stevedoria.net

fciv.py is a Python module that I implemented to generate file integrity data in a format used by Microsoft File Checksum Integrity Verifier. My use case involves copying files from a Linux workstation to a Microsoft Windows workstation. I wanted to generate integrity data on Linux using Python 3 and verify file integrity on Microsoft Windows without installing 3rd party software.

FCIV file content is generated with the following Python snippet:

import fciv
digests = fciv.fciv_compute('mydirectory/**')
fciv.fciv_write(digests)

With the output of the generation script redirected to a file named ‘fciv.xml’, the following snippet performs verification:

import fciv
reference_digests = fciv.fciv_read('fciv.xml')
actual_digests = fciv.fciv_compute('mydirectory/**')
fciv.fciv_verify(actual_digests, reference_digests)

The verification performed by fciv.py reports mismatches between expected and actual file checksums. Files missing from and files in addition to that of the verification data are also reported.

From The TypeScript Handbook:

The easiest way to remember whether to use readonly or const is to ask whether your using it on a variable or a property. Variables use const whereas properties use readonly.

Using Microsoft Windows Subsystem for Linux (WSL) to gain access to Linux command line tools within Microsoft Windows 10, I was able to create a consistent backup procedure that can be performed in Windows and Linux environments. I used SyncToy and File Checksum Integrity Verifier (FCIV) to perform backups before adopting this standard approach.

Except where noted, the following procedure can be performed in both Windows and Linux environments.

1. Navigate to Desired Folder’s Parent.

   $ cd /mnt/c/myfolderparent

2. Generate SHA1 Digest File.

   $ find ./myfolder -type f -exec sha1sum -b "{}" + > ~/myfolder.sha1

3. Verify SHA1 Digest File (optional).

   $ sha1sum -c ~/myfolder.sha1

   or

   $ sha1sum -c --quiet ~/myfolder.sha1

   Note: myfolder.sha1 contains relative paths. The above command requires execution from a directory where relative paths lead to the files desired for integrity checks.

4. Mount Destination (optional)
   1. Create Mount Point

      $ mkdir /mnt/usbdrive

   2. Review Mount Options of Mounted Fixed Drives

      $ mount

      

   3. Mount Drive

      $ sudo mount -t drvfs f: /mnt/usbdrive \
      -o noatime,uid=1000,gid=1000

      This command is specific to Microsoft Windows; a similar command is available in the Linux environment. “f:” is the drive letter that Microsoft Windows assigned to the inserted USB drive in this example. Options are specified to match those highlighted above for the already mounted fixed drives.

5. Perform Copy
   1. Dry Run

      $ rsync -n -av --delete --force --progress \
      --human-readable ./myfolder/ /mnt/usbdrive/myfolder

   2. Live Run

      $ rsync -av --delete --force --progress \
      --human-readable ./myfolder/ /mnt/usbdrive/myfolder

      The trailing ‘/’ of the source folder is important to the command’s correctness.

6. Move Checksum File

   $ cp ~/myfolder.sha1 /mnt/usbdrive/.

7. Verify File Integrity

   $ cd /mnt/usbdrive
   $ sha1sum -c myfolder.sha1

Introduced in C# 8.0, the using-declaration language enhancement eliminates nested using-statements. The following code:

using System.IO;
class Program
{
  static void Main(string[] args)
  {
    var filename = "hello.txt";
    using (var stream = new FileStream(filename, FileMode.Create))
    {
      using (var writer = new StreamWriter(stream))
      {
        writer.WriteLine("Hello, World!");
      }
    }
  }
}

is improved with using declarations to the following:

using System.IO;
class Program
{
  static void Main(string[] args)
  {
    var filename = "hello.txt";
    using var stream = new FileStream(filename, FileMode.Create);
    using var writer = new StreamWriter(stream);

    writer.WriteLine("Hello, World!");
  }
}