1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249

#region Copyright 2011 by Roger Knapp, Licensed under the Apache License, Version 2.0
/* Licensed 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.
 */
#endregion
using System;
using System.IO;

namespace CSharpTest.Net.IO
{
    /// <summary>
    /// Provides a stream that clamps the usage of the input stream to a specific range, length or offset
    /// </summary>
    public class ClampedStream : Stream
    {
        private readonly Stream _rawStream;

        private readonly bool _disposeOfStream;
        private readonly long _startPosition;
        private readonly long _limitPosition;
        private bool _disposed;
        private long _current;

        /// <summary>
        /// Creates a stream that limits the users ability to modify data to the specified range
        /// </summary>
        /// <param name="rawStream">The stream to use for read/write</param>
        /// <param name="start">The position in the stream that should start the range of allowed bytes</param>
        /// <param name="length">The maximum length that can be read from the stream</param>
        public ClampedStream(Stream rawStream, long start, long length)
            : this(rawStream, start, length, true) { }

        /// <summary>
        /// Creates a stream that limits the users ability to modify data to the specified range
        /// </summary>
        /// <param name="rawStream">The stream to use for read/write</param>
        /// <param name="start">The position in the stream that should start the range of allowed bytes</param>
        /// <param name="length">The maximum length that can be read from the stream</param>
        /// <param name="disposeOfStream">True to dispose of the rawStream when this stream is disposed</param>
        public ClampedStream(Stream rawStream, long start, long length, bool disposeOfStream)
        {
            _rawStream = rawStream;
            _disposeOfStream = disposeOfStream;
            _startPosition = start;

            Check.InRange(start, 0, long.MaxValue);
            Check.InRange(length, 0, long.MaxValue);

            if (length < long.MaxValue)
            {
                if (((ulong)start) + ((ulong)length) > long.MaxValue)
                    throw new ArgumentOutOfRangeException();
                _limitPosition = start + length;
            }
            else _limitPosition = long.MaxValue;

            if (_rawStream.CanSeek)
                _current = _rawStream.Seek(_startPosition, SeekOrigin.Begin);
            else if (_startPosition > 0)
                throw new ArgumentException("Unable to seek to the offset required.");
        }

        /// <summary>
        /// Closes the current stream and releases any resources (such as sockets and file handles) associated with the current stream.
        /// </summary>
        public override void Close() 
        {
            if(_disposeOfStream)
                _rawStream.Close();

            base.Close();
        }

        /// <summary>
        /// Releases the unmanaged resources used by the <see cref="T:System.IO.Stream"/> and optionally releases the managed resources.
        /// </summary>
        protected override void Dispose(bool disposing)
        {
            if (!_disposed)
            {
                _disposed = true;
                if (disposing && _disposeOfStream)
                    _rawStream.Dispose();
            }
            base.Dispose(disposing);
        }

        private void IsNotDisposed()
        {
            if (_disposed) throw new ObjectDisposedException(GetType().FullName);
        }

        /// <summary>
        /// When overridden in a derived class, gets a value indicating whether the current stream supports reading.
        /// </summary>
        public override bool CanRead { get { return _rawStream.CanRead; } }
        /// <summary>
        /// When overridden in a derived class, gets a value indicating whether the current stream supports seeking.
        /// </summary>
        public override bool CanSeek { get { return _rawStream.CanSeek; } }
        /// <summary>
        /// When overridden in a derived class, gets a value indicating whether the current stream supports writing.
        /// </summary>
        public override bool CanWrite { get { return _rawStream.CanWrite; } }

        /// <summary>
        /// When overridden in a derived class, clears all buffers for this stream and causes any buffered data to be written to the underlying device.
        /// </summary>
        public override void Flush()
        {
            IsNotDisposed();
            if(_rawStream.CanWrite)
                _rawStream.Flush();
        }

