csharp/src/Google.Protobuf/MessageParser.cs - third_party/protobuf - Git at Google

 #region Copyright notice and license
 // Protocol Buffers - Google's data interchange format
 // Copyright 2015 Google Inc.  All rights reserved.
 // https://developers.google.com/protocol-buffers/
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 // copyright notice, this list of conditions and the following disclaimer
 // in the documentation and/or other materials provided with the
 // distribution.
 //     * Neither the name of Google Inc. nor the names of its
 // contributors may be used to endorse or promote products derived from
 // this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #endregion

 using System;
 using System.Buffers;
 using System.IO;
 using System.Security;

 namespace Google.Protobuf
 {
     /// <summary>
     /// A general message parser, typically used by reflection-based code as all the methods
     /// return simple <see cref="IMessage"/>.
     /// </summary>
     public class MessageParser
     {
         private readonly Func<IMessage> factory;
         private protected bool DiscardUnknownFields { get; }

         internal ExtensionRegistry Extensions { get; }

         internal MessageParser(Func<IMessage> factory, bool discardUnknownFields, ExtensionRegistry extensions)
         {
             this.factory = factory;
             DiscardUnknownFields = discardUnknownFields;
             Extensions = extensions;
         }

         /// <summary>
         /// Creates a template instance ready for population.
         /// </summary>
         /// <returns>An empty message.</returns>
         internal IMessage CreateTemplate()
         {
             return factory();
         }

         /// <summary>
         /// Parses a message from a byte array.
         /// </summary>
         /// <param name="data">The byte array containing the message. Must not be null.</param>
         /// <returns>The newly parsed message.</returns>
         public IMessage ParseFrom(byte[] data)
         {
             IMessage message = factory();
             message.MergeFrom(data, DiscardUnknownFields, Extensions);
             return message;
         }

         /// <summary>
         /// Parses a message from a byte array slice.
         /// </summary>
         /// <param name="data">The byte array containing the message. Must not be null.</param>
         /// <param name="offset">The offset of the slice to parse.</param>
         /// <param name="length">The length of the slice to parse.</param>
         /// <returns>The newly parsed message.</returns>
         public IMessage ParseFrom(byte[] data, int offset, int length)
         {
             IMessage message = factory();
             message.MergeFrom(data, offset, length, DiscardUnknownFields, Extensions);
             return message;
         }

         /// <summary>
         /// Parses a message from the given byte string.
         /// </summary>
         /// <param name="data">The data to parse.</param>
         /// <returns>The parsed message.</returns>
         public IMessage ParseFrom(ByteString data)
         {
             IMessage message = factory();
             message.MergeFrom(data, DiscardUnknownFields, Extensions);
             return message;
         }

         /// <summary>
         /// Parses a message from the given stream.
         /// </summary>
         /// <param name="input">The stream to parse.</param>
         /// <returns>The parsed message.</returns>
         public IMessage ParseFrom(Stream input)
         {
             IMessage message = factory();
             message.MergeFrom(input, DiscardUnknownFields, Extensions);
             return message;
         }

         /// <summary>
         /// Parses a message from the given sequence.
         /// </summary>
         /// <param name="data">The data to parse.</param>
         /// <returns>The parsed message.</returns>
         [SecuritySafeCritical]
         public IMessage ParseFrom(ReadOnlySequence<byte> data)
         {
             IMessage message = factory();
             message.MergeFrom(data, DiscardUnknownFields, Extensions);
             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>
         /// <remarks>
         /// The stream is expected to contain a length and then the data. Only the amount of data
         /// specified by the length will be consumed.
         /// </remarks>
         /// <param name="input">The stream to parse.</param>
         /// <returns>The parsed message.</returns>
         public IMessage ParseDelimitedFrom(Stream input)
         {
             IMessage message = factory();
             message.MergeDelimitedFrom(input, DiscardUnknownFields, Extensions);
             return message;
         }

         /// <summary>
         /// Parses a message from the given coded input stream.
         /// </summary>
         /// <param name="input">The stream to parse.</param>
         /// <returns>The parsed message.</returns>
         public IMessage ParseFrom(CodedInputStream input)
         {
             IMessage message = factory();
             MergeFrom(message, input);
             return message;
         }

