2010-04-06 Jb Evain <jbevain@novell.com>

[mcs.git] / class / corlib / System.IO / FileStream.cs

//
// System.IO.FileStream.cs
//
// Authors:
//      Dietmar Maurer (dietmar@ximian.com)
//      Dan Lewis (dihlewis@yahoo.co.uk)
//      Gonzalo Paniagua Javier (gonzalo@ximian.com)
//  Marek Safar (marek.safar@gmail.com)
//
// (C) 2001-2003 Ximian, Inc.  http://www.ximian.com
// Copyright (C) 2004-2005, 2008 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using System.Collections;
using System.Globalization;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Runtime.Remoting.Messaging;
using System.Security.Permissions;
using System.Threading;

using Microsoft.Win32.SafeHandles;
#if NET_2_1
using System.IO.IsolatedStorage;
using System.Security;
#else
using System.Security.AccessControl;
#endif

namespace System.IO
{
        [ComVisible (true)]
        public class FileStream : Stream
        {
                // construct from handle
                
                [Obsolete ("Use FileStream(SafeFileHandle handle, FileAccess access) instead")]
                public FileStream (IntPtr handle, FileAccess access)
                        : this (handle, access, true, DefaultBufferSize, false) {}

                [Obsolete ("Use FileStream(SafeFileHandle handle, FileAccess access) instead")]
                public FileStream (IntPtr handle, FileAccess access, bool ownsHandle)
                        : this (handle, access, ownsHandle, DefaultBufferSize, false) {}
                
                [Obsolete ("Use FileStream(SafeFileHandle handle, FileAccess access, int bufferSize) instead")]
                public FileStream (IntPtr handle, FileAccess access, bool ownsHandle, int bufferSize)
                        : this (handle, access, ownsHandle, bufferSize, false) {}

                [Obsolete ("Use FileStream(SafeFileHandle handle, FileAccess access, int bufferSize, bool isAsync) instead")]
                public FileStream (IntPtr handle, FileAccess access, bool ownsHandle, int bufferSize, bool isAsync)
                        : this (handle, access, ownsHandle, bufferSize, isAsync, false) {}

                [SecurityPermission (SecurityAction.Demand, UnmanagedCode = true)]
                internal FileStream (IntPtr handle, FileAccess access, bool ownsHandle, int bufferSize, bool isAsync, bool isZeroSize)
                {
                        this.handle = MonoIO.InvalidHandle;
                        if (handle == this.handle)
                                throw new ArgumentException ("handle", Locale.GetText ("Invalid."));

                        if (access < FileAccess.Read || access > FileAccess.ReadWrite)
                                throw new ArgumentOutOfRangeException ("access");

                        MonoIOError error;
                        MonoFileType ftype = MonoIO.GetFileType (handle, out error);

                        if (error != MonoIOError.ERROR_SUCCESS) {
                                throw MonoIO.GetException (name, error);
                        }
                        
                        if (ftype == MonoFileType.Unknown) {
                                throw new IOException ("Invalid handle.");
                        } else if (ftype == MonoFileType.Disk) {
                                this.canseek = true;
                        } else {
                                this.canseek = false;
                        }

                        this.handle = handle;
                        this.access = access;
                        this.owner = ownsHandle;
                        this.async = isAsync;
#if MOONLIGHT
                        // default the browser to 'all' anonymous files and let other usage (like smcs) with 'normal'
                        // (i.e. non-anonymous except for isolated storage) files and paths
                        this.anonymous = SecurityManager.SecurityEnabled;
#else
                        this.anonymous = false;
#endif
                        if (isZeroSize)
                                bufferSize = 1;

                        InitBuffer (bufferSize);

                        if (canseek) {
                                buf_start = MonoIO.Seek (handle, 0, SeekOrigin.Current, out error);
                                if (error != MonoIOError.ERROR_SUCCESS) {
                                        throw MonoIO.GetException (name, error);
                                }
                        }

                        /* Can't set append mode */
                        this.append_startpos=0;
                }

