dockerfile-wget

Create a bash function in Dockerfile, and use it to download static compile wget.

Way one

Does you use Dockerfile like this?

# install wget
RUN  apt-get update && apt-get install -qq -y --no-install-recommends wget && rm -rf /var/lib/apt/lists/*

#####################

# do whatever tasks which need wget to download somethings ...

######################

# remove wget
RUN apt-get purge -y --auto-remove wget

This is not the correct way to do this. If run docker history your_image, you will see

...
41753cb4a6be        4 hours ago         /bin/sh -c apt-get purge -y --auto-remove ...   445 kB              
1eae68198132        17 hours ago        /bin/sh -c apt-get update && apt-get insta...   34.4 MB
...

Because you install wget and remove wget in seperate step, you got about 34MB unuseful data into docker layout, in other word, you image size get bigger.

Way two

Another way CORRECT way to do this is, in every step you need wget, write as followings

RUN apt-get update && apt-get install -qq -y --no-install-recommends wget && rm -rf /var/lib/apt/lists/* && \
         do-whatever-process-need-wget && \
         RUN apt-get purge -y --auto-remove wget

This method is good, but too much redundant code, not perfect.

Why 3

ADD some_static_wget_url/static_get /usr/local/bin/wget
RUN chmod +x /usr/local/bin/wget

This is the way i currently use, only one problem, we have to download this wget again and again when build image, And, same file is saved to two layer in docker as in report by docker history.

d266e671e16f        About a minute ago   /bin/sh -c chmod +x /usr/local/bin/wget         618 kB              
56d3e171fa7c        About a minute ago   /bin/sh -c #(nop) ADD tarsum.v1+sha256:e32...   618 kB

Why not use bash to download a static compiled wget, and then use it ?

This project is the attempt to do this, following is a example dockerfile

FROM ruby:2.3-slim

MAINTAINER Billy Zheng(zw963) <vil963@gmail.com>

RUN bash -c 'function __wget() { \
    local URL=$1; \
    read proto server path <<<$(echo ${URL//// }); \
    local SCHEME=${proto//:*} PATH=/${path// //} HOST=${server//:*} PORT=${server//*:}; \
    [[ "${HOST}" == "${PORT}" ]] && PORT=80; \
    exec 3<>/dev/tcp/${HOST}/${PORT}; \
    echo -en "GET ${PATH} HTTP/1.1\r\nHost: ${HOST}\r\nConnection: close\r\n\r\n" >&3; \
    local state=0 line_number=0; \
    while read line; do \
        line_number=$(($line_number + 1)); \
        case $state in \
            0) \
                echo "$line" >&2; \
                if [ $line_number -eq 1 ]; then \
                    if [[ $line =~ ^HTTP/1\.[01][[:space:]]([0-9]{3}).*$ ]]; then \
                        [[ "${BASH_REMATCH[1]}" = "200" ]] && state=1 || return 1; \
                    else \
                        printf "invalid http response from '%s'" "$URL" >&2; \
                        return 1; \
                    fi; \
                fi; \
                ;; \
            1) \
                [[ "$line" =~ ^.$ ]] && state=2; \
                ;; \
            2) \
                echo "$line"; \
        esac \
    done <&3; \
    exec 3>&-; \
}; \

__wget http://202.56.13.13/base64_encoded_static_wget |base64 -d > /usr/local/bin/wget; \

if [ -s /usr/local/bin/wget ]; then \
    chmod +x /usr/local/bin/wget; \
else \
    echo "Network is not connected?" >&2; \
    exit 1; \
fi;'


CMD ["ruby"]

When it build, we can see docker history image_name

9d95c852997c        31 seconds ago      /bin/sh -c bash -c 'function __wget() {     l   618.3 kB

Only 618.3 KB is added into new build image, and we almost save 35MB space compare to first method. And, we no need download it again and again when next build.

Thanks

this static_wget is got from minos-static project,

what i does is just:

download static compiled wget, and pack with upx (size from 1.5M reduce to 604kb)
create __wget function in Dockrfile, please refer to this StackExchange answer, and this, for a complete example, please see this
encode wget binary with base64, because __wget function not full-suppot binary data transfer.
save base64 encoded static compiled wget in some place which not need https, because __wget not support.
use _wget function to download wget.

dockerfile-wget

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dockerfile-wget

Way one

Way two

Why 3

Why not use bash to download a static compiled wget, and then use it ?

Thanks