Add instrumentation for ActionController::Live#send_stream

Allows subscribing to `send_stream` events.
The event payload contains the filename, disposition, and type.

Author: hannahramadan

actionpack/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Add instrumentation for ActionController::Live#send_stream
+
+    Allows subscribing to `send_stream` events. The event payload contains the filename, disposition, and type.
+
+    *Hannah Ramadan*
+
 *   Add support for `with_routing` test helper in `ActionDispatch::IntegrationTest`
 
     *Gannon McGibbon*

actionpack/lib/action_controller/metal/live.rb

@@ -343,15 +343,18 @@ def response_body=(body)
     #      end
     #    end
     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("."))&.to_s ||
-        "application/octet-stream"
+      payload = { filename: filename, disposition: disposition, type: type }
+      ActiveSupport::Notifications.instrument("send_stream.action_controller", payload) do
+        response.headers["Content-Type"] =
+          (type.is_a?(Symbol) ? Mime[type].to_s : type) ||
+          Mime::Type.lookup_by_extension(File.extname(filename).downcase.delete("."))&.to_s ||
+          "application/octet-stream"
 
-      response.headers["Content-Disposition"] =
-        ActionDispatch::Http::ContentDisposition.format(disposition: disposition, filename: filename)
+        response.headers["Content-Disposition"] =
+          ActionDispatch::Http::ContentDisposition.format(disposition: disposition, filename: filename)
 
-      yield response.stream
+        yield response.stream
+      end
     ensure
       response.stream.close
     end

actionpack/test/controller/live_stream_test.rb

@@ -373,6 +373,19 @@ def test_send_stream
       assert_match "my.csv", @response.headers["Content-Disposition"]
     end
 
+    def test_send_stream_instrumentation
+      payload = nil
+      subscriber = proc { |event| payload = event.payload }
+
+      ActiveSupport::Notifications.subscribed(subscriber, "send_stream.action_controller") do
+        get :send_stream_with_explicit_content_type
+      end
+
+      assert_equal "sample.csv", payload[:filename]
+      assert_equal "attachment", payload[:disposition]
+      assert_equal "text/csv", payload[:type]
+    end
+
     def test_send_stream_with_options
       get :send_stream_with_options
       assert_equal %[{ name: "David", age: 41 }], @response.body

guides/source/active_support_instrumentation.md

@@ -196,6 +196,22 @@ Additional keys may be added by the caller.
 | `:keys`       | The unpermitted keys                                                          |
 | `:context`    | Hash with the following keys: `:controller`, `:action`, `:params`, `:request` |
 
+#### `send_stream.action_controller`
+
+| Key            | Value                                    |
+| -------------- | ---------------------------------------- |
+| `:filename`    | The filename                             |
+| `:type`        | HTTP content type                        |
+| `:disposition` | HTTP content disposition                 |
+
+```ruby
+{
+  filename: "subscribers.csv",
+  type: "text/csv",
+  disposition: "attachment"
+}
+```
+
 ### Action Controller — Caching
 
 #### `write_fragment.action_controller`