feat(‎google-apis-core): allow setting the faraday adapter to use

google-apis-core/OVERVIEW.md

@@ -22,6 +22,14 @@ should pin `google-apis-core` to a 0.x version in your Gemfile. For example:
 
     gem "google-apis-core", "~> 0.18"
 
+The `faraday` integration ships with, and only tests against the default adapter, which wraps [net-http](https://github.com/ruby/net-http). You can change the adapter by setting the `:adapter` client option:
+
+```ruby
+Google::Apis::ClientOptions.default.adapter = :net_http_persistent # or :httpx, or...
+```
+
+There a **caveat** though: downloading media requires a `faraday` adapter which [implements the `on_data` streaming API](https://lostisland.github.io/faraday/#/advanced/streaming-responses?id=streaming-responses).
+
 ## Documentation
 
 More detailed descriptions of the Google legacy REST clients are available in two documents.

google-apis-core/lib/google/apis/core/base_service.rb

@@ -567,6 +567,7 @@ def new_client
           Faraday.new options do |faraday|
             faraday.response :logger, Google::Apis.logger if client_options.log_http_requests
             faraday.response :follow_redirects_google_apis_core, limit: 5
+            faraday.adapter client_options.adapter if client_options.adapter
           end
         end
 

google-apis-core/lib/google/apis/options.rb

@@ -23,7 +23,8 @@ module Apis
       :read_timeout_sec,
       :send_timeout_sec,
       :log_http_requests,
-      :transparent_gzip_decompression)
+      :transparent_gzip_decompression,
+      :adapter)
 
     RequestOptions = Struct.new(
       :authorization,
@@ -50,6 +51,8 @@ class ClientOptions
       #   @return [String] Name of the application, for identification in the User-Agent header
       # @!attribute [rw] application_version
       #   @return [String] Version of the application, for identification in the User-Agent header
+      # @!attribute [rw] adapter
+      #   @return [Symbol, Class] Faraday adapter to use (https://lostisland.github.io/faraday/#/adapters/index?id=adapters)
       # @!attribute [rw] proxy_url
       #   @return [String] URL of a proxy server
       # @!attribute [rw] log_http_requests
@@ -82,7 +85,7 @@ class RequestOptions
       # @!attribute [rw] max_interval
       #   @return [Integer] The maximum interval in seconds that any individual retry can reach.
       # @!attribute [rw] multiplier
-      #   @return [Numeric] Each successive interval grows by this factor. A multipler of 1.5 means the next interval 
+      #   @return [Numeric] Each successive interval grows by this factor. A multipler of 1.5 means the next interval
       #              will be 1.5x the current interval.
       # @!attribute [rw] header
       #   @return [Hash<String,String>] Additional HTTP headers to include in requests.

google-apis-core/spec/google/apis/core/service_spec.rb

@@ -114,6 +114,18 @@
     end
   end
 
+  context 'with adapter' do
+    after(:example) do
+      Google::Apis::ClientOptions.default.adapter = nil
+    end
+
+    it 'should allow switching the adapter' do
+      Google::Apis::ClientOptions.default.adapter = Faraday::Adapter::Test
+      expect(service.client).to be_a(Faraday::Connection)
+      expect(service.client.builder.adapter).to eq(Faraday::Adapter::Test)
+    end
+  end
+
   context 'when making simple commands' do
     let(:command) { service.send(:make_simple_command, :get, 'zoo/animals', authorization: 'foo') }