        /// <summary>
        /// When overridden in a derived class, sets the position within the current stream.
        /// </summary>
        public override long Seek(long offset, SeekOrigin origin)
        {
            IsNotDisposed();
            if (origin == SeekOrigin.Begin)
                offset += _startPosition;
            else if (origin == SeekOrigin.Current)
                offset += _rawStream.Position;
            else if (origin == SeekOrigin.End)
                offset += Math.Min(_limitPosition, _rawStream.Length);
            else
                throw new ArgumentOutOfRangeException("origin");

            if (offset < _startPosition)
            {
                _rawStream.Seek(-1, SeekOrigin.Begin);
                throw new ArgumentOutOfRangeException("offset");
            }
            if (offset > _limitPosition)
                throw new ArgumentOutOfRangeException("offset", "Attempt to seek past end of stream.");

            _current = _rawStream.Seek(offset, SeekOrigin.Begin);
            return _current - _startPosition;
        }

        /// <summary>
        /// When overridden in a derived class, sets the length of the current stream.
        /// </summary>
        /// <exception cref="NotSupportedException">Thrown when length != long.MaxValue</exception>
        public override void SetLength(long value)
        {
            IsNotDisposed();
            Check.Assert<NotSupportedException>(_limitPosition == long.MaxValue); 
            Check.InRange(value, 0, _limitPosition - _startPosition);

            value += _startPosition;
            value = Math.Min(_limitPosition, value);

            _rawStream.SetLength(value);
        }

        /// <summary>
        /// When overridden in a derived class, gets the length in bytes of the stream.
        /// </summary>
        public override long Length
        {
            get { return Math.Max(0, Math.Min(_limitPosition, _rawStream.Length) - _startPosition); }
        }

        /// <summary>
        /// When overridden in a derived class, gets or sets the position within the current stream.
        /// </summary>
        public override long Position
        {
            get { IsNotDisposed(); return _current - _startPosition; }
            set { IsNotDisposed(); Seek(value, SeekOrigin.Begin); }
        }

        /// <summary>
        /// When overridden in a derived class, reads a sequence of bytes from the current stream and advances the position within the stream by the number of bytes read.
        /// </summary>
        public override int Read(byte[] buffer, int offset, int count)
        {
            IsNotDisposed();
            Check.Assert<NotSupportedException>(CanRead);
            long remaining = _limitPosition - _current;
            if (remaining < count)
                count = (int)remaining;
            if (count <= 0)
                return 0;

            int amt = _rawStream.Read(buffer, offset, count);
            _current += amt;
            return amt;
        }

        /// <summary>
        /// Reads a byte from the stream and advances the position within the stream by one byte, or returns -1 if at the end of the stream.
        /// </summary>
        public override int ReadByte()
        {
            IsNotDisposed();
            Check.Assert<NotSupportedException>(CanRead);
            long remaining = _limitPosition - _current;
            if (remaining < 1)
                return -1;
            
            int result = _rawStream.ReadByte();
            _current++;
            return result;
        }

        /// <summary>
        /// When overridden in a derived class, writes a sequence of bytes to the current stream and advances the current position within this stream by the number of bytes written.
        /// </summary>
        public override void Write(byte[] buffer, int offset, int count)
        {
            IsNotDisposed();
            Check.Assert<NotSupportedException>(CanWrite);
            long remaining = _limitPosition - _current;
            if (remaining < count)
                throw new InvalidOperationException("Attempt to write past end of stream.");

            _rawStream.Write(buffer, offset, count);
            _current += count;
        }

        /// <summary>
        /// Writes a byte to the current position in the stream and advances the position within the stream by one byte.
        /// </summary>
        public override void WriteByte(byte value)
        {
            IsNotDisposed();
            Check.Assert<NotSupportedException>(CanWrite);
            long remaining = _limitPosition - _current;
            if (remaining < 1)
                throw new InvalidOperationException("Attempt to write past end of stream.");

            base.WriteByte(value);
            _current++;
        }
    }
}