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

#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
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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#endregion

using System;
using System.IO;

namespace Google.Protobuf
{
    /// <summary>
    /// Stream implementation which proxies another stream, only allowing a certain amount
    /// of data to be read. Note that this is only used to read delimited streams, so it
    /// doesn't attempt to implement everything.
    /// </summary>
    internal sealed class LimitedInputStream : Stream
    {
        private readonly Stream proxied;
        private int bytesLeft;

        internal LimitedInputStream(Stream proxied, int size)
        {
            this.proxied = proxied;
            bytesLeft = size;
        }

        public override bool CanRead => true;
        public override bool CanSeek => false;
        public override bool CanWrite => false;

        public override void Flush()
        {
        }

        public override long Length => throw new NotSupportedException();

        public override long Position
        {
            get => throw new NotSupportedException();
            set => throw new NotSupportedException();
        }

        public override int Read(byte[] buffer, int offset, int count)
        {
            if (bytesLeft > 0)
            {
                int bytesRead = proxied.Read(buffer, offset, Math.Min(bytesLeft, count));
                bytesLeft -= bytesRead;
                return bytesRead;
            }
            return 0;
        }

        public override long Seek(long offset, SeekOrigin origin) => throw new NotSupportedException();

        public override void SetLength(long value) => throw new NotSupportedException();

        public override void Write(byte[] buffer, int offset, int count) => throw new NotSupportedException();
    }
}