From e15fa4117031614968faca09e6a112cdfca344bc Mon Sep 17 00:00:00 2001
From: Midgard <midgard@zeus.ugent.be>
Date: Wed, 6 Nov 2019 13:47:23 +0100
Subject: [PATCH] Initial commit

---
 README.md     | 41 ++++++++++++++++++++++++++++
 git-mirror.sh | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 116 insertions(+)
 create mode 100644 README.md
 create mode 100755 git-mirror.sh

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..c83e988
--- /dev/null
+++ b/README.md
@@ -0,0 +1,41 @@
+# Git mirror
+
+Run this script to synchronize a repository once.
+
+## Dependencies
+* bash
+* git
+* Tor and torify (see section "Tor")
+
+## Usage
+```
+./git-mirror.sh <workdir> <leader> <follower...>
+```
+
+## Get started
+Create a git repo, add remotes for the leader and the followers:
+```bash
+mkdir ~/git-mirror-my-repo; cd ~/git-mirror-my-repo
+git init
+git remote add github https://github.com/interesting/repo
+git remote add gitea ssh://git@git.example.org/me/interesting-repo
+git remote add gitlab ssh://git@git.example.com/myself/interesting-repo
+```
+
+Make sure Tor is running (see section "Tor"). Then run the mirroring script:
+```bash
+cd
+git clone https://git.zeus.gent/midgard/git-mirror.git; cd git-mirror
+./git-mirror.sh ~/git-mirror-my-repo github gitea gitlab
+```
+The first remote, github is the leader. The others are followers that are updated.
+
+## Tor
+The leader is fetched over Tor through torify. Make sure Tor is running, or edit the script,
+changing `torify git fetch` into `git fetch`.
+
+## Motivation
+GitHub has always been hypocritical, promoting open source while keeping its own stack closed. When
+GitHub was bought by Microsoft, the author decided to stop using it. Unfortunately a lot of
+software still only has a presence on GitHub. To make it easier to work with those, this simple
+mirror script was written.
diff --git a/git-mirror.sh b/git-mirror.sh
new file mode 100755
index 0000000..16c4288
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+++ b/git-mirror.sh
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+#!/bin/bash
+set -euo pipefail
+IFS=$'\n'
+
+if [[ $# -lt 3 ]]; then
+	echo "Usage: $0 <workdir> <leader> <follower...>"
+	exit 1
+fi
+
+cd "$1"
+
+leader="$2"
+shift 2
+followers=( "$@" )
+
+echo "Working directory: $PWD"
+echo "Leader remote:     $leader"
+echo "Follower remotes:  ${followers[*]}" | tr '\n' ' '
+echo; echo
+
+torify git fetch --prune --multiple "$leader"
+git fetch --prune --multiple "${followers[@]}"
+echo
+
+echo "Leader remote information:"
+git remote show -n "$leader"
+echo
+echo "Follower remotes information:"
+git remote show -n "${followers[@]}"
+echo
+
+branches=( $(git show-ref | sed -n 's| refs/remotes/'"$leader"'/|\t|p') )
+echo -e "${#branches[*]} branches at leader:"
+echo "${branches[*]}"
+
+IFS=$'\t'
+
+errors=( )
+
+error() {
+	echo "XXX $1" >&2
+	errors[${#errors[*]}]="$1"
+}
+
+for branchspec in "${branches[@]}"; do
+	set $branchspec
+	leader_sha="$1"
+	branch="$2"
+
+	for remote in "${followers[@]}"; do
+		echo
+		echo "Updating $remote/$branch"
+
+		# Prepare state to push
+		follower_ref="refs/remotes/$remote/$branch"
+		if ! git show-ref --verify --quiet "$follower_ref"; then
+			echo "Branch doesn't exist yet at remote, creating"
+			git reset --hard "$leader_sha" --
+		else
+			echo "Branch existed at remote, updating"
+			git reset --hard "$follower_ref" --
+			git merge --ff-only "$leader_sha" || { error "$remote $branch: FF not possible"; continue; }
+		fi
+
+		git push "$remote" "+HEAD:$branch" || { error "$remote $branch: failed to push"; continue; }
+
+	done
+done
+
+if [[ "${#errors[*]}" -ge 0 ]]; then
+	echo "Errors:"
+	echo "${errors[@]}"
+else
+	echo "No errors."
+fi