protobuf/csharp/src/Google.Protobuf/ParseContext.cs

#region Copyright notice and license
// Protocol Buffers - Google's data interchange format
// Copyright 2008 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
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#endregion

using System;
using System.Buffers;
using System.Buffers.Binary;
using System.Collections.Generic;
using System.IO;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Security;
using System.Text;
using Google.Protobuf.Collections;

namespace Google.Protobuf
{
    /// <summary>
    /// An opaque struct that represents the current parsing state and is passed along
    /// as the parsing proceeds.
    /// All the public methods are intended to be invoked only by the generated code,
    /// users should never invoke them directly.
    /// </summary>
    [SecuritySafeCritical]
    public ref struct ParseContext
    {
        internal const int DefaultRecursionLimit = 100;
        internal const int DefaultSizeLimit = Int32.MaxValue;

        internal ReadOnlySpan<byte> buffer;
        internal ParserInternalState state;

        internal ParseContext(ref ReadOnlySpan<byte> buffer, ref ParserInternalState state)
        {
            this.buffer = buffer;
            this.state = state;
        }

        /// <summary>
        /// Creates a ParseContext instance from CodedInputStream.
        /// WARNING: internally this copies the CodedInputStream's state, so after done with the ParseContext,
        /// the CodedInputStream's state needs to be updated.
        /// </summary>
        internal ParseContext(CodedInputStream input)
        {
            this.buffer = new ReadOnlySpan<byte>(input.InternalBuffer);
            // TODO: ideally we would use a reference to the original state, but that doesn't seem possible
            this.state = input.InternalState;  // creates copy of the state
        }

        internal ParseContext(ReadOnlySequence<byte> input) : this(input, DefaultRecursionLimit)
        {
        }

        internal ParseContext(ReadOnlySequence<byte> input, int recursionLimit)
        {
            this.buffer = default;
            this.state = default;
            this.state.lastTag = 0;
            this.state.recursionDepth = 0;
            this.state.sizeLimit = DefaultSizeLimit;
            this.state.recursionLimit = recursionLimit;
            this.state.currentLimit = int.MaxValue;
            this.state.segmentedBufferHelper = new SegmentedBufferHelper(input, out this.buffer);
            this.state.bufferPos = 0;
            this.state.bufferSize = this.buffer.Length;
            this.state.codedInputStream = null;

            this.state.DiscardUnknownFields = false;
            this.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.
        /// </summary>
        internal uint LastTag { get { return state.lastTag; } }

        /// <summary>
        /// Internal-only property; when set to true, unknown fields will be discarded while parsing.
        /// </summary>
        internal bool DiscardUnknownFields {
            get { return state.DiscardUnknownFields; }
            set { state.DiscardUnknownFields = value; }
        }

        /// <summary>
        /// Internal-only property; provides extension identifiers to compatible messages while parsing.
        /// </summary>
        internal ExtensionRegistry ExtensionRegistry
        {
            get { return state.ExtensionRegistry; }
            set { state.ExtensionRegistry = value; }
        }

        /// <summary>
        /// Reads a field tag, returning the tag of 0 for "end of input".
        /// </summary>
        /// <remarks>
        /// If this method returns 0, it doesn't necessarily mean the end of all
        /// the data in this CodedInputReader; it may be the end of the logical input
        /// for an embedded message, for example.
        /// </remarks>
        /// <returns>The next field tag, or 0 for end of input. (0 is never a valid tag.)</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]

        public uint ReadTag()
        {
            return ParsingPrimitives.ParseTag(ref buffer, ref state);
        }

        /// <summary>
        /// Reads a double field from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public double ReadDouble()
        {
            return ParsingPrimitives.ParseDouble(ref buffer, ref state);
        }

        /// <summary>
        /// Reads a float field from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public float ReadFloat()
        {
            return ParsingPrimitives.ParseFloat(ref buffer, ref state);
        }

