Implement H2 Early Hints for Rails #30744

eileencodes · 2017-09-28T18:50:53Z

When puma/puma#1403 is merged Puma will support the Early Hints status
code for sending assets before a request has finished.

While the Early Hints spec is still in draft, this PR prepares Rails to
allowing this status code.

If the proxy server supports Early Hints, it will send H2 pushes to the
client.

This PR adds a method for setting Early Hints Link headers via Rails,
and also automatically sends Early Hints if supported from the
stylesheet_link_tag and the javascript_include_tag.

Once puma supports Early Hints the --early-hints argument can be
passed to the server to enable this. Note that for Early Hints to work
in the browser the requirements are 1) a proxy that can handle H2,
and 2) HTTPS.

To start the server with Early Hints enabled pass --early-hints to rails s.

This has been verified to work with h2o, Puma, and Rails with Chrome.

The commit adds a new option to the rails server to enable early hints
for Puma.

Early Hints spec:
https://tools.ietf.org/html/draft-ietf-httpbis-early-hints-04

cc/ @tenderlove who I worked with on this feature

In the screenshot below you can see the pushes from early hints.

kaspth

iirc, sprockets-rails overrides these helpers, but that won't make it so that the early hints will be removed, right?

Looking great otherwise!

kaspth · 2017-09-28T19:25:25Z

actionpack/lib/action_dispatch/http/request.rb

@@ -199,6 +199,23 @@ def headers
      @headers ||= Http::Headers.new(self)
    end

+    # Early Hints is an H2 status code that indicates hints to help a client start


Is H2 an accepted short hand for HTTP2? Otherwise we should probably stick to HTTP2 through out.

While it is an accepted shorthand I've replaced this with HTTP/2 because documentation should not assume knowledge of that.

kaspth · 2017-09-28T19:26:10Z

actionpack/lib/action_dispatch/http/request.rb

+    #
+    # The +send_early_hints+ method accepts an array of links as follows:
+    #
+    #   send_early_hints({ link: "path/to/stylesheet.css", as: "stylesheet}, { link: "path/to/javascript.js", as: "script"})


Missing a closing quote on as: "stylesheet. Should add a space before the two } as well.

kaspth · 2017-09-28T19:27:01Z

actionpack/test/dispatch/request_test.rb

+    assert_equal early_hints.first[:link], "a_path.css"
+    assert_equal early_hints.first[:as], "stylesheet"
+    assert_equal early_hints.last[:link], "a_path.js"
+    assert_equal early_hints.last[:as], "script"


The argument order here should be reversed. It's expected, then actual.

Fixed when the API was updated.

kaspth · 2017-09-28T19:27:14Z

actionview/lib/action_view/helpers/asset_tag_helper.rb

@@ -37,6 +37,9 @@ module AssetTagHelper
      # When the Asset Pipeline is enabled, you can pass the name of your manifest as
      # source, and include other JavaScript or CoffeeScript files inside the manifest.
      #
+      # If the server supports Early Hints header links for these assets  will be


Double space after assets.

kaspth · 2017-09-28T19:29:32Z

actionview/lib/action_view/helpers/asset_tag_helper.rb

          }.merge!(options)
          content_tag("script".freeze, "", tag_options)
        }.join("\n").html_safe
+
+        request.send_early_hints(early_hints_links)


This reads to me as if users can only call javascript_include_tag once, is that right?

It's possible people have calls in their application layout and then in individual template files (I'm not saying that's a good idea, but I think that does exist).

I wrote it this way so that if you pass multiple sources into javascript_include_tag that it will only send early hints once, but you can call javascript_include_tag as many times as you want and it will send early hints.

kaspth · 2017-09-28T19:34:36Z

actionview/lib/action_view/helpers/asset_tag_helper.rb

          tag_options = {
-            "src" => path_to_javascript(source, path_options)
+            "src" => href
          }.merge!(options)
          content_tag("script".freeze, "", tag_options)


Would it make sense to change this to tag.script(src: href, **options) while we're here? (Though that would probably necessitate shifting to symbolize_keys above).

Is that desirable in general in internal stuff? The improvement for user code is nice, but it feels like fairly pointless (and comparatively allocation-heavy) indirection for us.

Right, it's a bit of a back and forth. I was focusing on removing the freeze call. Let's defer to some other time, since it's out of scope for this particular thing 👍

grosser · 2017-09-28T23:15:29Z

actionpack/lib/action_dispatch/http/request.rb

+    def send_early_hints(links)
+      return unless env["rack.early_hints"]
+
+      env["rack.early_hints"].call(links)


could avoid calling doing the same lookup twice:

env["rack.early_hints"]&.call(links)

or

callback = env["rack.early_hints"] callback.call(links) if callback

It's a hash lookup. I'm sure it'll be fine.

