Mercurial > hg4j
view src/com/tmate/hgkit/fs/FilterDataAccess.java @ 51:9429c7bd1920 wrap-data-access
Try DataAccess to reach revision data instead of plain byte arrays
author | Artem Tikhomirov <tikhomirov.artem@gmail.com> |
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date | Sun, 16 Jan 2011 01:20:26 +0100 |
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/* * Copyright (c) 2011 Artem Tikhomirov */ package com.tmate.hgkit.fs; import java.io.IOException; /** * XXX Perhaps, DataAccessSlice? Unlike FilterInputStream, we limit amount of data read from DataAccess being filtered. * * @author artem */ public class FilterDataAccess extends DataAccess { private final DataAccess dataAccess; private final long offset; private final int length; private int count; public FilterDataAccess(DataAccess dataAccess, long offset, int length) { this.dataAccess = dataAccess; this.offset = offset; this.length = length; count = length; } protected int available() { return count; } @Override public void reset() throws IOException { count = length; } @Override public boolean isEmpty() { return count <= 0; } @Override public long length() { return length; } @Override public void seek(long localOffset) throws IOException { if (localOffset < 0 || localOffset > length) { throw new IllegalArgumentException(); } dataAccess.seek(offset + localOffset); count = (int) (length - localOffset); } @Override public void skip(int bytes) throws IOException { int newCount = count - bytes; if (newCount < 0 || newCount > length) { throw new IllegalArgumentException(); } seek(length - newCount); /* can't use next code because don't want to rewind backing DataAccess on reset() i.e. this.reset() modifies state of this instance only, while filtered DA may go further. Only actual this.skip/seek/read would rewind it to desired position dataAccess.skip(bytes); count = newCount; */ } @Override public byte readByte() throws IOException { if (count <= 0) { throw new IllegalArgumentException("Underflow"); // XXX be descriptive } if (count == length) { dataAccess.seek(offset); } count--; return dataAccess.readByte(); } @Override public void readBytes(byte[] b, int off, int len) throws IOException { if (count <= 0 || len > count) { throw new IllegalArgumentException("Underflow"); // XXX be descriptive } if (count == length) { dataAccess.seek(offset); } dataAccess.readBytes(b, off, len); count -= len; } // done shall be no-op, as we have no idea what's going on with DataAccess we filter }