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annotate src/com/tmate/hgkit/fs/FilterDataAccess.java @ 51:9429c7bd1920 wrap-data-access

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Try DataAccess to reach revision data instead of plain byte arrays
author Artem Tikhomirov <tikhomirov.artem@gmail.com>
date Sun, 16 Jan 2011 01:20:26 +0100
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51
9429c7bd1920 Try DataAccess to reach revision data instead of plain byte arrays
Artem Tikhomirov <tikhomirov.artem@gmail.com>
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1 /*
9429c7bd1920 Try DataAccess to reach revision data instead of plain byte arrays
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2 * Copyright (c) 2011 Artem Tikhomirov
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3 */
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4 package com.tmate.hgkit.fs;
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5
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6 import java.io.IOException;
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7
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8 /**
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9 * XXX Perhaps, DataAccessSlice? Unlike FilterInputStream, we limit amount of data read from DataAccess being filtered.
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10 *
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11 * @author artem
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12 */
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13 public class FilterDataAccess extends DataAccess {
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14 private final DataAccess dataAccess;
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15 private final long offset;
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16 private final int length;
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17 private int count;
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18
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19 public FilterDataAccess(DataAccess dataAccess, long offset, int length) {
9429c7bd1920 Try DataAccess to reach revision data instead of plain byte arrays
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20 this.dataAccess = dataAccess;
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21 this.offset = offset;
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22 this.length = length;
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23 count = length;
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24 }
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25
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26 protected int available() {
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27 return count;
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28 }
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29
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30 @Override
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Artem Tikhomirov <tikhomirov.artem@gmail.com>
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31 public void reset() throws IOException {
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32 count = length;
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33 }
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34
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35 @Override
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36 public boolean isEmpty() {
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37 return count <= 0;
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38 }
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39
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40 @Override
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41 public long length() {
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42 return length;
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43 }
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44
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45 @Override
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Artem Tikhomirov <tikhomirov.artem@gmail.com>
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46 public void seek(long localOffset) throws IOException {
9429c7bd1920 Try DataAccess to reach revision data instead of plain byte arrays
Artem Tikhomirov <tikhomirov.artem@gmail.com>
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47 if (localOffset < 0 || localOffset > length) {
9429c7bd1920 Try DataAccess to reach revision data instead of plain byte arrays
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48 throw new IllegalArgumentException();
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Artem Tikhomirov <tikhomirov.artem@gmail.com>
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49 }
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Artem Tikhomirov <tikhomirov.artem@gmail.com>
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50 dataAccess.seek(offset + localOffset);
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Artem Tikhomirov <tikhomirov.artem@gmail.com>
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51 count = (int) (length - localOffset);
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52 }
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53
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54 @Override
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55 public void skip(int bytes) throws IOException {
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56 int newCount = count - bytes;
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57 if (newCount < 0 || newCount > length) {
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58 throw new IllegalArgumentException();
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59 }
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60 seek(length - newCount);
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61 /*
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Artem Tikhomirov <tikhomirov.artem@gmail.com>
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62 can't use next code because don't want to rewind backing DataAccess on reset()
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63 i.e. this.reset() modifies state of this instance only, while filtered DA may go further.
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64 Only actual this.skip/seek/read would rewind it to desired position
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65 dataAccess.skip(bytes);
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66 count = newCount;
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67 */
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68
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69 }
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70
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71 @Override
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72 public byte readByte() throws IOException {
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73 if (count <= 0) {
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74 throw new IllegalArgumentException("Underflow"); // XXX be descriptive
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75 }
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76 if (count == length) {
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77 dataAccess.seek(offset);
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78 }
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79 count--;
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80 return dataAccess.readByte();
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81 }
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82
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83 @Override
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84 public void readBytes(byte[] b, int off, int len) throws IOException {
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85 if (count <= 0 || len > count) {
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86 throw new IllegalArgumentException("Underflow"); // XXX be descriptive
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87 }
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88 if (count == length) {
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89 dataAccess.seek(offset);
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90 }
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91 dataAccess.readBytes(b, off, len);
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92 count -= len;
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93 }
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94
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95 // done shall be no-op, as we have no idea what's going on with DataAccess we filter
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96 }