Android Question Bytes to fixed packet

[Philip Prins]

Hello ,

I need to send a jpeg in packets of maximum 30 bytes to a server.
The problem is that the jpeg are different sizes.
How do i divide it?
I tried this , but how to handle oneven total data size?

Public Sub SendPhoto(data() As Byte)
    Dim nbytes As Int=data.Length
    Dim bc As ByteConverter
    Dim ninp As Int
    Dim bufjpg(30) As Byte
    For ninp =0 To nbytes-1 Step 30
    bc.ArrayCopy(data,ninp,bufjpg,0,30)
    ptChannel.SendPublicCustomMessage(bufjpg,30)
    Next
End Sub

 

[emexes]

This won't work first go, but it'll be pretty close. I'll leave the assembly and polishing for you ;-)

Best put in a separate code module file (Project, add code module)

Call HandleImageMessage from that PTT incoming message routine, if all three of the following are true:

Data(0) = 0x01 'message is photo data
Data(1) = 0x01 'message is chunked (apparently everything is chunked, even small photos)
Data(8) = 0x01 or 0x02 or 0x03 'valid image types

HandleImageMessage will call ImageReceived whenever a full image has been received.

The image will probably be in JPEG file format. The easiest way to display it might be to write it to a file, then load the file to an ImageView.

static variables:
    Dim CurrentSender As String = ""
    Dim NumChunks As Int = 0    'non-zero = reception in progress
    Dim ChunkBuffer As Map
 
Sub HandleImageMessage (Sender As String, Data() As Byte)

    If Sender <> CurrentSender Then
        CurrentSender = Sender
        NumChunks = 0
    End If

    If NumChunks = 0 Then
        Dim HighByte As Int = Bit.And(Data(6), 0xFF)
        Dim LowByte As Int = Bit.And(Data(7), 0xFF)
        Dim NumChunks = Bit.Or(Bit.ShiftLeft(HighByte, 8), LowByte)    '16-bit chunk count from header

        ChunkBuffer.Initialize
    End if

    Dim HighByte As Int = Bit.And(Data(4), 0xFF)
    Dim LowByte As Int = Bit.And(Data(5), 0xFF)
    Dim ThisChunkNumber = Bit.Or(Bit.ShiftLeft(HighByte, 8), LowByte)    '16 bit current chunk number from header

    ChunkBuffer.Put(ThisChunkNumber, Data())    'header and all - will strip that off when we assemble full image

    If ChunkBuffer.Size = NumChunks Then    'we have all chunks
        'determine size of full image (not including headers)

        Dim FullImageSize As Int = 0
        For ChunkNumber = 1 to NumChunks
            Dim B() As Byte = ChunkBuffer.Get(ChunkNumber)
            FullImageSize = FullImageSize + B.Length - 12
        Next

        'allocate buffer for assembly of full image

        Dim FullImage(FullImageSize) As Byte

        'assemble image

        Dim FullImageSizeSoFar As Int = 0
        For ChunkNumber = 1 to NumChunks
            Dim B() As Byte = ChunkBuffer.Get(ChunkNumber)

            bc.ArrayCopy(B, 12, FullImage, FullImageSizeSoFar, B.Length - 12)
            FullImageSizeSoFar = FullImageSizeSoFar + B.Length - 12
        Next

        NumChunks = 0    'prepare for next incoming
        ImageBuffer.Initialize    'clear buffer

        'pass to somebody who knows what to do with it...

        ImageReceived(Sender, FullImage, FullImage.Length)
    End If

End Sub

 

[emexes]

Sender might be a reserved word in B4A. Should probably be using SenderID rather than Sender(name) anyway.

Also should probably check NumBlocks against each received packet, make sure that no monkey business is happening.

 

[emexes]

I think this will fix the problem of interrupted image transfers (as long as the new image transfer has a different number of chunks)

If Sender <> CurrentSender Then
    CurrentSender = Sender
    NumChunks = 0
End If

Dim HighByte As Int = Bit.And(Data(6), 0xFF)
Dim LowByte As Int = Bit.And(Data(7), 0xFF)
Dim ThisChunkNumChunks = Bit.Or(Bit.ShiftLeft(HighByte, 8), LowByte)    '16-bit chunk count from header

If ThisChunkNumChunks <> NumChunks Then    'resets reception if NumChunks = 0 or if NumChunks changes
    NumChunks = ThisChunkNumChunks
    ChunkBuffer.Initialize
End if

 

[Philip Prins]

Work fine, thanks for your support,
Let me now how to donate