                // construct from filename
                
                public FileStream (string path, FileMode mode)
                        : this (path, mode, (mode == FileMode.Append ? FileAccess.Write : FileAccess.ReadWrite), FileShare.Read, DefaultBufferSize, false, FileOptions.None)
                {
                }

                public FileStream (string path, FileMode mode, FileAccess access)
                        : this (path, mode, access, access == FileAccess.Write ? FileShare.None : FileShare.Read, DefaultBufferSize, false, false)
                {
                }

                public FileStream (string path, FileMode mode, FileAccess access, FileShare share)
                        : this (path, mode, access, share, DefaultBufferSize, false, FileOptions.None)
                {
                }

                public FileStream (string path, FileMode mode, FileAccess access, FileShare share, int bufferSize)
                        : this (path, mode, access, share, bufferSize, false, FileOptions.None)
                {
                }

                public FileStream (string path, FileMode mode, FileAccess access, FileShare share, int bufferSize, bool useAsync)
                        : this (path, mode, access, share, bufferSize, useAsync, FileOptions.None)
                {
                }

#if !NET_2_1
                public FileStream (string path, FileMode mode, FileAccess access, FileShare share, int bufferSize, FileOptions options)
                        : this (path, mode, access, share, bufferSize, false, options)
                {
                }

                public FileStream (SafeFileHandle handle, FileAccess access)
                        :this(handle, access, DefaultBufferSize, false)
                {
                }
                
                public FileStream (SafeFileHandle handle, FileAccess access,
                                   int bufferSize)
                        :this(handle, access, bufferSize, false)
                {
                }
                
                [MonoLimitationAttribute("Need to use SafeFileHandle instead of underlying handle")]
                public FileStream (SafeFileHandle handle, FileAccess access,
                                   int bufferSize, bool isAsync)
                        :this (handle.DangerousGetHandle (), access, false, bufferSize, isAsync)
                {
                        this.safeHandle = handle;
                }

                [MonoLimitation ("This ignores the rights parameter")]
                public FileStream (string path, FileMode mode,
                                   FileSystemRights rights, FileShare share,
                                   int bufferSize, FileOptions options)
                        : this (path, mode, (mode == FileMode.Append ? FileAccess.Write : FileAccess.ReadWrite), share, bufferSize, false, options)
                {
                }
                
                [MonoLimitation ("This ignores the rights and fileSecurity parameters")]
                public FileStream (string path, FileMode mode,
                                   FileSystemRights rights, FileShare share,
                                   int bufferSize, FileOptions options,
                                   FileSecurity fileSecurity)
                        : this (path, mode, (mode == FileMode.Append ? FileAccess.Write : FileAccess.ReadWrite), share, bufferSize, false, options)
                {
                }
#endif

                internal FileStream (string path, FileMode mode, FileAccess access, FileShare share, int bufferSize, bool isAsync, bool anonymous)
                        : this (path, mode, access, share, bufferSize, anonymous, isAsync ? FileOptions.Asynchronous : FileOptions.None)
                {
                }

                internal FileStream (string path, FileMode mode, FileAccess access, FileShare share, int bufferSize, bool anonymous, FileOptions options)
                {
                        if (path == null) {
                                throw new ArgumentNullException ("path");
                        }

                        if (path.Length == 0) {
                                throw new ArgumentException ("Path is empty");
                        }

                        // ignore the Inheritable flag
                        share &= ~FileShare.Inheritable;

                        if (bufferSize <= 0)
                                throw new ArgumentOutOfRangeException ("bufferSize", "Positive number required.");

                        if (mode < FileMode.CreateNew || mode > FileMode.Append) {
#if NET_2_1
                                if (anonymous)
                                        throw new ArgumentException ("mode", "Enum value was out of legal range.");
                                else
#endif
                                throw new ArgumentOutOfRangeException ("mode", "Enum value was out of legal range.");
                        }

                        if (access < FileAccess.Read || access > FileAccess.ReadWrite) {
#if NET_2_1
                                if (anonymous)
                                        throw new IsolatedStorageException ("Enum value for FileAccess was out of legal range.");
                                else
#endif
                                throw new ArgumentOutOfRangeException ("access", "Enum value was out of legal range.");
                        }

                        if (share < FileShare.None || share > (FileShare.ReadWrite | FileShare.Delete)) {
#if NET_2_1
                                if (anonymous)
                                        throw new IsolatedStorageException ("Enum value for FileShare was out of legal range.");
                                else
#endif
                                throw new ArgumentOutOfRangeException ("share", "Enum value was out of legal range.");
                        }

                        if (path.IndexOfAny (Path.InvalidPathChars) != -1) {
                                throw new ArgumentException ("Name has invalid chars");
                        }

