fixed: session hangs when HTTP/2 receives a 421

While adding a test, a bug was found, where an HTTP/2 connection
receiving a 421 response wasn't redirecting the request well to an
HTTP/1.1 one. This has been fixed by changing the way a new connection
is instantiated.

lib/httpx/connection.rb

@@ -120,8 +120,8 @@ module HTTPX
       end
     end
 
-    def create_idle
-      self.class.new(@type, @origin, @options)
+    def create_idle(options = {})
+      self.class.new(@type, @origin, @options.merge(options))
     end
 
     def merge(connection)
@@ -131,17 +131,6 @@ module HTTPX
       end
     end
 
-    def unmerge(connection)
-      @origins -= connection.instance_variable_get(:@origins)
-      purge_pending do |request|
-        request.uri.origin == connection.origin && begin
-          request.transition(:idle)
-          connection.send(request)
-          true
-        end
-      end
-    end
-
     def purge_pending(&block)
       pendings = []
       if @parser
@@ -399,7 +388,7 @@ module HTTPX
       parser.on(:error) do |request, ex|
         case ex
         when MisdirectedRequestError
-          emit(:uncoalesce, request.uri)
+          emit(:misdirected, request)
         else
           response = ErrorResponse.new(request, ex, @options)
           request.emit(:response, response)

lib/httpx/session.rb

@@ -77,10 +77,16 @@ module HTTPX
     end
 
     def set_connection_callbacks(connection, connections, options)
-      connection.on(:uncoalesce) do |uncoalesced_uri|
-        other_connection = build_connection(uncoalesced_uri, options)
+      connection.on(:misdirected) do |misdirected_request|
+        other_connection = connection.create_idle(ssl: { alpn_protocols: %w[http/1.1] })
+        other_connection.merge(connection)
+        catch(:coalesced) do
+          pool.init_connection(other_connection, options)
+        end
+        set_connection_callbacks(other_connection, connections, options)
         connections << other_connection
-        connection.unmerge(other_connection)
+        misdirected_request.transition(:idle)
+        other_connection.send(misdirected_request)
       end
       connection.on(:altsvc) do |alt_origin, origin, alt_params|
         other_connection = build_altsvc_connection(connection, connections, alt_origin, origin, alt_params, options)

test/https_test.rb

@@ -85,6 +85,17 @@ class HTTPSTest < Minitest::Test
     end
   end
 
+  def test_http2_uncoalesce_on_misdirected
+    uri = build_uri("/status/421")
+    HTTPX.plugin(SessionWithPool).wrap do |http|
+      response = http.get(uri)
+      verify_status(response, 421)
+      connection_count = http.pool.connection_count
+      assert connection_count == 2, "expected to have 2 connections, instead have #{connection_count}"
+      assert response.version == "1.1", "request should have been retried with HTTP/1.1"
+    end
+  end
+
   private
 
   def origin(orig = httpbin)