I've considered this but agree with @matthewd.

Drying things up isn't a benefit if the code is harder to read and understand and the performance impact of calling a hash lookup twice will be negligible.

I was just curious about the performance impact, so I did a quick benchmarking.

TL;DR

... the performance impact of calling a hash lookup twice will be negligible.

Details

# 1.18x slower than v2 if env["rack.early_hints"] def v1 return unless env["rack.early_hints"] env["rack.early_hints"].call(links) end # 1.09x slower than v1 IF NOT env["rack.early_hints"] def v2 callback = env["rack.early_hints"] callback.call(links) if callback end

Click to show code

#!/usr/bin/env ruby require 'benchmark/ips' require 'date' LOOKUP = { "foo" => ->() {} } def happy_case return unless LOOKUP["foo"] LOOKUP["foo"].call() end def happy_case_with_assignment callback = LOOKUP["foo"] callback.call() if callback end def alternase_case return unless LOOKUP["bar"] LOOKUP["bar"].call() end def alternase_case_with_assignment callback = LOOKUP["bar"] callback.call() if callback end # == Result # # happy_case: 1.18x slower Benchmark.ips do |x| # Configure the number of seconds used during # the warmup phase (default 2) and calculation phase (default 5) x.config(time: 5, warmup: 2) x.report("happy_case") { happy_case } x.report("happy_case_with_assignment") { happy_case_with_assignment } # Compare the iterations per second of the various reports! x.compare! end # == Result # # alternase_case_with_assignment: 1.09x slower Benchmark.ips do |x| # Configure the number of seconds used during # the warmup phase (default 2) and calculation phase (default 5) x.config(time: 5, warmup: 2) x.report("alternase_case") { alternase_case } x.report("alternase_case_with_assignment") { alternase_case_with_assignment } # Compare the iterations per second of the various reports! x.compare! end __END__ Calculating ------------------------------------- happy_case 111.305k i/100ms happy_case_with_assignment 127.680k i/100ms ------------------------------------------------- happy_case 3.704M (± 2.1%) i/s - 18.588M happy_case_with_assignment 4.353M (± 1.2%) i/s - 21.833M Comparison: happy_case_with_assignment: 4353466.9 i/s happy_case: 3704451.9 i/s - 1.18x slower Calculating ------------------------------------- alternase_case 146.388k i/100ms alternase_case_with_assignment 154.871k i/100ms ------------------------------------------------- alternase_case 7.631M (± 2.9%) i/s - 38.207M alternase_case_with_assignment 6.977M (± 6.8%) i/s - 34.846M Comparison: alternase_case: 7630584.3 i/s alternase_case_with_assignment: 6977239.4 i/s - 1.09x slower

interesting, would have been nice to see how the &. syntax compares.

grosser · 2017-09-28T23:16:36Z

railties/lib/rails/commands/server/server_command.rb

@@ -161,7 +162,8 @@ def server_options
            daemonize:             options[:daemon],
            pid:                   pid,
            caching:               options["dev-caching"],
-            restart_cmd:           restart_command
+            restart_cmd:           restart_command,
+            early_hints:           early_hints


use it directly like dev-caching / daemon ?

I put the documentation in the early hints option. It's passed in like --early-hints or can be set in the puma.config with early_hints(true).

grosser · 2017-09-29T14:27:30Z

just a bad pattern in general and not dry ... so prefer to avoid even if it's fine here

…

On Fri, Sep 29, 2017 at 12:24 AM, Matthew Draper ***@***.***> wrote: ***@***.**** commented on this pull request. ------------------------------ In actionpack/lib/action_dispatch/http/request.rb <#30744 (comment)>: > @@ -199,6 +199,23 @@ def headers @headers ||= Http::Headers.new(self) end + # Early Hints is an H2 status code that indicates hints to help a client start + # making preparations for processing the final response. + # + # If the env contains +rack.early_hints+ then the server accepts HTTP2 push for Link headers. + # + # The +send_early_hints+ method accepts an array of links as follows: + # + # send_early_hints({ link: "path/to/stylesheet.css", as: "stylesheet}, { link: "path/to/javascript.js", as: "script"}) + # + # If you are using +javascript_include_tag+ or +stylesheet_link_tag+ the + # Early Hints headers are included by default if supported. + def send_early_hints(links) + return unless env["rack.early_hints"] + + env["rack.early_hints"].call(links) It's a hash lookup. I'm sure it'll be fine. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#30744 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAAsZ0RzsToBpMY-tEMsTZq-csqYRJ5Vks5snJsxgaJpZM4PnuP3> .

eileencodes · 2017-10-03T18:25:40Z

@kaspth I've fixed the typos and other recommendations you made. Thanks for the review!