                        if (Directory.Exists (path)) {
                                // don't leak the path information for isolated storage
                                string msg = Locale.GetText ("Access to the path '{0}' is denied.");
                                throw new UnauthorizedAccessException (String.Format (msg, GetSecureFileName (path, false)));
                        }

                        /* Append streams can't be read (see FileMode
                         * docs)
                         */
                        if (mode==FileMode.Append &&
                                (access&FileAccess.Read)==FileAccess.Read) {
                                throw new ArgumentException("Append access can be requested only in write-only mode.");
                        }

                        if ((access & FileAccess.Write) == 0 &&
                                (mode != FileMode.Open && mode != FileMode.OpenOrCreate)) {
                                string msg = Locale.GetText ("Combining FileMode: {0} with " +
                                        "FileAccess: {1} is invalid.");
                                throw new ArgumentException (string.Format (msg, access, mode));
                        }

                        string dname = Path.GetDirectoryName (path);
                        if (dname.Length > 0) {
                                string fp = Path.GetFullPath (dname);
                                if (!Directory.Exists (fp)) {
                                        // don't leak the path information for isolated storage
                                        string msg = Locale.GetText ("Could not find a part of the path \"{0}\".");
                                        string fname = (anonymous) ? dname : Path.GetFullPath (path);
#if NET_2_1
                                        // don't use GetSecureFileName for the directory name
                                        throw new IsolatedStorageException (String.Format (msg, fname));
#else
                                        throw new DirectoryNotFoundException (String.Format (msg, fname));
#endif
                                }
                        }

                        if (access == FileAccess.Read && mode != FileMode.Create && mode != FileMode.OpenOrCreate &&
                                        mode != FileMode.CreateNew && !File.Exists (path)) {
                                // don't leak the path information for isolated storage
                                string msg = Locale.GetText ("Could not find file \"{0}\".");
                                string fname = GetSecureFileName (path);
#if NET_2_1
                                throw new IsolatedStorageException (String.Format (msg, fname));
#else
                                throw new FileNotFoundException (String.Format (msg, fname), fname);
#endif
                        }

                        // IsolatedStorage needs to keep the Name property to the default "[Unknown]"
                        if (!anonymous)
                                this.name = path;

                        // TODO: demand permissions

                        MonoIOError error;

                        this.handle = MonoIO.Open (path, mode, access, share, options, out error);
                        if (handle == MonoIO.InvalidHandle) {
                                // don't leak the path information for isolated storage
                                throw MonoIO.GetException (GetSecureFileName (path), error);
                        }

                        this.access = access;
                        this.owner = true;
                        this.anonymous = anonymous;

                        /* Can we open non-files by name? */
                        
                        if (MonoIO.GetFileType (handle, out error) == MonoFileType.Disk) {
                                this.canseek = true;
                                this.async = (options & FileOptions.Asynchronous) != 0;
                        } else {
                                this.canseek = false;
                                this.async = false;
                        }


                        if (access == FileAccess.Read && canseek && (bufferSize == DefaultBufferSize)) {
                                /* Avoid allocating a large buffer for small files */
                                long len = Length;
                                if (bufferSize > len) {
                                        bufferSize = (int)(len < 1000 ? 1000 : len);
                                }
                        }

                        InitBuffer (bufferSize);

                        if (mode==FileMode.Append) {
                                this.Seek (0, SeekOrigin.End);
                                this.append_startpos=this.Position;
                        } else {
                                this.append_startpos=0;
                        }
                }

                // properties
                
                public override bool CanRead {
                        get {
                                return access == FileAccess.Read ||
                                       access == FileAccess.ReadWrite;
                        }
                }

                public override bool CanWrite {
                        get {
                                return access == FileAccess.Write ||
                                        access == FileAccess.ReadWrite;
                        }
                }
                
                public override bool CanSeek {
                        get {
                                return(canseek);
                        }
                }

                public virtual bool IsAsync {
                        get {
                                return (async);
                        }
                }

                public string Name {
                        get {
                                return name; 
                        }
                }

                public override long Length {
                        get {
                                if (handle == MonoIO.InvalidHandle)
                                        throw new ObjectDisposedException ("Stream has been closed");

                                if (!CanSeek)
                                        throw new NotSupportedException ("The stream does not support seeking");

                                // Buffered data might change the length of the stream
                                FlushBufferIfDirty ();

                                MonoIOError error;
                                long length;
                                
