RAMInputStream.cs

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/* 
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System;

namespace Lucene.Net.Store
{
    
    /// <summary> A memory-resident <see cref="IndexInput" /> implementation.
    /// 
    /// </summary>
    public class RAMInputStream : IndexInput
    {
        internal static readonly int BUFFER_SIZE;
        
        private RAMFile file;
        private long length;
        
        private byte[] currentBuffer;
        private int currentBufferIndex;
        
        private int bufferPosition;
        private long bufferStart;
        private int bufferLength;
        
        public /*internal*/ RAMInputStream(RAMFile f)
        {
            file = f;
            length = file.length;
            if (length / BUFFER_SIZE >= System.Int32.MaxValue)
            {
                throw new System.IO.IOException("Too large RAMFile! " + length);
            }
            
            // make sure that we switch to the
            // first needed buffer lazily
            currentBufferIndex = - 1;
            currentBuffer = null;
        }
        
        protected override void Dispose(bool disposing)
        {
            // do nothing
        }
        
        public override long Length()
        {
            return length;
        }
        
        public override byte ReadByte()
        {
            if (bufferPosition >= bufferLength)
            {
                currentBufferIndex++;
                SwitchCurrentBuffer(true);
            }
            return currentBuffer[bufferPosition++];
        }
        
        public override void  ReadBytes(byte[] b, int offset, int len)
        {
            while (len > 0)
            {
                if (bufferPosition >= bufferLength)
                {
                    currentBufferIndex++;
                    SwitchCurrentBuffer(true);
                }
                
                int remainInBuffer = bufferLength - bufferPosition;
                int bytesToCopy = len < remainInBuffer?len:remainInBuffer;
                Array.Copy(currentBuffer, bufferPosition, b, offset, bytesToCopy);
                offset += bytesToCopy;
                len -= bytesToCopy;
                bufferPosition += bytesToCopy;
            }
        }
        
        private void  SwitchCurrentBuffer(bool enforceEOF)
        {
            if (currentBufferIndex >= file.NumBuffers())
            {
                // end of file reached, no more buffers left
                if (enforceEOF)
                    throw new System.IO.IOException("Read past EOF");
                else
                {
                    // Force EOF if a read takes place at this position
                    currentBufferIndex--;
                    bufferPosition = BUFFER_SIZE;
                }
            }
            else
            {
                currentBuffer = file.GetBuffer(currentBufferIndex);
                bufferPosition = 0;
                bufferStart = (long) BUFFER_SIZE * (long) currentBufferIndex;
                long buflen = length - bufferStart;
                bufferLength = buflen > BUFFER_SIZE?BUFFER_SIZE:(int) buflen;
            }
        }

        public override long FilePointer
        {
            get { return currentBufferIndex < 0 ? 0 : bufferStart + bufferPosition; }
        }

        public override void  Seek(long pos)
        {
            if (currentBuffer == null || pos < bufferStart || pos >= bufferStart + BUFFER_SIZE)
            {
                currentBufferIndex = (int) (pos / BUFFER_SIZE);
                SwitchCurrentBuffer(false);
            }
            bufferPosition = (int) (pos % BUFFER_SIZE);
        }
        
        static RAMInputStream()
        {
            BUFFER_SIZE = RAMOutputStream.BUFFER_SIZE;
        }
    }
}