Updated QueuedMessageList to extend ReadOnlyCollectionPage<QueuedMessage>

Author: sharwell

src/corelib/Core/Domain/Queues/QueuedMessageList.cs

@@ -2,110 +2,50 @@
 {
     using System;
     using System.Collections.Generic;
-    using System.Collections.ObjectModel;
-    using System.Linq;
+    using System.Threading;
+    using System.Threading.Tasks;
+    using net.openstack.Core.Collections;
     using net.openstack.Core.Providers;
-    using Newtonsoft.Json;
 
     /// <summary>
-    /// Represents a collection of messages stored in a queue in the <see cref="IQueueingService"/>.
+    /// This class extends the <see cref="ReadOnlyCollectionPage{T}"/> class
+    /// to provide access to the opaque marker used for paginating messages
+    /// in the <see cref="IQueueingService"/> (via the <see cref="NextPageId"/>
+    /// property.
     /// </summary>
     /// <threadsafety static="true" instance="false"/>
     /// <preliminary/>
-    [JsonObject(MemberSerialization.OptIn)]
-    public class QueuedMessageList
+    public class QueuedMessageList : BasicReadOnlyCollectionPage<QueuedMessage>
     {
         /// <summary>
-        /// This is the backing field for the <see cref="Empty"/> property.
+        /// This is the backing field for the <see cref="NextPageId"/> property.
         /// </summary>
-        private static readonly QueuedMessageList _empty = new QueuedMessageList(Enumerable.Empty<QueuedMessage>(), Enumerable.Empty<Link>());
-
-        /// <summary>
-        /// This is the backing field for the <see cref="Links"/> property.
-        /// </summary>
-        [JsonProperty("links")]
-        private Link[] _links;
-
-        /// <summary>
-        /// This is the backing field for the <see cref="Messages"/> property.
-        /// </summary>
-        [JsonProperty("messages")]
-        private QueuedMessage[] _messages;
-
-        /// <summary>
-        /// Initializes a new instance of the <see cref="QueuedMessageList"/> class during
-        /// JSON deserialization.
-        /// </summary>
-        [JsonConstructor]
-        protected QueuedMessageList()
-        {
-        }
-
+        private QueuedMessageListId _nextPageId;
+        
         /// <summary>
-        /// Initializes a new instance of the <see cref="QueuedMessageList"/> class.
+        /// Initializes a new instance of the <see cref="BasicReadOnlyCollectionPage{T}"/> class
+        /// that is a read-only wrapper around the specified list.
         /// </summary>
-        /// <param name="messages">A collection of <see cref="QueuedMessage"/> objects describing the messages in a queue.</param>
-        /// <param name="links">A collection of <see cref="Link"/> objects describing resources related to the list of messages.</param>
-        /// <exception cref="ArgumentException">
-        /// If <paramref name="messages"/> contains any <see langword="null"/> values.
-        /// <para>-or-</para>
-        /// <para>If <paramref name="links"/> contains any <see langword="null"/> values.</para>
+        /// <param name="list">The list to wrap.</param>
+        /// <param name="getNextPageAsync">A function that returns a <see cref="Task{TResult}"/> representing the asynchronous operation to get the next page of items in the collection. If specified, this function implements <see cref="BasicReadOnlyCollectionPage{T}.GetNextPageAsync"/>. If the value is <see langword="null"/>, then <see cref="BasicReadOnlyCollectionPage{T}.CanHaveNextPage"/> will return <see langword="false"/>.</param>
+        /// <param name="nextPageId">The identifier of the next page in the message list.</param>
+        /// <exception cref="ArgumentNullException">
+        /// If <paramref name="list"/> is <see langword="null"/>.
         /// </exception>
-        public QueuedMessageList(IEnumerable<QueuedMessage> messages, IEnumerable<Link> links)
+        public QueuedMessageList(IList<QueuedMessage> list, Func<CancellationToken, Task<ReadOnlyCollectionPage<QueuedMessage>>> getNextPageAsync, QueuedMessageListId nextPageId)
+            : base(list, getNextPageAsync)
         {
-            if (messages != null)
-            {
-                _messages = messages.ToArray();
-                if (_messages.Contains(null))
-                    throw new ArgumentException("messages cannot contain any null values", "messages");
-            }
-
-            if (links != null)
-            {
-                _links = links.ToArray();
-                if (_links.Contains(null))
-                    throw new ArgumentException("links cannot contain any null values", "links");
-            }
+            _nextPageId = nextPageId;
         }
 
