C#: Add ParseFrom/MergeFrom ReadOnlySpan<byte>

Address #7885

csharp/src/Google.Protobuf.Test/CodedInputStreamTest.cs

@@ -926,6 +926,39 @@ namespace Google.Protobuf
             }
         }
 
+        [Test]
+        public void TestParseFromSpan()
+        {
+            var testMessage = new TestAllTypes
+            {
+                RepeatedBool = { true, false },
+                SingleDouble = 42.0d,
+                SingleString = "testing"
+            };
+
+            ReadOnlySpan<byte> messagesBytes = testMessage.ToByteArray().AsSpan();
+            TestAllTypes parsedMessage = TestAllTypes.Parser.ParseFrom(messagesBytes);
+
+            Assert.AreEqual(testMessage, parsedMessage);
+        }
+
+        [Test]
+        public void TestMergeFromSpan()
+        {
+            var testMessage = new TestAllTypes
+            {
+                RepeatedBool = { true, false },
+                SingleDouble = 42.0d,
+                SingleString = "testing"
+            };
+
+            ReadOnlySpan<byte> messagesBytes = testMessage.ToByteArray().AsSpan();
+            var mergedMessage = new TestAllTypes();
+            mergedMessage.MergeFrom(messagesBytes);
+
+            Assert.AreEqual(testMessage, mergedMessage);
+        }
+
         /// <returns>A serialized big message</returns>
         private static byte[] GenerateBigSerializedMessage()
         {

csharp/src/Google.Protobuf/MessageExtensions.cs

@@ -79,6 +79,15 @@ namespace Google.Protobuf
         public static void MergeFrom(this IMessage message, Stream input) =>
             MergeFrom(message, input, false, null);
 
+        /// <summary>
+        /// Merges data from the given span into an existing message.
+        /// </summary>
+        /// <param name="message">The message to merge the data into.</param>
+        /// <param name="span">Span containing the data to merge, which must be protobuf-encoded binary data.</param>
+        [SecuritySafeCritical]
+        public static void MergeFrom(this IMessage message, ReadOnlySpan<byte> span) =>
+            MergeFrom(message, span, false, null);
+
         /// <summary>
         /// Merges length-delimited data from the given stream into an existing message.
         /// </summary>
@@ -294,6 +303,16 @@ namespace Google.Protobuf
             ParsingPrimitivesMessages.CheckReadEndOfStreamTag(ref ctx.state);
         }
 
+        [SecuritySafeCritical]
+        internal static void MergeFrom(this IMessage message, ReadOnlySpan<byte> data, bool discardUnknownFields, ExtensionRegistry registry)
+        {
+            ParseContext.Initialize(data, out ParseContext ctx);
+            ctx.DiscardUnknownFields = discardUnknownFields;
+            ctx.ExtensionRegistry = registry;
+            ParsingPrimitivesMessages.ReadRawMessage(ref ctx, message);
+            ParsingPrimitivesMessages.CheckReadEndOfStreamTag(ref ctx.state);
+        }
+
         internal static void MergeDelimitedFrom(this IMessage message, Stream input, bool discardUnknownFields, ExtensionRegistry registry)
         {
             ProtoPreconditions.CheckNotNull(message, "message");

csharp/src/Google.Protobuf/MessageParser.cs

@@ -128,6 +128,19 @@ namespace Google.Protobuf
             return message;
         }
 
+        /// <summary>
+        /// Parses a message from the given span.
+        /// </summary>
+        /// <param name="data">The data to parse.</param>
+        /// <returns>The parsed message.</returns>
+        [SecuritySafeCritical]
+        public IMessage ParseFrom(ReadOnlySpan<byte> data)
+        {
+            IMessage message = factory();
+            message.MergeFrom(data, DiscardUnknownFields, Extensions);
+            return message;
+        }
+
         /// <summary>
         /// Parses a length-delimited message from the given stream.
         /// </summary>
@@ -315,6 +328,19 @@ namespace Google.Protobuf
             return message;
         }
 
+        /// <summary>
+        /// Parses a message from the given span.
+        /// </summary>
+        /// <param name="data">The data to parse.</param>
+        /// <returns>The parsed message.</returns>
+        [SecuritySafeCritical]
+        public new T ParseFrom(ReadOnlySpan<byte> data)
+        {
+            T message = factory();
+            message.MergeFrom(data, DiscardUnknownFields, Extensions);
+            return message;
+        }
+
         /// <summary>
         /// Parses a length-delimited message from the given stream.
         /// </summary>

csharp/src/Google.Protobuf/ParseContext.cs

@@ -104,6 +104,29 @@ namespace Google.Protobuf
             ctx.state.ExtensionRegistry = null;
         }
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static void Initialize(ReadOnlySpan<byte> input, out ParseContext ctx)
+        {
+            Initialize(input, DefaultRecursionLimit, out ctx);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static void Initialize(ReadOnlySpan<byte> input, int recursionLimit, out ParseContext ctx)
+        {
+            ctx.buffer = input;
+            ctx.state = default;
+            ctx.state.lastTag = 0;
+            ctx.state.recursionDepth = 0;
+            ctx.state.sizeLimit = DefaultSizeLimit;
+            ctx.state.recursionLimit = recursionLimit;
+            ctx.state.currentLimit = int.MaxValue;
+            ctx.state.bufferPos = 0;
+            ctx.state.bufferSize = input.Length;
+
+            ctx.state.DiscardUnknownFields = false;
+            ctx.state.ExtensionRegistry = null;
+        }
+
         /// <summary>
         /// Returns the last tag read, or 0 if no tags have been read or we've read beyond
         /// the end of the input.