         /// <summary>
         /// Parses a message from the given JSON.
         /// </summary>
         /// <remarks>This method always uses the default JSON parser; it is not affected by <see cref="WithDiscardUnknownFields(bool)"/>.
         /// To ignore unknown fields when parsing JSON, create a <see cref="JsonParser"/> using a <see cref="JsonParser.Settings"/>
         /// with <see cref="JsonParser.Settings.IgnoreUnknownFields"/> set to true and call <see cref="JsonParser.Parse{T}(string)"/> directly.
         /// </remarks>
         /// <param name="json">The JSON to parse.</param>
         /// <returns>The parsed message.</returns>
         /// <exception cref="InvalidJsonException">The JSON does not comply with RFC 7159</exception>
         /// <exception cref="InvalidProtocolBufferException">The JSON does not represent a Protocol Buffers message correctly</exception>
         public IMessage ParseJson(string json)
         {
             IMessage message = factory();
             JsonParser.Default.Merge(message, json);
             return message;
         }

         // TODO: When we're using a C# 7.1 compiler, make this private protected.
         internal void MergeFrom(IMessage message, CodedInputStream codedInput)
         {
             bool originalDiscard = codedInput.DiscardUnknownFields;
             ExtensionRegistry originalRegistry = codedInput.ExtensionRegistry;
             try
             {
                 codedInput.DiscardUnknownFields = DiscardUnknownFields;
                 codedInput.ExtensionRegistry = Extensions;
                 message.MergeFrom(codedInput);
             }
             finally
             {
                 codedInput.DiscardUnknownFields = originalDiscard;
                 codedInput.ExtensionRegistry = originalRegistry;
             }
         }

         /// <summary>
         /// Creates a new message parser which optionally discards unknown fields when parsing.
         /// </summary>
         /// <remarks>Note that this does not affect the behavior of <see cref="ParseJson(string)"/>
         /// at all. To ignore unknown fields when parsing JSON, create a <see cref="JsonParser"/> using a <see cref="JsonParser.Settings"/>
         /// with <see cref="JsonParser.Settings.IgnoreUnknownFields"/> set to true and call <see cref="JsonParser.Parse{T}(string)"/> directly.</remarks>
         /// <param name="discardUnknownFields">Whether or not to discard unknown fields when parsing.</param>
         /// <returns>A newly configured message parser.</returns>
         public MessageParser WithDiscardUnknownFields(bool discardUnknownFields) =>
             new MessageParser(factory, discardUnknownFields, Extensions);

         /// <summary>
         /// Creates a new message parser which registers extensions from the specified registry upon creating the message instance
         /// </summary>
         /// <param name="registry">The extensions to register</param>
         /// <returns>A newly configured message parser.</returns>
         public MessageParser WithExtensionRegistry(ExtensionRegistry registry) =>
             new MessageParser(factory, DiscardUnknownFields, registry);
     }

     /// <summary>
     /// A parser for a specific message type.
     /// </summary>
     /// <remarks>
     /// <p>
     /// This delegates most behavior to the
     /// <see cref="IMessage.MergeFrom"/> implementation within the original type, but
     /// provides convenient overloads to parse from a variety of sources.
     /// </p>
     /// <p>
     /// Most applications will never need to create their own instances of this type;
     /// instead, use the static <c>Parser</c> property of a generated message type to obtain a
     /// parser for that type.
     /// </p>
     /// </remarks>
     /// <typeparam name="T">The type of message to be parsed.</typeparam>
     public sealed class MessageParser<T> : MessageParser where T : IMessage<T>
     {
         // Implementation note: all the methods here *could* just delegate up to the base class and cast the result.
         // The current implementation avoids a virtual method call and a cast, which *may* be significant in some cases.
         // Benchmarking work is required to measure the significance - but it's only a few lines of code in any case.
         // The API wouldn't change anyway - just the implementation - so this work can be deferred.
         private readonly Func<T> factory;

         /// <summary>
         /// Creates a new parser.
         /// </summary>
         /// <remarks>
         /// The factory method is effectively an optimization over using a generic constraint
         /// to require a parameterless constructor: delegates are significantly faster to execute.
         /// </remarks>
         /// <param name="factory">Function to invoke when a new, empty message is required.</param>
         public MessageParser(Func<T> factory) : this(factory, false, null)
         {
         }

         internal MessageParser(Func<T> factory, bool discardUnknownFields, ExtensionRegistry extensions) : base(() => factory(), discardUnknownFields, extensions)
         {
             this.factory = factory;
         }

