simplify composer installation

Dockerfile's COPY instruction supports copying from another image. This
feature simplifies composer installation significantly because composer
can simply be copied over from official image rather than programatically
installed.

Author: lavarou

files/Dockerfile

@@ -88,21 +88,7 @@ RUN if [ -z "$(grep '^8\.' /etc/debian_version)" ]; then \
     fi
 
 # install composer
-WORKDIR /usr/src
-
-# based on https://getcomposer.org/doc/faqs/how-to-install-composer-programmatically.md
-RUN \
- EXPECTED_CHECKSUM="$(php -r 'copy("https://composer.github.io/installer.sig", "php://stdout");')" \
- && php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');" \
- && ACTUAL_CHECKSUM="$(php -r "echo hash_file('sha384', 'composer-setup.php');")" \
- && if [ "$EXPECTED_CHECKSUM" != "$ACTUAL_CHECKSUM" ]; \
-  then \
-    >&2 echo 'ERROR: Invalid installer checksum'; \
-    rm composer-setup.php; \
-    exit 1; \
-  fi \
- && php composer-setup.php \
- && php -r "unlink('composer-setup.php');"
+COPY --from=composer ["/usr/bin/composer", "/usr/bin/composer"]
 
 #
 # The explain plan in the sql tests contain partition/filtered properties
@@ -152,13 +138,9 @@ RUN \
 # install predis
 # installation will be in /usr/src/vendor/predis/predis
 # which is value which should be used for PREDIS_HOME
-RUN php composer.phar require "predis/predis"
-RUN php composer.phar update
-
-#
-# install composer and make executable so it can be used in dev env
-#
-RUN cp composer.phar /usr/local/bin/composer && chmod +x /usr/local/bin/composer
+WORKDIR /usr/src
+RUN composer require "predis/predis"
+RUN composer update
 
 #
 # These args need to be repeated so we can propagate the VARS within this build context.