VB.Net实现Ftp下载的方法

调用方式：

DownloadFile("abc.rar","d:/abc.rar","Flase") '  3个参数分别为远程ftp的文件名、保存到本地的完整路径、是否续传

功能函数：

   Public Sub DownloadFile(ByVal Str_RemoteFileName As String, _
                               ByVal Str_LocalFileName As String, _
                               ByVal Bool_Resume As Boolean)
        Dim Data_St As Stream
        Dim output As FileStream
        Dim LobSocket As Socket
        Dim offset, npos As Long
        If (Not Logined()) Then  
            Logined()
        End If
        SetBinaryMode(True)
        If (Str_LocalFileName.Equals("")) Then
            Str_LocalFileName = Str_RemoteFileName
        End If

        If (Not (File.Exists(Str_LocalFileName))) Then
            Data_St = File.Create(Str_LocalFileName)
            Data_St.Close()
        End If

        output = New FileStream(Str_LocalFileName, FileMode.Open)
        LobSocket = CreateDataSocket()
        offset = 0

        If (Bool_Resume) Then
            offset = output.Length

            If (offset > 0) Then
                SendCommand("REST " & offset)
                Str_Reply = ServerReply(True)
                Int_Reply = Int32.Parse(Str_Reply.Substring(0, 3))
                If (Int_Reply <> 350) Then
                    offset = 0
                End If
            End If

            If (offset > 0) Then
                npos = output.Seek(offset, SeekOrigin.Begin)
            End If
        End If

        SendCommand("RETR " & Str_RemoteFileName)
        Str_Reply = ServerReply(True)
        Int_Reply = Int32.Parse(Str_Reply.Substring(0, 3))

        If (Not (Int_Reply = 150 Or Int_Reply = 125)) Then
            MsgBox(Str_Reply.Substring(4))
        End If

        Do While (True)
            Array.Clear(Byte_Buffer, 0, Byte_Buffer.Length)
            Int_Bytes = LobSocket.Receive(Byte_Buffer, Byte_Buffer.Length, 0)
            output.Write(Byte_Buffer, 0, Int_Bytes)

            If (Int_Bytes <= 0) Then
                Exit Do
            End If
        Loop

        output.Close()
        If (LobSocket.Connected) Then
            LobSocket.Close()
        End If

        Str_Reply = ServerReply(True)
        Int_Reply = Int32.Parse(Str_Reply.Substring(0, 3))
        If (Not (Int_Reply = 226 Or Int_Reply = 250)) Then
            MsgBox(Str_Reply.Substring(4))
        End If

    End Sub

    Private Function CreateDataSocket() As Socket

        Dim index1, index2, len As Int32
        Dim partCount, i, port As Int32
        Dim ipData, buf, ipAddress As String
        Dim parts(6) As Int32
        Dim ch As Char
        Dim s As Socket
        Dim ep As IPEndPoint
        SendCommand("PASV")
        Str_Reply = ServerReply(True)
        Int_Reply = Int32.Parse(Str_Reply.Substring(0, 3))
        If (Int_Reply <> 227) Then
            MsgBox(Str_Reply.Substring(4))
        End If
        index1 = Str_Reply.IndexOf("(")
        index2 = Str_Reply.IndexOf(")")
        ipData = Str_Reply.Substring(index1 + 1, index2 - index1 - 1)
        len = ipData.Length
        partCount = 0
        buf = ""
        For i = 0 To ((len - 1) And partCount <= 6)
            ch = Char.Parse(ipData.Substring(i, 1))
            If (Char.IsDigit(ch)) Then
                buf += ch
            ElseIf (ch <> ",") Then
                MsgBox(Str_Reply)
            End If

            If ((ch = ",") Or (i + 1 = len)) Then
                Try
                    parts(partCount) = Int32.Parse(buf)
                    partCount += 1
                    buf = ""
                Catch ex As Exception
                    MsgBox(Str_Reply)
                End Try
            End If
        Next
        ipAddress = parts(0) & "." & parts(1) & "." & parts(2) & "." & parts(3)
        port = parts(4) * (2 ^ 8)
        port = port + parts(5)
        s = New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)
        ep = New IPEndPoint(Dns.GetHostEntry(ipAddress).AddressList(0), port)
        Try
            s.Connect(ep)
        Catch ex As Exception

            MsgBox("无法连接到远程ftp服务器")
        End Try
        Return s

    End Function

    Public Sub SetBinaryMode(ByVal bMode As Boolean)

        If (bMode) Then
            SendCommand("TYPE I")
        Else
            SendCommand("TYPE A")
        End If
        Str_Reply = ServerReply(True)
        Int_Reply = Int32.Parse(Str_Reply.Substring(0, 3))
        If (Int_Reply <> 200) Then
            MsgBox("111" & Str_Reply.Substring(4))
        End If
    End Sub