git-streaker

A revisionist approach to git history.

git-streaker gives you a flexible way to rewrite commit dates and times in git repositories. It's a glorified --env-filter for git filter-branch, one that lets you specify a sequence of dates to use for the rewritten commits.

First, you generate a schedule with git streaker schedule, then you rewrite the dates on your commits according to the schedule with git streaker filter <schedule-file>.

Installing

npm install -g git-streaker

git-streaker is a CLI-only tool. You'll need git installed and available on the $PATH to use it. Git allows you to invoke git-streaker as git streaker if you prefer.

Getting Started

Overview

• Run git streaker schedule schedule.json --type=... to create a schedule file.
• Run git streaker filter -ac schedule.json to rewrite the dates on the commits in the current branch.

Command Line Interface

Get usage information with --help, both for git streaker itself, and the subcommands. All usages of this tool follow this pattern:

git streaker <subcommand> [options] <schedule-file>

You provide a subcommand as the first option. And with any of the subcommands, you also specify the relative path to a 'schedule' file.

You can turn boolean options off with --no-<option>.

Commands

Schedule

schedule generates a schedule file according to parameters you supply.

• There's a few required things to pass:
  • The path you want your schedule file to be written at, and
  • A schedule --type (see Current Schedule Types below), and
  • A commit --count
    • You can guess at the required --count for a repo with git rev-list <ref> --count
    • We don't do refparsing, or ask git any details about the commits being filtered, for simplicity. So, we need a hint here. (TODO?)
• Depending on the --type of schedule, you may be required to pass other options like --start or --end

Current Schedule Types

• streak which produces a once-a-day schedule
• interval, which just adds a random interval between commits
  • You can use --interval=300-600 to specify the interval, in seconds
  • The default interval is one second (but see --jitter below)

Common Options

• --start=<date> (required) the start date for the generated schedule
• --jitter randomizes the commit time slightly, splaying it through the hour after it would have otherwise occurred
• --hour=6,7,15-23 causes generated commits to fall within these hours (modulo jitter, above)

Usage

Usage: git streaker schedule --type=<type> [options] <schedule-out-file>
 
Options:
  --verbose, -v  Output more information (provide multiple times for more noise)  [count]
  --quiet, -q    Output less information (provide multiple times for less noise)  [count]
  -f, --force    Allow overwriting the destination file  [boolean] [default: false]
  --type, -t     The type of schedule to generate (a generator name)  [required] [choices: "streak", "interval"]
  --count, -c    The number of commits to generate  [required] [default: 1000]
  --hour         Restrict generated times to these hours  [string]
  --jitter, -j   Randomly generate minute and second information  [boolean] [default: true]
  --start, -s    A date string describing when to begin the scheduled dates  [string]
  --help         Show help  [boolean]

Filter

filter runs a filter-branch operation on the current git repo (relative to working directory).

• There's two required things to pass: the path to your schedule file, and -ac
• If you pass the --author, -a option, the author date with be overwritten
• If you pass the --committer, -c option, the committer date will be overwritten
• You can pass both, but you must pass one or the other

Useful filter-branch options

You can pass any number of command line flags directly to git filter-branch by specifying them after -- when using filter.

A particularly useful option is --original, which sets the namespace your refs will be backed up to before the filter operation takes place. It defaults to 'refs/original'. git filter-branch will refuse to run if there's already a backup set of refs, so it's a good idea to specify a different value of this flag each time you want to run the filter in succession. (For example you might use git streaker filter -a blah.json -- --original refs/streak/blah).

(You could also just use the --force flag, but that's much less safe!)

Usage

Usage: git streaker filter [--author] [--committer] [options] <schedule-file> [-- filter-branch-options...]
 
Options:
  --verbose, -v    Output more information (provide multiple times for more noise)  [count]
  --yes, -y        Do not ask for confirmation before running filter-branch  [boolean] [default: false]
  --author, -a     Reset author details  [boolean] [default: false]
  --committer, -c  Reset committer details  [boolean] [default: false]
  --help           Show help  [boolean]

Schedule File Format

A schedule is simply a JSON file with a list of date strings. It looks like this:

{
  "schedule": [
    "1997-07-16T19:00:00+01:00",
    "1997-07-17T19:00:00+01:00",
    "1997-07-18T19:00:00+01:00"
  ]
}

The format is "anything new Date("dateString") understands". Dates are consumed one by one from this file for commit dates, in the order that git filter-branch walks the commit range you give it.

Known Limitations

• Timezone information is limited to whatever $TZ says. Would probably need momentjs plus the timezone data to do better, and it'd be awkward.