I converted TGREER's C# implementation of a hacked StreamReader class to VB.NET and wanted to provide it for anybody who has run into the following issue: when using a StreamReader, and ReadLine, to process a text file, you cannot determine where you are "at" within a file.
The following is a Quote from http://www.daniweb.com/techtalkforums/thread35078.html
Here's my solution, for any interested. This is basically a hacked version of the .NET StreamReader code. It adds two public properties, LineLength and BytesRead. LineLength returns the actual length of the current record, inclusive of line-termination characters. BytesRead returns the actual real bytes read (regardless of the buffer mechanism). This value is suitable for passing into .BaseStream.Seek().
It could be better. The real StreamReader code uses some methods internal to some of the core .NET namespaces, so I did the best I could with those. If anyone would like to post improvements, they are welcome to do so.
I am currently using this version without any problems, however if you find any errors feel free to make note of them.
Oh and thanks to TGREER for writing and sharing the code in the first place! This implementation is much better than the other workarounds I have found to date and it only took me a few hours to convert and implement. Hopefully this will save someone some of that time and you could implement this within a few minutes now!
:cheesy:
Imports System
Imports System.Text
Imports System.Runtime.InteropServices
Imports System.IO
'// http://www.daniweb.com/techtalkforums/thread35078.html
Namespace TGREER
<Serializable()> _
Public Class myStreamReader
Inherits TextReader
Public Shared Shadows ReadOnly Null As myStreamReader = New NullmyStreamReader()
'Public Shared Null As myStreamReader = New NullmyStreamReader()
Friend Const DefaultBufferSize As Integer = 1024 ' Byte buffer size
Private Const DefaultFileStreamBufferSize As Integer = 4096
Private Const MinBufferSize As Integer = 128
Private stream As Stream
Private encoding As Encoding
Private decoder As Decoder
Private byteBuffer() As Byte
Private charBuffer() As Char
Private _preamble() As Byte
Private charPos As Integer
Private charLen As Integer
Private byteLen As Integer
Private _maxCharsPerBuffer As Integer
Private _detectEncoding As Boolean
Private _checkPreamble As Boolean
Private _isBlocked As Boolean
Private _lineLength As Integer
Public ReadOnly Property LineLength() As Integer
Get
Return _lineLength
End Get
End Property
Private _bytesRead As Integer
Public ReadOnly Property BytesRead() As Integer
Get
Return _bytesRead
End Get
End Property
Friend Sub New()
End Sub 'New
Public Sub New(stream As Stream)
MyClass.New(stream, Encoding.UTF8, True, DefaultBufferSize)
End Sub 'New
Public Sub New(stream As Stream, detectEncodingFromByteOrderMarks As Boolean)
MyClass.New(stream, Encoding.UTF8, detectEncodingFromByteOrderMarks, DefaultBufferSize)
End Sub 'New
Public Sub New(stream As Stream, encoding As Encoding)
MyClass.New(stream, encoding, True, DefaultBufferSize)
End Sub 'New
Public Sub New(stream As Stream, encoding As Encoding, detectEncodingFromByteOrderMarks As Boolean)
MyClass.New(stream, encoding, detectEncodingFromByteOrderMarks, DefaultBufferSize)
End Sub 'New
Public Sub New(stream As Stream, encoding As Encoding, detectEncodingFromByteOrderMarks As Boolean, bufferSize As Integer)
If stream Is Nothing OrElse encoding Is Nothing Then
Throw New ArgumentNullException(IIf(stream Is Nothing, "stream", "encoding"))
End If
If Not stream.CanRead Then
Throw New ArgumentException(Environment.GetEnvironmentVariable("Argument_StreamNotReadable"))
End If
If bufferSize <= 0 Then
Throw New ArgumentOutOfRangeException("bufferSize", Environment.GetEnvironmentVariable("ArgumentOutOfRange_NeedPosNum"))
End If
Init(stream, encoding, detectEncodingFromByteOrderMarks, bufferSize)
End Sub 'New
'/ <include file='doc\myStreamReader.uex' path='docs/doc[@for="myStreamReader.myStreamReader4"]/*' />
Public Sub New(path As String)
MyClass.New(path, Encoding.UTF8, True, DefaultBufferSize)
End Sub 'New
'/ <include file='doc\myStreamReader.uex' path='docs/doc[@for="myStreamReader.myStreamReader9"]/*' />
Public Sub New(path As String, detectEncodingFromByteOrderMarks As Boolean)
MyClass.New(path, Encoding.UTF8, detectEncodingFromByteOrderMarks, DefaultBufferSize)
End Sub 'New
'/ <include file='doc\myStreamReader.uex' path='docs/doc[@for="myStreamReader.myStreamReader5"]/*' />
Public Sub New(path As String, encoding As Encoding)
MyClass.New(path, encoding, True, DefaultBufferSize)
End Sub 'New
'/ <include file='doc\myStreamReader.uex' path='docs/doc[@for="myStreamReader.myStreamReader6"]/*' />
Public Sub New(path As String, encoding As Encoding, detectEncodingFromByteOrderMarks As Boolean)
MyClass.New(path, encoding, detectEncodingFromByteOrderMarks, DefaultBufferSize)
End Sub 'New
'/ <include file='doc\myStreamReader.uex' path='docs/doc[@for="myStreamReader.myStreamReader7"]/*' />
Public Sub New(path As String, encoding As Encoding, detectEncodingFromByteOrderMarks As Boolean, bufferSize As Integer)
' Don't open a Stream before checking for invalid arguments,
' or we'll create a FileStream on disk and we won't close it until
' the finalizer runs, causing problems for applications.
