To make the client easier to use, BroadcastResponse converts the arguments into a typed event object and raises an event. Remember, because you are writing a client, you don't know what the user may want to do with the data—you just know what the data means. This is an ideal situation for a delegate (also known as an event).
Listing 3 shows BroadcastResponse. Because BroadcastResponse reads the FTP code from the server and raises an event, you need to define these event types (as delegates) and the event argument classes that will contain the desired data. Listing 4 contains the complete listing for the FTP Client with the events you have elected to implement, useful constants, delegates, and event argument classes. (The complete listing is provided for convenience).
Listing 3: The Implementation of BroadcastResponse
Private Sub BroadcastResponse(ByVal reply As String)
' Permit handling as raw data
RaiseEvent OnRawDataReceivedEvent(Me, _
New RawDataReceivedEventArgs(reply))
Dim code As Integer = Int32.Parse(reply.Substring(0, 3))
Dim data As String = reply.Substring(4)
' Permit special handling as code and data
RaiseEvent OnTcpEvent(Me, New TcpEventArgs(code, data))
' Specific handling based on code
Select Case code
Case SENDING_DATA_PORT_20
Case COMMAND_NOT_IMPLEMENTED
Case CONNECTED
RaiseEvent OnConnectionEvent(Me, _
New ConnectionEventArgs(True, code, data))
Case AUTHENTICATED
RaiseEvent OnAuthentication(Me, _
New AuthenticationEventArgs(True, code, data))
Case NEED_PASSWORD
Case AUTHENTICATION_FAILED
RaiseEvent OnAuthentication(Me, _
New AuthenticationEventArgs(False, code, data))
End Select
End Sub
Listing 4: The entire listing for the FTP client includinged delegates, event fields, and event agrument classes.
Imports System
Imports System.Net
Imports System.IO
Imports System.Text
Imports System.Text.ASCIIEncoding
Imports System.Net.Sockets
Imports System.Configuration
Imports System.Resources
Public Class FtpClient
Public Shared ReadOnly SENDING_DATA_PORT_20 As Integer = 150
Public Shared ReadOnly COMMAND_NOT_IMPLEMENTED As Integer = 202
Public Shared ReadOnly CONNECTED As Integer = 220
Public Shared ReadOnly AUTHENTICATED As Integer = 230
Public Shared ReadOnly NEED_PASSWORD As Integer = 331
Public Shared ReadOnly AUTHENTICATION_FAILED As Integer = 530
Private FRemoteHost As String = "127.0.0.1"
Private FRemotePath As String = "."
Private FRemoteUser As String = "anonymous"
Private FRemotePassword As String = "anonymous@nowhere.com"
Private FRemotePort As Integer = 21
Private clientSocket As Socket = Nothing
Private response As String
Public Event OnAuthentication As AuthenticationEvent
Public Event OnConnectionEvent As ConnectionEvent
Public Event OnRawDataReceivedEvent As RawDataReceivedEvent
Public Event OnTcpEvent As TcpEvent
Public Sub New()
End Sub
Public Sub New(ByVal remoteHost As String, _
ByVal remotePath As String, _
ByVal remoteUser As String, ByVal remotePassword As String, _
ByVal remotePort As Integer)
FRemoteHost = remoteHost
FRemotePath = remotePath
FRemoteUser = remoteUser
FRemotePassword = remotePassword
FRemotePort = remotePort
End Sub
Public Sub Connect()
clientSocket = New Socket(AddressFamily.InterNetwork, _
SocketType.Stream, ProtocolType.Tcp)
Dim endpoint As IPEndPoint = _
New IPEndPoint(Dns.Resolve(FRemoteHost).AddressList(0), _
FRemotePort)
Try
clientSocket.Connect(endpoint)
Catch ex As Exception
Throw New IOException("Connect failed", ex)
End Try
ReadResponse()
End Sub
Public Sub Disconnect()
If (clientSocket Is Nothing = False) Then
clientSocket.Disconnect(True)
RaiseEvent OnConnectionEvent(Me, _
New ConnectionEventArgs(False))
End If
End Sub
Private Sub ReadResponse()
Dim reply As String = ReadLine()
'Figure out the response and raise that event
BroadcastResponse(reply)
End Sub
Private Function ReadLine() As String
Return ReadLine(False)
End Function
Private Function ReadLine(ByVal clearResponse As Boolean) _
As String
Const EndLine As Char = "\n"
Const BUFFER_SIZE As Integer = 512
Dim data As String = ""
Dim buffer(BUFFER_SIZE) As Byte
Dim bytesRead As Integer = 0
If (clearResponse = True) Then response = String.Empty
While (True)
Array.Clear(buffer, 0, BUFFER_SIZE)
bytesRead = clientSocket.Receive(buffer, buffer.Length, 0)
data += ASCII.GetString(buffer, 0, bytesRead)
If (bytesRead < buffer.Length) Then Exit While
