# Copyright 2016 The Kubernetes Authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# HOW TO USE THIS CONTAINER:
#
# The only commandline argument (or env var) that is really required is
# `--repo` ($GIT_SYNC_REPO).  Everything else is optional (run this with
# `--man` for details).
#
# This container will run as UID:GID 65533:65533 by default.  For most users,
# the simplest ways to use this container are either:
#   a) use the default UID/GID and mount a volume on /git writeable by those
#   b) set your own UID/GID and mount a volume on /git writeable by those
#
# If you mount a volume anywhere else, you must set `--root` ($GIT_SYNC_ROOT).
# If you do not mount a volume, this will run but you can't access the results
# (which might be useful for testing, but not much else).
#
# Newly created docker volumes (the very first `docker run -v`) are initialized
# based on the in-image mountpoint's UID/GID?mode, so another solution for
# using this with docker is to set your own UID/GID and also add the default
# GID as a supplemental group (see `docker run --group-add`).
#
# Kubernetes offers `Pod.spec.securityContext.fsGroup` to manage volume
# permissions.
#
# If you set any UID other than the default and want to use git over SSH, you
# should set `--add-user` ($GIT_SYNC_ADD_USER).

#############################################################################
# First we prepare the image that we want, regardless of build layers.
#############################################################################
FROM {ARG_FROM} as prep

# When building, we can pass a unique value (e.g. `date +%s`) for this arg,
# which will force a rebuild from here (by invalidating docker's cache).
ARG FORCE_REBUILD=0

RUN apt-get -q -y update
RUN apt-get -q -y upgrade
RUN apt-get -q -y install --no-install-recommends \
        ca-certificates \
        coreutils \
        socat \
        openssh-client \
        git
RUN apt-get -q -y autoremove
RUN rm -rf /var/lib/apt/lists/*

# Add the default UID to /etc/passwd so SSH is satisfied.
RUN echo "git-sync:x:65533:65533::/tmp:/sbin/nologin" >> /etc/passwd
# A user might choose a different UID and set the `--add-user` flag, which
# needs to be able to write to /etc/passwd.
RUN chmod 0666 /etc/passwd

# Add the default GID to /etc/group for completeness.
RUN echo "git-sync:x:65533:git-sync" >> /etc/group

# Make a directory that can be used to mount volumes.  Setting the mode to
# include group-write allows users to run this image as a different user, as
# long as they use our git-sync group.
RUN mkdir -m 02775 /git && chown 65533:65533 /git

# When building, we can pass a hash of the licenses tree, which docker checks
# against its cache and can force a rebuild from here.
ARG HASH_LICENSES=0

# Add third-party licenses.
COPY .licenses/ /LICENSES/

# When building, we can pass a hash of the binary, which docker checks against
# its cache and can force a rebuild from here.
ARG HASH_BINARY=0

# Add the platform-specific binary.
COPY bin/{ARG_OS}_{ARG_ARCH}/{ARG_BIN} /{ARG_BIN}

#############################################################################
# Now we make a "clean" final image.
#############################################################################
FROM scratch
COPY --from=prep / /

# Run as non-root by default.  There's simply no reason to run as root.
USER 65533:65533

# Setting HOME ensures that whatever UID this ultimately runs as can write to
# files like ~/.gitconfig.
ENV HOME=/tmp
WORKDIR /tmp

# Default values for flags.
# Git-sync itself does not default the `--root` ($GIT_SYNC_ROOT) flag, but we
# can set a default here, which makes the container image easier to use.  The
# permissions were set for the default git-sync UID and GID.  If the user needs
# a different group or sets `--root` ($GIT_SYNC_ROOT), their values will
# override this, and we assume they are handling permissions themselves.
ENV GIT_SYNC_ROOT=/git

ENTRYPOINT ["/{ARG_BIN}"]