FYI, this is on hold until the Puma branch is merged.

When puma/puma#1403 is merged Puma will support the Early Hints status code for sending assets before a request has finished. While the Early Hints spec is still in draft, this PR prepares Rails to allowing this status code. If the proxy server supports Early Hints, it will send H2 pushes to the client. This PR adds a method for setting Early Hints Link headers via Rails, and also automatically sends Early Hints if supported from the `stylesheet_link_tag` and the `javascript_include_tag`. Once puma supports Early Hints the `--early-hints` argument can be passed to the server to enable this or set in the puma config with `early_hints(true)`. Note that for Early Hints to work in the browser the requirements are 1) a proxy that can handle H2, and 2) HTTPS. To start the server with Early Hints enabled pass `--early-hints` to `rails s`. This has been verified to work with h2o, Puma, and Rails with Chrome. The commit adds a new option to the rails server to enable early hints for Puma. Early Hints spec: https://tools.ietf.org/html/draft-ietf-httpbis-early-hints-04 [Eileen M. Uchitelle, Aaron Patterson]

madmax · 2017-10-08T18:34:15Z

@eileencodes What about javascript_pack_tag? It will also work with it?

eileencodes · 2017-10-09T11:58:55Z

@madmax Is that implemented by webpacker? I haven't used Rails webpacker and I don't see a javascript_pack_tag in Rails.

madmax · 2017-10-09T15:53:44Z

Yes it is part of webpacker gem. And there is also manifest.json can't we use it?

eileencodes · 2017-10-09T15:56:23Z

At this moment I don't plan on implementing in webpacker but I don't see a reason to not implement it there if the tag has access to the request object and someone wants to work on that.

guilleiguaran · 2017-10-09T16:03:26Z

IIRC javascript_pack_tag just calls Rails' default javascript_include_tag underneath.

eileencodes · 2017-10-09T16:04:41Z

Ok then I think it will Just Work™️ 😄

printercu · 2017-10-10T10:47:38Z

According to code, links for early hints are formatted even when server does not support early hints. Should this be better enabled with early_hints: true option?

Also this should be a better option to provide method to send hints from controller, this way browser can start loading scripts even before server starts business logic and page rendering. Layout rendering is the last stage (except streaming mode) of request processing, hints can be even earlier (in before_action?).

WDYT?

mengqing · 2018-01-31T05:09:19Z

actionview/lib/action_view/helpers/asset_tag_helper.rb

+
+        sources_tags = sources.uniq.map { |source|
+          href = path_to_stylesheet(source, path_options)
+          early_hints_links << "<#{href}>; rel=preload; as=stylesheet"


According to the example described in https://w3c.github.io/preload/#as-attribute, it seems that the as target attribute for stylesheets should be style instead of stylesheet

leastbad · 2018-08-16T22:15:58Z

Hey @eileencodes! Thanks so much for your work getting early hints supported in Rails.

I'm seeing some intermittent socket timeout errors when I have --early-hints enabled on my app, which is hosted on Heroku. It's only showing up about once a day, and only in production.

Some lucky visitor's request is throwing one Puma:ConnectionError for each javascript_include_tag in my application layout. If one call fails, they all fail in proper sequence. I've never experienced the end-result personally, leading me to guess that the visitor probably won't notice as their script tags would just load normally.

Any hunches?