         /// <summary>
         /// Creates a template instance ready for population.
         /// </summary>
         /// <returns>An empty message.</returns>
         internal new T CreateTemplate()
         {
             return factory();
         }

         /// <summary>
         /// Parses a message from a byte array.
         /// </summary>
         /// <param name="data">The byte array containing the message. Must not be null.</param>
         /// <returns>The newly parsed message.</returns>
         public new T ParseFrom(byte[] data)
         {
             T message = factory();
             message.MergeFrom(data, DiscardUnknownFields, Extensions);
             return message;
         }

         /// <summary>
         /// Parses a message from a byte array slice.
         /// </summary>
         /// <param name="data">The byte array containing the message. Must not be null.</param>
         /// <param name="offset">The offset of the slice to parse.</param>
         /// <param name="length">The length of the slice to parse.</param>
         /// <returns>The newly parsed message.</returns>
         public new T ParseFrom(byte[] data, int offset, int length)
         {
             T message = factory();
             message.MergeFrom(data, offset, length, DiscardUnknownFields, Extensions);
             return message;
         }

         /// <summary>
         /// Parses a message from the given byte string.
         /// </summary>
         /// <param name="data">The data to parse.</param>
         /// <returns>The parsed message.</returns>
         public new T ParseFrom(ByteString data)
         {
             T message = factory();
             message.MergeFrom(data, DiscardUnknownFields, Extensions);
             return message;
         }

         /// <summary>
         /// Parses a message from the given stream.
         /// </summary>
         /// <param name="input">The stream to parse.</param>
         /// <returns>The parsed message.</returns>
         public new T ParseFrom(Stream input)
         {
             T message = factory();
             message.MergeFrom(input, DiscardUnknownFields, Extensions);
             return message;
         }

         /// <summary>
         /// Parses a message from the given sequence.
         /// </summary>
         /// <param name="data">The data to parse.</param>
         /// <returns>The parsed message.</returns>
         [SecuritySafeCritical]
         public new T ParseFrom(ReadOnlySequence<byte> data)
         {
             T message = factory();
             message.MergeFrom(data, DiscardUnknownFields, Extensions);
             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>
         /// <remarks>
         /// The stream is expected to contain a length and then the data. Only the amount of data
         /// specified by the length will be consumed.
         /// </remarks>
         /// <param name="input">The stream to parse.</param>
         /// <returns>The parsed message.</returns>
         public new T ParseDelimitedFrom(Stream input)
         {
             T message = factory();
             message.MergeDelimitedFrom(input, DiscardUnknownFields, Extensions);
             return message;
         }

         /// <summary>
         /// Parses a message from the given coded input stream.
         /// </summary>
         /// <param name="input">The stream to parse.</param>
         /// <returns>The parsed message.</returns>
         public new T ParseFrom(CodedInputStream input)
         {
             T message = factory();
             MergeFrom(message, input);
             return message;
         }

         /// <summary>
         /// Parses a message from the given JSON.
         /// </summary>
         /// <param name="json">The JSON to parse.</param>
         /// <returns>The parsed message.</returns>
         /// <exception cref="InvalidJsonException">The JSON does not comply with RFC 7159</exception>
         /// <exception cref="InvalidProtocolBufferException">The JSON does not represent a Protocol Buffers message correctly</exception>
         public new T ParseJson(string json)
         {
             T message = factory();
             JsonParser.Default.Merge(message, json);
             return message;
         }

         /// <summary>
         /// Creates a new message parser which optionally discards unknown fields when parsing.
         /// </summary>
         /// <param name="discardUnknownFields">Whether or not to discard unknown fields when parsing.</param>
         /// <returns>A newly configured message parser.</returns>
         public new MessageParser<T> WithDiscardUnknownFields(bool discardUnknownFields) =>
             new MessageParser<T>(factory, discardUnknownFields, Extensions);