If path Is Nothing OrElse encoding Is Nothing Then
Throw New ArgumentNullException(IIf(path Is Nothing, "path", "encoding"))
End If
If path.Length = 0 Then
Throw New ArgumentException(Environment.GetEnvironmentVariable("Argument_EmptyPath"))
End If
If bufferSize <= 0 Then
Throw New ArgumentOutOfRangeException("bufferSize", Environment.GetEnvironmentVariable("ArgumentOutOfRange_NeedPosNum"))
End If
Dim stream As FileStream = New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, DefaultFileStreamBufferSize)
Init(stream, encoding, detectEncodingFromByteOrderMarks, bufferSize)
End Sub 'New
Private Sub Init(stream As Stream, encoding As Encoding, detectEncodingFromByteOrderMarks As Boolean, bufferSize As Integer)
Me.stream = stream
Me.encoding = encoding
decoder = encoding.GetDecoder()
If bufferSize < MinBufferSize Then
bufferSize = MinBufferSize
End If
byteBuffer = New Byte(bufferSize) {}
_maxCharsPerBuffer = encoding.GetMaxCharCount(bufferSize)
charBuffer = New Char(_maxCharsPerBuffer) {}
byteLen = 0
_detectEncoding = detectEncodingFromByteOrderMarks
_preamble = encoding.GetPreamble()
_checkPreamble = _preamble.Length > 0
_isBlocked = False
End Sub 'Init
'/ <include file='doc\myStreamReader.uex' path='docs/doc[@for="myStreamReader.Close"]/*' />
Public Overrides Sub Close()
Dispose(True)
End Sub 'Close
'/ <include file='doc\myStreamReader.uex' path='docs/doc[@for="myStreamReader.Dispose"]/*' />
Protected Overrides Sub Dispose(disposing As Boolean)
If disposing Then
If Not (stream Is Nothing) Then
stream.Close()
End If
End If
If Not (stream Is Nothing) Then
stream = Nothing
encoding = Nothing
decoder = Nothing
byteBuffer = Nothing
charBuffer = Nothing
charPos = 0
charLen = 0
End If
MyBase.Dispose(disposing)
End Sub 'Dispose
'/ <include file='doc\myStreamReader.uex' path='docs/doc[@for="myStreamReader.CurrentEncoding"]/*' />
Public Overridable ReadOnly Property CurrentEncoding() As Encoding
Get
Return encoding
End Get
End Property
'/ <include file='doc\myStreamReader.uex' path='docs/doc[@for="myStreamReader.BaseStream"]/*' />
Public Overridable ReadOnly Property BaseStream() As Stream
Get
Return stream
End Get
End Property
' DiscardBufferedData tells myStreamReader to throw away its internal
' buffer contents. This is useful if the user needs to seek on the
' underlying stream to a known location then wants the myStreamReader
' to start reading from this new point. This method should be called
' very sparingly, if ever, since it can lead to very poor performance.
' However, it may be the only way of handling some scenarios where
' users need to re-read the contents of a myStreamReader a second time.
