added first draft of proxy plugin: connection gets extended; proxy creates a proxy channel, which initializes with a separate parser and an initial connect request; it's still failing, though

lib/httpx/plugins/proxy.rb

@@ -0,0 +1,87 @@
+# frozen_string_literal: true
+
+require "forwardable"
+
+module HTTPX
+  module Plugins
+    module Proxy
+      module ConnectionMethods
+        private
+
+        def build_channel(uri)
+          return super unless @options.proxy
+          parameters = Parameters.new(**@options.proxy)
+          io = TCP.new(parameters.uri, @options)
+          channel = ProxyChannel.new(io, @options) do |request, response|
+            @responses[request] = response
+          end 
+          connect_request = Request.new(:connect, uri)
+          if parameters.authenticated?
+            connect_request.headers["proxy-authentication"] = parameters.token_authentication
+          end
+          channel.send(connect_request)
+          register_channel(channel)
+          channel 
+        end
+      end
+
+      module InstanceMethods
+        def initialize(*)
+          super
+          @connection.extend(ConnectionMethods)
+        end
+
+        def with_proxy(*args)
+          branch(default_options.with_proxy(*args))
+        end
+      end
+    end
+    register_plugin :proxy, Proxy
+  end
+
+  class ProxyChannel < Channel
+    def initialize(*)
+      super
+      @connected = false
+    end
+
+    private
+
+    def parser
+      return super if @connected
+      @parser || begin
+      @parser = HTTP1.new(@write_buffer, @options.merge(max_concurrent_requests: 1))
+        @parser.once(:response, &method(:on_connect))
+        @parser.on(:close) { throw(:close, self) }
+        @parser
+      end
+    end
+
+    def on_connect(request, response)
+      if response.status == 200
+        @connected = true
+        @parser.close
+        @parser = nil 
+      else
+        pending = @parser.instance_variable_get(:@pending)
+        while req = pending.shift
+          @on_response.call(req, response)
+        end
+      end
+    end
+  end
+
+  class Parameters
+    attr_reader :uri
+
+    def initialize(proxy_uri: , username: nil, password: nil)
+      @uri = proxy_uri.is_a?(URI::Generic) ? proxy_uri : URI(proxy_uri)
+      @username = username
+      @password = password
+    end
+
+    def authenticated?
+      false
+    end
+  end
+end