Make preview host and port configurable in config.rb and also expose those variables to extensions which are curious. Closes #1477

middleman-core/fixtures/large-build-app/config.rb

@@ -1,3 +1,5 @@
 with_layout false do
   page "/spaces in file.html"
 end
+
+config[:port] = 5555

middleman-core/lib/middleman-core/application.rb

@@ -67,6 +67,14 @@ module Middleman
     end
     delegate :root_path, to: :"self.class"
 
+    # Which host preview should start on.
+    # @return [Fixnum]
+    config.define_setting :host, '0.0.0.0', 'The preview server host'
+
+    # Which port preview should start on.
+    # @return [Fixnum]
+    config.define_setting :port, 4567, 'The preview server port'
+
     # Name of the source directory
     # @return [String]
     config.define_setting :source,      'source', 'Name of the source directory'

middleman-core/lib/middleman-core/cli/server.rb

@@ -14,11 +14,9 @@ module Middleman::Cli
     method_option :host,
                   type: :string,
                   aliases: '-h',
-                  default: '0.0.0.0',
                   desc: 'Bind to HOST address'
     method_option :port,
                   aliases: '-p',
-                  default: '4567',
                   desc: 'The port Middleman will listen on'
     method_option :verbose,
                   type: :boolean,

middleman-core/lib/middleman-core/preview_server.rb

@@ -5,8 +5,6 @@ require 'middleman-core/logger'
 # rubocop:disable GlobalVars
 module Middleman
   module PreviewServer
-    DEFAULT_PORT = 4567
-
     class << self
       attr_reader :app, :host, :port
       delegate :logger, to: :app
@@ -15,8 +13,6 @@ module Middleman
       # @return [void]
       def start(opts={})
         @options = opts
-        @host = @options[:host] || '0.0.0.0'
-        @port = @options[:port] || DEFAULT_PORT
 
         mount_instance(new_app)
         logger.info "== The Middleman is standing watch at http://#{host}:#{port}"
@@ -92,6 +88,7 @@ module Middleman
 
       def new_app
         opts = @options.dup
+
         server = ::Middleman::Application.server
 
         # Add in the meta pages application
@@ -107,7 +104,14 @@ module Middleman
           )
 
           config[:environment] = opts[:environment].to_sym if opts[:environment]
+          config[:host] = opts[:host] if opts[:host]
+          config[:port] = opts[:port] if opts[:port]
         end
+
+        @host = @app.config[:host]
+        @port = @app.config[:port]
+
+        @app
       end
 
       def start_file_watcher