Add Server#base_url and make Session#server_url part of the public API

lib/capybara/server.rb

@@ -86,6 +86,10 @@ def boot
       self
     end
 
+    def base_url
+      "http#{'s' if using_ssl?}://#{host}:#{port}"
+    end
+
   private
 
     def middleware

lib/capybara/session.rb

@@ -806,6 +806,10 @@ def config
       end
     end
 
+    def server_url
+      @server&.base_url
+    end
+
   private
 
     @@instance_created = false # rubocop:disable Style/ClassVars
@@ -863,10 +867,6 @@ def element_script_result(arg)
       end
     end
 
-    def server_url
-      "http#{'s' if @server.using_ssl?}://#{@server.host}:#{@server.port}" if @server
-    end
-
     def adjust_server_port(uri)
       uri.port ||= @server.port if @server && config.always_include_port
     end

spec/server_spec.rb

@@ -74,6 +74,13 @@
     end
   end
 
+  it 'should return its #base_url' do
+    app = proc { |_env| [200, {}, ['Hello Server!']] }
+    server = Capybara::Server.new(app).boot
+    uri = ::Addressable::URI.parse(server.base_url)
+    expect(uri.to_hash).to include(scheme: 'http', host: server.host, port: server.port)
+  end
+
   it 'should support SSL' do
     begin
       key = File.join(Dir.pwd, 'spec', 'fixtures', 'key.pem')
@@ -93,6 +100,8 @@
       end
 
       expect(res.body).to include('Hello SSL Server!')
+      uri = ::Addressable::URI.parse(server.base_url)
+      expect(uri.to_hash).to include(scheme: 'https', host: server.host, port: server.port)
     ensure
       Capybara.server = :default
     end