fat32_reader

A Go program to extract files from a FAT32 .bin disk image (e.g., piusb.bin), optionally verifying checksums and cleaning up files afterward. Primarily tested with the go-diskfs library, it can open a partition from the image, list directories, and selectively extract files based on provided CLI arguments.

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Table of Contents

• Project Overview
• Features
• Usage
  • CLI Arguments
  • Examples
• Build Instructions
  • Building for Raspberry Pi Zero W
• Functions Explained
  • main()
  • readPath()
  • readAndExtractFile()
  • loopThroughFilesToExtract()
  • getChecksum()
  • tidyUp()
• License

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Project Overview

This script:

1. Opens a FAT32 .bin disk image (e.g., piusb.bin) using go-diskfs.
2. Lists files and directories (and can recurse if desired).
3. Sorts the files by modification time, optionally verifies checksums, and extracts them to a local target directory.
4. Cleans up (removes) extracted files if desired.

Primary Goal: Automate extraction of the latest file(s) from a disk image, such as those created by certain instruments or devices.

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Features

• Opens the first partition of a .bin image and lists files/folders (FAT32).
• Sorts the files by modification time (descending).
• Optional Checksum comparison for duplicates.
• Selective file extraction based on arguments: --latest, --all, --latestSame.
• Cleanup option to remove files after successful extraction, either from:
  • The host OS (os.Remove)
  • The FAT32 filesystem (filesystem.FileSystem.Remove)

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Usage

CLI Arguments

1. Argument 1: <device> – If empty, works on the root directory (/).

   • If SMP50 or another name is provided, it will target /<device>/results.
   • If all, it will recurse from /.

2. Argument 2: <rangeArgument> – Usually --latest, --latestSame, or --all.

   • --latest: Extract only the single newest file.
   • --latestSame: Attempt to extract additional files with the same basename.
   • --all: Extract all files in the sorted list.

3. Argument 3: <shouldTidyUp> – A boolean (true/false). If true, files in the FAT32 image are removed after extraction, or the local file system path is removed (depending on usage).

Examples

# 1) Running without arguments:
#    - Targets root directory
#    - Sorts by modification time
#    - Extracts the newest file only
./fat32_reader

# 2) Running with device SMP50 (no second argument -> default is "--latest"):
#    - Moves into /SMP50/results
#    - Extracts the newest file only
./fat32_reader SMP50

# 3) Extract all files in "/SMP50/results" and do not tidy up:
./fat32_reader SMP50 --all false

# 4) Extract only the newest file, 
#    then remove it from the .bin FS once done:
./fat32_reader SMP50 --latest true

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Build Instructions

General Build (for Linux)

go mod tidy
go build -o fat32_reader

This produces a binary named fat32_reader (or fat32_reader.exe on Windows).

Building for Raspberry Pi Zero W

A Raspberry Pi Zero W uses ARMv6. So you need to cross-compile with:

# For 32-bit ARMv6 (Pi Zero / Zero W):
GOOS=linux GOARCH=arm GOARM=6 go build -o fat32_reader

Then transfer fat32_reader to your Pi Zero W (e.g., via scp). Once on the Pi, you can run:

chmod +x fat32_reader
./fat32_reader

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Functions Explained

main()

1. Parses os.Args for optional arguments:
   • [1]: Device (e.g., SMP50).
   • [2]: --latest, --latestSame, --all (default --latest).
   • [3]: Boolean for shouldTidyUp.
2. Opens the disk image with diskfs.Open(imagePath).
3. Reads the first partition with disk.GetFilesystem(0).
4. Lists files using readPath(), optionally recurses depending on arguments.
5. Sorts files by modification time, ignoring “System Volume Information”.
6. Calls loopThroughFilesToExtract() to handle extraction based on your rules.

readPath(myFS, mypath, recursive) -> []FileWithPath

• Reads a path mypath in the myFS filesystem.
• Ignores special directories like ".", "..", "System Volume Information".
• If recursive == true, it calls itself on subdirectories.
• Returns a slice of FileWithPath, which includes the fs.FileInfo and the ItsPath.

loopThroughFilesToExtract(files, myFS) -> bool

• Iterates through sorted files.
• Checks arguments (--latest, --latestSame, --all) and calls readAndExtractFile().
• If argument [3] is set to true, calls tidyUp() on the extracted file(s).
• Returns true if an error condition arises, otherwise false.

readAndExtractFile(file, myFS, check ...bool) -> bool

1. file: A FileWithPath containing fs.FileInfo and a path.
2. Opens the file with myFS.OpenFile(absolutePath, 0).
3. Optionally calculates checksums if check[0] == true.
4. Creates the local output directory (under targetDir).
5. Copies the data from the filesystem.File to an output file.
6. Returns true if successful, false if any error.

getChecksum(fileOrPath interface{}) -> (string, error)

• Can handle either a filesystem.File or a local file path (string).
• Uses a SHA-256 hash, reading with io.Copy.
• Returns the hex-encoded result via hex.EncodeToString.

tidyUp(osFileOrFSFile interface{}) -> error

• Switches on type:
  • FSFileWithPath: Calls fs.Remove(filePath).
  • string: Calls os.Remove(path).
• Lets you remove a file from the disk image’s FS or from the local system, depending on what is passed.

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License

This project is licensed under the MIT License. See the header in fat32_reader.go for the full text:

MIT License

Copyright (c) 2024 David Herrmann
...

You’re free to use, modify, and distribute this software, provided the license text remains intact.

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Feedback or Contributions

Feel free to open issues or pull requests to improve or extend functionality. This docu was initial created by ChatGPT AI.