INT422 Internet III Web Programming on Windows

1
INT422 Internet III Web Programming on
Windows

• File I/O to and from the web server

2
System.IO Namespace

• All File I/O operations in .NET are done using
  classes found in the System.IO namespace
• using System.IO
• There are 5 main File I/O classes
• Directory
• File
• Path
• DirectoryInfo
• FileInfo

3
Static Classes vs. Instance Objects

• Recall that Static classes, methods, properties,
  etc. belong to the CLASS and not to a particular
  object.
• In other words, you dont need to make a New
  object based on the class in order to use its
  methods
• Directory, File, Path Static
• File.Copy(c\temp\myfile.txt, c\docs)
• DirectoryInfo, FileInfo Instance
• FileInfo fi New FileInfo(c\temp\myfile.txt)
• fi.CopyTo(c\docs) //Note No Source fi is
  the source

4
System.IO.Directory - Highlights

• Delete(path, recursive)
• Move(source, dest) Used for Rename too
• Exists(path) -gt returns Boolean
• GetParent(path) -gt returns DirectoryInfo
• GetDirectoryRoot(path) -gt returns String
• CreateDirectory(path) -gt returns DirectoryInfo
• GetFiles(path) -gt returns String()
• GetDirectories(path) -gt returns String()
• GetFileSystemEntries(path) -gt returns String()

5
System.IO.File - Highlights

• Used to work with Closed files. If you want to
  open a file and work with it, you need a FileInfo
  object instead
• Delete(path)
• Move(source, dest) Used for Rename too
• Exists(path) -gt returns Boolean
• Copy(source, dest, overwrite)

6
System.IO.Path - Highlights

• Static methods and properties for working with
  file system Paths
• string tempPath Path.GetTempPath()
• // Side effect creates the temp file
• string tempFile Path.GetTempFileName()
• string p "c\temp\mydocs\readme.txt
• string info
• info Path.GetDirectoryName(p) //
  c\temp\mydocs
• info Path.GetFileName(p) // readme.txt
• info Path.GetExtension(p) // .txt
• info Path.GetFileNameWithoutExtension(p) //
  readme
• info Path.Combine(Path.GetDirectoryName(p),
  "data.txt")
• // c\temp\mydocs\data.txt

7
System.IO.DirectoryInfo - Highlights

• Represents an actual Directory, and then allows
  you to enumerate (i.e., loop across) its contents
• DirectoryInfo di new DirectoryInfo(".\temp")
• string n di.Name // temp
• string fn di.FullName // C\temp
• DirectoryInfo subDir di.CreateSubdirectory("a")
  
• fn subDir.FullName / C\Temp\a
• foreach(FileInfo txtFile In di.GetFiles(".txt"))
  
• // Do something with Text File
• subDir.Delete()

8
System.IO.FileInfo Highlights

• Represents an actual File
• FileInfo fi New FileInfo("c\temp\a.txt")
• DirectoryInfo di New DirectoryInfo("c\temp")
• string n fi.Name // a.txt
• string fn fi.FullName // C\temp\a.txt
• DirectoryInfo subDir di.CreateSubdirectory("a")
  
• long l fi.Length // Size in bytes
• string pdir fi.DirectoryName // temp
• fi.CopyTo("c\documents")

9
Reading and Writing Files

• Streams
• StreamReader
• StreamWriter

10
The Stream Class

• .NET I/O uses Streams to Read and Write data
• A Stream represents a sequence of bytes going or
  coming from a storage medium (e.g., a file)
• Streams are low-level objects that work at the
  Byte level. Most Streams allow the following
• Read Read a specified number of bytes
• Write Write a specified number of bytes

11
The Stream Class continued

• Stream is an Abstract Class, which means you
  cant create a new Stream object
• Instead, you use classes that Inherit from
  Stream
• FileStream - This is what we need for File I/O
• MemoryStream - Use RAM like a File (very fast)
• NetworkStream - Used for network communication
• Data in a Stream is Buffered transparently, and
  only written to the storage medium when Flushed
  or when the Stream is closed.

12
StreamReader and StreamWriter

• Normally you dont work with a Stream directly
• Most of the time we need to Read or Write lines
  of text, Integers, Doubles, etc.
• Streams only understand Bytes (data type)
• To make things easier we use a StreamReader or
  StreamWriter, which sits on top of a Stream and
  converts our data into / from Bytes.

13
The Complete IO Picture Reading
File
.NET App
StreamBuffer
FileStream
StreamReader

• StreamReader sr1 File.OpenText(a.txt)
• OR
• FileInfo fi new FileInfo(a.txt)
• StreamReader sr2 fi.OpenText()
• OR
• StreamReader sr3 New StreamReader(a.txt)

14
Reading Text From a StreamReader

• If the file is small (lt50 KB), consider reading
  the whole thing at once. Otherwise, go into a
  loop
• string entireFile sr1.ReadToEnd()
• sr1.Close()
• OR
• string oneLine
• while(sr1.Peek ! -1)
• oneLine sr1.ReadLine() // sr1.Read gives 1
  letter
• // Process onLine here
• sr1.Close()

15
The Complete IO Picture - Writing
File
.NET App
StreamBuffer
FileStream
StreamWriter

• StreamWriter sw1 File.CreateText(a.txt)
• OR
• StreamWriter sw2 New StreamWriter(a.txt)
• OR
• string tempFile Path.GetTempFileName()
• StreamWriter sw3 New StreamWriter(File.Open(temp
  File, FileMode.Open))

16
Writing Text with a StreamWriter

• If you have a string which includes NewLine
  characters, you just write the whole thing at
  once and the NewLines will be preserved. If you
  want to add NewLines, you have do it manually.
• string someText Im going to disk
• sw1.WriteLine(someText) // Adds NewLine to end
• sw1.Close()
• OR
• sw1.Write(txtUserInput.Text) // No NewLine at
  end
• sw1.Close()