        /// <summary>
        /// Reads a uint64 field from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public ulong ReadUInt64()
        {
            return ParsingPrimitives.ParseRawVarint64(ref buffer, ref state);
        }

        /// <summary>
        /// Reads an int64 field from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public long ReadInt64()
        {
            return (long)ParsingPrimitives.ParseRawVarint64(ref buffer, ref state);
        }

        /// <summary>
        /// Reads an int32 field from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public int ReadInt32()
        {
            return (int)ParsingPrimitives.ParseRawVarint32(ref buffer, ref state);
        }

        /// <summary>
        /// Reads a fixed64 field from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public ulong ReadFixed64()
        {
            return ParsingPrimitives.ParseRawLittleEndian64(ref buffer, ref state);
        }

        /// <summary>
        /// Reads a fixed32 field from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public uint ReadFixed32()
        {
            return ParsingPrimitives.ParseRawLittleEndian32(ref buffer, ref state);
        }

        /// <summary>
        /// Reads a bool field from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public bool ReadBool()
        {
            return ParsingPrimitives.ParseRawVarint64(ref buffer, ref state) != 0;
        }
        /// <summary>
        /// Reads a string field from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public string ReadString()
        {
            int length = ParsingPrimitives.ParseLength(ref buffer, ref state);
            return ParsingPrimitives.ReadRawString(ref buffer, ref state, length);
        }

        /// <summary>
        /// Reads an embedded message field value from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void ReadMessage(IMessage message)
        {
            // TODO: add a fallback if IMessage does not implement IBufferMessage 
            ParsingPrimitivesMessages.ReadMessage(ref this, message);
        }

        /// <summary>
        /// Reads an embedded group field from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void ReadGroup(IMessage message)
        {
            ParsingPrimitivesMessages.ReadGroup(ref this, message);
        }

        /// <summary>
        /// Reads a bytes field value from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public ByteString ReadBytes()
        {
            int length = ParsingPrimitives.ParseLength(ref buffer, ref state);
            return ByteString.AttachBytes(ParsingPrimitives.ReadRawBytes(ref buffer, ref state, length));
        }
        /// <summary>
        /// Reads a uint32 field value from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public uint ReadUInt32()
        {
            return ParsingPrimitives.ParseRawVarint32(ref buffer, ref state);
        }

        /// <summary>
        /// Reads an enum field value from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public int ReadEnum()
        {
            // Currently just a pass-through, but it's nice to separate it logically from WriteInt32.
            return (int)ParsingPrimitives.ParseRawVarint32(ref buffer, ref state);
        }

        /// <summary>
        /// Reads an sfixed32 field value from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public int ReadSFixed32()
        {
            return (int)ParsingPrimitives.ParseRawLittleEndian32(ref buffer, ref state);
        }

        /// <summary>
        /// Reads an sfixed64 field value from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public long ReadSFixed64()
        {
            return (long)ParsingPrimitives.ParseRawLittleEndian64(ref buffer, ref state);
        }

        /// <summary>
        /// Reads an sint32 field value from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public int ReadSInt32()
        {
            return ParsingPrimitives.DecodeZigZag32(ParsingPrimitives.ParseRawVarint32(ref buffer, ref state));
        }

        /// <summary>
        /// Reads an sint64 field value from the input.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public long ReadSInt64()
        {
            return ParsingPrimitives.DecodeZigZag64(ParsingPrimitives.ParseRawVarint64(ref buffer, ref state));
        }

        /// <summary>
        /// Reads a length for length-delimited data.
        /// </summary>
        /// <remarks>
        /// This is internally just reading a varint, but this method exists
        /// to make the calling code clearer.
        /// </remarks>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public int ReadLength()
        {
            return (int)ParsingPrimitives.ParseRawVarint32(ref buffer, ref state);
        }

        internal void CopyStateTo(CodedInputStream input)
        {
            input.InternalState = state;
        }
    }
}