Visual Basic 2008 : Using FTP in the Service (part 1)

11/10/2011 11:30:47 AM

Creating FTP Directories

I have created an upload and download directory beneath the FTP Home Directory, which in my case is c:\inetpub\ftproot. I have assigned write privileges to the upload directory and read privileges to the download directory, and set the anonymous logons to true. Microsoft FTP Publishing Service does not support authentication over secured sockets, so we will use anonymous logons.

Adding an FTP Class

Our FTP class is very simple. It allows for uploading and downloading files, but it lacks more in-depth features, such as listing directories locally or remotely. For our purposes, though, it will be sufficient. In this section, we’ll simulate downloading and processing files from one FTP folder that can exist anywhere in the world. This could mean moving the file from its current location to another intranet or extranet location where a predefined process such as a SQL Task, Web Service, or other mechanism is in place to process the file further. This procedure works well for moving data from one data store to another, where a process specific to that data store has been created to export data to a flat file. In many cases the systems that create these files have no access to other intranet or extranet sites and thus have no ability themselves to directly or indirectly move or process this data on behalf of the remote data store. Imagine that you have a small Web store application that uses SQL Server as its back-end data store. Your shipping and receiving, purchase order information, and customer database is stored in your back-end mainframe or other secondary centralized SQL Server. If the two databases can’t communicate—whether because of security issues or network limitations—you can use an intermediate process, such as a service that sits on both subnets and has the proper authority to move the data between network segments or data stores.

We’ll use the FTP class to read data files from our download directory and store it in our locally defined folder. In this section, we will do no other processing because the service will only simulate moving data between network subnets, allowing a predefined process running on the upload directory’s subnet, or with access to that subnet, to capture that file and process it. Let’s review the FTP class, shown in Listing 1.

Listing 1. FTP class implementation.

Imports System.Net
Imports System.IO
Imports System.Text
Imports System.Threading

Public Class FTP
    Public m_Error As String = Nothing
    Private m_Uri As String
    Private m_User As String
    Private m_Pwd As String
    Private m_Port As Integer
    Private m_LocalFolder As String
    Private m_File As String
    Private m_Files() As String
    Public m_Incoming As Thread
    Private m_ThreadAction As Thread_Action_State

    Public Sub New(ByRef threadaction As Thread_Action_State)
        m_ThreadAction = threadaction
    End Sub

    Public Sub Start()
        m_Incoming = New Thread(AddressOf DownloadFiles)
        m_Incoming.Priority = ThreadPriority.Normal
        m_Incoming.IsBackground = True
        m_Incoming.Start()
    End Sub

    Public Function GetError() As String
        Try
            Return m_Error
        Catch ex As Exception
            Return ex.ToString
        End Try
    End Function

    Private Sub DownloadFiles()
        While Not m_ThreadAction.StopThread
            If Not m_ThreadAction.Pause Then
                Try
                    Dim bDownload As Boolean
                    bDownload = GetFile(Me.URI, Me.File, Me.User, Me.Pwd,
                         Me.Port, Me.LocalFolder)

                    If Not (bDownload) Then
                        Throw New Exception("Failed to Download File: " +
                               Me.File)
                    End If
                Catch tab As ThreadAbortException
                    WriteLogEvent(My.Resources.ThreadAbortMessage + "_" +
                        tab.ToString + "_" + Now.ToString, THREAD_ABORT_ERROR,
                         EventLogEntryType.Error, My.Resources.Source)
                Catch ex As Exception
                    WriteLogEvent(My.Resources.ThreadErrorMessage + "_" +
                     ex.ToString + "_" + Now.ToString, THREAD_ERROR,
                     EventLogEntryType.Error, My.Resources.Source)
                End Try
            End If

            If Not m_ThreadAction.StopThread Then
                Thread.Sleep(THREAD_WAIT)
            End If
        End While

    End Sub

    Private Shared Sub WriteLogEvent(ByVal pszMessage As String,
                 ByVal dwID As Long, ByVal iType As EventLogEntryType,
                 ByVal pszSource As String)
        Try
            Dim eLog As EventLog = New EventLog("Application")
            eLog.Source = pszSource

            Dim eInstance As EventInstance = New EventInstance(dwID, 0, iType)
            Dim strArray() As String

            ReDim strArray(1)
            strArray(0) = pszMessage
            eLog.WriteEvent(eInstance, strArray)

            eLog.Dispose()
        Catch ex As Exception
            'Do not Catch here as it doesn't do any good for now
        End Try
    End Sub

    Public Property URI() As String
        Get
            Return m_Uri
        End Get
        Set(ByVal value As String)
            m_Uri = value
        End Set
    End Property

