Add an ItemCount property to the Page class

Microsoft.Azure.Cosmos/src/ChangeFeed/Pagination/ChangeFeedNotModifiedPage.cs

@@ -12,14 +12,16 @@ internal sealed class ChangeFeedNotModifiedPage : ChangeFeedPage
         private static readonly ImmutableHashSet<string> bannedHeaders = new HashSet<string>().ToImmutableHashSet();
 
         public ChangeFeedNotModifiedPage(
-            double requestCharge,
+            double requestCharge,
             string activityId,
             IReadOnlyDictionary<string, string> additionalHeaders,
             ChangeFeedState state)
             : base(requestCharge, activityId, additionalHeaders, state)
         {
-        }
-
+        }
+
+        public override int ItemCount => 0;
+
         protected override ImmutableHashSet<string> DerivedClassBannedHeaders => bannedHeaders;
     }
 }

Microsoft.Azure.Cosmos/src/ChangeFeed/Pagination/ChangeFeedSuccessPage.cs

@@ -15,17 +15,21 @@ internal sealed class ChangeFeedSuccessPage : ChangeFeedPage
 
         public ChangeFeedSuccessPage(
             Stream content,
-            double requestCharge,
+            double requestCharge,
+            int itemCount,
             string activityId,
             IReadOnlyDictionary<string, string> additionalHeaders,
             ChangeFeedState state)
             : base(requestCharge, activityId, additionalHeaders, state)
         {
-            this.Content = content ?? throw new ArgumentNullException(nameof(content));
+            this.Content = content ?? throw new ArgumentNullException(nameof(content));
+            this.ItemCount = itemCount;
         }
 
-        public Stream Content { get; }
-
+        public Stream Content { get; }
+
+        public override int ItemCount { get; }
+
         protected override ImmutableHashSet<string> DerivedClassBannedHeaders => bannedHeaders;
     }
 }

Microsoft.Azure.Cosmos/src/ChangeFeed/Pagination/CrossPartitionChangeFeedAsyncEnumerator.cs

@@ -99,15 +99,16 @@ public async ValueTask<bool> MoveNextAsync(ITrace trace, CancellationToken cance
                             {
                                 backendPage = new ChangeFeedSuccessPage(
                                     changeFeedSuccessPage.Content,
-                                    totalRequestCharge,
+                                    totalRequestCharge,
+                                    changeFeedSuccessPage.ItemCount,
                                     changeFeedSuccessPage.ActivityId,
                                     changeFeedSuccessPage.AdditionalHeaders,
                                     changeFeedSuccessPage.State);
                             }
                             else
                             {
                                 backendPage = new ChangeFeedNotModifiedPage(
-                                    totalRequestCharge,
+                                    totalRequestCharge,
                                     backendPage.ActivityId,
                                     backendPage.AdditionalHeaders,
                                     backendPage.State);

Microsoft.Azure.Cosmos/src/Headers/Headers.cs

@@ -267,7 +267,14 @@ internal virtual string EndEpk
             set => this.CosmosMessageHeaders.EndEpk = value;
         }
 
-        internal virtual string ItemCount => this.CosmosMessageHeaders.Get(HttpConstants.HttpHeaders.ItemCount);
+        internal virtual int ItemCount
+        {
+            get
+            {
+                string itemCountText = this.CosmosMessageHeaders.Get(HttpConstants.HttpHeaders.ItemCount);
+                return int.Parse(itemCountText, NumberStyles.Integer, CultureInfo.InvariantCulture);
+            }
+        }
 
         /// <summary>
         /// Creates a new instance of <see cref="Headers"/>.

Microsoft.Azure.Cosmos/src/Pagination/BufferedPartitionRangePageAsyncEnumerator.cs

@@ -28,7 +28,11 @@ public override Exception BufferedException
 
                 return null;
             }
-        }
+        }
+
+        public override int BufferedItemCount => this.bufferedPage.HasValue && this.bufferedPage.Value.Succeeded ?
+            this.bufferedPage.Value.Result.ItemCount :
+            0;
 
         public BufferedPartitionRangePageAsyncEnumerator(PartitionRangePageAsyncEnumerator<TPage, TState> enumerator)
             : base(enumerator.FeedRangeState)

Microsoft.Azure.Cosmos/src/Pagination/BufferedPartitionRangePageAsyncEnumeratorBase.cs

@@ -18,7 +18,9 @@ protected BufferedPartitionRangePageAsyncEnumeratorBase(FeedRangeState<TState> f
         {
         }
 