'/ <include file='doc\myStreamReader.uex' path='docs/doc[@for="myStreamReader.DiscardBufferedData"]/*' />
Public Sub DiscardBufferedData()
byteLen = 0
charLen = 0
charPos = 0
decoder = encoding.GetDecoder()
_isBlocked = False
End Sub 'DiscardBufferedData
'/ <include file='doc\myStreamReader.uex' path='docs/doc[@for="myStreamReader.Peek"]/*' />
Public Overrides Function Peek() As Integer
'if (stream == null)
'__Error.ReaderClosed();
If charPos = charLen Then
If _isBlocked OrElse ReadBuffer() = 0 Then
Return - 1
End If
End If
'Return charBuffer(charPos)
Return AscW(charBuffer(charPos))
End Function 'Peek
Overloads Public Overrides Function Read() As Integer
'if (stream == null)
'__Error.ReaderClosed();
If charPos = charLen Then
If ReadBuffer() = 0 Then
Return - 1
End If
End If
Return AscW(charBuffer(charPos + 1))
'Return charBuffer(charPos + 1)
End Function 'Read
'Public override Integer Read((In, Out) Char() buffer, Integer index, Integer count)
Public Overloads Overrides Function Read(<[In](), Out()> ByVal buffer() As Char, ByVal index As Integer, ByVal count As Integer) As Integer
'if (stream == null)
'__Error.ReaderClosed();
If buffer Is Nothing Then
Throw New ArgumentNullException("buffer", Environment.GetEnvironmentVariable("ArgumentNull_Buffer"))
End If
If index < 0 OrElse count < 0 Then
Throw New ArgumentOutOfRangeException(IIf(index < 0, "index", "count"), Environment.GetEnvironmentVariable("ArgumentOutOfRange_NeedNonNegNum"))
End If
If buffer.Length - index < count Then
Throw New ArgumentException(Environment.GetEnvironmentVariable("Argument_InvalidOffLen"))
End If
Dim charsRead As Integer = 0
' As a perf optimization, if we had exactly one buffer's worth of
' data read in, let's try writing directly to the user's buffer.
Dim readToUserBuffer As Boolean = False
While count > 0
Dim n As Integer = charLen - charPos
If n = 0 Then
n = ReadBuffer(buffer, index + charsRead, count, readToUserBuffer)
End If
If n = 0 Then
Exit While ' We're at EOF
End If
If n > count Then
n = count
End If
If Not readToUserBuffer Then
System.Buffer.BlockCopy(charBuffer, charPos * 2, buffer, (index + charsRead) * 2, n * 2)
'buffer.BlockCopy(charBuffer, charPos * 2, buffer, (index + charsRead) * 2, n * 2)
charPos += n
End If
charsRead += n
count -= n
' This function shouldn't block for an indefinite amount of time,
' or reading from a network stream won't work right. If we got
' fewer bytes than we requested, then we want to break right here.
If _isBlocked Then
Exit While
End If
End While
Return charsRead
End Function 'Read
'/ <include file='doc\myStreamReader.uex' path='docs/doc[@for="myStreamReader.ReadToEnd"]/*' />
Public Overrides Function ReadToEnd() As String
'if (stream == null)
'__Error.ReaderClosed();
' For performance, call Read(char[], int, int) with a buffer
' as big as the myStreamReader's internal buffer, to get the
' readToUserBuffer optimization.
Dim chars(charBuffer.Length) As Char
Dim len As Integer
Dim sb As New StringBuilder(charBuffer.Length)
While (len = Read(chars, 0, chars.Length)) <> 0
sb.Append(chars, 0, len)
End While
Return sb.ToString()
End Function 'ReadToEnd
' Trims n bytes from the front of the buffer.
Private Sub CompressBuffer(ByVal n As Integer)
Buffer.BlockCopy(byteBuffer, n, byteBuffer, 0, byteLen - n)
byteLen -= n
End Sub 'CompressBuffer
' returns whether the first array starts with the second array.
