iOS Question FTP - slow download

jhagerup · Jul 11, 2015

I'm downloading a number of png's and have experienced this:

When I don't use "persistConnection" it goes fast, but requires as many connection pr. account as the number of files !

Using "persistConnection" there is a delay at about 30 seconds between each file.

(Nearly) same code in B4A is as fast as not "persistConnection" in B4i.

Comments on code: the files to download is found in a database (DBResult) and is saved in a KeyValueStore (kvs) for later use.

B4X:

Sub process_getallmain(result As DBResult)
    Dim but As String
    Dim background As String
    Dim link As String
    pendingDownloadCount = 0
    ftpService.Initialize("FTP",serverIP,21,"apps","apps")

    Dim no As NativeObject = ftpService
    no.GetField("server").SetField("persistConnection", True)

    For Each records() As Object In  result.Rows
        but=records(result.Columns.Get("button"))
        background = records(result.Columns.Get("background"))
        link = records(result.Columns.Get("link"))
        kvs.PutSimple(but & "_background", background)   
        kvs.PutSimple(but & "_link", link)
        ftpList.Add(background)
        pendingDownloadCount = pendingDownloadCount +1
    Next
    getButtonImage(ftpList.Get(pendingDownloadCount - 1))   
End Sub

Sub getButtonImage(background As String)
    ftpService.DownloadFile("/apps/1/" & background,False,File.DirLibrary, background)
End Sub

Sub FTP_DownloadCompleted (ServerPath As String, Success As Boolean)
    If Success Then 
        Log(ServerPath & " - OK")
        pendingDownloadCount = pendingDownloadCount - 1
        If pendingDownloadCount = 0 Then 
            PrepareAll
            hd.ProgressDialogHide
        Else
            getButtonImage(ftpList.Get(pendingDownloadCount - 1))               
        End If
    Else
        Log(ServerPath & " - " & LastException.Description)
        getButtonImage(ftpList.Get(pendingDownloadCount - 1))       
    End If
End Sub

Attached: Application-logs & FTP-server-log (csv)

Erel · Jul 12, 2015

jhagerup said:
When I don't use "persistConnection" it goes fast, but requires as many connection pr. account as the number of files !

If you are using the same ftp object then it will create a single connection. It will reconnect each time. However it doesn't create any load on the server.

jhagerup · Jul 12, 2015

I am only using one ftp object. The problem is that B4i causes a 30 seconds delay between each file in persistent mode. There is no delay in B4A, and it seems to be persistent - according to ftp-server log. Same timeout as for the delayed ftp-session logout ?

Erel · Jul 12, 2015

Does it work properly if you don't set the persistConnection field?

jhagerup · Jul 12, 2015

Yes, but it makes a connection for each file. When more files than allowed sessions, the download fails until one of the open connections logs out - after about 30 secs. - about the same delay as between files in persistant mode

Erel · Jul 12, 2015

I don't see this behavior here. Maybe you can configure your ftp server to close disconnected clients automatically.

You can try to use persistent mode and send QUIT with FTP.SendCommand after each download.

jhagerup · Jul 12, 2015

With pesistent mode and a QUIT command the behavior changed to:
login - read - login - logout - 30 secs delay - read - login - logout - 30 secs delay - read......
According to the ftp-log. The "next" login seems to happen before the "last" logout and the delay seems to relate to the read.
And I have no "disconnect clients automatically" settings in my ftp-server.

Erel · Jul 13, 2015

Is this FTP server accessible through the internet? If yes then I can try it myself if you like.

jhagerup · Jul 13, 2015

Yes: 94.145.79.229 - apps - apps and there are a couple of .png
But... it works fine in B4A, so I don't think that it's a server problem.

Erel · Jul 13, 2015

I've tried it with this code:

B4X:

Sub Process_Globals
   Public App As Application
   Public NavControl As NavigationController
   Private Page1 As Page
   Private ftp As FTP
End Sub

Private Sub Application_Start (Nav As NavigationController)
   NavControl = Nav
   Page1.Initialize("Page1")
   Page1.Title = "Page 1"
   Page1.RootPanel.Color = Colors.White
   NavControl.ShowPage2(Page1, True)
   ftp.Initialize("ftp", "94.145.79.229", 21, "apps", "apps")
   ftp.PassiveMode = True
   ftp.List("/apps/1")
End Sub

Sub ftp_ListCompleted (ServerPath As String, Success As Boolean, Folders() As FTPEntry, Files() As FTPEntry)
   For Each fe As FTPEntry In Files
     If fe.Size < 100000 Then ftp.DownloadFile("/apps/1/" & fe.Name, False, File.DirTemp, fe.Name)
   Next
End Sub

Sub ftp_DownloadCompleted (ServerPath As String, Success As Boolean)
   Log($"$Time{DateTime.Now}: ${ServerPath}, success = ${Success}"$)
End Sub

The output is:

Application_Start
Application_Active
11:12:34: /apps/1/calender.png, success = 1
11:12:35: /apps/1/email.png, success = 1
11:12:37: /apps/1/fitness.png, success = 1
11:12:39: /apps/1/kniv+gaffel.png, success = 1
11:12:40: /apps/1/navigation.png, success = 1
11:12:42: /apps/1/phone.png, success = 1
11:12:43: /apps/1/q.png, success = 1
11:12:45: /apps/1/sgf2.png, success = 1
11:12:46: /apps/1/skalsdata.png, success = 1
11:12:48: /apps/1/skytteforeningen.png, success = 1
11:12:50: /apps/1/valkyrien.png, success = 1
11:12:52: /apps/1/web.png, success = 1

Tested on the simulator. It looks fine.

jhagerup · Jul 13, 2015

This runs fine with me too, and the project too.

Thanks

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