-        public abstract Exception BufferedException { get; }
+        public abstract Exception BufferedException { get; }
+
+        public abstract int BufferedItemCount { get; }
 
         public abstract ValueTask PrefetchAsync(ITrace trace, CancellationToken cancellationToken);
     }

Microsoft.Azure.Cosmos/src/Pagination/CrossFeedRangePage.cs

@@ -19,8 +19,10 @@ public CrossFeedRangePage(TBackendPage backendEndPage, CrossFeedRangeState<TBack
             this.Page = backendEndPage;
         }
 
-        public TBackendPage Page { get; }
-
+        public TBackendPage Page { get; }
+
+        public override int ItemCount => this.Page.ItemCount;
+
         protected override ImmutableHashSet<string> DerivedClassBannedHeaders => bannedHeaders;
     }
 }

Microsoft.Azure.Cosmos/src/Pagination/FullyBufferedPartitionRangeAsyncEnumerator.cs

@@ -16,12 +16,15 @@ internal sealed class FullyBufferedPartitionRangeAsyncEnumerator<TPage, TState>
     {
         private readonly PartitionRangePageAsyncEnumerator<TPage, TState> enumerator;
         private readonly List<TPage> bufferedPages;
-        private int currentIndex;
+        private int currentIndex;
+        private int bufferedItemCount;
         private Exception exception;
 
         private bool hasPrefetched;
 
-        public override Exception BufferedException => this.exception;
+        public override Exception BufferedException => this.exception;
+
+        public override int BufferedItemCount => this.bufferedItemCount;
 
         public FullyBufferedPartitionRangeAsyncEnumerator(PartitionRangePageAsyncEnumerator<TPage, TState> enumerator)
             : this(enumerator, null)
@@ -67,7 +70,8 @@ public override async ValueTask PrefetchAsync(ITrace trace, CancellationToken ca
                     TryCatch<TPage> current = this.enumerator.Current;
                     if (current.Succeeded)
                     {
-                        this.bufferedPages.Add(current.Result);
+                        this.bufferedPages.Add(current.Result);
+                        this.bufferedItemCount += current.Result.ItemCount;
                     }
                     else
                     {

Microsoft.Azure.Cosmos/src/Pagination/NetworkAttachedDocumentContainer.cs

@@ -206,15 +206,17 @@ public async Task<TryCatch<ReadFeedPage>> MonadicReadFeedAsync(
             if (responseMessage.StatusCode == HttpStatusCode.OK)
             {
                 double requestCharge = responseMessage.Headers.RequestCharge;
-                string activityId = responseMessage.Headers.ActivityId;
+                string activityId = responseMessage.Headers.ActivityId;
+                int itemCount = responseMessage.Headers.ItemCount;
                 ReadFeedState state = responseMessage.Headers.ContinuationToken != null ? ReadFeedState.Continuation(CosmosString.Create(responseMessage.Headers.ContinuationToken)) : null;
                 Dictionary<string, string> additionalHeaders = GetAdditionalHeaders(
                     responseMessage.Headers.CosmosMessageHeaders,
                     ReadFeedPage.BannedHeaders);
 
                 ReadFeedPage readFeedPage = new ReadFeedPage(
                     responseMessage.Content,
-                    requestCharge,
+                    requestCharge,
+                    itemCount,
                     activityId,
                     additionalHeaders,
                     state);
@@ -327,7 +329,8 @@ public async Task<TryCatch<ChangeFeedPage>> MonadicChangeFeedAsync(
             if (pageHasResult)
             {
                 double requestCharge = responseMessage.Headers.RequestCharge;
-                string activityId = responseMessage.Headers.ActivityId;
+                string activityId = responseMessage.Headers.ActivityId;
+                int itemCount = responseMessage.Headers.ItemCount;
                 ChangeFeedState state = ChangeFeedState.Continuation(CosmosString.Create(responseMessage.Headers.ETag));
                 Dictionary<string, string> additionalHeaders = GetAdditionalHeaders(
                     responseMessage.Headers.CosmosMessageHeaders,
@@ -338,7 +341,8 @@ public async Task<TryCatch<ChangeFeedPage>> MonadicChangeFeedAsync(
                 {
                     changeFeedPage = new ChangeFeedSuccessPage(
                         responseMessage.Content,
-                        requestCharge,
+                        requestCharge,
+                        itemCount,
                         activityId,
                         additionalHeaders,
                         state);