Private Shared Function BytesMatch(ByVal buffer() As Byte, ByVal compareTo() As Byte) As Boolean
Dim i As Integer
For i = 0 To compareTo.Length - 1
If buffer(i) <> compareTo(i) Then
Return False
End If
Next i
Return True
End Function 'BytesMatch
Private Sub DetectEncoding()
If byteLen < 2 Then
Return
End If
_detectEncoding = False
Dim changedEncoding As Boolean = False
If byteBuffer(0) = &HFE AndAlso byteBuffer(1) = &HFF Then
' Big Endian Unicode
encoding = New UnicodeEncoding(True, True)
decoder = encoding.GetDecoder()
CompressBuffer(2)
changedEncoding = True
ElseIf byteBuffer(0) = &HFF AndAlso byteBuffer(1) = &HFE Then
' Little Endian Unicode
encoding = New UnicodeEncoding(False, True)
decoder = encoding.GetDecoder()
CompressBuffer(2)
changedEncoding = True
ElseIf byteLen >= 3 AndAlso byteBuffer(0) = &HEF AndAlso byteBuffer(1) = &HBB AndAlso byteBuffer(2) = &HBF Then
' UTF-8
encoding = Text.Encoding.UTF8
decoder = encoding.GetDecoder()
CompressBuffer(3)
changedEncoding = True
ElseIf byteLen = 2 Then
_detectEncoding = True
End If ' Note: in the future, if we change this algorithm significantly,
' we can support checking for the preamble of the given encoding.
If changedEncoding Then
_maxCharsPerBuffer = encoding.GetMaxCharCount(byteBuffer.Length)
charBuffer = New Char(_maxCharsPerBuffer) {}
End If
End Sub 'DetectEncoding
Private Overloads Function ReadBuffer() As Integer
charLen = 0
byteLen = 0
charPos = 0
Do
byteLen = stream.Read(byteBuffer, 0, byteBuffer.Length)
If byteLen = 0 Then ' We're at EOF
Return charLen
End If
' _isBlocked == whether we read fewer bytes than we asked for.
' Note we must check it here because CompressBuffer or
' DetectEncoding will screw with byteLen.
_isBlocked = byteLen < byteBuffer.Length
If _checkPreamble AndAlso byteLen >= _preamble.Length Then
_checkPreamble = False
If BytesMatch(byteBuffer, _preamble) Then
_detectEncoding = False
CompressBuffer(_preamble.Length)
End If
End If
' If we're supposed to detect the encoding and haven't done so yet,
' do it. Note this may need to be called more than once.
If _detectEncoding AndAlso byteLen >= 2 Then
DetectEncoding()
End If
charLen += decoder.GetChars(byteBuffer, 0, byteLen, charBuffer, charLen)
Loop While charLen = 0
'Console.WriteLine("ReadBuffer called. chars: "+charLen);
Return charLen
End Function 'ReadBuffer
' This version has a perf optimization to decode data DIRECTLY into the
' user's buffer, bypassing StreamWriter's own buffer.
' This gives a > 20% perf improvement for our encodings across the board,
' but only when asking for at least the number of characters that one
' buffer's worth of bytes could produce.
' This optimization, if run, will break SwitchEncoding, so we must not do
' this on the first call to ReadBuffer.
Private Overloads Function ReadBuffer(ByVal userBuffer() As Char, ByVal userOffset As Integer, ByVal desiredChars As Integer, ByRef readToUserBuffer As Boolean) As Integer
charLen = 0
byteLen = 0
charPos = 0
Dim charsRead As Integer = 0
' As a perf optimization, we can decode characters DIRECTLY into a
' user's char[]. We absolutely must not write more characters
' into the user's buffer than they asked for. Calculating
' encoding.GetMaxCharCount(byteLen) each time is potentially very
' expensive - instead, cache the number of chars a full buffer's
' worth of data may produce. Yes, this makes the perf optimization
' less aggressive, in that all reads that asked for fewer than AND
' returned fewer than _maxCharsPerBuffer chars won't get the user
' buffer optimization. This affects reads where the end of the
' Stream comes in the middle somewhere, and when you ask for
' fewer chars than than your buffer could produce.
readToUserBuffer = desiredChars >= _maxCharsPerBuffer
Do
byteLen = stream.Read(byteBuffer, 0, byteBuffer.Length)
If byteLen = 0 Then ' EOF
Return charsRead
End If
' _isBlocked == whether we read fewer bytes than we asked for.
' Note we must check it here because CompressBuffer or
' DetectEncoding will screw with byteLen.
_isBlocked = byteLen < byteBuffer.Length
' On the first call to ReadBuffer, if we're supposed to detect the encoding, do it.
