Add experimental support for HTTP/2 built on top of curb/curl/nghttp2

Author: yuki24

Gemfile

@@ -7,3 +7,4 @@ gem 'oven', '0.1.0.rc1'
 gem 'rubocop'
 gem 'pry'
 gem 'http_logger'
+gem 'curb'

README.md

@@ -68,6 +68,31 @@ payload = {
 response = client.push(payload) # => sends a message to the topic
 ```
 
+## Using HTTP/2 (Exmerimental)
+
+The current GitHub master branch ships with experimental support for HTTP/2. It takes advantage of the fantastic library, [libcurl](https://curl.haxx.se/libcurl/). In order to use it, replace `Android.new(...)` with `Android.http2(...)`:
+
+```diff
++# Do not forget to add the curb gem to your Gemfile
++require 'curb'
+
+-client = Andpush.new(server_key, pool_size: 25)
++client = Andpush.http2(server_key) # no need to specify the `pool_size' as HTTP/2 maintains a single connection
+```
+
+### Prerequisites
+
+ * [libcurl](https://curl.haxx.se/download.html) 7.43.0 or later
+ * [nghttp2](https://nghttp2.org/blog/) 1.0 or later
+
+**Make sure that your production environment has the compatible versions installed. If you are not sure what version of libcurl you are using, try running `curl --version` and make sure it has `HTTP2` listed in the Features:**
+
+![Curl version](assets/curl-version.png "Curl version")
+
+**If you wish to use the HTTP/2 client in heroku, make sure you are using [the `Heroku-18` stack](https://devcenter.heroku.com/articles/heroku-18-stack). Older stacks, such as `Heroku-16` and `Cedar-14` do not ship with a version of libcurl that has support for HTTP/2.**
+
+If you are using an older version of libcurl that doesn't support HTTP/2, don't worry. It will just fall back to HTTP 1.1 (of course without header compression and multiplexing.)
+
 ## Performance
 
 The andpush gem uses [HTTP persistent connections](https://en.wikipedia.org/wiki/HTTP_persistent_connection) to improve performance. This is done by [the net-http-persistent gem](https://github.com/drbrain/net-http-persistent). [A simple benchmark](https://gist.github.com/yuki24/e0db97e887b8b6eb1932c41b4cea4a99) shows that the andpush gem performs at least 3x faster than the fcm gem:

assets/curl-version.png

@@ -13,6 +13,22 @@ def build(server_key, domain: nil, name: nil, proxy: nil, pool_size: Net::HTTP::
         .register_interceptor(Authenticator.new(server_key))
     end
     alias new build
+
+    def http2(server_key, domain: nil)
+      begin
+        require 'curb' if !defined?(Curl)
+      rescue LoadError => error
+        raise LoadError, "Could not load the curb gem. Make sure to install the gem by running:\n\n" \
+                         "  $ gem i curb\n\n" \
+                         "Or the Gemfile has the following declaration:\n\n" \
+                         "  gem 'curb'\n\n" \
+                         "  (#{error.class}: #{error.message})"
+      end
+
+      ::Andpush::Client
+        .new(domain || DOMAIN, request_handler: Http2RequestHandler.new)
+        .register_interceptor(Authenticator.new(server_key))
+    end
   end
 
   class Authenticator
@@ -42,5 +58,47 @@ def call(request_class, uri, headers, body, *_)
     end
   end
 
-  private_constant :Authenticator, :ConnectionPool
+  class Http2RequestHandler
+    BY_HEADER_LINE   = /[\r\n]+/.freeze
+    HEADER_VALUE     = /^(\S+): (.+)/.freeze
+
+    attr_reader :multi
+
+    def initialize(max_connects: 100)
+      @multi = Curl::Multi.new
+
+      @multi.pipeline     = Curl::CURLPIPE_MULTIPLEX
+      @multi.max_connects = max_connects
+    end
+
+    def call(request_class, uri, headers, body, *_)
+      easy = Curl::Easy.new(uri.to_s)
+
+      # This ensures libcurl waits for the connection to reveal if it is
+      # possible to pipeline/multiplex on before it continues.
+      easy.setopt(Curl::CURLOPT_PIPEWAIT, 1)
+
+      easy.multi       = @multi
+      easy.version     = Curl::HTTP_2_0
+      easy.headers     = headers || {}
+      easy.post_body   = body if request_class::REQUEST_HAS_BODY
+
+      easy.public_send(:"http_#{request_class::METHOD.downcase}")
+
+      Response.new(
+        Hash[easy.header_str.split(BY_HEADER_LINE).flat_map {|s| s.scan(HEADER_VALUE) }],
+        easy.body,
+        easy.response_code.to_s, # to_s for comatibility with Net::HTTP
+        easy,
+      ).freeze
+    end
+
+    Response = Struct.new(:headers, :body, :code, :raw_response) do
+      alias to_hash headers
+    end
+
+    private_constant :BY_HEADER_LINE, :HEADER_VALUE, :Response
+  end
+
+  private_constant :Authenticator, :ConnectionPool, :Http2RequestHandler
 end

lib/andpush.rb

@@ -30,4 +30,36 @@ def test_it_makes_http_request_to_fcm
     assert_equal  0, json[:canonical_ids]
     assert_equal "fake_message_id", json[:results][0][:message_id]
   end
+
+  def test_http2_client_makes_http2_request_to_fcm
+    server_key   = ENV.fetch('FCM_TEST_SERVER_KEY')
+    device_token = ENV.fetch('FCM_TEST_REGISTRATION_TOKEN')
+
+    client = Andpush.http2(server_key)
+    json   = {
+      to: device_token,
+      dry_run: true,
+      notification: {
+        title: "Update",
+        body: "Your weekly summary is ready"
+      },
+      data: {
+        extra: "data"
+      }
+    }
+
+    response = client.push(json)
+
+    assert_equal '200', response.code
+
+    json = response.json
+
+    assert_equal(-1, json[:multicast_id])
+    assert_equal  1, json[:success]
+    assert_equal  0, json[:failure]
+    assert_equal  0, json[:canonical_ids]
+    assert_equal "fake_message_id", json[:results][0][:message_id]
+
+    assert_match "HTTP/2", response.raw_response.header_str
+  end
 end