[Gambas-user] perl unpack

Tue Sep 20 00:45:24 CEST 2011

Don't stress too much over the `, it's just a kind of non-standard
padding character.  The % at the beginning of the string says we only
have 5 characters to decode so we shouldn't worry...we SHOULD always
have an exact multiple of 4 characters after the first length byte...
but some of them may not matter... 

This should do it:

======================================================================
Private Function decodeUU(codedStr As String) As Byte[]

  Dim idx, idy, ptr As Integer
  Dim result As Byte[]
  Dim lengthUU, ascAChar, ascMin32 As Integer
  Dim binFour As String = ""
  ' First character's ascii code - 32 is the length
  ascAChar = Asc(Left$(codedStr, 1))
  ascMin32 = ascAChar - 32
  lengthUU = ascMin32
  Print "Expecting a length of: " & lengthUU
  ' Set the size of the result array
  result = New Byte[lengthUU]
  ' Initialise pointer into the result array
  ptr = 0
  ' Step through the uuencoded string character by character starting at
the 2nd character (1st is the length)
  For idx = 2 To Len(codedStr)
    ascAChar = Asc(Mid$(codedStr, idx, 1))
    ' Only include what is not whitespace
    If ascAChar > 31 And ascAChar < 97 Then
      ' Subtract 32 from the ascii code of the character
      ascMin32 = ascAChar - 32
      ' Assemble a block of four 6-bit values
      binFour = binFour & Right$("000000" & intToBase(ascMin32,
BASE_BINARY), 6)
      ' Once we have 4 binary 6-bit 'characters' in our string
      If Len(binFour) = 24 Then
        ' Treat the 4 6-bit characters as 3 8-bit characters
        For idy = 1 To 3
          ' Make sure we don't go trying to convert more than the length
says we have to
          If ptr < result.Length
            Print "Bin to convert: " & Mid$(binFour, 1 + ((idy - 1) *
8), 8)
            ' Converts each block of 8 bits to its decimal value and
assigns to the output byte array 
            result[ptr] = toInt(Mid$(binFour, 1 + ((idy - 1) * 8), 8),
BASE_BINARY)
            Inc ptr
          End If
        Next
        ' Be sure to clear out binFour for the next unit of UUencoding
        binFour = ""
      End If
    End If
  Next
  Return result

End
======================================================================

You probably need the routines to convert between bases too:

======================================================================
Private Function convertBase(numberIn As String, fromBase As Integer,
toBase As Integer) As String

  Dim value As Integer
  value = toInt(numberIn, fromBase)
  Return intToBase(value, toBase)

End

Private Function intToBase(numberIn As Integer, base As Integer) As
String

  Dim remain, numToDivide As Integer
  Dim result As String = ""

  numToDivide = numberIn
  Do While numToDivide / base > 0
    remain = numToDivide Mod base
    numToDivide = (Int)(numToDivide / base)
    result = DIGITS[remain] & result
  Loop

  Return result

End

Private Function toInt(inputStr As String, base As Integer) As Integer

  Dim idx, mult, result, value As Integer
  mult = 1
  For idx = Len(inputStr) To 1 Step -1
    ' If we're in a base with digits bigger than 9
    ' we need the Find to return 10 for A, 11 for B, 12 for C etc.
    value = DIGITS.Find(UCase(Mid$(inputStr, idx, 1))) * mult
    result = result + value
    mult = mult * base
  Next
  Return result

End
======================================================================

And don't forget a few Consts for convenience:

======================================================================
Private Const TEST_STR As String = "%<V5N9#H`"
Private Const BASE_BINARY As Integer = 2
Private Const BASE_OCTAL As Integer = 8
Private Const BASE_DENARY As Integer = 10
Private Const BASE_HEX As Integer = 16
Private DIGITS As String[] = ["0", "1", "2", "3", "4", "5", "6", "7",
"8", "9", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L",
"M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"]
======================================================================

Oh and just for fun, here's an encode function too... you will notice
that I encode "send:" CORRECTLY... LOL!

======================================================================
Private Function encodeUU(source As Byte[]) As String

  Dim idx, idy, idxThree As Integer
  Dim result As String
  Dim aByte As Byte
  Dim aBinChar, binCharGroup As String
  Dim threeChars As Byte[]
  binCharGroup = ""
  result = result & Chr$(source.Count + 32)
  For idx = 0 To source.Max
    aByte = source[idx]
    ' Convert the byte to exactly 8 digits of binary
    ' so for e.g. pad 1 to become 00000001
    aBinChar = Right$("00000000" & intToBase(aByte, BASE_BINARY), 8)
    Print "aByte: " & aByte & " abinChar: " & aBinChar 
    ' Add bytes together to make blocks of 3 8-bit characters
    binCharGroup = binCharGroup & aBinChar
    ' Pad if we're at the end of the string and don't have a full 3-char
block
    If idx = source.Max Then
      binCharGroup = Left$(binCharGroup & "000000000000000000000000",
24)
    Endif
    If Len(binCharGroup) = 24 Then
      Print binCharGroup
      ' Now treat the 3 blocks of 8 bits like 4 blocks of 6 bits....
      For idy = 1 To 4
        Print "char: " & idy & " has value: " & (toInt(Mid
$(binCharGroup, 1 + ((idy - 1) * 6), 6), BASE_BINARY) + 32)
        ' Append the Chr$ of the value of the 6-bit byte + 32 to our
result
        result = result & Chr$(toInt(Mid$(binCharGroup, 1 + ((idy - 1) *
6), 6), BASE_BINARY) + 32)
      Next
      binCharGroup = ""
    Endif
  Next
  Return result

End
======================================================================

Kind regards,
Caveat

On Mon, 2011-09-19 at 13:24 +0200, Ron wrote:
> I'm trying to decode this with gambas, no luck, anyone has an idea?
> 
> #!/usr/bin/perl
> print pack('u', "send:");
> 
> %<V5N9#H`
> 
> So decoding %<V5N9#H` should result in 'send:'
> 
> The pack 'u' function does uuencoding  but all vb alike code doesn't 
> reproduce the correct result, or struggles with the `...
> 
> 
> Thanks in advance!!
> 
> Regards,
> Ron_2nd.
> 
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