Microsoft.Azure.Cosmos/src/Pagination/Page.cs

@@ -20,12 +20,12 @@ internal abstract class Page<TState>
         private static readonly IReadOnlyDictionary<string, string> EmptyDictionary = new Dictionary<string, string>();
 
         protected Page(
-            double requestCharge,
+            double requestCharge,
             string activityId,
             IReadOnlyDictionary<string, string> additionalHeaders,
             TState state)
         {
-            this.RequestCharge = requestCharge < 0 ? throw new ArgumentOutOfRangeException(nameof(requestCharge)) : requestCharge;
+            this.RequestCharge = requestCharge < 0 ? throw new ArgumentOutOfRangeException(nameof(requestCharge)) : requestCharge;
             this.ActivityId = activityId;
             this.State = state;
 
@@ -47,7 +47,9 @@ protected Page(
             this.AdditionalHeaders = additionalHeaders ?? EmptyDictionary;
         }
 
-        public double RequestCharge { get; }
+        public double RequestCharge { get; }
+
+        public abstract int ItemCount { get; }
 
         public string ActivityId { get; }
 

Microsoft.Azure.Cosmos/src/Query/Core/Pipeline/CrossPartition/OrderBy/OrderByQueryPage.cs

@@ -28,8 +28,10 @@ public OrderByQueryPage(QueryPage queryPage)
 
         public QueryPage Page { get; }
 
-        public IEnumerator<CosmosElement> Enumerator { get; }
-
+        public IEnumerator<CosmosElement> Enumerator { get; }
+
+        public override int ItemCount => this.Page.ItemCount;
+
         protected override ImmutableHashSet<string> DerivedClassBannedHeaders => bannedHeaders;
     }
 }

Microsoft.Azure.Cosmos/src/Query/Core/Pipeline/CrossPartition/OrderBy/OrderByQueryPartitionRangePageAsyncEnumerator.cs

@@ -6,7 +6,6 @@ namespace Microsoft.Azure.Cosmos.Query.Core.Pipeline.CrossPartition.OrderBy
 {
     using System;
     using System.Collections.Generic;
-    using System.Runtime.CompilerServices;
     using System.Threading;
     using System.Threading.Tasks;
     using Microsoft.Azure.Cosmos.Pagination;
@@ -63,7 +62,9 @@ private OrderByQueryPartitionRangePageAsyncEnumerator(
 
         public string Filter => this.innerEnumerator.Filter;
 
-        public QueryState StartOfPageState { get; private set; }
+        public QueryState StartOfPageState { get; private set; }
+
+        public int BufferedResultCount => this.bufferedEnumerator.BufferedItemCount;
 
         public override ValueTask DisposeAsync()
         {

Microsoft.Azure.Cosmos/src/Query/Core/Pipeline/Pagination/QueryPage.cs

@@ -50,6 +50,8 @@ public QueryPage(
 
         public bool? Streaming { get; }
 
+        public override int ItemCount => this.Documents.Count;
+
         protected override ImmutableHashSet<string> DerivedClassBannedHeaders => QueryPage.BannedHeaders;
     }
 }

Microsoft.Azure.Cosmos/src/ReadFeed/Pagination/ReadFeedPage.cs

@@ -22,17 +22,21 @@ internal sealed class ReadFeedPage : Page<ReadFeedState>
 
         public ReadFeedPage(
             Stream content,
-            double requestCharge,
+            double requestCharge,
+            int itemCount,
             string activityId,
             IReadOnlyDictionary<string, string> additionalHeaders,
             ReadFeedState state)
             : base(requestCharge, activityId, additionalHeaders, state)
         {
-            this.Content = content ?? throw new ArgumentNullException(nameof(content));
+            this.Content = content ?? throw new ArgumentNullException(nameof(content));
+            this.ItemCount = itemCount;
         }
 
-        public Stream Content { get; }
-
+        public Stream Content { get; }
+
+        public override int ItemCount { get; }
+
         protected override ImmutableHashSet<string> DerivedClassBannedHeaders => BannedHeaders;
     }
 }

