Serializing and deserializing a file in a spreadsheet - excel

Question

I feel dirty asking this because it's such a hacky workaround, but I have a project where the deliverable must be a single .xlsm file. However, we have no restrictions on what files that deliverable may write or execute. VBA and Excel's macro editor have limitations that don't work with the project.
So I'm trying to save the binary values of a Python interpreter in a worksheet and then write that .exe to the client's computer when the macro is run. (It's pretty much a virus and a bad idea, I know, but the requirements are strict and unchangeable.)
I have a macro to read python.exe into a worksheet:
Function ReadFromFile(path)
Dim bytes() As Byte
Dim fileInt As Integer: fileInt = FreeFile
Open path For Binary Access Read As #fileInt
ReDim bytes(0 To LOF(fileInt) - 1)
Get #fileInt, , bytes
Close #fileInt
Set ReadFromFile = bytes
End Function
Sub ReadCompiler_Click()
Dim path As String: path = ActiveWorkbook.path & "\python.exe.original"
Dim bytes() As Byte
bytes = ReadFromFile(path)
Dim cell As Range
Set cell = Worksheets("PythonEXE").Range("A1")
For Each chunk In bytes
cell.Value = chunk
Set cell = cell.Offset(1, 0)
Next chunk
End Sub
I have verified that this copies the binary file byte-for-byte into column A of my PythonEXE worksheet.
My problem is when writing the bytes back to a file, the written file is significantly different than the original. I'm using the following functions to write from the worksheet to the output file:
Function WriteToFile(path, data)
Dim fileNo As Integer
fileNo = FreeFile
Open path For Binary Access Write As #fileNo
Put #fileNo, 1, data
Close #fileNo
End Function
Sub WriteCompiler_Click()
Dim TotalRows As Long
Dim bytes() As Byte
TotalRows = Worksheets("PythonEXE").Rows(Worksheets("PythonEXE").Rows.Count).End(xlUp).Row
ReDim bytes(TotalRows)
For i = 1 To TotalRows
bytes(i) = CByte(Worksheets("PythonEXE").Cells(i, 1).Value)
Next i
Dim path As String: path = ActiveWorkbook.path & "\python.exe.written"
WriteToFile path, bytes
End Sub
Why is my output binary different than the input binary? It's not human readable, but their checksums are different and when I open them both in an IDE the output file looks like it has a bunch of rectangle glyphs at the beginning where the input file does not.

Answer 1

I changed a couple of things (guided by this answer to get around the problem:
When VBA writes a Variant, it puts some header info in the output. So I changed WriteToFile to copy data to a Byte array before writing it:
Dim buffer() As Byte
ReDim buffer(UBound(data))
buffer = data
For i = 0 To UBound(data)
Put #fileNo, i + 1, CByte(buffer(i))
Next i
I had an off-by-one error by going to UBound(data) instead of UBound(data) - 1. This is a little hairy because Put takes the write position as one-based instead of zero-based, but array indexers are zero-based:
Dim buffer() As Byte
ReDim buffer(UBound(data))
buffer = data
For i = 0 To (UBound(data) - 1)
Put #fileNo, i + 1, CByte(buffer(i))
Next i
Here's the full solution:
Function WriteToFile(path, data)
Dim fileNo As Integer
fileNo = FreeFile
Open path For Binary Access Write As #fileNo
Dim buffer() As Byte
ReDim buffer(UBound(data))
buffer = data
For i = 0 To (UBound(data) - 1)
Put #fileNo, i + 1, CByte(buffer(i))
Next i
Close #fileNo
' Shell ("explorer.exe " & path)
End Function
Function ReadFromFile(path)
Application.StatusBar = "Reading " & path
Dim bytes() As Byte
Dim fileInt As Integer: fileInt = FreeFile
Open path For Binary Access Read As #fileInt
ReDim bytes(0 To LOF(fileInt) - 1)
Get #fileInt, , bytes
Close #fileInt
ReadFromFile = bytes
End Function
Sub UpdatePython_Click()
Application.Calculation = xlCalculationManual
Dim path As String: path = ActiveWorkbook.path & "\python.exe.original"
Dim bytes() As Byte
bytes = ReadFromFile(path)
Worksheets("PythonEXE").Columns(1).EntireColumn.Clear
Dim cell As range
Set cell = Worksheets("PythonEXE").range("A1")
For Each chunk In bytes
cell.Value = chunk
Set cell = cell.Offset(1, 0)
Next chunk
Application.ActiveWorkbook.Save
Application.Calculation = xlCalculationAutomatic
End Sub
Sub WriteCompiler_Click()
Dim TotalRows As Long
Dim bytes() As Byte
TotalRows = Worksheets("PythonEXE").Rows(Worksheets("PythonEXE").Rows.Count).End(xlUp).Row
ReDim bytes(TotalRows)
For i = 0 To TotalRows
bytes(i) = CByte(Worksheets("PythonEXE").Cells(i + 1, 1).Value)
Next i
Dim path As String: path = ActiveWorkbook.path & "\python.exe.written"
If Dir(path) <> "" Then
Kill path
End If
WriteToFile path, bytes
Shell ActiveWorkbook.path & "\checksum.bat", vbNormalFocus
End Sub