         /// <summary>
         /// Creates a new message parser which registers extensions from the specified registry upon creating the message instance
         /// </summary>
         /// <param name="registry">The extensions to register</param>
         /// <returns>A newly configured message parser.</returns>
         public new MessageParser<T> WithExtensionRegistry(ExtensionRegistry registry) =>
             new MessageParser<T>(factory, DiscardUnknownFields, registry);
     }
 }
	#region Copyright notice and license
	// Protocol Buffers - Google's data interchange format
	// Copyright 2015 Google Inc. All rights reserved.
	// https://developers.google.com/protocol-buffers/
	//
	// Redistribution and use in source and binary forms, with or without
	// modification, are permitted provided that the following conditions are
	// met:
	//
	// * Redistributions of source code must retain the above copyright
	// notice, this list of conditions and the following disclaimer.
	// * Redistributions in binary form must reproduce the above
	// copyright notice, this list of conditions and the following disclaimer
	// in the documentation and/or other materials provided with the
	// distribution.
	// * Neither the name of Google Inc. nor the names of its
	// contributors may be used to endorse or promote products derived from
	// this software without specific prior written permission.
	//
	// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
	// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
	// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
	// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
	// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
	// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	#endregion

	using System;
	using System.Buffers;
	using System.IO;
	using System.Security;

	namespace Google.Protobuf
	{
	/// <summary>
	/// A general message parser, typically used by reflection-based code as all the methods
	/// return simple <see cref="IMessage"/>.
	/// </summary>
	public class MessageParser
	{
	private readonly Func<IMessage> factory;
	private protected bool DiscardUnknownFields { get; }

	internal ExtensionRegistry Extensions { get; }

	internal MessageParser(Func<IMessage> factory, bool discardUnknownFields, ExtensionRegistry extensions)
	{
	this.factory = factory;
	DiscardUnknownFields = discardUnknownFields;
	Extensions = extensions;
	}

	/// <summary>
	/// Creates a template instance ready for population.
	/// </summary>
	/// <returns>An empty message.</returns>
	internal IMessage CreateTemplate()
	{
	return factory();
	}

	/// <summary>
	/// Parses a message from a byte array.
	/// </summary>
	/// <param name="data">The byte array containing the message. Must not be null.</param>
	/// <returns>The newly parsed message.</returns>
	public IMessage ParseFrom(byte[] data)
	{
	IMessage message = factory();
	message.MergeFrom(data, DiscardUnknownFields, Extensions);
	return message;
	}

	/// <summary>
	/// Parses a message from a byte array slice.
	/// </summary>
	/// <param name="data">The byte array containing the message. Must not be null.</param>
	/// <param name="offset">The offset of the slice to parse.</param>
	/// <param name="length">The length of the slice to parse.</param>
	/// <returns>The newly parsed message.</returns>
	public IMessage ParseFrom(byte[] data, int offset, int length)
	{
	IMessage message = factory();
	message.MergeFrom(data, offset, length, DiscardUnknownFields, Extensions);
	return message;
	}

	/// <summary>
	/// Parses a message from the given byte string.
	/// </summary>
	/// <param name="data">The data to parse.</param>
	/// <returns>The parsed message.</returns>
	public IMessage ParseFrom(ByteString data)
	{
	IMessage message = factory();
	message.MergeFrom(data, DiscardUnknownFields, Extensions);
	return message;
	}

	/// <summary>
	/// Parses a message from the given stream.
	/// </summary>
	/// <param name="input">The stream to parse.</param>
	/// <returns>The parsed message.</returns>
	public IMessage ParseFrom(Stream input)
	{
	IMessage message = factory();
	message.MergeFrom(input, DiscardUnknownFields, Extensions);
	return message;
	}

	/// <summary>
	/// Parses a message from the given sequence.
	/// </summary>
	/// <param name="data">The data to parse.</param>
	/// <returns>The parsed message.</returns>
	[SecuritySafeCritical]
	public IMessage ParseFrom(ReadOnlySequence<byte> data)
	{
	IMessage message = factory();
	message.MergeFrom(data, DiscardUnknownFields, Extensions);
	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>
	/// <remarks>
	/// The stream is expected to contain a length and then the data. Only the amount of data
	/// specified by the length will be consumed.
	/// </remarks>
	/// <param name="input">The stream to parse.</param>
	/// <returns>The parsed message.</returns>
	public IMessage ParseDelimitedFrom(Stream input)
	{
	IMessage message = factory();
	message.MergeDelimitedFrom(input, DiscardUnknownFields, Extensions);
	return message;
	}

	/// <summary>
	/// Parses a message from the given coded input stream.
	/// </summary>
	/// <param name="input">The stream to parse.</param>
	/// <returns>The parsed message.</returns>
	public IMessage ParseFrom(CodedInputStream input)
	{
	IMessage message = factory();
	MergeFrom(message, input);
	return message;
	}

