Action Controller Live
Mix this module into your controller, and all actions in that controller will be able to stream data to the client as it’s written.
class MyController < ActionController::Base
include ActionController::Live
def stream
response.headers['Content-Type'] = 'text/event-stream'
100.times {
response.stream.write "hello world\n"
sleep 1
}
ensure
response.stream.close
end
end
There are a few caveats with this module. You cannot write headers after the response has been committed (Response#committed? will return truthy). Calling write
or close
on the response stream will cause the response object to be committed. Make sure all headers are set before calling write or close on your stream.
You must call close on your stream when you’re finished, otherwise the socket may be left open forever.
The final caveat is that your actions are executed in a separate thread than the main thread. Make sure your actions are thread safe, and this shouldn’t be a problem (don’t share state across threads, etc).
Note that Rails
includes Rack::ETag
by default, which will buffer your response. As a result, streaming responses may not work properly with Rack 2.2.x, and you may need to implement workarounds in your application. You can either set the ETag
or Last-Modified
response headers or remove Rack::ETag
from the middleware stack to address this issue.
Here’s an example of how you can set the Last-Modified
header if your Rack version is 2.2.x:
def stream
response.headers["Content-Type"] = "text/event-stream"
response.headers["Last-Modified"] = Time.now.httpdate # Add this line if your Rack version is 2.2.x
...
end
- MODULE ActionController::Live::ClassMethods
- CLASS ActionController::Live::ClientDisconnected
- CLASS ActionController::Live::SSE
Class Public methods
live_thread_pool_executor() Link
Instance Public methods
process(name) Link
# File actionpack/lib/action_controller/metal/live.rb, line 276 def process(name) t1 = Thread.current locals = t1.keys.map { |key| [key, t1[key]] } error = nil # This processes the action in a child thread. It lets us return the response # code and headers back up the Rack stack, and still process the body in # parallel with sending data to the client. new_controller_thread { ActiveSupport::Dependencies.interlock.running do t2 = Thread.current # Since we're processing the view in a different thread, copy the thread locals # from the main thread to the child thread. :'( locals.each { |k, v| t2[k] = v } ActiveSupport::IsolatedExecutionState.share_with(t1) begin super(name) rescue => e if @_response.committed? begin @_response.stream.write(ActionView::Base.streaming_completion_on_exception) if request.format == :html @_response.stream.call_on_error rescue => exception log_error(exception) ensure log_error(e) @_response.stream.close end else error = e end ensure # Ensure we clean up any thread locals we copied so that the thread can reused. ActiveSupport::IsolatedExecutionState.clear locals.each { |k, _| t2[k] = nil } @_response.commit! end end } ActiveSupport::Dependencies.interlock.permit_concurrent_loads do @_response.await_commit end raise error if error end
response_body=(body) Link
send_stream(filename:, disposition: "attachment", type: nil) Link
Sends a stream to the browser, which is helpful when you’re generating exports or other running data where you don’t want the entire file buffered in memory first. Similar to send_data, but where the data is generated live.
Options: * :filename
- suggests a filename for the browser to use. * :type
- specifies an HTTP content type. You can specify either a string or a symbol for a registered type with Mime::Type.register
, for example :json. If omitted, type will be inferred from the file extension specified in :filename
. If no content type is registered for the extension, the default type ‘application/octet-stream’ will be used. * :disposition
- specifies whether the file will be shown inline or downloaded. Valid values are ‘inline’ and ‘attachment’ (default).
Example of generating a csv export:
send_stream(filename: "subscribers.csv") do |stream|
stream.write "email_address,updated_at\n"
@subscribers.find_each do |subscriber|
stream.write "#{subscriber.email_address},#{subscriber.updated_at}\n"
end
end
# File actionpack/lib/action_controller/metal/live.rb, line 355 def send_stream(filename:, disposition: "attachment", type: nil) 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) yield response.stream end ensure response.stream.close end