         /// <summary>
-        /// Gets an empty list of messages, which is not specific to any queue.
+        /// Gets the identifier of the next page of the message list.
         /// </summary>
-        public static QueuedMessageList Empty
+        public QueuedMessageListId NextPageId
         {
             get
             {
-                return _empty;
-            }
-        }
-
-        /// <summary>
-        /// Gets a collection of <see cref="Link"/> objects describing resources related
-        /// to this list of messages.
-        /// </summary>
-        public ReadOnlyCollection<Link> Links
-        {
-            get
-            {
-                if (_links == null)
-                    return null;
-
-                return new ReadOnlyCollection<Link>(_links);
-            }
-        }
-
-        /// <summary>
-        /// Gets a list of <see cref="QueuedMessage"/> objects describing the messages in
-        /// the queue.
-        /// </summary>
-        public ReadOnlyCollection<QueuedMessage> Messages
-        {
-            get
-            {
-                if (_messages == null)
-                    return null;
-
-                return new ReadOnlyCollection<QueuedMessage>(_messages);
+                return _nextPageId;
             }
         }
     }

src/corelib/Core/Domain/Queues/QueuedMessageListId.cs

@@ -0,0 +1,44 @@
+namespace net.openstack.Core.Domain.Queues
+{
+    using System;
+    using net.openstack.Core;
+    using net.openstack.Core.Providers;
+    using Newtonsoft.Json;
+
+    /// <summary>
+    /// Represents the unique identifier of a message list page in the <see cref="IQueueingService"/>.
+    /// </summary>
+    /// <seealso cref="IQueueingService.ListMessagesAsync"/>
+    /// <seealso cref="QueuedMessageList.NextPageId"/>
+    /// <threadsafety static="true" instance="false"/>
+    /// <preliminary/>
+    [JsonConverter(typeof(QueuedMessageListId.Converter))]
+    public sealed class QueuedMessageListId : ResourceIdentifier<QueuedMessageListId>
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="QueuedMessageListId"/> class
+        /// with the specified identifier value.
+        /// </summary>
+        /// <param name="id">The identifier value.</param>
+        /// <exception cref="ArgumentNullException">If <paramref name="id"/> is <c>null</c>.</exception>
+        /// <exception cref="ArgumentException">If <paramref name="id"/> is empty.</exception>
+        public QueuedMessageListId(string id)
+            : base(id)
+        {
+        }
+
+        /// <summary>
+        /// Provides support for serializing and deserializing <see cref="QueuedMessageListId"/>
+        /// objects to JSON string values.
+        /// </summary>
+        /// <threadsafety static="true" instance="false"/>
+        private sealed class Converter : ConverterBase
+        {
+            /// <inheritdoc/>
+            protected override QueuedMessageListId FromValue(string id)
+            {
+                return new QueuedMessageListId(id);
+            }
+        }
+    }
+}

src/corelib/Core/Providers/IQueueingService.cs

@@ -160,7 +160,7 @@ Task<T> GetQueueMetadataAsync<T>(QueueName queueName, CancellationToken cancella
         /// Gets a list of messages currently in a queue.
         /// </summary>
         /// <param name="queueName">The queue name.</param>
-        /// <param name="marker">The <see cref="QueuedMessageList"/> object returned by a previous call to <see cref="ListMessagesAsync"/>. If this value is <see langword="null"/>, the list starts at the beginning.</param>
+        /// <param name="marker">The identifier of the message list page to return. This is obtained from <see cref="QueuedMessageList.NextPageId"/>. If this value is <see langword="null"/>, the list starts at the beginning.</param>
         /// <param name="limit">The maximum number of messages to return. If this value is <see langword="null"/>, a provider-specific default value is used.</param>
         /// <param name="echo"><see langword="true"/> to include messages created by the current client; otherwise, <see langword="false"/>.</param>
         /// <param name="includeClaimed"><see langword="true"/> to include claimed messages; otherwise <see langword="false"/> to return only unclaimed messages.</param>
@@ -170,7 +170,7 @@ Task<T> GetQueueMetadataAsync<T>(QueueName queueName, CancellationToken cancella
         /// <exception cref="ArgumentOutOfRangeException">If <paramref name="limit"/> is less than or equal to 0.</exception>
         /// <exception cref="WebException">If the REST request does not return successfully.</exception>
         /// <seealso href="https://wiki.openstack.org/w/index.php?title=Marconi/specs/api/v1#List_Messages">List Messages (OpenStack Marconi API v1 Blueprint)</seealso>
-        Task<QueuedMessageList> ListMessagesAsync(QueueName queueName, QueuedMessageList marker, int? limit, bool echo, bool includeClaimed, CancellationToken cancellationToken);
+        Task<QueuedMessageList> ListMessagesAsync(QueueName queueName, QueuedMessageListId marker, int? limit, bool echo, bool includeClaimed, CancellationToken cancellationToken);
 