17
Writing Textcont

• Writing a file for the Web? For Unix? Change the
  NewLine character used by StreamWriter
• string line1 This is line 1
• string line2 This is line 2
• sw.NewLine ltbr /gt// Assume sw has been
  declared
• sw.WriteLine(line1) // Adds ltbr /gt to end
• sw.WriteLine(line2) // Adds ltbr /gt to end
• sw.Close()
• OR
• sw.NewLine ControlChars.LF // For Unix EOL
• sw.WriteLine(line1) // Adds LF to end (not CRLF)
• sw.Close()

18
Another StreamReader StringReader

• While were discussing StreamReaders, you should
  also be aware of StringReader.
• Imagine you want to read a very long String Line
  by Line (e.g., a Textbox control)
• string oneLine
• StringReader strR New StringReader(txtInput.Text)
  
• while( strR.Peek ! -1)
• oneLine strR.ReadLine() // Removes NewLine
• // Process oneLine here

19
Working with Files on a Server

• File System Paths
• Virtual Paths
• Dealing with Errors
• Permissions

20
Understanding Server Paths

• When you work on a Web Server, you deal with
  three types of paths
• Virtual Path
• http//warp.senecac.on.ca/int422_xxx/MyDirectory/
• Actual File System Path
• D\students\int422_xxx\webcontent\MyDirectory
• Absolute path from your web forms
• /MyDirectory
• If you want to work with first two types on the
  server, you have to convert / map between them

21
Mapping Virtual to Actual Paths

• Its easy to map between these two, using the
  Server.MapPath(path) method
• string appPath Server.MapPath( _
• http//warp.senecac.on.ca/jsmith/MyWebApp/)
• If you pass a null path (e.g., Nothing), MapPath
  returns the fully rooted (i.e., absolute) file
  system path to the current directory
• string appPath Server.MapPath(Nothing)

22
Working with Server Files

• Imagine a Web App called
• TextApp with this File Structure
• How would you
• Get the Path to Sample1.txt?
• Read the contents of the file?
• Display it in a Label Web Control?
• Hint Assume that your ASP.NET web form is in the
  root of the TextApp directory, and that Docs is a
  sub-directory under TextApp

23
One Possible Answer

• Get the path to Sample1.txt
• string p Path.Combine(Server.MapPath(Nothing),
  _
• \docs\samples\sample1.txt)
• Open Sample1.txt for Reading
• StreamReader sr New StreamReader(p)
• Read the entire File into a Label
• lblSampleText.Text sr.ReadToEnd()
• Close the Sample1.txt file
• sr.Close()

24
Things Can (and Do) Go Wrong

• Any time you work with Static resources (e.g.,
  files, directories) errors can occur
• Try to Open a file the OS is currently reading or
  writing, and youll get an error
• Try to Move a file that isnt there, youll get
  an error
• Try to use a Directory which you dont have
  rights to, youll get an error.

25
Recover From I/O Errors

• Any I/O action that can cause an error should be
  placed in a trycatch block
• This is called Structured Exception Handling.
  When an error occurs, an Exception Object will be
  Thrown, which you have to Catch and deal
  with, otherwise the user gets an error
• try
• File.Delete(txtFilename.Text)
• lblResult.Text "File Deleted
• catch // Any Generic Exception
• lblresult.Text "Could not Delete File

26
Catching Specific Exceptions

• There are lots of different Exceptions that get
  thrown, and Exception is just a generic Base
  Class for all of them. I/O specific Exceptions
• DirectoryNotFoundException
• FileLoadException PathTooLongException
• FileNotFoundException IOException
• Catch(FileNotFoundException fnfEx)
• lblResult.Text Couldnt Find the File
• Catch(DirectoryNotFoundException dnfEx)
• lblResult.Text No such Directory

27
ASP.NET File I/O and Security

• Question When your Web Apps I/O code runs,
  which users Security Context is it running in?
• IUSR_warp
• jsmith (or whatever user owns the application)
• ASPNET
• NETWORK SERVICE
• Account of User Logged-into the Web Application
• Something else???

28
Operating system dependent

• Answer It depends upon the operating system
• Warp runs Windows Server 2003, and IIS 6
• The account is NETWORK SERVICE
• Your Windows XP or Windows 2000 Server computer
  uses IIS 5.x
• The account is ASPNET
• This is the ASP.NET worker process account

29
File I/O and Securitymore

• Why is this important? Whatever NTFS rights this
  user has, so will your program. Therefore,
  depending on who runs your code it may not have
  sufficient rights.

30
File I/O and Securitymore

• Note
• If you are using Anonymous or Forms based
  Authentication (most of our INT422 work), it is
  NETWORK SERVICE (or ASPNET if you are on your
  WXP/W2K PC)
• If you are using Windows Based authentication, it
  will be the Account of the User Logged-into your
  Web App

31
Read OK Write?

• The worker process account has read access to
  files in the web server virtual directories
• It does NOT have write access by default
• On the following pages, you will learn what you
  need to know about doing file I/O on warp and on
  a home PC

32
warp configuration

• Every INT422 student already has a folder beside
  their website that can be used for file I/O
• This folder is called data
• Data is not accessible through URL because it is
  not in your website root (this minimizes security
  risks for hacking the website through web server)
• The absolute path to this folder
  is_at_c\inetpub\int422_xxxxx\data
• Use this data folder for file I/O

33
Home PC configuration

• Use My Computer or Windows Explorer to locate
  your web app in the file system
• It is probably under C\inetpub\wwwroot
• Create a data folder beside wwwroot_at_c\inetpu
  b\data
• Change its permissions to allow Modify for the
  ASPNET user.