	/// <summary>
	/// Parses a message from the given JSON.
	/// </summary>
	/// <remarks>This method always uses the default JSON parser; it is not affected by <see cref="WithDiscardUnknownFields(bool)"/>.
	/// To ignore unknown fields when parsing JSON, create a <see cref="JsonParser"/> using a <see cref="JsonParser.Settings"/>
	/// with <see cref="JsonParser.Settings.IgnoreUnknownFields"/> set to true and call <see cref="JsonParser.Parse{T}(string)"/> directly.
	/// </remarks>
	/// <param name="json">The JSON to parse.</param>
	/// <returns>The parsed message.</returns>
	/// <exception cref="InvalidJsonException">The JSON does not comply with RFC 7159</exception>
	/// <exception cref="InvalidProtocolBufferException">The JSON does not represent a Protocol Buffers message correctly</exception>
	public IMessage ParseJson(string json)
	{
	IMessage message = factory();
	JsonParser.Default.Merge(message, json);
	return message;
	}

	// TODO: When we're using a C# 7.1 compiler, make this private protected.
	internal void MergeFrom(IMessage message, CodedInputStream codedInput)
	{
	bool originalDiscard = codedInput.DiscardUnknownFields;
	ExtensionRegistry originalRegistry = codedInput.ExtensionRegistry;
	try
	{
	codedInput.DiscardUnknownFields = DiscardUnknownFields;
	codedInput.ExtensionRegistry = Extensions;
	message.MergeFrom(codedInput);
	}
	finally
	{
	codedInput.DiscardUnknownFields = originalDiscard;
	codedInput.ExtensionRegistry = originalRegistry;
	}
	}

	/// <summary>
	/// Creates a new message parser which optionally discards unknown fields when parsing.
	/// </summary>
	/// <remarks>Note that this does not affect the behavior of <see cref="ParseJson(string)"/>
	/// at all. To ignore unknown fields when parsing JSON, create a <see cref="JsonParser"/> using a <see cref="JsonParser.Settings"/>
	/// with <see cref="JsonParser.Settings.IgnoreUnknownFields"/> set to true and call <see cref="JsonParser.Parse{T}(string)"/> directly.</remarks>
	/// <param name="discardUnknownFields">Whether or not to discard unknown fields when parsing.</param>
	/// <returns>A newly configured message parser.</returns>
	public MessageParser WithDiscardUnknownFields(bool discardUnknownFields) =>
	new MessageParser(factory, discardUnknownFields, Extensions);

	/// <summary>
	/// Creates a new message parser which registers extensions from the specified registry upon creating the message instance
	/// </summary>
	/// <param name="registry">The extensions to register</param>
	/// <returns>A newly configured message parser.</returns>
	public MessageParser WithExtensionRegistry(ExtensionRegistry registry) =>
	new MessageParser(factory, DiscardUnknownFields, registry);
	}

	/// <summary>
	/// A parser for a specific message type.
	/// </summary>
	/// <remarks>
	/// <p>
	/// This delegates most behavior to the
	/// <see cref="IMessage.MergeFrom"/> implementation within the original type, but
	/// provides convenient overloads to parse from a variety of sources.
	/// </p>
	/// <p>
	/// Most applications will never need to create their own instances of this type;
	/// instead, use the static <c>Parser</c> property of a generated message type to obtain a
	/// parser for that type.
	/// </p>
	/// </remarks>
	/// <typeparam name="T">The type of message to be parsed.</typeparam>
	public sealed class MessageParser<T> : MessageParser where T : IMessage<T>
	{
	// Implementation note: all the methods here could just delegate up to the base class and cast the result.
	// The current implementation avoids a virtual method call and a cast, which may be significant in some cases.
	// Benchmarking work is required to measure the significance - but it's only a few lines of code in any case.
	// The API wouldn't change anyway - just the implementation - so this work can be deferred.
	private readonly Func<T> factory;

	/// <summary>
	/// Creates a new parser.
	/// </summary>
	/// <remarks>
	/// The factory method is effectively an optimization over using a generic constraint
	/// to require a parameterless constructor: delegates are significantly faster to execute.
	/// </remarks>
	/// <param name="factory">Function to invoke when a new, empty message is required.</param>
	public MessageParser(Func<T> factory) : this(factory, false, null)
	{
	}

	internal MessageParser(Func<T> factory, bool discardUnknownFields, ExtensionRegistry extensions) : base(() => factory(), discardUnknownFields, extensions)
	{
	this.factory = factory;
	}

