support/download/git

#!/usr/bin/env bash

# We want to catch any unexpected failure, and exit immediately
set -E

# Download helper for git, to be called from the download wrapper script
#
# Options:
#   -q          Be quiet.
#   -r          Clone and archive sub-modules.
#   -o FILE     Generate archive in FILE.
#   -u URI      Clone from repository at URI.
#   -c CSET     Use changeset CSET.
#   -n NAME     Use basename NAME.
#
# Environment:
#   GIT      : the git command to call

# Save our path and options in case we need to call ourselves again
myname="${0}"
declare -a OPTS=("${@}")

# This function is called when an error occurs. Its job is to attempt a
# clone from scratch (only once!) in case the git tree is borked, or in
# case an unexpected and unsupported situation arises with submodules
# or uncommitted stuff (e.g. if the user manually mucked around in the
# git cache).
_on_error() {
    local ret=${?}

    printf "Detected a corrupted git cache.\n" >&2
    if ${BR_GIT_BACKEND_FIRST_FAULT:-false}; then
        printf "This is the second time in a row; bailing out\n" >&2
        exit ${ret}
    fi
    export BR_GIT_BACKEND_FIRST_FAULT=true

    printf "Removing it and starting afresh.\n" >&2

    popd >/dev/null
    rm -rf "${git_cache}"

    exec "${myname}" "${OPTS[@]}" || exit ${ret}
}

verbose=
recurse=0
while getopts "${BR_BACKEND_DL_GETOPTS}" OPT; do
    case "${OPT}" in
    q)  verbose=-q; exec >/dev/null;;
    r)  recurse=1;;
    o)  output="${OPTARG}";;
    u)  uri="${OPTARG}";;
    c)  cset="${OPTARG}";;
    d)  dl_dir="${OPTARG}";;
    n)  basename="${OPTARG}";;
    :)  printf "option '%s' expects a mandatory argument\n" "${OPTARG}"; exit 1;;
    \?) printf "unknown option '%s'\n" "${OPTARG}" >&2; exit 1;;
    esac
done

shift $((OPTIND-1)) # Get rid of our options

# Create and cd into the directory that will contain the local git cache
git_cache="${dl_dir}/git"
mkdir -p "${git_cache}"
pushd "${git_cache}" >/dev/null

# Any error now should try to recover
trap _on_error ERR

# Caller needs to single-quote its arguments to prevent them from
# being expanded a second time (in case there are spaces in them)
_git() {
    eval GIT_DIR="${git_cache}/.git" ${GIT} "${@}"
}

# Create a warning file, that the user should not use the git cache.
# It's ours. Our precious.
cat <<-_EOF_ >"${dl_dir}/git.readme"
	IMPORTANT NOTE!

	The git tree located in this directory is for the exclusive use
	by Buildroot, which uses it as a local cache to reduce bandwidth
	usage.

	Buildroot *will* trash any changes in that tree whenever it needs
	to use it. Buildroot may even remove it in case it detects the
	repository may have been damaged or corrupted.

	Do *not* work in that directory; your changes will eventually get
	lost. Do *not* even use it as a remote, or as the source for new
	worktrees; your commits will eventually get lost.
_EOF_

# Initialise a repository in the git cache. If the repository already
# existed, this is a noop, unless the repository was broken, in which
# case this magically restores it to working conditions. In the latter
# case, we might be missing blobs, but that's not a problem: we'll
# fetch what we need later anyway.
#
# We can still go through the wrapper, because 'init' does not use the
# path pointed to by GIT_DIR, but really uses the directory passed as
# argument.
_git init .

# Ensure the repo has an origin (in case a previous run was killed).
if ! _git remote |grep -q -E '^origin$'; then
    _git remote add origin "'${uri}'"
fi

_git remote set-url origin "'${uri}'"

printf "Fetching all references\n"
_git fetch origin
_git fetch origin -t

# Try to get the special refs exposed by some forges (pull-requests for
# github, changes for gerrit...). There is no easy way to know whether
# the cset the user passed us is such a special ref or a tag or a sha1
# or whatever else. We'll eventually fail at checking out that cset,
# below, if there is an issue anyway. Since most of the cset we're gonna
# have to clone are not such special refs, consign the output to oblivion
# so as not to alarm unsuspecting users, but still trace it as a warning.
if ! _git fetch origin "'${cset}:${cset}'" >/dev/null 2>&1; then
    printf "Could not fetch special ref '%s'; assuming it is not special.\n" "${cset}"
fi

# Check that the changeset does exist. If it does not, re-cloning from
# scratch won't help, so we don't want to trash the repository for a
# missing commit. We just exit without going through the ERR trap.
if ! _git rev-parse --quiet --verify "'${cset}^{commit}'" >/dev/null 2>&1; then
    printf "Commit '%s' does not exist in this repository\n." "${cset}"
    exit 1
fi

# The new cset we want to checkout might have different submodules, or
# have sub-dirs converted to/from a submodule. So we would need to
# deregister _current_ submodules before we checkout.
#
# Using "git submodule deinit --all" would remove all the files for
# all submodules, including the corresponding .git files or directories.
# However, it  was only introduced with git-1.8.3, which is too recent
# for some enterprise-grade distros.
#
# So, we fall-back to just removing all submodules directories. We do
# not need to be recursive, as removing a submodule will de-facto remove
# its own submodules.
#
# For recent git versions, the repository for submodules is stored
# inside the repository of the super repository, so the following will
# only remove the working copies of submodules, effectively caching the
# submodules.
#
# For older versions however, the repository is stored in the .git/ of
# the submodule directory, so the following will effectively remove the
# the working copy as well as the repository, which means submodules
# will not be cached for older versions.
#
cmd='printf "Deregistering submodule \"%s\"\n" "${path}" && cd .. && rm -rf "${path##*/}"'
_git submodule --quiet foreach "'${cmd}'"

# Checkout the required changeset, so that we can update the required
# submodules.
_git checkout -f -q "'${cset}'"

# Get rid of now-untracked directories (in case a git operation was
# interrupted in a previous run, or to get rid of empty directories
# that were parents of submodules removed above).
_git clean -ffdx

# Get date of commit to generate a reproducible archive.
# %cD is RFC2822, so it's fully qualified, with TZ and all.
date="$( _git log -1 --pretty=format:%cD )"

# There might be submodules, so fetch them.
if [ ${recurse} -eq 1 ]; then
    _git submodule update --init --recursive
fi

# Generate the archive, sort with the C locale so that it is reproducible.
# We do not want the .git dir; we keep other .git files, in case they are the
# only files in their directory.
# The .git dir would generate non reproducible tarballs as it depends on
# the state of the remote server. It also would generate large tarballs
# (gigabytes for some linux trees) when a full clone took place.
find . -not -type d \
       -and -not -path "./.git/*" >"${output}.list"
LC_ALL=C sort <"${output}.list" >"${output}.list.sorted"

# Create GNU-format tarballs, since that's the format of the tarballs on
# sources.buildroot.org and used in the *.hash files
tar cf - --transform="s#^\./#${basename}/#" \
         --numeric-owner --owner=0 --group=0 --mtime="${date}" --format=gnu \
         -T "${output}.list.sorted" >"${output}.tar"
gzip -6 -n <"${output}.tar" >"${output}"

rm -f "${output}.list"
rm -f "${output}.list.sorted"

popd >/dev/null