Send platform as a query parameter on container create

lib/docker/container.rb

@@ -324,10 +324,15 @@ def store_file(path, file_content)
     archive_in_stream("/", overwrite: true) { output_io.read }
   end
 
+  # Keys that /containers/create takes as query parameters rather than in the
+  # request body. The daemon silently ignores them if they are sent in the
+  # body, so a misplaced key means the option has no effect at all.
+  CREATE_QUERY_KEYS = %w[name platform].freeze
+
   # Create a new Container.
   def self.create(opts = {}, conn = Docker.connection)
-    query = opts.select {|key| ['name', :name].include?(key) }
-    clean_opts = opts.reject {|key| ['name', :name].include?(key) }
+    query = opts.select { |key| CREATE_QUERY_KEYS.include?(key.to_s) }
+    clean_opts = opts.reject { |key| CREATE_QUERY_KEYS.include?(key.to_s) }
     resp = conn.post('/containers/create', query, :body => MultiJson.dump(clean_opts))
     hash = Docker::Util.parse_json(resp) || {}
     new(conn, hash)

spec/docker/container_spec.rb

@@ -163,6 +163,32 @@
         expect(subject.json["Name"]).to eq("/bob")
       end
     end
+
+    context 'when a platform is given' do
+      let(:opts) { {"platform" => "linux/amd64"} }
+
+      # /containers/create takes platform as a query parameter. A "platform"
+      # body key is accepted and silently ignored by the daemon, so sending it
+      # in the body means the requested platform has no effect at all.
+      it 'sends the platform as a query parameter' do
+        expect(Docker.connection).to receive(:post).with(
+          '/containers/create',
+          hash_including('platform' => 'linux/amd64'),
+          anything
+        ).and_return('{"Id":"deadbeef"}')
+
+        subject
+      end
+
+      it 'does not send the platform in the body' do
+        expect(Docker.connection).to receive(:post) { |_path, _query, opts|
+          expect(MultiJson.load(opts[:body])).to_not have_key('platform')
+          '{"Id":"deadbeef"}'
+        }
+
+        subject
+      end
+    end
   end
 
   describe '#rename' do