VB - How to compress a buffer with ZLIB.dll

[CVMichael]

If you want to compress data without saving to the drive, for example if you want to compress, and send it right away on a socket over the net. NOTE, you need to send/save the original size of the data, with the compressed data.

Private Declare Function Compress Lib "zlib.dll" Alias "compress" (dest As Any, destLen As Any, src As Any, ByVal srcLen As Long) As Long
Private Declare Function Uncompress Lib "zlib.dll" Alias "uncompress" (dest As Any, destLen As Any, src As Any, ByVal srcLen As Long) As Long
 
Private Sub Form_Load()
    Dim Str As String, CompStr As String
    Dim InData() As Byte, OutData() As Byte, DecompData() As Byte, OriginalSize As Long
    
    Str = "Testing... blah blah blah .....   " & String(40, "A") & String(55, "B")
    InData = StrConv(Str, vbFromUnicode)
    
    OriginalSize = UBound(InData) + 1
    
    If CompressData(InData, OutData) Then
        ' save the data or something, you have to save the OriginalSize also
        ' you need it when decompressing...
    End If
    
    Debug.Print "Original: " & UBound(InData) + 1 & " Bytes", "Compressed: " & UBound(OutData) + 1 & " Bytes"
    Debug.Print "Compression rate: " & Format((1 - (CDbl(UBound(OutData)) / UBound(InData))) * 100#, "##0.00")
    
    Erase InData
    
    ' read the data in OutData (in our case right now is actually the IN data)
    
    ReDim DecompData(OriginalSize - 1)
    Uncompress DecompData(0), OriginalSize, OutData(0), UBound(OutData) + 1
    
    Debug.Print "Decompressed string:"
    Debug.Print StrConv(DecompData, vbUnicode)
End Sub
 
Public Function CompressData(InData() As Byte, OutData() As Byte) As Boolean
    Dim BufferSize As Long
    BufferSize = (UBound(InData) + 1) * 1.01 + 12
 
    ReDim OutData(BufferSize)
 
    CompressData = Compress(OutData(0), BufferSize, InData(0), UBound(InData) + 1) = 0
 
    ReDim Preserve OutData(BufferSize - 1)
End Function