Add MessagePackStreamReader.DiscardBufferedData method

3 files changed, 35 insertions, 0 deletions

diff --git a/src/MessagePack.UnityClient/Assets/Scripts/MessagePack/MessagePackStreamReader.cs b/src/MessagePack.UnityClient/Assets/Scripts/MessagePack/MessagePackStreamReader.cs
index 3aa65cad..fb439ddc 100644
--- a/src/MessagePack.UnityClient/Assets/Scripts/MessagePack/MessagePackStreamReader.cs
+++ b/src/MessagePack.UnityClient/Assets/Scripts/MessagePack/MessagePackStreamReader.cs
@@ -90,6 +90,20 @@ namespace MessagePack
             }
         }
 
+        /// <summary>
+        /// Arranges for the next read operation to start by reading from the underlying <see cref="Stream"/>
+        /// instead of any data buffered from a previous read.
+        /// </summary>
+        /// <remarks>
+        /// This is appropriate if the underlying <see cref="Stream"/> has been repositioned such that
+        /// any previously buffered data is no longer applicable to what the caller wants to read.
+        /// </remarks>
+        public void DiscardBufferedData()
+        {
+            this.sequenceRental.Value.Reset();
+            this.endOfLastMessage = default;
+        }
+
         /// <inheritdoc/>
         public void Dispose()
         {
diff --git a/src/MessagePack.UnityClient/Assets/Scripts/Tests/ShareTests/MessagePackStreamReaderTests.cs b/src/MessagePack.UnityClient/Assets/Scripts/Tests/ShareTests/MessagePackStreamReaderTests.cs
index b5896e49..fddb4cad 100644
--- a/src/MessagePack.UnityClient/Assets/Scripts/Tests/ShareTests/MessagePackStreamReaderTests.cs
+++ b/src/MessagePack.UnityClient/Assets/Scripts/Tests/ShareTests/MessagePackStreamReaderTests.cs
@@ -140,6 +140,26 @@ namespace MessagePack.Tests
         }
 
         [Fact]
+        public async Task DiscardBufferedData()
+        {
+            var ms = new MemoryStream(this.twoMessages.ToArray());
+            using (var reader = new MessagePackStreamReader(ms))
+            {
+                var message1a = await reader.ReadAsync(this.TimeoutToken);
+                Assert.NotNull(message1a);
+                Assert.Equal(this.twoMessages.Slice(0, this.messagePositions[0]).ToArray(), message1a.Value.ToArray());
+
+                ms.Position = 0;
+                reader.DiscardBufferedData();
+
+                // Verify that we can read the message at the start of the new position.
+                var message1b = await reader.ReadAsync(this.TimeoutToken);
+                Assert.NotNull(message1b);
+                Assert.Equal(this.twoMessages.Slice(0, this.messagePositions[0]).ToArray(), message1b.Value.ToArray());
+            }
+        }
+
+        [Fact]
         public void DisposeClosesStream()
         {
             var ms = new MemoryStream();
diff --git a/src/MessagePack/PublicAPI.Unshipped.txt b/src/MessagePack/PublicAPI.Unshipped.txt
index f5d69265..3c481910 100644
--- a/src/MessagePack/PublicAPI.Unshipped.txt
+++ b/src/MessagePack/PublicAPI.Unshipped.txt
@@ -7,6 +7,7 @@ MessagePack.MessagePackReader.ReadDateTime(MessagePack.ExtensionHeader header) -
 MessagePack.MessagePackReader.TryReadArrayHeader(out int count) -> bool
 MessagePack.MessagePackReader.TryReadExtensionFormatHeader(out MessagePack.ExtensionHeader extensionHeader) -> bool
 MessagePack.MessagePackReader.TryReadMapHeader(out int count) -> bool
+MessagePack.MessagePackStreamReader.DiscardBufferedData() -> void
 MessagePack.MessagePackStreamReader.MessagePackStreamReader(System.IO.Stream stream, bool leaveOpen) -> void
 MessagePack.MessagePackStreamReader.ReadArrayAsync(System.Threading.CancellationToken cancellationToken) -> System.Collections.Generic.IAsyncEnumerable<System.Buffers.ReadOnlySequence<byte>>
 MessagePack.MessagePackWriter.WriteBinHeader(int length) -> void