                                length = MonoIO.GetLength (handle, out error);
                                if (error != MonoIOError.ERROR_SUCCESS) {
                                        // don't leak the path information for isolated storage
                                        throw MonoIO.GetException (GetSecureFileName (name), error);
                                }

                                return(length);
                        }
                }

                public override long Position {
                        get {
                                if (handle == MonoIO.InvalidHandle)
                                        throw new ObjectDisposedException ("Stream has been closed");

                                if(CanSeek == false)
                                        throw new NotSupportedException("The stream does not support seeking");
                                
                                return(buf_start + buf_offset);
                        }
                        set {
                                if (handle == MonoIO.InvalidHandle)
                                        throw new ObjectDisposedException ("Stream has been closed");

                                if(CanSeek == false) {
                                        throw new NotSupportedException("The stream does not support seeking");
                                }

                                if(value < 0) {
                                        throw new ArgumentOutOfRangeException("Attempt to set the position to a negative value");
                                }
                                
                                Seek (value, SeekOrigin.Begin);
                        }
                }

                [Obsolete ("Use SafeFileHandle instead")]
                public virtual IntPtr Handle {
                        [SecurityPermission (SecurityAction.LinkDemand, UnmanagedCode = true)]
                        [SecurityPermission (SecurityAction.InheritanceDemand, UnmanagedCode = true)]
                        get {
                                return handle;
                        }
                }

                public virtual SafeFileHandle SafeFileHandle {
                        [SecurityPermission (SecurityAction.LinkDemand, UnmanagedCode = true)]
                        [SecurityPermission (SecurityAction.InheritanceDemand, UnmanagedCode = true)]
                        get {
                                SafeFileHandle ret;

                                if (safeHandle != null)
                                        ret = safeHandle;
                                else
                                        ret = new SafeFileHandle (handle, owner);

                                FlushBuffer ();
                                return ret;
                        }
                }

                // methods

                public override int ReadByte ()
                {
                        if (handle == MonoIO.InvalidHandle)
                                throw new ObjectDisposedException ("Stream has been closed");

                        if (!CanRead)
                                throw new NotSupportedException ("Stream does not support reading");
                        
                        if (buf_size == 0) {
                                int n = ReadData (handle, buf, 0, 1);
                                if (n == 0) return -1;
                                else return buf[0];
                        }
                        else if (buf_offset >= buf_length) {
                                RefillBuffer ();

                                if (buf_length == 0)
                                        return -1;
                        }
                        
                        return buf [buf_offset ++];
                }

                public override void WriteByte (byte value)
                {
                        if (handle == MonoIO.InvalidHandle)
                                throw new ObjectDisposedException ("Stream has been closed");

                        if (!CanWrite)
                                throw new NotSupportedException ("Stream does not support writing");

                        if (buf_offset == buf_size)
                                FlushBuffer ();

                        if (buf_size == 0) { // No buffering
                                buf [0] = value;
                                buf_dirty = true;
                                buf_length = 1;
                                FlushBuffer ();
                                return;
                        }

                        buf [buf_offset ++] = value;
                        if (buf_offset > buf_length)
                                buf_length = buf_offset;

                        buf_dirty = true;
                }

                public override int Read ([In,Out] byte[] array, int offset, int count)
                {
                        if (handle == MonoIO.InvalidHandle)
                                throw new ObjectDisposedException ("Stream has been closed");
                        if (array == null)
                                throw new ArgumentNullException ("array");
                        if (!CanRead)
                                throw new NotSupportedException ("Stream does not support reading");
                        int len = array.Length;
                        if (offset < 0)
                                throw new ArgumentOutOfRangeException ("offset", "< 0");
                        if (count < 0)
                                throw new ArgumentOutOfRangeException ("count", "< 0");
                        if (offset > len)
                                throw new ArgumentException ("destination offset is beyond array size");
                        // reordered to avoid possible integer overflow
                        if (offset > len - count)
                                throw new ArgumentException ("Reading would overrun buffer");

                        if (async) {
                                IAsyncResult ares = BeginRead (array, offset, count, null, null);
                                return EndRead (ares);
                        }

                        return ReadInternal (array, offset, count);
                }

                int ReadInternal (byte [] dest, int offset, int count)
                {
                        int copied = 0;

                        int n = ReadSegment (dest, offset, count);
                        copied += n;
                        count -= n;
                        
                        if (count == 0) {
                                /* If there was already enough
                                 * buffered, no need to read
                                 * more from the file.
                                 */
                                return (copied);
                        }

