Mercurial > hg4j
diff 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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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/com/tmate/hgkit/fs/FilterDataAccess.java Sun Jan 16 01:20:26 2011 +0100 @@ -0,0 +1,96 @@ +/* + * 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 +}