Fix content-type header with send_stream

actionpack/lib/action_controller/metal/live.rb

@@ -321,7 +321,7 @@ def response_body=(body)
     def send_stream(filename:, disposition: "attachment", type: nil)
       response.headers["Content-Type"] =
         (type.is_a?(Symbol) ? Mime[type].to_s : type) ||
-        Mime::Type.lookup_by_extension(File.extname(filename).downcase.delete(".")) ||
+        Mime::Type.lookup_by_extension(File.extname(filename).downcase.delete("."))&.to_s ||
         "application/octet-stream"
 
       response.headers["Content-Disposition"] =

actionpack/test/controller/live_stream_test.rb

@@ -168,6 +168,27 @@ def send_stream_with_options
         end
       end
 
+      def send_stream_with_inferred_content_type
+        send_stream(filename: "sample.csv") do |stream|
+          stream.writeln "fruit,quantity"
+          stream.writeln "apple,5"
+        end
+      end
+
+      def send_stream_with_implicit_content_type
+        send_stream(filename: "sample.csv", type: :csv) do |stream|
+          stream.writeln "fruit,quantity"
+          stream.writeln "apple,5"
+        end
+      end
+
+      def send_stream_with_explicit_content_type
+        send_stream(filename: "sample.csv", type: "text/csv") do |stream|
+          stream.writeln "fruit,quantity"
+          stream.writeln "apple,5"
+        end
+      end
+
       def blocking_stream
         response.headers["Content-Type"] = "text/event-stream"
         %w{ hello world }.each do |word|
@@ -360,6 +381,36 @@ def test_send_stream_with_options
       assert_match "export", @response.headers["Content-Disposition"]
     end
 
+    def test_send_stream_with_explicit_content_type
+      get :send_stream_with_explicit_content_type
+
+      assert_equal "fruit,quantity\napple,5\n", @response.body
+
+      content_type = @response.headers.fetch("Content-Type")
+      assert_equal String, content_type.class
+      assert_equal "text/csv", content_type
+    end
+
+    def test_send_stream_with_implicit_content_type
+      get :send_stream_with_implicit_content_type
+
+      assert_equal "fruit,quantity\napple,5\n", @response.body
+
+      content_type = @response.headers.fetch("Content-Type")
+      assert_equal String, content_type.class
+      assert_equal "text/csv", content_type
+    end
+
+    def test_send_stream_with_inferred_content_type
+      get :send_stream_with_inferred_content_type
+
+      assert_equal "fruit,quantity\napple,5\n", @response.body
+
+      content_type = @response.headers.fetch("Content-Type")
+      assert_equal String, content_type.class
+      assert_equal "text/csv", content_type
+    end
+
     def test_delayed_autoload_after_write_within_interlock_hook
       # Simulate InterlockHook
       ActiveSupport::Dependencies.interlock.start_running