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comparison 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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50:f1db8610da62 51:9429c7bd1920
1 /*
2 * Copyright (c) 2011 Artem Tikhomirov
3 */
4 package com.tmate.hgkit.fs;
5
6 import java.io.IOException;
7
8 /**
9 * XXX Perhaps, DataAccessSlice? Unlike FilterInputStream, we limit amount of data read from DataAccess being filtered.
10 *
11 * @author artem
12 */
13 public class FilterDataAccess extends DataAccess {
14 private final DataAccess dataAccess;
15 private final long offset;
16 private final int length;
17 private int count;
18
19 public FilterDataAccess(DataAccess dataAccess, long offset, int length) {
20 this.dataAccess = dataAccess;
21 this.offset = offset;
22 this.length = length;
23 count = length;
24 }
25
26 protected int available() {
27 return count;
28 }
29
30 @Override
31 public void reset() throws IOException {
32 count = length;
33 }
34
35 @Override
36 public boolean isEmpty() {
37 return count <= 0;
38 }
39
40 @Override
41 public long length() {
42 return length;
43 }
44
45 @Override
46 public void seek(long localOffset) throws IOException {
47 if (localOffset < 0 || localOffset > length) {
48 throw new IllegalArgumentException();
49 }
50 dataAccess.seek(offset + localOffset);
51 count = (int) (length - localOffset);
52 }
53
54 @Override
55 public void skip(int bytes) throws IOException {
56 int newCount = count - bytes;
57 if (newCount < 0 || newCount > length) {
58 throw new IllegalArgumentException();
59 }
60 seek(length - newCount);
61 /*
62 can't use next code because don't want to rewind backing DataAccess on reset()
63 i.e. this.reset() modifies state of this instance only, while filtered DA may go further.
64 Only actual this.skip/seek/read would rewind it to desired position
65 dataAccess.skip(bytes);
66 count = newCount;
67 */
68
69 }
70
71 @Override
72 public byte readByte() throws IOException {
73 if (count <= 0) {
74 throw new IllegalArgumentException("Underflow"); // XXX be descriptive
75 }
76 if (count == length) {
77 dataAccess.seek(offset);
78 }
79 count--;
80 return dataAccess.readByte();
81 }
82
83 @Override
84 public void readBytes(byte[] b, int off, int len) throws IOException {
85 if (count <= 0 || len > count) {
86 throw new IllegalArgumentException("Underflow"); // XXX be descriptive
87 }
88 if (count == length) {
89 dataAccess.seek(offset);
90 }
91 dataAccess.readBytes(b, off, len);
92 count -= len;
93 }
94
95 // done shall be no-op, as we have no idea what's going on with DataAccess we filter
96 }