If _detectEncoding AndAlso byteLen >= 2 Then
DetectEncoding()
' DetectEncoding changes some buffer state. Recompute this.
readToUserBuffer = desiredChars >= _maxCharsPerBuffer
End If
If _checkPreamble AndAlso byteLen >= _preamble.Length Then
_checkPreamble = False
If BytesMatch(byteBuffer, _preamble) Then
_detectEncoding = False
CompressBuffer(_preamble.Length)
' CompressBuffer changes some buffer state. Recompute this.
readToUserBuffer = desiredChars >= _maxCharsPerBuffer
End If
End If
'
' if (readToUserBuffer)
' Console.Write('.');
' else {
' Console.WriteLine("Desired chars is wrong. byteBuffer.length: "+byteBuffer.Length+" max chars is: "+encoding.GetMaxCharCount(byteLen)+" desired: "+desiredChars);
' }
'
charPos = 0
If readToUserBuffer Then
charsRead += decoder.GetChars(byteBuffer, 0, byteLen, userBuffer, userOffset + charsRead)
charLen = 0 ' myStreamReader's buffer is empty.
Else
charsRead = decoder.GetChars(byteBuffer, 0, byteLen, charBuffer, charsRead)
charLen += charsRead ' Number of chars in myStreamReader's buffer.
End If
Loop While charsRead = 0
'Console.WriteLine("ReadBuffer: charsRead: "+charsRead+" readToUserBuffer: "+readToUserBuffer);
Return charsRead
End Function 'ReadBuffer
' Reads a line. A line is defined as a sequence of characters followed by
' a carriage return ('\r'), a line feed ('\n'), or a carriage return
' immediately followed by a line feed. The resulting string does not
' contain the terminating carriage return and/or line feed. The returned
' value is null if the end of the input stream has been reached.
'
'/ <include file='doc\myStreamReader.uex' path='docs/doc[@for="myStreamReader.ReadLine"]/*' />
Public Overrides Function ReadLine() As String
_lineLength = 0
'if (stream == null)
' __Error.ReaderClosed();
If charPos = charLen Then
If ReadBuffer() = 0 Then
Return Nothing
End If
End If
Dim sb As StringBuilder = Nothing
Do
Dim i As Integer = charPos
Do
Dim ch As Char = charBuffer(i)
Dim EolChars As Integer = 0
If ch = ControlChars.Cr OrElse ch = ControlChars.Lf Then
EolChars = 1
Dim s As String
If Not (sb Is Nothing) Then
sb.Append(charBuffer, charPos, i - charPos)
s = sb.ToString()
Else
s = New String(charBuffer, charPos, i - charPos)
End If
charPos = i + 1
If ch = ControlChars.Cr AndAlso (charPos < charLen OrElse ReadBuffer() > 0) Then
If charBuffer(charPos) = ControlChars.Lf Then
charPos += 1
EolChars = 2
End If
End If
_lineLength = s.Length + EolChars
_bytesRead = _bytesRead + _lineLength
Return s
End If
i += 1
Loop While i < charLen
i = charLen - charPos
If sb Is Nothing Then
sb = New StringBuilder(i + 80)
End If
sb.Append(charBuffer, charPos, i)
Loop While ReadBuffer() > 0
Dim ss As String = sb.ToString()
_lineLength = ss.Length
_bytesRead = _bytesRead + _lineLength
Return ss
End Function 'ReadLine
' No data, class doesn't need to be serializable.
' Note this class is threadsafe.
Private Class NullmyStreamReader
Inherits myStreamReader
Public Overrides ReadOnly Property BaseStream() As Stream
Get
Return stream.Null
End Get
End Property
Public Overrides ReadOnly Property CurrentEncoding() As Encoding
Get
Return Text.Encoding.Unicode
End Get
End Property
Public Overrides Function Peek() As Integer
Return -1
End Function 'Peek
Public Overloads Overrides Function Read() As Integer
Return -1
End Function 'Read
'/ <include file='doc\myStreamReader.uex' path='docs/doc[@for="myStreamReader.NullmyStreamReader.Read"]/*' />
Public Overloads Overrides Function Read(ByVal buffer() As Char, ByVal index As Integer, ByVal count As Integer) As Integer
Return 0
End Function 'Read
'/ <include file='doc\myStreamReader.uex' path='docs/doc[@for="myStreamReader.NullmyStreamReader.ReadLine"]/*' />
Public Overrides Function ReadLine() As String
Return Nothing
End Function 'ReadLine
Public Overrides Function ReadToEnd() As String
Return String.Empty
End Function 'ReadToEnd
End Class 'NullmyStreamReader
End Class 'myStreamReader
EndNamespace'TGREER