Metadata diff of binary files
by Jakub Narębski, Rasmus Voss, Aske Olsson, Ferdinando Santacroce
Git: Mastering Version Control
- Git: Mastering Version Control
- Table of Contents
- Git: Mastering Version Control
- Git: Mastering Version Control
- Credits
- Preface
- I. Module 1
- 1. Getting Started with Git
- 2. Git Fundamentals – Working Locally
- 3. Git Fundamentals – Working Remotely
- 4. Git Fundamentals – Niche Concepts, Configurations, and Commands
- Dissecting the Git configuration
- Configuration architecture
- Configuration levels
- Listing configurations
- Editing configuration files manually
- Setting up other environment configurations
- Basic configurations
- 5. Obtaining the Most – Good Commits and Workflows
- The art of committing
- Adopting a workflow – a wise act
- Summary
- 6. Migrating to Git
- 7. Git Resources
- II. Module 2
- 1. Navigating Git
- 2. Configuration
- 3. Branching, Merging, and Options
- 4. Rebase Regularly and Interactively, and Other Use Cases
- 5. Storing Additional Information in Your Repository
- 6. Extracting Data from the Repository
- 7. Enhancing Your Daily Work with Git Hooks, Aliases, and Scripts
- Introduction
- Using a branch description in the commit message
- Creating a dynamic commit message template
- Using external information in the commit message
- Preventing the push of specific commits
- Configuring and using Git aliases
- Configuring and using Git scripts
- Setting up and using a commit template
- 8. Recovering from Mistakes
- Introduction
- Undo – remove a commit completely
- Undo – remove a commit and retain the changes to files
- Undo – remove a commit and retain the changes in the staging area
- Undo – working with a dirty area
- Redo – recreate the latest commit with new changes
- Revert – undo the changes introduced by a commit
- Reverting a merge
- Viewing past Git actions with git reflog
- Finding lost changes with git fsck
- 9. Repository Maintenance
- Introduction
- Pruning remote branches
- Running garbage collection manually
- Turning off automatic garbage collection
- Splitting a repository
- Rewriting history – changing a single file
- Back up your repositories as mirror repositories
- A quick submodule how-to
- Subtree merging
- Submodule versus subtree merging
- 10. Patching and Offline Sharing
- 11. Git Plumbing and Attributes
- Introduction
- Displaying the repository information
- Displaying the tree information
- Displaying the file information
- Writing a blob object to the database
- Writing a tree object to the database
- Writing a commit object to the database
- Keyword expansion with attribute filters
- Metadata diff of binary files
- Storing binaries elsewhere
- Checking the attributes of a file
- Attributes to export an archive
- 12. Tips and Tricks
- III. Module 3
- 1. Git Basics in Practice
- An introduction to version control and Git
- Git by example
- Repository setup
- Creating a Git repository
- Cloning the repository and creating the first commit
- Publishing changes
- Examining history and viewing changes
- Renaming and moving files
- Updating your repository (with merge)
- Creating a tag
- Resolving a merge conflict
- Adding files in bulk and removing files
- Undoing changes to a file
- Creating a new branch
- Merging a branch (no conflicts)
- Undoing an unpublished merge
- Summary
- 2. Exploring Project History
- 3. Developing with Git
- 4. Managing Your Worktree
- Ignoring files
- File attributes
- Fixing mistakes with the reset command
- Stashing away your changes
- Managing worktrees and the staging area
- Multiple working directories
- Summary
- 5. Collaborative Development with Git
- 6. Advanced Branching Techniques
- Types and purposes of branches
- Branching workflows and release engineering
- Interacting with branches in remote repositories
- Summary
- 7. Merging Changes Together
- 8. Keeping History Clean
- An introduction to Git internals
- Rewriting history
- Amending history without rewriting
- Summary
- 9. Managing Subprojects – Building a Living Framework
- Managing library and framework dependencies
- Managing large Git repositories
- Summary
- 10. Customizing and Extending Git
- 11. Git Administration
- 12. Git Best Practices
- 1. Git Basics in Practice
- A. Bibliography
- Index
- Configuration architecture
- Dissecting the Git configuration
Binary files can be hard to diff, depending on the type of the file. Often, the only option is to load two instances of the program to show the files and check the differences visually. In this recipe we'll see how we can use EXIF metadata to diff images in the repository.
