Professional ASP.NET 3.5 in C# and Visual Basic Part 122 docx

Listing 25-15: Writing to a MemoryStream VB Dim data As Byte = System.Text.Encoding.ASCII.GetBytes"This is a string" Dim ms As New System.IO.MemoryStream ms.Writedata, 0, data.Length ms.

FileStreamresources asClosedoes, it can be very useful if you are going to perform multiple write

operations and do not want to release and then reacquire the resources for each write operation

As you can see, so far reading and writing to files is really quite easy The good thing is that, as mentioned

earlier, because NET uses the same basicStreammodel for a variety of data stores, you can use these

same techniques for reading and writing to any of theStreamderived classes Listing 25-15 shows how

you can use the same basic code to write to aMemoryStream, and Listing 25-16 demonstrates reading a

Telnet server response using theNetworkStream

Listing 25-15: Writing to a MemoryStream

VB

Dim data() As Byte = System.Text.Encoding.ASCII.GetBytes("This is a string")

Dim ms As New System.IO.MemoryStream()

ms.Write(data, 0, data.Length)

ms.Close()

C#

byte[] data = System.Text.Encoding.ASCII.GetBytes("This is a string");

System.IO.MemoryStream ms = new System.IO.MemoryStream();

ms.Write(data, 0, data.Length);

ms.Close();

Listing 25-16: Reading from a NetworkStream

VB

Dim client As New System.Net.Sockets.TcpClient()

’ Note: You can find a large list of Telnet accessible

’ BBS systems at http://www.dmine.com/telnet/brieflist.htm

’ The WCS Online BBS (http://bbs.wcssoft.com)

Dim addr As System.Net.IPAddress = System.Net.IPAddress.Parse("65.182.234.52")

Dim endpoint As New System.Net.IPEndPoint(addr, 23)

client.Connect(endpoint)

Dim ns As System.Net.Sockets.NetworkStream = client.GetStream()

If (ns.DataAvailable) Then

Dim data(client.ReceiveBufferSize) As Byte

ns.Read(data, 0, client.ReceiveBufferSize)

Dim response As String = System.Text.Encoding.ASCII.GetString(data)

End If

ns.Close()

C#

System.Net.Sockets.TcpClient client = new System.Net.Sockets.TcpClient();

// Note: You can find a large list of Telnet accessible

// BBS systems at http://www.dmine.com/telnet/brieflist.htm

// The WCS Online BBS (http://bbs.wcssoft.com)

System.Net.IPAddress addr = System.Net.IPAddress.Parse("65.182.234.52");

System.Net.IPEndPoint endpoint = new System.Net.IPEndPoint(addr,23);

System.Net.Sockets.NetworkStream ns = client.GetStream();

if (ns.DataAvailable)

{

byte[] bytes = new byte[client.ReceiveBufferSize];

ns.Read(bytes, 0, client.ReceiveBufferSize);

string data = System.Text.Encoding.ASCII.GetString(bytes);

}

ns.Close();

Notice that the concept in both examples is virtually identical You create aStreamobject, read the bytes into a byte array for processing, and then close the stream The code varies only in the implementation of specific Streams

Readers and Writers

Other main parts of I/O in the NET Framework areReaderandWriterclasses These classes help

insulate you from having to deal with reading and writing individual bytes to and from Streams, enabling you to concentrate on the data you are working with The NET Framework provides a wide variety of

reader and writer classes, each designed for reading or writing according to a specific set of rules The

first table following shows a partial list of the readers available in the NET Framework The second table lists the corresponding writer classes

Class Description

System.IO

.TextReader

Abstract class that enables the reading of a sequential series of characters

System.IO

.StreamReader

Reads characters from a byte stream Derived fromTextReader

System.IO

.StringReader

Reads textual information as a stream of in-memory characters Derived fromTextReader

System.IO

.BinaryReader

Reads primitive data types as binary values from a stream

System.Xml

.XmlTextReader

Provides fast, non-cached, forward-only access to XML

Class Description

System.IO

.TextWriter

Abstract class that enables the writing of a sequential series of characters

System.IO

.StreamWriter

Writes characters to a stream Derived fromTextWriter

System.IO

.StringWriter

Writes textual information as a stream of in-memory characters Derived fromTextWriter

Class Description

System.IO

.BinaryWriter

Writes primitive data types in binary to a stream

System.Xml

.XmlTextWriter

Provides a fast, non-cached, forward-only way of generating XML streams

or files

Now look at using several different types of readers and writers, starting with a simple example