                        if (count > buf_size) {
                                /* Read as much as we can, up
                                 * to count bytes
                                 */
                                FlushBuffer();
                                n = ReadData (handle, dest,
                                              offset+copied,
                                              count);
                        
                                /* Make the next buffer read
                                 * start from the right place
                                 */
                                buf_start += n;
                        } else {
                                RefillBuffer ();
                                n = ReadSegment (dest,
                                                 offset+copied,
                                                 count);
                        }

                        copied += n;

                        return copied;
                }

                delegate int ReadDelegate (byte [] buffer, int offset, int count);

                public override IAsyncResult BeginRead (byte [] array, int offset, int numBytes,
                                                        AsyncCallback userCallback, object stateObject)
                {
                        if (handle == MonoIO.InvalidHandle)
                                throw new ObjectDisposedException ("Stream has been closed");

                        if (!CanRead)
                                throw new NotSupportedException ("This stream does not support reading");

                        if (array == null)
                                throw new ArgumentNullException ("array");

                        if (numBytes < 0)
                                throw new ArgumentOutOfRangeException ("numBytes", "Must be >= 0");

                        if (offset < 0)
                                throw new ArgumentOutOfRangeException ("offset", "Must be >= 0");

                        // reordered to avoid possible integer overflow
                        if (numBytes > array.Length - offset)
                                throw new ArgumentException ("Buffer too small. numBytes/offset wrong.");

                        if (!async)
                                return base.BeginRead (array, offset, numBytes, userCallback, stateObject);

                        ReadDelegate r = new ReadDelegate (ReadInternal);
                        return r.BeginInvoke (array, offset, numBytes, userCallback, stateObject);
                }
                
                public override int EndRead (IAsyncResult asyncResult)
                {
                        if (asyncResult == null)
                                throw new ArgumentNullException ("asyncResult");

                        if (!async)
                                return base.EndRead (asyncResult);

                        AsyncResult ares = asyncResult as AsyncResult;
                        if (ares == null)
                                throw new ArgumentException ("Invalid IAsyncResult", "asyncResult");

                        ReadDelegate r = ares.AsyncDelegate as ReadDelegate;
                        if (r == null)
                                throw new ArgumentException ("Invalid IAsyncResult", "asyncResult");

                        return r.EndInvoke (asyncResult);
                }

                public override void Write (byte[] array, int offset, int count)
                {
                        if (handle == MonoIO.InvalidHandle)
                                throw new ObjectDisposedException ("Stream has been closed");
                        if (array == null)
                                throw new ArgumentNullException ("array");
                        if (offset < 0)
                                throw new ArgumentOutOfRangeException ("offset", "< 0");
                        if (count < 0)
                                throw new ArgumentOutOfRangeException ("count", "< 0");
                        // ordered to avoid possible integer overflow
                        if (offset > array.Length - count)
                                throw new ArgumentException ("Reading would overrun buffer");
                        if (!CanWrite)
                                throw new NotSupportedException ("Stream does not support writing");

                        if (async) {
                                IAsyncResult ares = BeginWrite (array, offset, count, null, null);
                                EndWrite (ares);
                                return;
                        }

                        WriteInternal (array, offset, count);
                }

                void WriteInternal (byte [] src, int offset, int count)
                {
                        if (count > buf_size) {
                                // shortcut for long writes
                                MonoIOError error;

                                FlushBuffer ();
                                int wcount = count;
                                
                                while (wcount > 0){
                                        int n = MonoIO.Write (handle, src, offset, wcount, out error);
                                        if (error != MonoIOError.ERROR_SUCCESS)
                                                throw MonoIO.GetException (GetSecureFileName (name), error);
                                        
                                        wcount -= n;
                                        offset += n;
                                } 
                                buf_start += count;
                        } else {

                                int copied = 0;
                                while (count > 0) {
                                        
                                        int n = WriteSegment (src, offset + copied, count);
                                        copied += n;
                                        count -= n;

                                        if (count == 0) {
                                                break;
                                        }

                                        FlushBuffer ();
                                }
                        }
                }

                delegate void WriteDelegate (byte [] buffer, int offset, int count);

                public override IAsyncResult BeginWrite (byte [] array, int offset, int numBytes,
                                                        AsyncCallback userCallback, object stateObject)
                {
                        if (handle == MonoIO.InvalidHandle)
                                throw new ObjectDisposedException ("Stream has been closed");