         /// <summary>
         /// Gets detailed information about a specific queued message.

src/corelib/Core/Synchronous/QueueingServiceExtensions.cs

@@ -338,7 +338,7 @@ public static QueueStatistics GetQueueStatistics(this IQueueingService queueingS
         /// </summary>
         /// <param name="queueingService">The queueing service instance.</param>
         /// <param name="queueName">The queue name.</param>
-        /// <param name="marker">The <see cref="QueuedMessageList"/> object returned by a previous call to <see cref="IQueueingService.ListMessagesAsync"/>. If this value is <see langword="null"/>, the list starts at the beginning.</param>
+        /// <param name="marker">The identifier of the message list page to return. This is obtained from <see cref="QueuedMessageList.NextPageId"/>. If this value is <see langword="null"/>, the list starts at the beginning.</param>
         /// <param name="limit">The maximum number of messages to return. If this value is <see langword="null"/>, a provider-specific default value is used.</param>
         /// <param name="echo"><see langword="true"/> to include messages created by the current client; otherwise, <see langword="false"/>.</param>
         /// <param name="includeClaimed"><see langword="true"/> to include claimed messages; otherwise <see langword="false"/> to return only unclaimed messages.</param>
@@ -348,7 +348,7 @@ public static QueueStatistics GetQueueStatistics(this IQueueingService queueingS
         /// <exception cref="ArgumentOutOfRangeException">If <paramref name="limit"/> is less than or equal to 0.</exception>
         /// <exception cref="WebException">If the REST request does not return successfully.</exception>
         /// <seealso href="https://wiki.openstack.org/w/index.php?title=Marconi/specs/api/v1#List_Messages">List Messages (OpenStack Marconi API v1 Blueprint)</seealso>
-        public static QueuedMessageList ListMessages(this IQueueingService queueingService, QueueName queueName, QueuedMessageList marker, int? limit, bool echo, bool includeClaimed)
+        public static QueuedMessageList ListMessages(this IQueueingService queueingService, QueueName queueName, QueuedMessageListId marker, int? limit, bool echo, bool includeClaimed)
         {
             if (queueingService == null)
                 throw new ArgumentNullException("queueingService");

src/corelib/Providers/Rackspace/CloudQueuesProvider.cs

@@ -353,7 +353,7 @@ public Task<QueueStatistics> GetQueueStatisticsAsync(QueueName queueName, Cancel
         }
 
         /// <inheritdoc/>
-        public Task<QueuedMessageList> ListMessagesAsync(QueueName queueName, QueuedMessageList marker, int? limit, bool echo, bool includeClaimed, CancellationToken cancellationToken)
+        public Task<QueuedMessageList> ListMessagesAsync(QueueName queueName, QueuedMessageListId marker, int? limit, bool echo, bool includeClaimed, CancellationToken cancellationToken)
         {
             if (queueName == null)
                 throw new ArgumentNullException("queueName");
@@ -369,49 +369,60 @@ public Task<QueuedMessageList> ListMessagesAsync(QueueName queueName, QueuedMess
                     { "echo", echo.ToString() },
                     { "include_claimed", includeClaimed.ToString() }
                 };
-
             if (marker != null)
-            {
-                Link nextLink = null;
-                if (marker.Links != null)
+                parameters["marker"] = marker.Value;
+            if (limit != null)
+                parameters["limit"] = limit.ToString();
+
+            Func<Task<Tuple<IdentityToken, Uri>>, HttpWebRequest> prepareRequest =
+                PrepareRequestAsyncFunc(HttpMethod.GET, template, parameters);
+
+            Func<Task<HttpWebRequest>, Task<ListCloudQueueMessagesResponse>> requestResource =
+                GetResponseAsyncFunc<ListCloudQueueMessagesResponse>(cancellationToken);
+
+            Func<Task<ListCloudQueueMessagesResponse>, QueuedMessageList> resultSelector =
+                task =>
                 {
-                    foreach (Link link in marker.Links)
+                    ReadOnlyCollection<QueuedMessage> messages = null;
+                    if (task.Result != null)
+                        messages = task.Result.Messages;
+
+                    QueuedMessageListId nextMarker = null;
+                    if (task.Result != null && task.Result.Links != null)
                     {
-                        if (link.Rel == "next")
+                        Link nextLink = task.Result.Links.FirstOrDefault(i => string.Equals(i.Rel, "next", StringComparison.OrdinalIgnoreCase));
+                        if (nextLink != null)
                         {
-                            nextLink = link;
-                            break;
+                            Uri baseUri = new Uri("https://example.com");
+                            Uri absoluteUri;
+                            if (nextLink.Href.StartsWith("/v1"))
+                                absoluteUri = new Uri(baseUri, nextLink.Href.Substring("/v1".Length));
+                            else
+                                absoluteUri = new Uri(baseUri, nextLink.Href);
+
+                            UriTemplateMatch match = template.Match(baseUri, absoluteUri);
+                            if (!string.IsNullOrEmpty(match.BoundVariables["marker"]))
+                                nextMarker = new QueuedMessageListId(match.BoundVariables["marker"]);
                         }
                     }
-                }
-
-                if (nextLink == null)
-                {
-                    return InternalTaskExtensions.CompletedTask(QueuedMessageList.Empty);
-                }
-
-                Uri baseUri = new Uri("https://example.com");
-                Uri absoluteUri;
-                if (nextLink.Href.StartsWith("/v1"))
-                    absoluteUri = new Uri(baseUri, nextLink.Href.Substring("/v1".Length));
-                else
-                    absoluteUri = new Uri(baseUri, nextLink.Href);
-
-                UriTemplateMatch match = template.Match(baseUri, absoluteUri);
-                parameters.Add("marker", match.BoundVariables["marker"]);
-            }
-
-            if (limit != null)
-                parameters["limit"] = limit.ToString();
 