We'll use the same repository as we did in the last example and either re-clone it or checkout the exif branch:
$ git clone https://github.com/dvaske/attributes_example.git $ cd attributes_example $ git checkout exif
In order to use the EXIF data while diffing binary files, we need to set up a filter to tell Git what to do when a file of *.jpg is to be diffed. EXIF data is metadata embedded in images and is often used by digital cameras to record timestamps, the size of an image, and so on.
We'll write the following line to .gitattributes:
*.jpg diff=exif-diff
This only tells Git that JPG files should use the exif-diff filter; we still need to set it up. To extract the EXIF metadata, there are different programs such as exiftool, jhead, and so on. In this example, we're using exiftool, so make sure you have it installed and available on your PATH. To set up the
exiftool diff filter, we create the following Git config:
git config diff.exif-diff.textconv exiftool
From now on, every time jpg is to be diffed, you'll just see a comparison of exifdata. To see the actual change in the image, you still have to show the two images and visually compare them.
Now that the filter is set up, we can try to check the output of it. The last two commits in the repository on the exif branch contain pictures that have had their size changed; let's see how they looks with the exif-diff filter. First, check log for the last two commits:
$ git log --name-status -2 commit 0beb82c65d8cd667e1ffe61860a42a106be3c1a6 Author: Aske Olsson <[email protected]> Date: Sat May 3 14:55:50 2014 +0200 Changes sizes of images M europe_needles.jpg M hello_world.jpg M pic_credits.txt commit a25d0defc70b9a1842463c1e9894a88dfb897cd8 Author: Aske Olsson <[email protected]> Date: Sun Apr 27 16:02:51 2014 +0200 Adds pictures to repository Picture credits found in pic_credits.txt M README.md A europe_needles.jpg A hello_world.jpg A pic_credits.txt
Let's look at the diff between the two commits (the output you get might not match the following output 1:1 and depends on the exiftool version, OS, and so on. The following output is generated with exiftool 9.61 on OS X 10.9.3):
$ git diff HEAD^..HEAD diff --git a/europe_needles.jpg b/europe_needles.jpg index 7291028..44e98e3 100644 --- a/europe_needles.jpg +++ b/europe_needles.jpg @@ -1,11 +1,11 @@ ExifTool Version Number : 9.54 -File Name : Gnepvw_europe_needles.jpg -Directory : /var/folders/3r/6f35b4t11rv2nmbrx5x32t4w0000gn/T -File Size : 813 kB +File Name : europe_needles.jpg +Directory : . +File Size : 328 kB File Modification Date/Time : 2014:05:03 22:08:05+02:00 -File Access Date/Time : 2014:05:03 22:08:05+02:00 +File Access Date/Time : 2014:05:03 22:08:06+02:00 File Inode Change Date/Time : 2014:05:03 22:08:05+02:00 -File Permissions : rw------- +File Permissions : rw-r--r-- File Type : JPEG MIME Type : image/jpeg JFIF Version : 1.01 @@ -79,8 +79,8 @@ Sub Sec Time Original : 00 Sub Sec Time Digitized : 00 Flashpix Version : 0100 Color Space : sRGB -Exif Image Width : 1620 -Exif Image Height : 1080 +Exif Image Width : 1024 +Exif Image Height : 683 ...
It is also possible to set up diffing of binary files for other types than images. As long as some useful data from the file type can be extracted, it's possible to create a custom diff filter for that file type. With the catdoc program, Microsoft Word files can, for example, be translated from the .doc format to plain text, which makes it easy to diff the text content in two files, but not their formatting.
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