GZip detection

Question

Hello all

I need to detect GZip file format by its content, not just file extension, using this code recently given:

Dim file_is_CFBF As Boolean

Using fs = File.OpenRead("path to my file...")
    Dim bytes(8 - 1) As Byte
    Dim expected_bytes As Byte() = {&HD0, &HCF, &H11, &HE0, &HA1, &HB1, &H1A, &HE1}
    fs.Read(bytes, 0, 8)
    file_is_CFBF = bytes.SequenceEqual(expected_bytes)
End Using

MsgBox(file_is_CFBF)

No idea how to change the code to cover GZip? Don't have its expected bytes, anyone have? :)

Answer 1

Hello Peter

The code you provided checks for the CFBF (Compound File Binary Format) file format by comparing the first 8 bytes of a file with an expected byte sequence. To detect the GZip file format, you can modify the code as follows:

Dim file_is_GZip As Boolean

Using fs = File.OpenRead("path to your file...")
    Dim bytes(2 - 1) As Byte
    Dim expected_bytes As Byte() = {&H1F, &H8B}
    fs.Read(bytes, 0, 2)
    file_is_GZip = bytes.SequenceEqual(expected_bytes)
End Using

MsgBox(file_is_GZip)

In the modified code, we are checking for the GZip file format by comparing the first 2 bytes of the file with the expected byte sequence ({&H1F, &H8B}). GZip files typically start with these two bytes.

Make sure to replace "path to your file..." with the actual path to the file you want to detect. After running this code, the file_is_GZip variable will indicate whether the file is in the GZip format (True if it is, False otherwise). The MsgBox will display the result.

Please note that this method only checks the file format based on the first few bytes and does not perform a thorough validation of the entire file. It assumes that the file is not corrupted and follows the expected format.

thanks

santhiswaroop