Task: Add docker entrypoint script

docker-entrypoint.sh

@@ -0,0 +1,56 @@
+#!/bin/sh
+set -eu
+
+# first arg is `-f` or `--some-option`
+if [ "${1#-}" != "$1" ]; then
+	set -- docker "$@"
+fi
+
+# if our command is a valid Docker subcommand, let's invoke it through Docker instead
+# (this allows for "docker run docker ps", etc)
+if docker help "$1" > /dev/null 2>&1; then
+	set -- docker "$@"
+fi
+
+_should_tls() {
+	[ -n "${DOCKER_TLS_CERTDIR:-}" ] \
+	&& [ -s "$DOCKER_TLS_CERTDIR/client/ca.pem" ] \
+	&& [ -s "$DOCKER_TLS_CERTDIR/client/cert.pem" ] \
+	&& [ -s "$DOCKER_TLS_CERTDIR/client/key.pem" ]
+}
+
+# if we have no DOCKER_HOST but we do have the default Unix socket (standard or rootless), use it explicitly
+if [ -z "${DOCKER_HOST:-}" ] && [ -S /var/run/docker.sock ]; then
+	export DOCKER_HOST=unix:///var/run/docker.sock
+elif [ -z "${DOCKER_HOST:-}" ] && XDG_RUNTIME_DIR="${XDG_RUNTIME_DIR:-/run/user/$(id -u)}" && [ -S "$XDG_RUNTIME_DIR/docker.sock" ]; then
+	export DOCKER_HOST="unix://$XDG_RUNTIME_DIR/docker.sock"
+fi
+
+# if DOCKER_HOST isn't set (no custom setting, no default socket), let's set it to a sane remote value
+if [ -z "${DOCKER_HOST:-}" ]; then
+	if _should_tls || [ -n "${DOCKER_TLS_VERIFY:-}" ]; then
+		export DOCKER_HOST='tcp://docker:2376'
+	else
+		export DOCKER_HOST='tcp://docker:2375'
+	fi
+fi
+if [ "${DOCKER_HOST#tcp:}" != "$DOCKER_HOST" ] \
+	&& [ -z "${DOCKER_TLS_VERIFY:-}" ] \
+	&& [ -z "${DOCKER_CERT_PATH:-}" ] \
+	&& _should_tls \
+; then
+	export DOCKER_TLS_VERIFY=1
+	export DOCKER_CERT_PATH="$DOCKER_TLS_CERTDIR/client"
+fi
+
+if [ "$1" = 'dockerd' ]; then
+	cat >&2 <<-'EOW'
+		📎 Hey there!  It looks like you're trying to run a Docker daemon.
+		   You probably should use the "dind" image variant instead, something like:
+		     docker run --privileged --name some-docker ... docker:dind ...
+		   See https://hub.docker.com/_/docker/ for more documentation and usage examples.
+	EOW
+	sleep 3
+fi
+
+exec "$@"