.Mail;
+using System.ServiceModel.Syndication;
 using System.Text;
 using System.Threading.Tasks;
 using System.Web;
@@ -27,6 +28,7 @@
 using NuGetGallery.Diagnostics;
 using NuGetGallery.Filters;
 using NuGetGallery.Helpers;
+using NuGetGallery.Infrastructure;
 using NuGetGallery.Infrastructure.Lucene;
 using NuGetGallery.Infrastructure.Mail.Messages;
 using NuGetGallery.Infrastructure.Mail.Requests;
@@ -734,6 +736,78 @@ public virtual async Task<ActionResult> DisplayPackage(string id, string version
             return View(model);
         }
 
+        [HttpGet]
+        public virtual ActionResult AtomFeed(string id, bool allowPrerelease = false)
+        {
+            var packageRegistration = _packageService.FindPackageRegistrationById(id);
+            if (packageRegistration == null)
+            {
+                return HttpNotFound();
+            }
+
+            var packageVersions = packageRegistration.Packages
+                                   .Where(x => x.Listed && x.PackageStatusKey == PackageStatus.Available)
+                                   .OrderByDescending(p => NuGetVersion.Parse(p.NormalizedVersion))
+                                   .ToList();
+
+            if (packageVersions.Count == 0)
+            {
+                return HttpNotFound();
+            }
+
+            // most recent version for feed title/description
+            var newestVersionPackage = packageVersions.First();
+
+            // the last edited or created package is used as the feed timestamp
+            var lastUpdatedPackage = packageVersions.Max(x => x.LastEdited ?? x.Created);
+
+            SyndicationFeed feed = new SyndicationFeed()
+            {
+                Id = Url.Package(packageRegistration.Id, version: null, relativeUrl: false),
+                Title = SyndicationContent.CreatePlaintextContent($"{_config.Brand} Feed for {packageRegistration.Id}"),
+                Description = SyndicationContent.CreatePlaintextContent(newestVersionPackage.Description),
+                LastUpdatedTime = lastUpdatedPackage
+            };
+
+            if (!string.IsNullOrWhiteSpace(newestVersionPackage.IconUrl))
+            {
+                feed.ImageUrl = new Uri(newestVersionPackage.IconUrl);
+            }
+
+            List<SyndicationItem> feedItems = new List<SyndicationItem>();
+
+            List<SyndicationPerson> ownersAsAuthors = new List<SyndicationPerson>();
+            foreach (var packageOwner in packageRegistration.Owners)
+            {
+                ownersAsAuthors.Add(new SyndicationPerson() { Name = packageOwner.Username, Uri = Url.User(packageOwner, relativeUrl: false) });
+            }
+
+            foreach (var packageVersion in packageVersions)
+            {
+                SyndicationItem syndicationItem = new SyndicationItem($"{packageVersion.Id} {packageVersion.Version}",
+                                                                      packageVersion.Description,
+                                                                      new Uri(Url.Package(packageRegistration.Id, version: packageVersion.Version, relativeUrl: false)));
+                syndicationItem.Id = Url.Package(packageRegistration.Id, version: packageVersion.Version, relativeUrl: false);
+                syndicationItem.LastUpdatedTime = packageVersion.LastEdited ?? packageVersion.Created;
+                syndicationItem.PublishDate = packageVersion.Created;
+
+                syndicationItem.Authors.AddRange(ownersAsAuthors);
+                feedItems.Add(syndicationItem);
+            }
+
+            feed.Items = feedItems;
+
+            feed.Links.Add(SyndicationLink.CreateSelfLink(
+                new Uri(Url.PackageAtomFeed(packageRegistration.Id, relativeUrl: false)),
+                "application/atom+xml"));
+
+            feed.Links.Add(SyndicationLink.CreateAlternateLink(
+                new Uri(Url.Package(packageRegistration.Id, version: null, relativeUrl: false)),
+                "text/html"));
+
+            return new SyndicationAtomActionResult(feed);
+        }
+
         [HttpGet]
         public virtual async Task<ActionResult> License(string id, string version)
         {