Listing 25-17 shows you how to use aStreamReaderto read aFileStream

Listing 25-17: Reading and writing a text file with a StreamReader

VB

Dim streamwriter As New System.IO.StreamWriter( _

System.IO.File.Open("C:\Wrox\temp.txt", System.IO.FileMode.Open) )

streamwriter.Write("This is a string")

streamwriter.Close()

Dim reader As New System.IO.StreamReader( _

System.IO.File.Open("C:\Wrox\temp.txt", System.IO.FileMode.Open) )

Dim tmp As String = reader.ReadToEnd()

reader.Close()

C#

System.IO.StreamWriter streamwriter =

new System.IO.StreamWriter(

System.IO.File.Open(@"C:\Wrox\temp.txt", System.IO.FileMode.Open) );

streamwriter.Write("This is a string");

streamwriter.Close();

System.IO.StreamReader reader =

new System.IO.StreamReader(

System.IO.File.Open(@"C:\Wrox\temp.txt",System.IO.FileMode.Open) );

string tmp = reader.ReadToEnd();

reader.Close();

Notice that when you create aStreamReader, you must pass an existing stream instance as a constructor

parameter The reader uses this stream as its underlying data source In this sample, you use theFile

class’s staticOpenmethod to open a writableFileStreamfor yourStreamWriter

Also notice that you no longer have to deal with byte arrays TheStreamReadertakes care of converting

the data to a type that’s more user-friendly than a byte array In this case, you are using theReadToEnd

method to read the entire stream and convert it to a string TheStreamReaderprovides a number of

different methods for reading data that you can use depending on exactly how you want to read the data,

from reading a single character using theReadmethod, to reading the entire file using theReadToEnd

method

Figure 25-12 shows the results of your write when you open the file in Notepad

Figure 25-12

Now use theBinaryReaderandBinaryWriterclasses to read and write some primitive types to a file

TheBinaryWriterwrites primitive objects in their native format, so in order to read them using the

BinaryReader, you must select the appropriateReadmethod Listing 25-18 shows you how to do that; in this case, you are writing a value from a number of different primitive types to the text file, then reading the same value

Listing 25-18: Reading and writing binary data

VB

Dim binarywriter As New System.IO.BinaryWriter( _

System.IO.File.Create("C:\Wrox\binary.dat"))

binarywriter.Write("a string")

binarywriter.Write(&H12346789ABCDEF)

binarywriter.Write(&H12345678)

binarywriter.Write("c"c)

binarywriter.Write(1.5F)

binarywriter.Write(100.2D)

binarywriter.Close()

Dim binaryreader As New System.IO.BinaryReader( _

System.IO.File.Open("C:\Wrox\binary.dat", System.IO.FileMode.Open))

Dim a As String = binaryreader.ReadString()

Dim l As Long = binaryreader.ReadInt64()

Dim i As Integer = binaryreader.ReadInt32()

Dim c As Char = binaryreader.ReadChar()

Dim f As Double = binaryreader.ReadSingle()

Dim d As Decimal = binaryreader.ReadDecimal()

binaryreader.Close()

C#

System.IO.BinaryWriter binarywriter =

new System.IO.BinaryWriter(

System.IO.File.Create(@"C:\Wrox\binary.dat") );

binarywriter.Write("a string");

binarywriter.Write(0x12346789abcdef);

Continued

binarywriter.Write(’c’);

binarywriter.Write(1.5f);

binarywriter.Write(100.2m);

binarywriter.Close();

System.IO.BinaryReader binaryreader =

new System.IO.BinaryReader(

System.IO.File.Open(@"C:\Wrox\binary.dat", System.IO.FileMode.Open));

string a = binaryreader.ReadString();

long l = binaryreader.ReadInt64();

int i = binaryreader.ReadInt32();

char c = binaryreader.ReadChar();

float f = binaryreader.ReadSingle();

decimal d = binaryreader.ReadDecimal();

binaryreader.Close();

If you open this file in Notepad, you should see that theBinaryWriterhas written the nonreadable binary

data to the file Figure 25-13 shows what the content of the file looks like TheBinaryReaderprovides a

number of different methods for reading various kinds of primitive types from the stream

In this sample, you use a differentReadmethod for each primitive type that you write to the file

Figure 25-13

Finally, notice that the basic usage of both theStreamReader/StreamWriterandBinaryReader/

BinaryWriterclasses is virtually identical You can apply the same basic ideas to use any of the reader

or writer classes

Encodings

TheStreamReaderby default attempts to determine the encoding format of the file If one of the

sup-ported encodings such as UTF-8 or UNICODE is detected, it is used If the encoding is not recognized,

the default encoding of UTF-8 is used Depending on the constructor you call, you can change the default

encoding used and optionally turn off encoding detection The following example shows how you can

control the encoding that theStreamReaderuses

StreamReader reader =

new StreamReader(@"C:\Wrox\text.txt",System.Text.Encoding.Unicode);

