SQLStreamStore · yreynhout · Jul 2, 2020
diff --git a/src/SqlStreamStore/IReadonlyStreamStore.cs b/src/SqlStreamStore/IReadonlyStreamStore.cs
@@ -210,9 +210,19 @@ IAllStreamSubscription SubscribeToAll(
         ///     The cancellation instruction.
         /// </param>
         /// <returns>
-        ///     The head position.
+        ///     The head position, or <c>-1</c> if there is none.
         /// </returns>
         Task<long> ReadHeadPosition(CancellationToken cancellationToken = default);
+        /// <summary>
+        ///     Reads the head message (the very latest message).
+        /// </summary>
+        /// <param name="cancellationToken">
+        ///     The cancellation instruction.
+        /// </param>
+        /// <returns>
+        ///     The head message, or <c>null</c> if there is no head message.
+        /// </returns>
+        Task<StreamMessage?> ReadHeadMessage(CancellationToken cancellationToken = default);
 
         /// <summary>
         ///     Reads the head position (the position of the very latest message) of a particular stream.
@@ -242,6 +252,20 @@ IAllStreamSubscription SubscribeToAll(
         /// </returns>
         Task<int> ReadStreamHeadVersion(StreamId streamId, CancellationToken cancellationToken = default);
 
+        /// <summary>
+        ///     Reads the head message (the very latest message) of a particular stream.
+        /// </summary>
+        /// <param name="streamId">
+        ///     The stream to read the head message of.
+        /// </param>
+        /// <param name="cancellationToken">
+        ///     The cancellation instruction.
+        /// </param>
+        /// <returns>
+        ///     The head message of the stream, or <c>null</c> if no such stream or an empty stream.
+        /// </returns>
+        Task<StreamMessage?> ReadStreamHeadMessage(StreamId streamId, CancellationToken cancellationToken = default);
+
         /// <summary>
         ///     Gets the stream metadata.
         /// </summary>

diff --git a/src/SqlStreamStore/InMemory/InMemoryStreamStore.cs b/src/SqlStreamStore/InMemory/InMemoryStreamStore.cs
@@ -713,6 +713,35 @@ protected override Task<int> ReadStreamHeadVersionInternal(string streamId, Canc
             }
         }
 
+        protected override Task<StreamMessage?> ReadHeadMessageInternal(CancellationToken cancellationToken)
+        {
+            var message = _allStream.LastOrDefault();
+            return message == null 
+                ? Task.FromResult<StreamMessage?>(default) 
+                : Task.FromResult<StreamMessage?>(
+                    new StreamMessage(
+                        message.StreamId, message.MessageId, 
+                        message.StreamVersion, message.Position, 
+                        message.Created, message.Type, 
+                        message.JsonMetadata, message.JsonData));
+        }
+
+        protected override Task<StreamMessage?> ReadStreamHeadMessageInternal(string streamId, CancellationToken cancellationToken)
+        {
+            using(_lock.UseReadLock())
+            {
+                if(!_streams.TryGetValue(streamId, out InMemoryStream stream))
+                    return Task.FromResult<StreamMessage?>(default);
+                var message = stream.Messages[stream.Messages.Count - 1];
+                return Task.FromResult<StreamMessage?>(
+                    new StreamMessage(
+                        message.StreamId, message.MessageId, 
+                        message.StreamVersion, message.Position, 
+                        message.Created, message.Type, 
+                        message.JsonMetadata, message.JsonData));
+            }
+        }
+
         protected override IAllStreamSubscription SubscribeToAllInternal(
             long? fromPosition,
             AllStreamMessageReceived streamMessageReceived,

diff --git a/src/SqlStreamStore/Infrastructure/ReadonlyStreamStoreBase.cs b/src/SqlStreamStore/Infrastructure/ReadonlyStreamStoreBase.cs
@@ -240,6 +240,22 @@ public Task<long> ReadStreamHeadPosition(StreamId streamId, CancellationToken ca
             return ReadStreamHeadPositionInternal(streamId, cancellationToken);
         }
 
