MemoryStream.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / clr / src / BCL / System / IO / MemoryStream.cs / 1 / MemoryStream.cs
                        

                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
/*============================================================
** 
** Class:  MemoryStream 
**
** 
** Purpose: A Stream whose backing store is memory.  Great
** for temporary storage without creating a temp file.  Also
** lets users expose a byte[] as a stream.
** 
**
===========================================================*/ 
 
using System;
using System.Runtime.InteropServices; 

namespace System.IO {
    // A MemoryStream represents a Stream in memory (ie, it has no backing store).
    // This stream may reduce the need for temporary buffers and files in 
    // an application.
    // 
    // There are two ways to create a MemoryStream.  You can initialize one 
    // from an unsigned byte array, or you can create an empty one.  Empty
    // memory streams are resizable, while ones created with a byte array provide 
    // a stream "view" of the data.
    [Serializable]
    [ComVisible(true)]
    public class MemoryStream : Stream 
    {
        private byte[] _buffer;    // Either allocated internally or externally. 
        private int _origin;       // For user-provided arrays, start at this origin 
        private int _position;     // read/write head.
        private int _length;       // Number of bytes within the memory stream 
        private int _capacity;     // length of usable portion of buffer for stream
        // Note that _capacity == _buffer.Length for non-user-provided byte[]'s

        private bool _expandable;  // User-provided buffers aren't expandable. 
        private bool _writable;    // Can user write to this stream?
        private bool _exposable;   // Whether the array can be returned to the user. 
        private bool _isOpen;      // Is this stream open or closed? 

        // < 

        private const int MemStreamMaxLength = Int32.MaxValue;

        public MemoryStream() 
            : this(0) {
        } 
 
        public MemoryStream(int capacity) {
            if (capacity < 0) { 
                throw new ArgumentOutOfRangeException("capacity", Environment.GetResourceString("ArgumentOutOfRange_NegativeCapacity"));
            }

            _buffer = new byte[capacity]; 
            _capacity = capacity;
            _expandable = true; 
            _writable = true; 
            _exposable = true;
            _origin = 0;      // Must be 0 for byte[]'s created by MemoryStream 
            _isOpen = true;
        }

        public MemoryStream(byte[] buffer) 
            : this(buffer, true) {
        } 
 
        public MemoryStream(byte[] buffer, bool writable) {
            if (buffer == null) throw new ArgumentNullException("buffer", Environment.GetResourceString("ArgumentNull_Buffer")); 
            _buffer = buffer;
            _length = _capacity = buffer.Length;
            _writable = writable;
            _exposable = false; 
            _origin = 0;
            _isOpen = true; 
        } 

        public MemoryStream(byte[] buffer, int index, int count) 
            : this(buffer, index, count, true, false) {
        }

        public MemoryStream(byte[] buffer, int index, int count, bool writable) 
            : this(buffer, index, count, writable, false) {
        } 
 
        public MemoryStream(byte[] buffer, int index, int count, bool writable, bool publiclyVisible) {
            if (buffer==null) 
                throw new ArgumentNullException("buffer", Environment.GetResourceString("ArgumentNull_Buffer"));
            if (index < 0)
                throw new ArgumentOutOfRangeException("index", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
            if (count < 0) 
                throw new ArgumentOutOfRangeException("count", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
            if (buffer.Length - index < count) 
                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen")); 

            _buffer = buffer; 
            _origin = _position = index;
            _length = _capacity = index + count;
            _writable = writable;
            _exposable = publiclyVisible;  // Can GetBuffer return the array? 
            _expandable = false;
            _isOpen = true; 
        } 

        public override bool CanRead { 
            get { return _isOpen; }
        }

        public override bool CanSeek { 
            get { return _isOpen; }
        } 
 
        public override bool CanWrite {
            get { return _writable; } 
        }

        protected override void Dispose(bool disposing)
        { 
            try {
                if (disposing) { 
                    _isOpen = false; 
                    _writable = false;
                    _expandable = false; 
                    // Don't set buffer to null - allow GetBuffer & ToArray to work.
                }
            }
            finally { 
                // Call base.Close() to cleanup async IO resources
                base.Dispose(disposing); 
            } 
        }
 
        // returns a bool saying whether we allocated a new array.
        private bool EnsureCapacity(int value) {
            // Check for overflow
            if (value < 0) 
                throw new IOException(Environment.GetResourceString("IO.IO_StreamTooLong"));
            if (value > _capacity) { 
                int newCapacity = value; 
                if (newCapacity < 256)
                    newCapacity = 256; 
                if (newCapacity < _capacity * 2)
                    newCapacity = _capacity * 2;
                Capacity = newCapacity;
                return true; 
            }
            return false; 
        } 

        public override void Flush() { 
        }

        public virtual byte[] GetBuffer() {
            if (!_exposable) 
                throw new UnauthorizedAccessException(Environment.GetResourceString("UnauthorizedAccess_MemStreamBuffer"));
            return _buffer; 
        } 