                        if (!CanWrite)
                                throw new NotSupportedException ("This stream does not support writing");

                        if (array == null)
                                throw new ArgumentNullException ("array");

                        if (numBytes < 0)
                                throw new ArgumentOutOfRangeException ("numBytes", "Must be >= 0");

                        if (offset < 0)
                                throw new ArgumentOutOfRangeException ("offset", "Must be >= 0");

                        // reordered to avoid possible integer overflow
                        if (numBytes > array.Length - offset)
                                throw new ArgumentException ("array too small. numBytes/offset wrong.");

                        if (!async)
                                return base.BeginWrite (array, offset, numBytes, userCallback, stateObject);

                        FileStreamAsyncResult result = new FileStreamAsyncResult (userCallback, stateObject);
                        result.BytesRead = -1;
                        result.Count = numBytes;
                        result.OriginalCount = numBytes;

                        if (buf_dirty) {
                                MemoryStream ms = new MemoryStream ();
                                FlushBuffer (ms);
                                ms.Write (array, offset, numBytes);
                                offset = 0;
                                numBytes = (int) ms.Length;
                        }

                        WriteDelegate w = new WriteDelegate (WriteInternal);
                        return w.BeginInvoke (array, offset, numBytes, userCallback, stateObject);                      
                }
                
                public override void EndWrite (IAsyncResult asyncResult)
                {
                        if (asyncResult == null)
                                throw new ArgumentNullException ("asyncResult");

                        if (!async) {
                                base.EndWrite (asyncResult);
                                return;
                        }

                        AsyncResult ares = asyncResult as AsyncResult;
                        if (ares == null)
                                throw new ArgumentException ("Invalid IAsyncResult", "asyncResult");

                        WriteDelegate w = ares.AsyncDelegate as WriteDelegate;
                        if (w == null)
                                throw new ArgumentException ("Invalid IAsyncResult", "asyncResult");

                        w.EndInvoke (asyncResult);
                        return;
                }

                public override long Seek (long offset, SeekOrigin origin)
                {
                        long pos;

                        if (handle == MonoIO.InvalidHandle)
                                throw new ObjectDisposedException ("Stream has been closed");
                        
                        // make absolute

                        if(CanSeek == false) {
                                throw new NotSupportedException("The stream does not support seeking");
                        }

                        switch (origin) {
                        case SeekOrigin.End:
                                pos = Length + offset;
                                break;

                        case SeekOrigin.Current:
                                pos = Position + offset;
                                break;

                        case SeekOrigin.Begin:
                                pos = offset;
                                break;

                        default:
                                throw new ArgumentException ("origin", "Invalid SeekOrigin");
                        }

                        if (pos < 0) {
                                /* LAMESPEC: shouldn't this be
                                 * ArgumentOutOfRangeException?
                                 */
                                throw new IOException("Attempted to Seek before the beginning of the stream");
                        }

                        if(pos < this.append_startpos) {
                                /* More undocumented crap */
                                throw new IOException("Can't seek back over pre-existing data in append mode");
                        }

                        FlushBuffer ();

                        MonoIOError error;
                
                        buf_start = MonoIO.Seek (handle, pos,
                                                 SeekOrigin.Begin,
                                                 out error);

                        if (error != MonoIOError.ERROR_SUCCESS) {
                                // don't leak the path information for isolated storage
                                throw MonoIO.GetException (GetSecureFileName (name), error);
                        }
                        
                        return(buf_start);
                }

                public override void SetLength (long value)
                {
                        if (handle == MonoIO.InvalidHandle)
                                throw new ObjectDisposedException ("Stream has been closed");

                        if(CanSeek == false)
                                throw new NotSupportedException("The stream does not support seeking");

                        if(CanWrite == false)
                                throw new NotSupportedException("The stream does not support writing");

                        if(value < 0)
                                throw new ArgumentOutOfRangeException("value is less than 0");
                        
                        Flush ();

                        MonoIOError error;
                        
                        MonoIO.SetLength (handle, value, out error);
                        if (error != MonoIOError.ERROR_SUCCESS) {
                                // don't leak the path information for isolated storage
                                throw MonoIO.GetException (GetSecureFileName (name), error);
                        }

                        if (Position > value)
                                Position = value;
                }

                public override void Flush ()
                {
                        if (handle == MonoIO.InvalidHandle)
                                throw new ObjectDisposedException ("Stream has been closed");