+        public Task<StreamMessage?> ReadHeadMessage(CancellationToken cancellationToken = default)
+        {
+            GuardAgainstDisposed();
+
+            return ReadHeadMessageInternal(cancellationToken);
+        }
+
+        public Task<StreamMessage?> ReadStreamHeadMessage(StreamId streamId, CancellationToken cancellationToken = default)
+        {
+            if (streamId == null) throw new ArgumentNullException(nameof(streamId));
+
+            GuardAgainstDisposed();
+
+            return ReadStreamHeadMessageInternal(streamId, cancellationToken);
+        }
+
         public Task<int> ReadStreamHeadVersion(StreamId streamId, CancellationToken cancellationToken = default)
         {
             if (streamId == null) throw new ArgumentNullException(nameof(streamId));
@@ -318,6 +334,8 @@ protected abstract Task<ReadStreamPage> ReadStreamBackwardsInternal(
         protected abstract Task<long> ReadHeadPositionInternal(CancellationToken cancellationToken);
         protected abstract Task<long> ReadStreamHeadPositionInternal(string streamId, CancellationToken cancellationToken);
         protected abstract Task<int> ReadStreamHeadVersionInternal(string streamId, CancellationToken cancellationToken);
+        protected abstract Task<StreamMessage?> ReadHeadMessageInternal(CancellationToken cancellationToken);
+        protected abstract Task<StreamMessage?> ReadStreamHeadMessageInternal(string streamId, CancellationToken cancellationToken);
 
         protected abstract IStreamSubscription SubscribeToStreamInternal(
             string streamId,

diff --git a/tests/SqlStreamStore.AcceptanceTests/AcceptanceTests.ReadHeadCheckpoint.cs b/tests/SqlStreamStore.AcceptanceTests/AcceptanceTests.ReadHeadCheckpoint.cs
@@ -94,5 +94,65 @@ public async Task Given_filled_stream_when_get_head_version_then_returns_expecte
 
             head.ShouldBe(2);
         }
+
+        [Fact]
+        public async Task Given_empty_store_when_get_head_message_Then_should_be_minus_one()
+        {
+            var head = await Store.ReadHeadMessage();
+
+            head.ShouldBe(default);
+        }
+
+        [Fact]
+        public async Task Given_store_with_empty_stream_when_get_head_message_Then_should_be_minus_one()
+        {
+            await Store.AppendToStream("stream-1", ExpectedVersion.NoStream, CreateNewStreamMessages());
+
+            var head = await Store.ReadHeadMessage();
+
+            head.ShouldBe(default);
+        }
+
+        [Fact]
+        public async Task Given_store_with_messages_then_can_get_head_message()
+        {
+            var messages = CreateNewStreamMessages(1, 2, 3);
+            await Store.AppendToStream("stream-1", ExpectedVersion.NoStream, messages);
+
+            var head = await Store.ReadHeadMessage();
+
+            head.ShouldBe(messages[3]);
+        }
+
+        [Fact]
+        public async Task Given_no_stream_when_get_stream_head_message_then_returns_expected_result()
+        {
+            await Store.AppendToStream("other-stream", ExpectedVersion.NoStream, CreateNewStreamMessages(1));
+
+            var head = await Store.ReadStreamHeadMessage("this-stream");
+
+            head.ShouldBe(default);
+        }
+
+        [Fact]
+        public async Task Given_empty_stream_when_get_stream_head_message_then_returns_expected_result()
+        {
+            await Store.AppendToStream("this-stream", ExpectedVersion.NoStream, CreateNewStreamMessages());
+
+            var head = await Store.ReadStreamHeadMessage("this-stream");
+
+            head.ShouldBe(default);
+        }
+
+        [Fact]
+        public async Task Given_filled_stream_when_get_stream_head_message_then_returns_expected_result()
+        {
+            var messages = CreateNewStreamMessages(1, 2, 3);
+            await Store.AppendToStream("this-stream", ExpectedVersion.NoStream, messages);
+
+            var head = await Store.ReadStreamHeadMessage("this-stream");
+
+            head.ShouldBe(messages[3]);
+        }
     }
 }