src/NuGetGallery/Controllers/PackagesController.cs

@@ -0,0 +1,49 @@
+using System.ServiceModel.Syndication;
+using System.Web;
+using System.Web.Mvc;
+using System.Xml;
+
+namespace NuGetGallery.Infrastructure
+{
+    /// <summary>
+    /// ActionResult to render an Atom 1.0 feed by using an <see cref="SyndicationFeed"/> instance 
+    /// representing the feed.
+    /// </summary>
+    public sealed class SyndicationAtomActionResult : ActionResult
+    {
+        public readonly SyndicationFeed SyndicationFeed;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="SyndicationAtomActionResult"/> class.
+        /// </summary>
+        /// <param name="syndicationFeed">The Atom 1.0 <see cref="SyndicationFeed" />.</param>
+        public SyndicationAtomActionResult(SyndicationFeed syndicationFeed)
+        {
+            SyndicationFeed = syndicationFeed;
+        }
+
+        /// <summary>
+        /// Executes the call to the ActionResult method and returns the created feed to the output response.
+        /// </summary>
+        /// <param name="context">The context in which the result is executed. The context information includes the 
+        /// controller, HTTP content, request context, and route data.</param>
+        public override void ExecuteResult(ControllerContext context)
+        {
+            context.HttpContext.Response.ContentType = "application/atom+xml";
+            Atom10FeedFormatter feedFormatter = new Atom10FeedFormatter(SyndicationFeed);
+            XmlWriterSettings xmlWriterSettings = new XmlWriterSettings();
+
+            if (HttpContext.Current.IsDebuggingEnabled)
+            {
+                // Indent the XML for easier viewing but only in Debug mode. In Release mode, everything is output on 
+                // one line for best performance.
+                xmlWriterSettings.Indent = true;
+            }
+
+            using (XmlWriter xmlWriter = XmlWriter.Create(context.HttpContext.Response.Output, xmlWriterSettings))
+            {
+                feedFormatter.WriteTo(xmlWriter);
+            }
+        }
+    }
+}

src/NuGetGallery/Infrastructure/SyndicationAtomActionResult.cs

@@ -333,6 +333,7 @@
     <Compile Include="Infrastructure\Mail\Messages\ReportPackageMessageBase.cs" />
     <Compile Include="Infrastructure\Mail\Messages\SigninAssistanceMessage.cs" />
     <Compile Include="Infrastructure\Mail\Requests\ReportPackageRequest.cs" />
+    <Compile Include="Infrastructure\SyndicationAtomActionResult.cs" />
     <Compile Include="Migrations\201711082145351_AddAccountDelete.cs" />
     <Compile Include="Migrations\201711082145351_AddAccountDelete.Designer.cs">
       <DependentUpon>201711082145351_AddAccountDelete.cs</DependentUpon>
@@ -1312,6 +1313,7 @@
     <Content Include="Content\admin\SupportRequestStyles.css" />
     <Content Include="Content\fabric.css" />
     <Content Include="Content\gallery\img\logo-og-600x600.png" />
+    <Content Include="Content\gallery\img\rss-24x24.png" />
     <Content Include="Content\Images\icons\apiKey.png" />
     <Content Include="Content\Images\icons\apiKeyExpired.png" />
     <Content Include="Content\Images\icons\apiKeyLegacy.png" />

src/NuGetGallery/NuGetGallery.csproj

@@ -26,6 +26,7 @@ public static class RouteName
         public const string ApiKeys = "ApiKeys";
         public const string Profile = "Profile";
         public const string DisplayPackage = "package-route";
+        public const string DisplayPackageFeed = "package-route-feed";
         public const string DownloadPackage = "DownloadPackage";
         public const string DownloadSymbolsPackage = "DownloadSymbolsPackage";
         public const string DownloadNuGetExe = "DownloadNuGetExe";

src/NuGetGallery/RouteName.cs

@@ -238,6 +238,23 @@ public static string PackageDefaultIcon(this UrlHelper url)
                 + VirtualPathUtility.ToAbsolute("~/Content/Images/packageDefaultIcon-50x50.png", url.RequestContext.HttpContext.Request.ApplicationPath);
         }
 
+        public static string PackageAtomFeed(
+            this UrlHelper url,
+            string id,
+            bool relativeUrl = true)
+        {
+            string result = GetRouteLink(
+                url,
+                RouteName.DisplayPackageFeed,
+                relativeUrl,
+                routeValues: new RouteValueDictionary
+                {
+                    { "id", id },
+                });
+
+            return result;
+        }
+
         public static string PackageDownload(
             this UrlHelper url,
             int feedVersion,

src/NuGetGallery/UrlHelperExtensions.cs

@@ -85,6 +85,8 @@
     <meta property="og:description" content="@Model.Description" />
     <meta property="og:determiner" content="a" />
     <meta property="og:image" content="@(PackageHelper.ShouldRenderUrl(Model.IconUrl) ? Model.IconUrl : Url.Absolute("~/Content/gallery/img/default-package-icon-256x256.png"))" />
+
+    <link rel="alternate" type="application/atom+xml" title="Subscribe to @Model.Id updates" href="@Url.PackageAtomFeed(Model.Id)" />
 }
 
 @helper VersionListDivider(int rowCount, bool versionsExpanded)
@@ -860,6 +862,11 @@ foreach (var owner in Model.Owners)
                              src="@Url.Absolute("~/Content/gallery/img/twitter.svg")"
                              @ViewHelpers.ImageFallback(Url.Absolute("~/Content/gallery/img/twitter-24x24.png")) />
                     </a>
+                    <a href="@Url.PackageAtomFeed(Model.Id)" data-track="atom-feed">
+                        <img width="24" height="24" alt="Use the Atom feed to subscribe to new versions of @Model.Id"
+                             src="@Url.Absolute("~/Content/gallery/img/rss.svg")"
+                             @ViewHelpers.ImageFallback(Url.Absolute("~/Content/gallery/img/rss-24x24.png")) />
+                    </a>
                 </p>
             }
         </aside>