    Public Property LocalFolder() As String
        Get
            Return m_LocalFolder
        End Get
        Set(ByVal value As String)
            m_LocalFolder = value
        End Set
    End Property

    Public Property User() As String
        Get
            Return m_User
        End Get
        Set(ByVal value As String)
            m_User = value
        End Set
    End Property

    Public Property Pwd() As String
        Get
            Return m_Pwd
        End Get
        Set(ByVal value As String)
            m_Pwd = value
        End Set
    End Property

    Public Property Port() As Integer
        Get
            Return m_Port
        End Get
        Set(ByVal value As Integer)
            m_Port = value
        End Set
    End Property

    Public Property File() As String
        Get
            Return m_File
        End Get
        Set(ByVal value As String)
            m_File = value
        End Set
    End Property

    Public Property Files() As String()
        Get
            Return m_Files
        End Get
        Set(ByVal value As String())
            Array.Copy(value, m_Files, value.Length)
        End Set
    End Property

    Public Function GetFile( _
                        ByVal pszUri As String, _
                        ByVal pszFile As String, _
                        ByVal pszUser As String, _
                        ByVal pszPWD As String, _
                        ByVal dwPort As Integer, _
                        ByVal pszLocalDir As String) _
                        As Boolean
        Try
            ' Set up the request
            Dim ftpURI As New Uri(pszUri + "/" + pszFile)

            Dim ftpRequest As FtpWebRequest = _
                                CType(FtpWebRequest.Create(ftpURI),
                                     FtpWebRequest)
            'Setup the Credentials
            If pszUser.ToUpper <> "ANONYMOUS" Then
                ftpRequest.Credentials = New NetworkCredential(pszUser, pszPWD)
            End If

            'Download a file.
            ftpRequest.Method = WebRequestMethods.Ftp.DownloadFile

            ' get the response object
            Dim ftpResponse As FtpWebResponse = _
                            CType(ftpRequest.GetResponse, FtpWebResponse)

            Dim tmpStream As Stream = Nothing
            Dim tmpReader As StreamReader = Nothing
            Dim tmpWriter As StreamWriter = Nothing

            'Read the Stream from the Response and Save the File Locally
            Try
                tmpStream = ftpResponse.GetResponseStream
                tmpReader = New StreamReader(tmpStream, Encoding.UTF8)
                tmpWriter = New StreamWriter(pszLocalDir + "\" + pszFile,
                                                False)
                tmpWriter.Write(tmpReader.ReadToEnd)
            Finally
                tmpStream.Close()
                tmpReader.Close()
                tmpWriter.Close()
            End Try

            Return True
        Catch ex As Exception
            m_Error = ex.ToString
            Return False
        End Try

    End Function

    Public Function GetFiles( _
                        ByVal pszUri As String, _
                        ByVal pszFiles() As String, _
                        ByVal pszUser As String, _
                        ByVal pszPWD As String, _
                        ByVal dwPort As Integer, _
                        ByVal pszLocalDir As String) _
                        As Boolean()
        Try
            'Setup our Return Object
            Dim bRet(pszFiles.Length - 1) As Boolean

            Dim iLoop As Short

            For iLoop = 0 To pszFiles.Length - 1
                Try
                    bRet(iLoop) = GetFile( _
                                            pszUri, _
                                            pszFiles(iLoop), _
                                            pszUser, _
                                            pszPWD, _
                                            dwPort, _
                                            pszLocalDir _
                                        )
                Catch ex As Exception
                    bRet(iLoop) = False
                End Try
            Next

            Return bRet
        Catch ex As Exception
            m_Error = ex.ToString
            Return Nothing
        End Try

    End Function

    Public Function SendFile( _
                        ByVal pszServer As String, _
                        ByVal pszRemoteDir As String, _
                        ByVal pszFile As String, _
                        ByVal pszUser As String, _
                        ByVal pszPWD As String, _
                        ByVal dwPort As Integer, _
                        ByVal pszLocalDir As String) _
                        As Boolean
        Try
            ' Set up the request
            Dim ftpURI As New Uri("FTP://" + pszServer + "/" + pszRemoteDir +
                                    "/" + pszFile)

            Dim ftpRequest As FtpWebRequest = _
                                CType(FtpWebRequest.Create(ftpURI),
                                        FtpWebRequest)

            'Setup the Credentials
            ftpRequest.Credentials = New NetworkCredential(pszUser, pszPWD)

            'Upload a file.
            'setup options
            ftpRequest.Method = WebRequestMethods.Ftp.UploadFile
            ftpRequest.UseBinary = False
            '            ftpRequest.UsePassive = True