The default encoding for theStreamWriteris also UTF-8, and you can override it in the same manner as theStreamReaderclass

I/O Shortcuts

Although knowing how to create and use streams is always very useful and worth studying, the NET

Framework provides you with numerous shortcuts for common tasks like reading and writing to files

For instance, if you want to read the entire file, you can simply use one of the static Read All methods

of theFileclass Using these methods, you cause NET to handle the process of creating theStreamand

StreamReaderfor you, and simply return the resulting string of data This is just one example of the

shortcuts that the NET Framework provides Listing 25-19 shows some of the others, with explanatory comments Keep in mind that Listing 25-19 is showing individual code snippets; do not try to run the

listing as a single block of code

Listing 25-19: Using the static method of the File and Directory classes

VB

’ Opens a file and returns a FileStream

Dim fs As System.IO FileStream = _

System.IO.File.Open("C:\Wrox\temp.txt", System.IO.FileMode.Open)

’ Opens a file and returns a StreamReader for reading the data

Dim sr As System.IO.StreamReader = System.IO.File.OpenText("C:\Wrox\temp.txt")

’ Opens a filestream for reading

Dim fs As System.IO.FileStream = System.IO.File.OpenRead("C:\Wrox\temp.txt")

’ Opens a filestream for writing

Dim fs As System.IO.FileStream = System.IO.File.OpenWrite("C:\Wrox\temp.txt")

’ Reads the entire file and returns a string of data

Dim data As String = System.IO.File.ReadAllText("C:\Wrox\temp.txt")

’ Writes the string of data to the file

System.IO.File.WriteAllText("C:\Wrox\temp.txt", data)

C#

// Opens a file and returns a FileStream

System.IO.FileStream fs =

System.IO.File.Open(@"C:\Wrox\temp.txt", System.IO.FileMode.Open);

// Opens a file and returns a StreamReader for reading the data

System.IO.StreamReader sr = System.IO.File.OpenText(@"C:\Wrox\temp.txt");

// Opens a filestream for reading

Continued

System.IO.FileStream fs = System.IO.File.OpenRead(@"C:\Wrox\temp.txt");

// Opens a filestream for writing

System.IO.FileStream fs = System.IO.File.OpenWrite(@"C:\Wrox\temp.txt");

// Reads the entire file and returns a string of data

string data = System.IO.File.ReadAllText(@"C:\Wrox\temp.txt");

// Writes the string of data to the file

System.IO.File.WriteAllText(@"C:\Wrox\temp.txt", data);

Compressing Streams

Introduced in the NET 2.0 Framework, the System.IO.Compression namespace includes classes for

compressing and decompressing data using either theGZipStreamor theDeflateStreamclasses

GZip Compression

Because both new classes are derived from theStreamclass, using them should be relatively similar

to using the otherStreamoperations you have examined so far in this chapter Listing 25-20 shows an

example of compressing your text file using theGZipStreamclass

Listing 25-20: Compressing a file using GZipStream

VB

’ Read the file we are going to compress into a FileStream

Dim filename As String = Server.MapPath("TextFile.txt")

Dim infile As System.IO.FileStream = System.IO.File.OpenRead(filename)

Dim buffer(infile.Length) As Byte

infile.Read(buffer, 0, buffer.Length)

infile.Close()

’ Create the output file

Dim outfile As System.IO.FileStream = _

System.IO.File.Create(System.IO.Path.ChangeExtension(filename, "zip"))

’ Compress the input stream and write it to the output FileStream

Dim gzipStream As New System.IO.Compression.GZipStream(

outfile, System.IO.Compression.CompressionMode.Compress)

gzipStream.Write(buffer, 0, buffer.Length)

gzipStream.Close()

C#

// Read the file we are going to compress into a FileStream

string filename = Server.MapPath("TextFile.txt");

System.IO.FileStream infile = System.IO.File.OpenRead(filename);

byte[] buffer = new byte[infile.Length];

infile.Read(buffer, 0, buffer.Length);

infile.Close();

// Create the output file

System.IO.FileStream outfile =

System.IO.File.Create(System.IO.Path.ChangeExtension(filename, "zip"));

// Compress the input stream and write it to the output FileStream

System.IO.Compression.GZipStream gzipStream =

new System.IO.Compression.GZipStream(outfile,

System.IO.Compression.CompressionMode.Compress);

gzipStream.Write(buffer, 0, buffer.Length);

gzipStream.Close();