	/// <summary>
	/// Creates a template instance ready for population.
	/// </summary>
	/// <returns>An empty message.</returns>
	internal new T CreateTemplate()
	{
	return factory();
	}

	/// <summary>
	/// Parses a message from a byte array.
	/// </summary>
	/// <param name="data">The byte array containing the message. Must not be null.</param>
	/// <returns>The newly parsed message.</returns>
	public new T ParseFrom(byte[] data)
	{
	T message = factory();
	message.MergeFrom(data, DiscardUnknownFields, Extensions);
	return message;
	}

	/// <summary>
	/// Parses a message from a byte array slice.
	/// </summary>
	/// <param name="data">The byte array containing the message. Must not be null.</param>
	/// <param name="offset">The offset of the slice to parse.</param>
	/// <param name="length">The length of the slice to parse.</param>
	/// <returns>The newly parsed message.</returns>
	public new T ParseFrom(byte[] data, int offset, int length)
	{
	T message = factory();
	message.MergeFrom(data, offset, length, DiscardUnknownFields, Extensions);
	return message;
	}

	/// <summary>
	/// Parses a message from the given byte string.
	/// </summary>
	/// <param name="data">The data to parse.</param>
	/// <returns>The parsed message.</returns>
	public new T ParseFrom(ByteString data)
	{
	T message = factory();
	message.MergeFrom(data, DiscardUnknownFields, Extensions);
	return message;
	}

	/// <summary>
	/// Parses a message from the given stream.
	/// </summary>
	/// <param name="input">The stream to parse.</param>
	/// <returns>The parsed message.</returns>
	public new T ParseFrom(Stream input)
	{
	T message = factory();
	message.MergeFrom(input, DiscardUnknownFields, Extensions);
	return message;
	}

	/// <summary>
	/// Parses a message from the given sequence.
	/// </summary>
	/// <param name="data">The data to parse.</param>
	/// <returns>The parsed message.</returns>
	[SecuritySafeCritical]
	public new T ParseFrom(ReadOnlySequence<byte> data)
	{
	T message = factory();
	message.MergeFrom(data, DiscardUnknownFields, Extensions);
	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>
	/// <remarks>
	/// The stream is expected to contain a length and then the data. Only the amount of data
	/// specified by the length will be consumed.
	/// </remarks>
	/// <param name="input">The stream to parse.</param>
	/// <returns>The parsed message.</returns>
	public new T ParseDelimitedFrom(Stream input)
	{
	T message = factory();
	message.MergeDelimitedFrom(input, DiscardUnknownFields, Extensions);
	return message;
	}

	/// <summary>
	/// Parses a message from the given coded input stream.
	/// </summary>
	/// <param name="input">The stream to parse.</param>
	/// <returns>The parsed message.</returns>
	public new T ParseFrom(CodedInputStream input)
	{
	T message = factory();
	MergeFrom(message, input);
	return message;
	}

	/// <summary>
	/// Parses a message from the given JSON.
	/// </summary>
	/// <param name="json">The JSON to parse.</param>
	/// <returns>The parsed message.</returns>
	/// <exception cref="InvalidJsonException">The JSON does not comply with RFC 7159</exception>
	/// <exception cref="InvalidProtocolBufferException">The JSON does not represent a Protocol Buffers message correctly</exception>
	public new T ParseJson(string json)
	{
	T message = factory();
	JsonParser.Default.Merge(message, json);
	return message;
	}

	/// <summary>
	/// Creates a new message parser which optionally discards unknown fields when parsing.
	/// </summary>
	/// <param name="discardUnknownFields">Whether or not to discard unknown fields when parsing.</param>
	/// <returns>A newly configured message parser.</returns>
	public new MessageParser<T> WithDiscardUnknownFields(bool discardUnknownFields) =>
	new MessageParser<T>(factory, discardUnknownFields, Extensions);

	/// <summary>
	/// Creates a new message parser which registers extensions from the specified registry upon creating the message instance
	/// </summary>
	/// <param name="registry">The extensions to register</param>
	/// <returns>A newly configured message parser.</returns>
	public new MessageParser<T> WithExtensionRegistry(ExtensionRegistry registry) =>
	new MessageParser<T>(factory, DiscardUnknownFields, registry);
	}
	}