Aug 16 12:34:37 /app/vendor/bundle/ruby/2.4.0/gems/puma-3.11.4/lib/puma/server.rb:972:in 'rescue in fast_write' 
Aug 16 12:34:37 /app/vendor/bundle/ruby/2.4.0/gems/puma-3.11.4/lib/puma/server.rb:963:in 'fast_write' 
Aug 16 12:34:37 /app/vendor/bundle/ruby/2.4.0/gems/puma-3.11.4/lib/puma/server.rb:609:in 'block in handle_request' 
Aug 16 12:34:37 /app/vendor/bundle/ruby/2.4.0/gems/actionpack-5.2.0/lib/action_dispatch/http/request.rb:217:in 'send_early_hints' 
Aug 16 12:34:37 /app/vendor/bundle/ruby/2.4.0/gems/actionview-5.2.0/lib/action_view/helpers/asset_tag_helper.rb:96:in 'javascript_include_tag' 
Aug 16 12:34:37 /app/vendor/bundle/ruby/2.4.0/gems/sprockets-rails-3.2.1/lib/sprockets/rails/helper.rb:156:in 'block in javascript_include_tag' 
Aug 16 12:34:37 /app/vendor/bundle/ruby/2.4.0/gems/sprockets-rails-3.2.1/lib/sprockets/rails/helper.rb:154:in 'map' 
Aug 16 12:34:37 /app/vendor/bundle/ruby/2.4.0/gems/sprockets-rails-3.2.1/lib/sprockets/rails/helper.rb:154:in 'javascript_include_tag' 
Aug 16 12:34:37 /app/app/views/layouts/application.html.erb:97:in 'block in _app_views_layouts_application_html_erb__4118899528439397404_70152019751760' 
Aug 16 12:34:37 /app/app/views/layouts/application.html.erb:95:in 'each' 
Aug 16 12:34:37 /app/app/views/layouts/application.html.erb:95:in '_app_views_layouts_application_html_erb__4118899528439397404_70152019751760'```

eileencodes · 2018-08-25T23:37:06Z

Hey @pjforde1978 I'm not sure what's going on but I suspect that this is more on the puma side than the Rails side since Rails just adds the tags, but Puma makes the early hints actually work. Can you open an issue over there including what your application is using (Ruby version, Rails version, Puma version, proxy you're using), and anything else that can help us track this down. Unfortunately we're not able to use this in prod at GitHub yet so I'm not sure where to start looking.

Jesus · 2019-06-18T22:01:27Z

Message for Eileen:

Hi @eileencodes, thanks for adding this fantastic feature.

I've been investigating the error reported by @pjforde1978. This happens if the connection is lost before we're able to send any response headers. Rails will try to write the early hints on a socket which no longer exists so it'll fail. This happens very rarely and probably no end-users are being affected as I'm assuming the connection is lost when the user abandons the page load.

From Rails' perspective, there's nothing we can do if the socket has been closed. I think we can ignore this error safely.

But do you think Rails should bother to abort completing this request if the early hints report a lost connection somehow?

eileencodes added the actionpack label Sep 28, 2017

eileencodes force-pushed the early-hints branch 3 times, most recently from 0528011 to 063d77b Compare September 28, 2017 19:10

eileencodes self-assigned this Sep 28, 2017

eileencodes added this to the 5.2.0 milestone Sep 28, 2017

kaspth reviewed Sep 28, 2017

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grosser reviewed Sep 28, 2017

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eileencodes force-pushed the early-hints branch from 063d77b to 9ee7c4a Compare October 3, 2017 18:23

eileencodes force-pushed the early-hints branch from 9ee7c4a to 64ce53b Compare October 4, 2017 12:35

eileencodes changed the title ~~WIP: Implement H2 Early Hints for Rails~~ Implement H2 Early Hints for Rails Oct 4, 2017

eileencodes force-pushed the early-hints branch from 64ce53b to 59a02fb Compare October 4, 2017 13:17

eileencodes merged commit bd2542b into rails:master Oct 4, 2017

eileencodes deleted the early-hints branch October 4, 2017 13:48

ghost mentioned this pull request Oct 8, 2017

Broken for Rails 5.2 alpha fphilipe/premailer-rails#199

Closed

yhirano55 mentioned this pull request Oct 13, 2017

Enable test with edge Rails rails/webpacker#944

Merged

mengqing reviewed Jan 31, 2018

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bogdanvlviv mentioned this pull request Jan 31, 2018

Fix as attribute value for preload link #31838

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PikachuEXE mentioned this pull request Mar 2, 2018

ActionController::Streaming doesn't stream #23828

Open

This was referenced Mar 20, 2018

Support H2 early hints phusion/passenger#2047

Open

H2 Early Hints cannot be used with response streaming #32329

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leastbad mentioned this pull request Aug 26, 2018

Early hints + javascript_include_tag = Puma:ConnectionError puma/puma#1640

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dgilperez mentioned this pull request Dec 11, 2018

backporting early_hints i4a/rails#1

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evanleck mentioned this pull request Feb 21, 2019

HTTP 103 Early Hints ohler55/agoo#52

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composerinteralia mentioned this pull request Oct 25, 2019

Use HTTP/2 early hints thoughtbot/suspenders#1006

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casperisfine mentioned this pull request Jul 28, 2020

Specify rack.provisional_response to send 1xx responses rack/rack#1701

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Implement H2 Early Hints for Rails #30744

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