Notice that theGZipStreamconstructor requires two parameters, the stream to write the compressed data

to, and theCompressionModeenumeration, which tells the class if you want to compress or decompress data After the code runs, be sure there is a file calledtext.zipin your Web site directory

Deflate Compression

TheCompressionnamespace also allows to you decompress a file using theGZiporDeflatemethods

Listing 25-21 shows an example of decompressing a file using theDeflatemethod

Listing 25-21: Decompressing a file using DeflateStream

VB

Dim filename As String = Server.MapPath("TextFile.zip")

Dim infile As System.IO.FileStream = System.IO.File.OpenRead(filename)

Dim deflateStream As New System.IO.Compression.DeflateStream( _

infile, System.IO.Compression.CompressionMode.Decompress)

Dim buffer(infile.Length + 100) As Byte

Dim offset As Integer = 0

Dim totalCount As Integer = 0

While True

Dim bytesRead As Integer = deflateStream.Read(buffer, offset, 100)

If bytesRead = 0 Then

Exit While End If

offset += bytesRead

totalCount += bytesRead

End While

Dim outfile As System.IO.FileStream = _

System.IO.File.Create(System.IO.Path.ChangeExtension(filename, "txt"))

outfile.Write(buffer, 0, buffer.Length)

outfile.Close()

C#

string filename = Server.MapPath("TextFile.zip");

System.IO.FileStream infile = System.IO.File.OpenRead(filename);

Continued

System.IO.Compression.DeflateStream deflateStream =

new System.IO.Compression.DeflateStream(infile,

System.IO.Compression.CompressionMode.Decompress);

byte[] buffer = new byte[infile.Length + 100];

int offset = 0;

int totalCount = 0;

while (true)

{

int bytesRead = deflateStream.Read(buffer, offset, 100);

if (bytesRead == 0)

{ break; }

offset += bytesRead;

totalCount += bytesRead;

}

System.IO.FileStream outfile =

System.IO.File.Create(System.IO.Path.ChangeExtension(filename, "txt"));

outfile.Write(buffer, 0, buffer.Length);

outfile.Close();

Compressing HTTP Output

Besides compressing files, one other very good use of the compression features of the NET Framework

in an ASP.NET application is to implement your ownHttpModuleclass that compresses the HTTP output

of your application This is easier than it might sound, and it will save you precious bandwidth by

com-pressing the data that is sent from your Web server to the browsers that support the HTTP 1.1 Protocol

standard (which most do) The browser can then decompress the data before rendering it

IIS 6 does offer built-in HTTP compression capabilities, and there are several third-party HTTP

com-pression modules available, such as the Blowery Http Comcom-pression Module (www.blowery.org).

Start by creating a Windows Class library project Add a new class to your project called

Compression-Module This class is your compressionHttpModule Listing 25-22 shows the code for creating the class

Listing 25-22: Compressing HTTP output with an HttpModule

VB

Imports System

Imports System.Collections.Generic

Imports System.Text

Imports System.Web

Imports System.IO

Imports System.IO.Compression

Namespace Wrox.Demo.Compression

Public Class CompressionModule

Implements IHttpModule

Continued

Public Sub Dispose() Implements System.Web.IHttpModule.Dispose

Throw New Exception("The method or operation is not implemented.")

End Sub

Public Sub Init(ByVal context As System.Web.HttpApplication) _

Implements System.Web.IHttpModule.Init

AddHandler context.BeginRequest, AddressOf context_BeginRequest

End Sub

Public Sub context_BeginRequest(ByVal sender As Object, ByVal e As EventArgs)

Dim app As HttpApplication = CType(sender, HttpApplication)

’Get the Accept-Encoding HTTP header from the request

’The requesting browser sends this header which we will use

’ to determine if it supports compression, and if so, what type

’ of compression algorithm it supports

Dim encodings As String = app.Request.Headers.Get("Accept-Encoding")

If (encodings = Nothing) Then

Return

End If

Dim s As Stream = app.Response.Filter

encodings = encodings.ToLower()

If (encodings.Contains("gzip")) Then

app.Response.Filter = New GZipStream(s, CompressionMode.Compress)

app.Response.AppendHeader("Content-Encoding", "gzip")

app.Context.Trace.Warn("GZIP Compression on")

Else

app.Response.Filter = _

New DeflateStream(s, CompressionMode.Compress) app.Response.AppendHeader("Content-Encoding", "deflate")

app.Context.Trace.Warn("Deflate Compression on")

End If

End Sub

End Class

End Namespace

C#

using System;

using System.Collections.Generic;

using System.Text;

using System.Web;

using System.IO;

using System.IO.Compression;

namespace Wrox.Demo.Compression

{

public class CompressionModule : IHttpModule

Continued