        // -------------- PERF: Internal functions for fast direct access of MemoryStream buffer (cf. BinaryReader for usage) --------------- 

        // PERF: Internal sibling of GetBuffer, always returns a buffer (cf. GetBuffer())
        internal byte[] InternalGetBuffer() {
            return _buffer; 
        }
 
        // PERF: Get origin and length - used in ResourceWriter. 
        internal void InternalGetOriginAndLength(out int origin, out int length)
        { 
            if (!_isOpen) __Error.StreamIsClosed();
            origin = _origin;
            length = _length;
        } 

        // PERF: True cursor position, we don't need _origin for direct access 
        internal int InternalGetPosition() { 
            if (!_isOpen) __Error.StreamIsClosed();
            return _position; 
        }

        // PERF: Takes out Int32 as fast as possible
        internal int InternalReadInt32() { 
           if (!_isOpen)
               __Error.StreamIsClosed(); 
 
           int pos = (_position += 4); // use temp to avoid race
           if (pos > _length) 
           {
               _position = _length;
               __Error.EndOfFile();
           } 
           return (int)(_buffer[pos-4] | _buffer[pos-3] << 8 | _buffer[pos-2] << 16 | _buffer[pos-1] << 24);
        } 
 
        // PERF: Get actual length of bytes available for read; do sanity checks; shift position - i.e. everything except actual copying bytes
        internal int InternalEmulateRead(int count) { 
            if (!_isOpen) __Error.StreamIsClosed();

            int n = _length - _position;
            if (n > count) n = count; 
            if (n < 0) n = 0;
 
            BCLDebug.Assert(_position + n >= 0, "_position + n >= 0");  // len is less than 2^31 -1. 
            _position += n;
            return n; 
        }

        // Gets &; sets the capacity (number of bytes allocated) for this stream.
        // The capacity cannot be set to a value less than the current length 
        // of the stream.
        // 
        public virtual int Capacity { 
            get {
                if (!_isOpen) __Error.StreamIsClosed(); 
                return _capacity - _origin;
            }
            set {
                if (!_isOpen) __Error.StreamIsClosed(); 
                if (value != _capacity) {
                    if (!_expandable) __Error.MemoryStreamNotExpandable(); 
                    if (value < _length) throw new ArgumentOutOfRangeException("value", Environment.GetResourceString("ArgumentOutOfRange_SmallCapacity")); 
                    if (value > 0) {
                        byte[] newBuffer = new byte[value]; 
                        if (_length > 0) Buffer.InternalBlockCopy(_buffer, 0, newBuffer, 0, _length);
                        _buffer = newBuffer;
                    }
                    else { 
                        _buffer = null;
                    } 
                    _capacity = value; 
                }
            } 
        }

        public override long Length {
            get { 
                if (!_isOpen) __Error.StreamIsClosed();
                return _length - _origin; 
            } 
        }
 
        public override long Position {
            get {
                if (!_isOpen) __Error.StreamIsClosed();
                return _position - _origin; 
            }
            set { 
                if (!_isOpen) __Error.StreamIsClosed(); 
                if (value < 0)
                    throw new ArgumentOutOfRangeException("value", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum")); 
                if (value > MemStreamMaxLength)
                    throw new ArgumentOutOfRangeException("value", Environment.GetResourceString("ArgumentOutOfRange_MemStreamLength"));
                _position = _origin + (int)value;
            } 
        }
 
        public override int Read([In, Out] byte[] buffer, int offset, int count) { 
            if (!_isOpen) __Error.StreamIsClosed();
            if (buffer==null) 
                throw new ArgumentNullException("buffer", Environment.GetResourceString("ArgumentNull_Buffer"));
            if (offset < 0)
                throw new ArgumentOutOfRangeException("offset", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
            if (count < 0) 
                throw new ArgumentOutOfRangeException("count", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
            if (buffer.Length - offset < count) 
                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen")); 

            int n = _length - _position; 
            if (n > count) n = count;
            if (n <= 0)
                return 0;
 
            BCLDebug.Assert(_position + n >= 0, "_position + n >= 0");  // len is less than 2^31 -1.
 