-            Func<Task<Tuple<IdentityToken, Uri>>, HttpWebRequest> prepareRequest =
-                PrepareRequestAsyncFunc(HttpMethod.GET, template, parameters);
+                    if (messages == null || messages.Count == 0)
+                    {
+                        // use the same marker again
+                        messages = messages ?? new ReadOnlyCollection<QueuedMessage>(new QueuedMessage[0]);
+                        nextMarker = marker;
+                    }
 
-            Func<Task<HttpWebRequest>, Task<QueuedMessageList>> requestResource =
-                GetResponseAsyncFunc<QueuedMessageList>(cancellationToken);
+                    Func<CancellationToken, Task<ReadOnlyCollectionPage<QueuedMessage>>> getNextPageAsync = null;
+                    if (nextMarker != null || messages.Count == 0)
+                    {
+                        getNextPageAsync =
+                            nextCancellationToken => ListMessagesAsync(queueName, nextMarker, limit, echo, includeClaimed, nextCancellationToken)
+                                .ContinueWith(t => (ReadOnlyCollectionPage<QueuedMessage>)t.Result, TaskContinuationOptions.ExecuteSynchronously);
+                    }
 
-            Func<Task<QueuedMessageList>, QueuedMessageList> resultSelector =
-                task => (task.Result != null && task.Result.Messages != null ? task.Result : null) ?? QueuedMessageList.Empty;
+                    return new QueuedMessageList(messages, getNextPageAsync, nextMarker);
+                };
 
             return AuthenticateServiceAsync(cancellationToken)
                 .ContinueWith(prepareRequest)

src/corelib/corelib.v3.5.csproj

@@ -103,6 +103,7 @@
     <Compile Include="Core\Domain\Queues\NamespaceDoc.cs" />
     <Compile Include="Core\Domain\Queues\QueuedMessage.cs" />
     <Compile Include="Core\Domain\Queues\QueuedMessageList.cs" />
+    <Compile Include="Core\Domain\Queues\QueuedMessageListId.cs" />
     <Compile Include="Core\Domain\Queues\QueueMessagesStatistics.cs" />
     <Compile Include="Core\Domain\Queues\QueueName.cs" />
     <Compile Include="Core\Domain\Queues\QueueStatistics.cs" />

src/corelib/corelib.v4.0.csproj

@@ -93,6 +93,7 @@
     <Compile Include="Core\Domain\Queues\NamespaceDoc.cs" />
     <Compile Include="Core\Domain\Queues\QueuedMessage.cs" />
     <Compile Include="Core\Domain\Queues\QueuedMessageList.cs" />
+    <Compile Include="Core\Domain\Queues\QueuedMessageListId.cs" />
     <Compile Include="Core\Domain\Queues\QueueMessagesStatistics.cs" />
     <Compile Include="Core\Domain\Queues\QueueName.cs" />
     <Compile Include="Core\Domain\Queues\QueueStatistics.cs" />