org.archive.io.BufferedSeekInputStream Maven / Gradle / Ivy
/*
* This file is part of the Heritrix web crawler (crawler.archive.org).
*
* Licensed to the Internet Archive (IA) by one or more individual
* contributors.
*
* The IA 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.
*/
package org.archive.io;
import java.io.IOException;
/**
* Buffers data from some other SeekInputStream.
*
* @author pjack
*/
public class BufferedSeekInputStream extends SeekInputStream {
/**
* The underlying input stream.
*/
final private SeekInputStream input;
/**
* The buffered data.
*/
final private byte[] buffer;
/**
* The maximum offset of valid data in the buffer. Usually the same
* as buffer.length, but may be shorter if we're in the last region
* of the stream.
*/
private int maxOffset;
/**
* The offset of within the buffer of the next byte to read.
*/
private int offset;
/**
* Constructor.
*
* @param input the underlying input stream
* @param capacity the size of the buffer
* @throws IOException if an IO occurs filling the first buffer
*/
public BufferedSeekInputStream(SeekInputStream input, int capacity)
throws IOException {
this.input = input;
this.buffer = new byte[capacity];
buffer();
}
/**
* Fills the buffer.
*
* @throws IOException if an IO error occurs
*/
private void buffer() throws IOException {
int remaining = buffer.length;
while (remaining > 0) {
int r = input.read(buffer, buffer.length - remaining, remaining);
if (r <= 0) {
// Not enough information to fill the buffer
offset = 0;
maxOffset = buffer.length - remaining;
return;
}
remaining -= r;
}
maxOffset = buffer.length;
offset = 0;
}
/**
* Ensures that the buffer is valid.
*
* @throws IOException if an IO error occurs
*/
private void ensureBuffer() throws IOException {
if (offset >= maxOffset) {
buffer();
}
}
/**
* Returns the number of unread bytes in the current buffer.
*
* @return the remaining bytes
*/
private int remaining() {
return maxOffset - offset;
}
@Override
public int read() throws IOException {
ensureBuffer();
if (maxOffset == 0) {
return -1;
}
int ch = buffer[offset] & 0xFF;
offset++;
return ch;
}
@Override
public int read(byte[] buf, int ofs, int len) throws IOException {
ensureBuffer();
if (maxOffset == 0) {
return 0;
}
len = Math.min(len, remaining());
System.arraycopy(buffer, offset, buf, ofs, len);
offset += len;
return len;
}
@Override
public int read(byte[] buf) throws IOException {
return read(buf, 0, buf.length);
}
@Override
public long skip(long c) throws IOException {
ensureBuffer();
if (maxOffset == 0) {
return 0;
}
int count = (c > Integer.MAX_VALUE) ? Integer.MAX_VALUE : (int)c;
int skip = Math.min(count, remaining());
offset += skip;
return skip;
}
/**
* Returns the stream's current position.
*
* @return the current position
*/
public long position() throws IOException {
return input.position() - buffer.length + offset;
}
/**
* Seeks to the given position. This method avoids re-filling the buffer
* if at all possible.
*
* @param p the position to set
* @throws IOException if an IO error occurs
*/
public void position(long p) throws IOException {
long blockStart = (input.position() - maxOffset)
/ buffer.length * buffer.length;
long blockEnd = blockStart + maxOffset;
if ((p >= blockStart) && (p < blockEnd)) {
// Desired position is somewhere inside current buffer
long adj = p - blockStart;
offset = (int)adj;
return;
}
positionDirect(p);
}
/**
* Positions the underlying stream at the given position, then refills
* the buffer.
*
* @param p the position to set
* @throws IOException if an IO error occurs
*/
private void positionDirect(long p) throws IOException {
long newBlockStart = p / buffer.length * buffer.length;
input.position(newBlockStart);
buffer();
offset = (int)(p % buffer.length);
}
/**
* Close the stream, including the wrapped input stream.
*/
public void close() throws IOException {
super.close();
if(this.input!=null) {
this.input.close();
}
}
}