docker-update

#!/bin/bash

## Updates an existing image with given script coming from stdin.
##

exname=$(basename $0)

usage="$exname DOCKER_IMAGE

Update image with stdin instruction.
"

if [ -z "$1" ]; then
    echo "Error: you should specify a parent image as first argument." >&2
    echo "usage: $usage"
    exit 1
fi

image="$1"
shift
DOCKER_VERSION=$(docker -v | sed -r 's/^[^0-9.]+([0-9.]+).*$/\1/g')


is_cached_code_same() {
    local cmd
    cmd="$@"
    code="$(cat -)"
    [ "$1" == "-c" ] || return 1
    [ "$2" == "$code" ] || return 1
    if echo "$code" | egrep "#\s*docker:\s*ALWAYS\s*" >/dev/null 2>&1; then
	return 1
    fi
    return 0
}


DOCKER_INSPECT_CACHE_FORMAT='{{.Id}}{{"\x00"}}
{{.Parent}}{{"\x00"}}
{{if .Config}}{{range $p := .Config.Cmd}}{{$p}}{{"\x00"}}
{{end}}{{end}}{{"\x00"}}'

DOCKER_INSPECT_CACHE_FORMAT="$(echo "$DOCKER_INSPECT_CACHE_FORMAT" | tr -d "\n")"
export DOCKER_INSPECT_CACHE_FORMAT


##
# check_cache PARENT_IMAGE
#
# Checks if no already stored image has PARENT_IMAGE as parent and
# same code. If it founds such an image, it'll output its id in stdout
# and return 0 errlvl. Otherwise it'll return 1 errlvl.
check_cache() {
    local image
    image="$1"
    shift
    code="$(cat -)"
    image_id=$(get_image_id "$image")
    while read-0 id parent; do
        cmd=()
        while true; do
            read-0 elt
            if [ "$elt" ]; then
                cmd=("${cmd[@]}" "$elt")
            else
                break
            fi
        done
        if [ "$parent" != "$image_id" ]; then
            continue
        fi
        if echo "$code" | is_cached_code_same "${cmd[@]}"; then
            ## not used "$id" as there is a spurious \n that is inserted by --format
            echo $id
            return 0
        fi
    done < <(docker inspect --format "$DOCKER_INSPECT_CACHE_FORMAT" $(docker images -qa))
    return 1
}

docker_update() {
    local image
    image="$1"
    shift
    code=$(cat -)

    ## Saving CMD and ENTRYPOINT

    save_cmd=$(docker inspect --format='{{json .Config.Cmd}}' "$image")
    save_entrypoint=$(docker inspect --format='{{json .Config.Entrypoint}}' "$image")

    ## Checking cache in case already built.

    if cached=$(echo "$code" | check_cache "$image"); then
	echo "cached"
        docker tag "$cached" "$image"
    else
        
        ## Running code in container

        container_id=$(docker run -d \
            --entrypoint /bin/bash \
            "$@" "$image" -c \
            "$code"
        )
        if [ "$(docker wait "$container_id")" != "0" ]; then
            echo "Update of image "$image" failed ! (container: $container_id)"
            echo "=== code:"
            echo "$code"
            echo "=== logs:"
            docker logs "$container_id"
            exit 1
        fi

        docker commit --author "$exname" --message "$exname" \
            "$container_id" "$image" >/dev/null &&
        docker rm $container_id >/dev/null
        echo "updated"
    fi

    ## Final commit to restore CMD and ENTRYPOINT

    docker build -t "$image" - <<EOF >/dev/null 2>&1

FROM $image

CMD $save_cmd
ENTRYPOINT $save_entrypoint

EOF
}


read-0() {
    while [ "$1" ]; do
        IFS=$'\0' read -r -d '' "$1" || return 1
        shift
    done
}


get_image_id() {
    docker inspect --format '{{.Id}}' "$1"
}


docker_update "$image" "$@"