Support podman in tasks/build.rake

Support podman in addition to docker in tasks/build.rake
via the DOCKER environment variable.

Author: gregorynisbet-google

tasks/build.rake

@@ -49,28 +49,43 @@ DEP_BUILD_ORDER = [
   'trapperkeeper-comidi-metrics',
 ].freeze
 
+# somewhat annoyingly, with --format=json there are differences between
+# podman and docker. Docker will output one JSON record per line, but podman
+# will put everything into an array. Do something simple that can handle both.
+def non_empty(output)
+  if output.strip.empty?
+    return true
+  end
+
+  begin
+    return !JSON.parse(output).empty?
+  rescue JSON::ParseError => e
+    return false
+  end
+end
+
 def image_exists
-  !`docker images -q #{@image}`.strip.empty?
+  non_empty(`${DOCKER-docker} images -q #{@image} --format=json`)
 end
 
 def container_exists
-  !`docker container ls --all --filter 'name=#{@container}' --format json`.strip.empty?
+  non_empty(`${DOCKER-docker} container ls --all --filter 'name=#{@container}' --format=json`)
 end
 
 def teardown
   if container_exists
     puts "Stopping #{@container}"
-    run_command("docker stop #{@container}", silent: false, print_command: true)
-    run_command("docker rm #{@container}", silent: false, print_command: true)
+    run_command("${DOCKER-docker} stop #{@container}", silent: false, print_command: true)
+    run_command("${DOCKER-docker} rm #{@container}", silent: false, print_command: true)
   end
 end
 
 def start_container(ezbake_dir)
-  run_command("docker run -d --name #{@container} -v .:/code -v #{ezbake_dir}:/deps #{@image} /bin/sh -c 'tail -f /dev/null'", silent: false, print_command: true)
+  run_command("${DOCKER-docker} run -d --name #{@container} -v .:/code -v #{ezbake_dir}:/deps #{@image} /bin/sh -c 'tail -f /dev/null'", silent: false, print_command: true)
 end
 
 def run(cmd)
-  run_command("docker exec #{@container} /bin/bash --login -c '#{cmd}'", silent: false, print_command: true)
+  run_command("${DOCKER-docker} exec #{@container} /bin/bash --login -c '#{cmd}'", silent: false, print_command: true)
 end
 
 namespace :vox do
@@ -89,7 +104,7 @@ namespace :vox do
       # delete all containers and do `docker rmi ezbake-builder`
       unless image_exists
         puts "Building ezbake-builder image"
-        run_command("docker build -t ezbake-builder .", silent: false, print_command: true)
+        run_command("${DOCKER-docker} build -t ezbake-builder .", silent: false, print_command: true)
       end
 
       libs_to_build_manually = {}