            'Now we have to read the local file into a stream
            Dim pFile As New FileInfo(pszLocalDir + pszFile)
            Dim bData(pFile.Length) As Byte
            Dim fStream As FileStream = pFile.OpenRead

            fStream.Read(bData, 0, pFile.Length)
            fStream.Close()

            ftpRequest.ContentLength = bData.Length
            Dim tmpStream As Stream = Nothing

            'Read the Stream from the Response and Save the File Locally
            Try
                tmpStream = ftpRequest.GetRequestStream
                tmpStream.Write(bData, 0, bData.Length)
            Finally
                tmpStream.Close()
            End Try

            'Whats the Response
            Dim ftpResponse As FtpWebResponse = _
                                        CType(ftpRequest.GetResponse,
                                             FtpWebResponse)
            Return True
        Catch ex As Exception
            m_Error = ex.ToString
            Return False
        End Try
    End Function

    Public Function SendFiles( _
                        ByVal pszServer As String, _
                        ByVal pszRemoteDir As String, _
                        ByVal pszFiles() As String, _
                        ByVal pszUser As String, _
                        ByVal pszPWD As String, _
                        ByVal dwPort As Integer, _
                        ByVal pszLocalDir As String) _
                        As Boolean()
        Try
            Dim iLoop As Short
            Dim bRet(pszFiles.Length - 1) As Boolean

            For iLoop = 0 To pszFiles.Length - 1
                Try

                    bRet(iLoop) = SendFile( _
                                            pszServer, _
                                            pszRemoteDir, _
                                            pszFiles(iLoop), _
                                            pszUser, _
                                            pszPWD, _
                                            dwPort, _
                                            pszLocalDir _
                                            )
                Catch ex As Exception
                    bRet(iLoop) = False
                End Try
            Next

            Return bRet
        Catch ex As Exception
            m_Error = ex.ToString
            Return Nothing
        End Try
    End Function

    Public Sub Dispose()
        Try
            Return
        Catch ex As Exception
            m_Error = ex.ToString
            Return
        End Try
    End Sub

    Public ReadOnly Property Incoming() As Thread
      Get
        Return m_Incoming
      End Get
    End Property
End Class

The <DownloadFiles> Method

<DownloadFiles> is our thread method, started by the <Start> method. It will use the <GetFile> method to download the files that have been specified in our modService.vb file. If the file doesn’t download successfully, we will throw a new exception of System.Exception type. Our Try/Catch will catch the exception and then write an event into the Application log. If the file downloads successfully, it will be saved locally in the local folder, which is specified in the LocalFolder property.

FTP Class Properties

The FTP class has several properties that are required to make our FTP class work. These properties are outlined in Listing 2.

Listing 2. FTP class properties.

Public Property URI() As String
    Get
        Return m_Uri
    End Get
    Set(ByVal value As String)
        m_Uri = value
    End Set
End Property

Public Property LocalFolder() As String
    Get
        Return m_LocalFolder
    End Get
    Set(ByVal value As String)
        m_LocalFolder = value
    End Set
End Property
Public Property User() As String
    Get
        Return m_User
    End Get
    Set(ByVal value As String)
        m_User = value
    End Set
End Property

Public Property Pwd() As String
    Get
        Return m_Pwd
    End Get
    Set(ByVal value As String)
        m_Pwd = value
    End Set
End Property

Public Property Port() As Integer
    Get
        Return m_Port
    End Get
    Set(ByVal value As Integer)
        m_Port = value
    End Set
End Property

Public Property File() As String
    Get
        Return m_File
    End Get
    Set(ByVal value As String)
        m_File = value
    End Set
End Property

The Uri property represents the physical path and virtual location of the server and FTP directory where the file that we want to download resides.
The User property represents the user that we want to log in as. Since we are using anonymous logins, I’ll use anonymous as my user entry.
The LocalFolder property represents where we will store the files after downloading them. This can represent a physical local or remote location.
The Pwd property represents the password used to log on. Since I am using anonymous, any e-mail address will be valid here.
The Port property represents the port being used by the FTP service. By default this will be 21 on an FTP server, so I’ll use 21. The File property represents the name of the file that we want to look for. This is not a very flexible FTP example. We could extend it to use a wild card or use the Files property to allow you to pass in an array of file names to download.

Adding New FTP Constants

Listing 3. FTP constant declaration.

Public Const FTP_ERROR As Integer = 6000
Public Const FTP_INFO As Integer = 6001

Related -----------------

- Visual Basic 2008 : Using FTP in the Service (part 2)

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