                        FlushBuffer ();
                }

#if NET_4_0
                public virtual void Flush (bool flushToDisk)
                {
                        FlushBuffer ();

                        // This does the fsync
                        if (flushToDisk){
                                MonoIOError error;
                                MonoIO.Flush (handle, out error);
                        }
                }
#endif

                public virtual void Lock (long position, long length)
                {
                        if (handle == MonoIO.InvalidHandle)
                                throw new ObjectDisposedException ("Stream has been closed");
                        if (position < 0) {
                                throw new ArgumentOutOfRangeException ("position must not be negative");
                        }
                        if (length < 0) {
                                throw new ArgumentOutOfRangeException ("length must not be negative");
                        }
                        if (handle == MonoIO.InvalidHandle) {
                                throw new ObjectDisposedException ("Stream has been closed");
                        }
                                
                        MonoIOError error;

                        MonoIO.Lock (handle, position, length, out error);
                        if (error != MonoIOError.ERROR_SUCCESS) {
                                // don't leak the path information for isolated storage
                                throw MonoIO.GetException (GetSecureFileName (name), error);
                        }
                }

                public virtual void Unlock (long position, long length)
                {
                        if (handle == MonoIO.InvalidHandle)
                                throw new ObjectDisposedException ("Stream has been closed");
                        if (position < 0) {
                                throw new ArgumentOutOfRangeException ("position must not be negative");
                        }
                        if (length < 0) {
                                throw new ArgumentOutOfRangeException ("length must not be negative");
                        }
                                
                        MonoIOError error;

                        MonoIO.Unlock (handle, position, length, out error);
                        if (error != MonoIOError.ERROR_SUCCESS) {
                                // don't leak the path information for isolated storage
                                throw MonoIO.GetException (GetSecureFileName (name), error);
                        }
                }

                // protected

                ~FileStream ()
                {
                        Dispose (false);
                }

                protected override void Dispose (bool disposing)
                {
                        Exception exc = null;
                        if (handle != MonoIO.InvalidHandle) {
                                try {
                                        FlushBuffer ();
                                } catch (Exception e) {
                                        exc = e;
                                }

                                if (owner) {
                                        MonoIOError error;
                                
                                        MonoIO.Close (handle, out error);
                                        if (error != MonoIOError.ERROR_SUCCESS) {
                                                // don't leak the path information for isolated storage
                                                throw MonoIO.GetException (GetSecureFileName (name), error);
                                        }

                                        handle = MonoIO.InvalidHandle;
                                }
                        }

                        canseek = false;
                        access = 0;
                        
                        if (disposing && buf != null) {
                                if (buf.Length == DefaultBufferSize && buf_recycle == null) {
                                        lock (buf_recycle_lock) {
                                                if (buf_recycle == null) {
                                                        buf_recycle = buf;
                                                }
                                        }
                                }
                                
                                buf = null;
                                GC.SuppressFinalize (this);
                        }
                        if (exc != null)
                                throw exc;
                }

#if !NET_2_1
                public FileSecurity GetAccessControl ()
                {
                        throw new NotImplementedException ();
                }
                
                public void SetAccessControl (FileSecurity fileSecurity)
                {
                        throw new NotImplementedException ();
                }
#endif

                // private.

                // ReadSegment, WriteSegment, FlushBuffer,
                // RefillBuffer and ReadData should only be called
                // when the Monitor lock is held, but these methods
                // grab it again just to be safe.

                private int ReadSegment (byte [] dest, int dest_offset, int count)
                {
                        if (count > buf_length - buf_offset) {
                                count = buf_length - buf_offset;
                        }
                        
                        if (count > 0) {
                                Buffer.BlockCopy (buf, buf_offset,
                                                  dest, dest_offset,
                                                  count);
                                buf_offset += count;
                        }
                        
                        return(count);
                }

                private int WriteSegment (byte [] src, int src_offset,
                                          int count)
                {
                        if (count > buf_size - buf_offset) {
                                count = buf_size - buf_offset;
                        }
                        
                        if (count > 0) {
                                Buffer.BlockCopy (src, src_offset,
                                                  buf, buf_offset,
                                                  count);
                                buf_offset += count;
                                if (buf_offset > buf_length) {
                                        buf_length = buf_offset;
                                }
                                