End While
Dim parts() As String = data.Split(EndLine)
If (parts.Length > 2) Then
response = parts(parts.Length - 2)
Else
response = parts(0)
End If
If (response.Substring(3, 1).Equals(" ") = False) Then
Return ReadLine(False)
End If
Return response
End Function
Private Sub BroadcastResponse(ByVal reply As String)
' Permit handling as raw data
RaiseEvent OnRawDataReceivedEvent(Me, _
New RawDataReceivedEventArgs(reply))
Dim code As Integer = Int32.Parse(reply.Substring(0, 3))
Dim data As String = reply.Substring(4)
' Permit special handling as code and data
RaiseEvent OnTcpEvent(Me, New TcpEventArgs(code, data))
' Specific handling based on code
Select Case code
Case SENDING_DATA_PORT_20
Case COMMAND_NOT_IMPLEMENTED
Case CONNECTED
RaiseEvent OnConnectionEvent(Me, _
New ConnectionEventArgs(True, code, data))
Case AUTHENTICATED
RaiseEvent OnAuthentication(Me, New _
AuthenticationEventArgs(True, code, data))
Case NEED_PASSWORD
Case AUTHENTICATION_FAILED
RaiseEvent OnAuthentication(Me, _
New AuthenticationEventArgs(False, code, data))
End Select
End Sub
Public Sub Login()
SendCommand("USER " + FRemoteUser)
SendCommand("PASS " + FRemotePassword)
End Sub
Public Sub Login(ByVal user As String, ByVal password As String)
FRemotePassword = password
FRemoteUser = user
Login()
End Sub
Private Sub SendCommand(ByVal command As String)
command += Environment.NewLine
Dim commandBytes() As Byte = ASCII.GetBytes(command)
clientSocket.Send(commandBytes, commandBytes.Length, 0)
ReadResponse()
End Sub
End Class
Public Class TcpEventArgs
Private FCode As Integer
Private FData As String
Public Sub New(ByVal code As Integer, ByVal data As String)
FCode = code
FData = data
End Sub
Public ReadOnly Property Code() As Integer
Get
Return FCode
End Get
End Property
Public ReadOnly Property Data() As String
Get
Return FData
End Get
End Property
End Class
Public Class ConnectionEventArgs
Inherits TcpEventArgs
Private FConnected As Boolean = False
Public Sub New(ByVal connected As Boolean)
MyBase.New(-1, "")
FConnected = connected
End Sub
Public Sub New(ByVal connected As Boolean, _
ByVal code As Integer, ByVal data As String)
MyBase.New(code, data)
FConnected = connected
End Sub
Public ReadOnly Property Connected() As Boolean
Get
Return FConnected
End Get
End Property
End Class
Public Class AuthenticationEventArgs
Inherits TcpEventArgs
Private FAuthenticated As Boolean = False
Public Sub New(ByVal authenticated As Boolean)
MyBase.New(-1, "")
FAuthenticated = authenticated
End Sub
Public Sub New(ByVal authenticated As Boolean, _
ByVal code As Integer, ByVal data As String)
MyBase.New(code, data)
FAuthenticated = authenticated
End Sub
Public ReadOnly Property Authenticated() As Boolean
Get
Return FAuthenticated
End Get
End Property
End Class
Public Class RawDataReceivedEventArgs
Inherits TcpEventArgs
Private FRawData As String
Public Sub New(ByVal rawData As String)
MyBase.New(-1, "")
FRawData = rawData
End Sub
Public Sub New(ByVal rawData As String, _
ByVal code As Integer, ByVal data As String)
MyBase.New(code, data)
FRawData = rawData
End Sub
Public ReadOnly Property RawData() As String
Get
Return FRawData
End Get
End Property
End Class
Public Delegate Sub AuthenticationEvent(ByVal sender As Object, _
ByVal e As AuthenticationEventArgs)
Public Delegate Sub ConnectionEvent(ByVal sender As Object, _
ByVal e As ConnectionEventArgs)
Public Delegate Sub RawDataReceivedEvent(ByVal sender As Object, _
ByVal e As RawDataReceivedEventArgs)
Public Delegate Sub TcpEvent(ByVal sender As Object, _
ByVal e As TcpEventArgs)
BroadcastResponse works the same for all responses: basically, I create an EventArgs-based class for the kind of arguments I think the user might want and a delegate that uses that type. The FtpClient exposes a public event and consumers can subscribe to the events they want. You can use the same technique to support the remaining FTP behaviors.
If you are unfamiliar with delegates and events then you may have to practice a little. A delegate is like a C or C++ function pointer. In .NET, a delegate is a special class that encapsulates a multicast delegate or a list of function pointers, and it is the mechanism that supports attaching event handlers to events. (This is an instance where the framework uses the Observer design pattern.)
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