            if (n <= 8) 
            {
                int byteCount = n; 
                while (--byteCount >= 0)
                    buffer[offset + byteCount] = _buffer[_position + byteCount];
            }
            else 
                Buffer.InternalBlockCopy(_buffer, _position, buffer, offset, n);
            _position += n; 
            return n; 
        }
 
        public override int ReadByte() {
            if (!_isOpen) __Error.StreamIsClosed();
            if (_position >= _length) return -1;
            return _buffer[_position++]; 
        }
 
 
        public override long Seek(long offset, SeekOrigin loc) {
            if (!_isOpen) __Error.StreamIsClosed(); 
            if (offset > MemStreamMaxLength)
                throw new ArgumentOutOfRangeException("offset", Environment.GetResourceString("ArgumentOutOfRange_MemStreamLength"));
            switch(loc) {
            case SeekOrigin.Begin: 
                if (offset < 0)
                    throw new IOException(Environment.GetResourceString("IO.IO_SeekBeforeBegin")); 
                _position = _origin + (int)offset; 
                break;
 
            case SeekOrigin.Current:
                if (offset + _position < _origin)
                    throw new IOException(Environment.GetResourceString("IO.IO_SeekBeforeBegin"));
                _position += (int)offset; 
                break;
 
            case SeekOrigin.End: 
                if (_length + offset < _origin)
                    throw new IOException(Environment.GetResourceString("IO.IO_SeekBeforeBegin")); 
                _position = _length + (int)offset;
                break;

            default: 
                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidSeekOrigin"));
            } 
 
            BCLDebug.Assert(_position >= 0, "_position >= 0");
            return _position; 
        }

        // Sets the length of the stream to a given value.  The new
        // value must be nonnegative and less than the space remaining in 
        // the array, Int32.MaxValue - origin
        // Origin is 0 in all cases other than a MemoryStream created on 
        // top of an existing array and a specific starting offset was passed 
        // into the MemoryStream constructor.  The upper bounds prevents any
        // situations where a stream may be created on top of an array then 
        // the stream is made longer than the maximum possible length of the
        // array (Int32.MaxValue).
        //
        public override void SetLength(long value) { 
            if (!_writable) __Error.WriteNotSupported();
            if (value > MemStreamMaxLength) 
                throw new ArgumentOutOfRangeException("value", Environment.GetResourceString("ArgumentOutOfRange_MemStreamLength")); 
            if (value < 0 || value > (Int32.MaxValue - _origin)) {
                throw new ArgumentOutOfRangeException("value", Environment.GetResourceString("ArgumentOutOfRange_MemStreamLength")); 
            }
            int newLength = _origin + (int)value;
            bool allocatedNewArray = EnsureCapacity(newLength);
            if (!allocatedNewArray && newLength > _length) 
                Array.Clear(_buffer, _length, newLength - _length);
            _length = newLength; 
            if (_position > newLength) _position = newLength; 
        }
 
        public virtual byte[] ToArray() {
            BCLDebug.Perf(_exposable, "MemoryStream::GetBuffer will let you avoid a copy.");
            byte[] copy = new byte[_length - _origin];
            Buffer.InternalBlockCopy(_buffer, _origin, copy, 0, _length - _origin); 
            return copy;
        } 
 
        public override void Write(byte[] buffer, int offset, int count) {
            if (!_isOpen) __Error.StreamIsClosed(); 
            if (!_writable) __Error.WriteNotSupported();
            if (buffer==null)
                throw new ArgumentNullException("buffer", Environment.GetResourceString("ArgumentNull_Buffer"));
            if (offset < 0) 
                throw new ArgumentOutOfRangeException("offset", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
            if (count < 0) 
                throw new ArgumentOutOfRangeException("count", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum")); 
            if (buffer.Length - offset < count)
                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen")); 

            int i = _position + count;
            // Check for overflow
            if (i < 0) 
                throw new IOException(Environment.GetResourceString("IO.IO_StreamTooLong"));
 
            if (i > _length) { 
                bool mustZero = _position > _length;
                if (i > _capacity) { 
                    bool allocatedNewArray = EnsureCapacity(i);
                    if (allocatedNewArray)
                        mustZero = false;
                } 
                if (mustZero)
                    Array.Clear(_buffer, _length, i - _length); 
                _length = i; 
            }
            if (count <= 8) 
            {
                int byteCount = count;
                while (--byteCount >= 0)
                    _buffer[_position + byteCount] = buffer[offset + byteCount]; 
            }
            else 
                Buffer.InternalBlockCopy(buffer, offset, _buffer, _position, count); 
            _position = i;
            return; 
        }

        public override void WriteByte(byte value) {
            if (!_isOpen) __Error.StreamIsClosed(); 
            if (!_writable) __Error.WriteNotSupported();
            if (_position >= _length) { 
                int newLength = _position + 1; 
                bool mustZero = _position > _length;
                if (newLength >= _capacity) { 
                    bool allocatedNewArray = EnsureCapacity(newLength);
                    if (allocatedNewArray)
                        mustZero = false;
                } 
                if (mustZero)
                    Array.Clear(_buffer, _length, _position - _length); 
                _length = newLength; 
            }
            _buffer[_position++] = value; 
        }

        // Writes this MemoryStream to another stream.
        public virtual void WriteTo(Stream stream) { 
            if (!_isOpen) __Error.StreamIsClosed();
            if (stream==null) 
                throw new ArgumentNullException("stream", Environment.GetResourceString("ArgumentNull_Stream")); 
            stream.Write(_buffer, _origin, _length - _origin);
        } 
    }
}

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