Microsoft.Azure.Cosmos/src/Telemetry/OpenTelemetry/OpenTelemetryResponse.cs

@@ -18,7 +18,7 @@ internal OpenTelemetryResponse(TransactionalBatchResponse responseMessage)
                   requestCharge: OpenTelemetryResponse.GetHeader(responseMessage)?.RequestCharge,
                   responseContentLength: null,
                   diagnostics: responseMessage.Diagnostics,
-                  itemCount: OpenTelemetryResponse.GetHeader(responseMessage)?.ItemCount,
+                  itemCount: OpenTelemetryResponse.GetHeader(responseMessage)?.ItemCount.ToString(),
                   requestMessage: null,
                   subStatusCode: OpenTelemetryResponse.GetHeader(responseMessage)?.SubStatusCode,
                   activityId: OpenTelemetryResponse.GetHeader(responseMessage)?.ActivityId,
@@ -32,7 +32,7 @@ internal OpenTelemetryResponse(ResponseMessage responseMessage)
                   requestCharge: OpenTelemetryResponse.GetHeader(responseMessage)?.RequestCharge,
                   responseContentLength: OpenTelemetryResponse.GetPayloadSize(responseMessage),
                   diagnostics: responseMessage.Diagnostics,
-                  itemCount: OpenTelemetryResponse.GetHeader(responseMessage)?.ItemCount,
+                  itemCount: OpenTelemetryResponse.GetHeader(responseMessage)?.ItemCount.ToString(),
                   requestMessage: responseMessage.RequestMessage,
                   subStatusCode: OpenTelemetryResponse.GetHeader(responseMessage)?.SubStatusCode,
                   activityId: OpenTelemetryResponse.GetHeader(responseMessage)?.ActivityId,

Microsoft.Azure.Cosmos/src/Telemetry/OpenTelemetry/OpenTelemetryResponse{T}.cs

@@ -17,7 +17,7 @@ internal OpenTelemetryResponse(FeedResponse<T> responseMessage)
                requestCharge: OpenTelemetryResponse<T>.GetHeader(responseMessage)?.RequestCharge,
                responseContentLength: OpenTelemetryResponse<T>.GetHeader(responseMessage)?.ContentLength,
                diagnostics: responseMessage.Diagnostics,
-               itemCount: OpenTelemetryResponse<T>.GetHeader(responseMessage)?.ItemCount,
+               itemCount: OpenTelemetryResponse<T>.GetHeader(responseMessage)?.ItemCount.ToString(),
                requestMessage: responseMessage.RequestMessage,
                subStatusCode: OpenTelemetryResponse<T>.GetHeader(responseMessage)?.SubStatusCode,
                activityId: OpenTelemetryResponse<T>.GetHeader(responseMessage)?.ActivityId,
@@ -32,7 +32,7 @@ internal OpenTelemetryResponse(Response<T> responseMessage)
                   requestCharge: OpenTelemetryResponse<T>.GetHeader(responseMessage)?.RequestCharge,
                   responseContentLength: OpenTelemetryResponse<T>.GetHeader(responseMessage)?.ContentLength,
                   diagnostics: responseMessage.Diagnostics,
-                  itemCount: OpenTelemetryResponse<T>.GetHeader(responseMessage)?.ItemCount,
+                  itemCount: OpenTelemetryResponse<T>.GetHeader(responseMessage)?.ItemCount.ToString(),
                   requestMessage: responseMessage.RequestMessage,
                   subStatusCode: OpenTelemetryResponse<T>.GetHeader(responseMessage)?.SubStatusCode,
                   activityId: OpenTelemetryResponse<T>.GetHeader(responseMessage)?.ActivityId,

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/ChangeFeed/CrossPartitionChangeFeedAsyncEnumeratorTests.cs

@@ -317,7 +317,13 @@ public async Task ShouldSkipNotModifiedAndReturnResults()
                 It.IsAny<ITrace>(),
                 It.IsAny<CancellationToken>())).ReturnsAsync(
                 (FeedRangeState<ChangeFeedState> state, ChangeFeedPaginationOptions options, ITrace trace, CancellationToken token)
-                    => TryCatch<ChangeFeedPage>.FromResult(new ChangeFeedSuccessPage(content: new MemoryStream(Encoding.UTF8.GetBytes("{\"Documents\": [], \"_count\": 0, \"_rid\": \"asdf\"}")), requestCharge: 5, activityId: string.Empty, additionalHeaders: default, state.State)));
+                    => TryCatch<ChangeFeedPage>.FromResult(new ChangeFeedSuccessPage(
+                        content: new MemoryStream(Encoding.UTF8.GetBytes("{\"Documents\": [], \"_count\": 0, \"_rid\": \"asdf\"}")),
+                        requestCharge: 5,
+                        itemCount: 0,
+                        activityId: string.Empty,
+                        additionalHeaders: default,
+                        state.State)));
 
             // Returns a 304 with 1RU charge on CC-FF
             documentContainer.Setup(c => c.MonadicChangeFeedAsync(