                                buf_dirty = true;
                        }
                        
                        return(count);
                }

                void FlushBuffer (Stream st)
                {
                        if (buf_dirty) {
                                MonoIOError error;

                                if (CanSeek == true) {
                                        MonoIO.Seek (handle, buf_start,
                                                     SeekOrigin.Begin,
                                                     out error);
                                        if (error != MonoIOError.ERROR_SUCCESS) {
                                                // don't leak the path information for isolated storage
                                                throw MonoIO.GetException (GetSecureFileName (name), error);
                                        }
                                }
                                if (st == null) {
                                        int wcount = buf_length;
                                        int offset = 0;
                                        while (wcount > 0){
                                                int n = MonoIO.Write (handle, buf, 0, buf_length, out error);
                                                if (error != MonoIOError.ERROR_SUCCESS) {
                                                        // don't leak the path information for isolated storage
                                                        throw MonoIO.GetException (GetSecureFileName (name), error);
                                                }
                                                wcount -= n;
                                                offset += n;
                                        }
                                } else {
                                        st.Write (buf, 0, buf_length);
                                }
                        }

                        buf_start += buf_offset;
                        buf_offset = buf_length = 0;
                        buf_dirty = false;
                }

                private void FlushBuffer ()
                {
                        FlushBuffer (null);
                }

                private void FlushBufferIfDirty ()
                {
                        if (buf_dirty)
                                FlushBuffer (null);
                }

                private void RefillBuffer ()
                {
                        FlushBuffer (null);
                        
                        buf_length = ReadData (handle, buf, 0,
                                               buf_size);
                }

                private int ReadData (IntPtr handle, byte[] buf, int offset,
                                      int count)
                {
                        MonoIOError error;
                        int amount = 0;

                        /* when async == true, if we get here we don't suport AIO or it's disabled
                         * and we're using the threadpool */
                        amount = MonoIO.Read (handle, buf, offset, count, out error);
                        if (error == MonoIOError.ERROR_BROKEN_PIPE) {
                                amount = 0; // might not be needed, but well...
                        } else if (error != MonoIOError.ERROR_SUCCESS) {
                                // don't leak the path information for isolated storage
                                throw MonoIO.GetException (GetSecureFileName (name), error);
                        }
                        
                        /* Check for read error */
                        if(amount == -1) {
                                throw new IOException ();
                        }
                        
                        return(amount);
                }
                                
                void InitBuffer (int size)
                {
                        if (size <= 0)
                                throw new ArgumentOutOfRangeException ("bufferSize", "Positive number required.");
                        
                        size = Math.Max (size, 8);
                        
                        //
                        // Instead of allocating a new default buffer use the
                        // last one if there is any available
                        //              
                        if (size <= DefaultBufferSize && buf_recycle != null) {
                                lock (buf_recycle_lock) {
                                        if (buf_recycle != null) {
                                                buf = buf_recycle;
                                                buf_recycle = null;
                                        }
                                }
                        }
                        
                        if (buf == null)
                                buf = new byte [size];
                        else
                                Array.Clear (buf, 0, size);
                                        
                        buf_size = size;
//                      buf_start = 0;
//                      buf_offset = buf_length = 0;
//                      buf_dirty = false;
                }

                private string GetSecureFileName (string filename)
                {
                        return (anonymous) ? Path.GetFileName (filename) : Path.GetFullPath (filename);
                }

                private string GetSecureFileName (string filename, bool full)
                {
                        return (anonymous) ? Path.GetFileName (filename) : 
                                (full) ? Path.GetFullPath (filename) : filename;
                }

                // fields

                internal const int DefaultBufferSize = 8192;

                // Input buffer ready for recycling                             
                static byte[] buf_recycle;
                static readonly object buf_recycle_lock = new object ();

                private FileAccess access;
                private bool owner;
                private bool async;
                private bool canseek;
                private long append_startpos;
                private bool anonymous;

                private byte [] buf;                    // the buffer
                private int buf_size;                   // capacity in bytes
                private int buf_length;                 // number of valid bytes in buffer
                private int buf_offset;                 // position of next byte
                private bool buf_dirty;                 // true if buffer has been written to
                private long buf_start;                 // location of buffer in file
                private string name = "[Unknown]";      // name of file.

                IntPtr handle;                          // handle to underlying file
                SafeFileHandle safeHandle;              // set only when using one of the
                                                        // constructors taking SafeFileHandle
        }
}