Nuclex.Support/Source/IO/PartialStream.cs

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#region CPL License
/*
Nuclex Framework
Copyright (C) 2002-2014 Nuclex Development Labs
This library is free software; you can redistribute it and/or
modify it under the terms of the IBM Common Public License as
published by the IBM Corporation; either version 1.0 of the
License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
IBM Common Public License for more details.
You should have received a copy of the IBM Common Public
License along with this library
*/
#endregion
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
namespace Nuclex.Support.IO {
/// <summary>Wraps a stream and exposes only a limited region of its data</summary>
public class PartialStream : Stream {
/// <summary>Initializes a new partial stream</summary>
/// <param name="stream">
/// Stream the wrapper will make a limited region accessible of
/// </param>
/// <param name="start">
/// Start index in the stream which becomes the beginning for the wrapper
/// </param>
/// <param name="length">
/// Length the wrapped stream should report and allow access to
/// </param>
public PartialStream(Stream stream, long start, long length) {
if(start < 0) {
throw new ArgumentException("Start index must not be less than 0", "start");
}
if(stream.CanSeek) {
if(start + length > stream.Length) {
throw new ArgumentException(
"Partial stream exceeds end of full stream", "length"
);
}
} else {
if(start != 0) {
throw new ArgumentException(
"The only valid start for unseekable streams is 0", "start"
);
}
}
this.stream = stream;
this.start = start;
this.length = length;
}
/// <summary>Whether data can be read from the stream</summary>
public override bool CanRead {
get { return this.stream.CanRead; }
}
/// <summary>Whether the stream supports seeking</summary>
public override bool CanSeek {
get { return this.stream.CanSeek; }
}
/// <summary>Whether data can be written into the stream</summary>
public override bool CanWrite {
get { return this.stream.CanWrite; }
}
/// <summary>
/// Clears all buffers for this stream and causes any buffered data to be written
/// to the underlying device.
/// </summary>
public override void Flush() {
this.stream.Flush();
}
/// <summary>Length of the stream in bytes</summary>
/// <exception cref="NotSupportedException">
/// The wrapped stream does not support seeking
/// </exception>
public override long Length {
get { return this.length; }
}
/// <summary>Absolute position of the file pointer within the stream</summary>
/// <exception cref="NotSupportedException">
/// The wrapped stream does not support seeking
/// </exception>
public override long Position {
get {
if(!this.stream.CanSeek) {
throw makeSeekNotSupportedException("seek");
}
return this.position;
}
set { moveFilePointer(value); }
}
/// <summary>
/// Reads a sequence of bytes from the stream and advances the position of
/// the file pointer by the number of bytes read.
/// </summary>
/// <param name="buffer">Buffer that will receive the data read from the stream</param>
/// <param name="offset">
/// Offset in the buffer at which the stream will place the data read
/// </param>
/// <param name="count">Maximum number of bytes that will be read</param>
/// <returns>
/// The number of bytes that were actually read from the stream and written into
/// the provided buffer
/// </returns>
/// <exception cref="NotSupportedException">
/// The wrapped stream does not support reading
/// </exception>
public override int Read(byte[] buffer, int offset, int count) {
if(!this.stream.CanRead) {
throw new NotSupportedException(
"Can't read: the wrapped stream doesn't support reading"
);
}
long remaining = this.length - this.position;
int bytesToRead = (int)Math.Min(count, remaining);
if(this.stream.CanSeek) {
this.stream.Position = this.position + this.start;
}
int bytesRead = this.stream.Read(buffer, offset, bytesToRead);
this.position += bytesRead;
return bytesRead;
}
/// <summary>Changes the position of the file pointer</summary>
/// <param name="offset">
/// Offset to move the file pointer by, relative to the position indicated by
/// the <paramref name="origin" /> parameter.
/// </param>
/// <param name="origin">
/// Reference point relative to which the file pointer is placed
/// </param>
/// <returns>The new absolute position within the stream</returns>
public override long Seek(long offset, SeekOrigin origin) {
switch(origin) {
case SeekOrigin.Begin: {
return Position = offset;
}
case SeekOrigin.Current: {
return Position += offset;
}
case SeekOrigin.End: {
return Position = (Length + offset);
}
default: {
throw new ArgumentException("Invalid seek origin", "origin");
}
}
}
/// <summary>Changes the length of the stream</summary>
/// <param name="value">New length the stream shall have</param>
/// <exception cref="NotSupportedException">
/// Always, the stream chainer does not support the SetLength() operation
/// </exception>
public override void SetLength(long value) {
throw new NotSupportedException("Resizing partial streams is not supported");
}
/// <summary>
/// Writes a sequence of bytes to the stream and advances the position of
/// the file pointer by the number of bytes written.
/// </summary>
/// <param name="buffer">
/// Buffer containing the data that will be written to the stream
/// </param>
/// <param name="offset">
/// Offset in the buffer at which the data to be written starts
/// </param>
/// <param name="count">Number of bytes that will be written into the stream</param>
/// <remarks>
/// The behavior of this method is as follows: If one or more chained streams
/// do not support seeking, all data is appended to the final stream in the
/// chain. Otherwise, writing will begin with the stream the current file pointer
/// offset falls into. If the end of that stream is reached, writing continues
/// in the next stream. On the last stream, writing more data into the stream
/// that it current size allows will enlarge the stream.
/// </remarks>
public override void Write(byte[] buffer, int offset, int count) {
long remaining = this.length - this.position;
if(count > remaining) {
throw new NotSupportedException(
"Cannot extend the length of the partial stream"
);
}
if(this.stream.CanSeek) {
this.stream.Position = this.position + this.start;
}
this.stream.Write(buffer, offset, count);
this.position += count;
}
/// <summary>Stream being wrapped by the partial stream wrapper</summary>
public Stream CompleteStream {
get { return this.stream; }
}
/// <summary>Moves the file pointer</summary>
/// <param name="position">New position the file pointer will be moved to</param>
private void moveFilePointer(long position) {
if(!this.stream.CanSeek) {
throw makeSeekNotSupportedException("seek");
}
// Seemingly, it is okay to move the file pointer beyond the end of
// the stream until you try to Read() or Write()
this.position = position;
}
/// <summary>
/// Constructs a NotSupportException for an error caused by the wrapped
/// stream having no seek support
/// </summary>
/// <param name="action">Action that was tried to perform</param>
/// <returns>The newly constructed NotSupportedException</returns>
private static NotSupportedException makeSeekNotSupportedException(string action) {
return new NotSupportedException(
string.Format(
"Can't {0}: the wrapped stream does not support seeking",
action
)
);
}
/// <summary>Streams that have been chained together</summary>
private Stream stream;
/// <summary>Start index of the partial stream in the wrapped stream</summary>
private long start;
/// <summary>Zero-based position of the partial stream's file pointer</summary>
/// <remarks>
/// If the stream does not support seeking, the position will simply be counted
/// up until it reaches <see cref="PartialStream.length" />.
/// </remarks>
private long position;
/// <summary>Length of the partial stream</summary>
private long length;
}
} // namespace Nuclex.Support.IO