rails4启动过程
本篇博文会从使用rails server命令到应用启动完成的代码调用顺序，介绍rails server的启动过程，是对rails guide的一个简略翻译和一些博主的认识，翻译的不好还请各位见谅。看的时候最好找一份rails4的源码一起对照的来看。
原文地址： http://guides.ruby-china.org/initialization.html
当我们使用rails c(onsole)或者rails s(erver)时会启动一个rails的应用，rails s其实相当于在当前路径下执行了一段ruby脚本：
version = ">=0"
load Gem.bin_path('railties', 'rails', version)
如果在Rails console里输入上面的命令，你会看到railties/bin/rails被执行了。
在railties/bin/rails源码的最后一行可以看到
require “rails/cli”
require了railties/lib/rails/cli，继续跟进，在railties/lib/rails/cli中：
require 'rails/app_rails_loader' # If we are inside a Rails application this method performs an exec and thus # the rest of this script is not run. Rails::AppRailsLoader.exec_app_rails
继续进入railties/lib/rails/app_rails_loader.rb
RUBY = Gem.ruby
EXECUTABLES = ['bin/rails', 'script/rails']
......
class << self
......
def exec_app_rails
original_cwd = Dir.pwd
loop do
if exe = find_executable
contents = File.read(exe)
if contents =~ /(APP|ENGINE)_PATH/
exec RUBY, exe, *ARGV
break # non reachable, hack to be able to stub exec in the test suite
elsif exe.end_with?('bin/rails') && contents.include?('This file was generated by Bundler')
$stderr.puts(BUNDLER_WARNING)
Object.const_set(:APP_PATH, File.expand_path('config/application', Dir.pwd))
require File.expand_path('../boot', APP_PATH)
require 'rails/commands'
break
end
end
# If we exhaust the search there is no executable, this could be a
# call to generate a new application, so restore the original cwd.
Dir.chdir(original_cwd) and return if Pathname.new(Dir.pwd).root?
# Otherwise keep moving upwards in search of an executable.
Dir.chdir('..')
end
end
def find_executable
EXECUTABLES.find { |exe| File.file?(exe) }
end
end
可以通过上面的代码看出Rails::AppRailsLoader.exec_app_rails会在当前目录下找bin/rails或script/rails，找到了就会执行：
exec Gem.ruby, bin/rails, *ARGV
即相当于
exec ruby bin/rails server
如果当前目录下没有bin/rails或script/rails就会一直递归向上直到找到bin(script)/rails，所以在rails项目的根目录以及子目录下的任何地方都可以使用rails server或rails console命令
bin/rails:
#!/usr/bin/env ruby
APP_PATH = File.expand_path('../../config/application', __FILE__)
require_relative '../config/boot'
require 'rails/commands'
APP_PATH常量将会在之后的rails/commands里使用，require_relative '../config/boot'是require了config/boot.rb文件，boot.rb负责加载启动Bundler
config/boot.rb
# Set up gems listed in the Gemfile.
ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../../Gemfile', __FILE__)
require 'bundler/setup' if File.exist?(ENV['BUNDLE_GEMFILE'])
在标准的的Rails应用中，Gemfile文件申明了所有应用依赖关系，ENV['BUNDLE_GEMFILE']存放Gemfile的文件地址，当Gemfile文件存在，回去require bundle/setup，用于Bundler配置加载Gemfile依赖关系的路径。
一个标准的Rails应用需要依赖几个gem包，如：
actionmailer
actionpack
actionview
activemodel
activerecord
activesupport
arel
builder
bundler
erubis
i18n
mail
mime-types
polyglot
rack
rack-cache
rack-mount
rack-test
rails
railties
rake
sqlite3
thor
treetop
tzinfo
require了config/boot.rb后回到bin/rails，最后还会require rails/commands
rails/commands.rb
主要用于扩展rails命令参数的别名：
rails/commands.rb
ARGV << '--help' if ARGV.empty?
aliases = {
"g" => "generate",
"d" => "destroy",
"c" => "console",
"s" => "server",
"db" => "dbconsole",
"r" => "runner"
}
command = ARGV.shift
command = aliases[command] || command
require 'rails/commands/commands_tasks'
Rails::CommandsTasks.new(ARGV).run_command!(command)
可以看到当不传参数时，实际上与rails --help等效，rails s等效于rails server
rails/commands/command_tasks.rb
当输入了一个错误的rails命令，run_command方法负责抛出一个错误信息。如果命令是有效的，就会调用相同名称的方法
COMMAND_WHITELIST = %(plugin generate destroy console server dbconsole application runner new version help)
def run_command!(command)
command = parse_command(command)
if COMMAND_WHITELIST.include?(command)
send(command)
else
write_error_message(command)
end
end
def write_error_message(command)
puts "Error: Command '#{command}' not recognized"
if %x{rake #{command} --dry-run 2>&1 } && $?.success?
puts "Did you mean: `$ rake #{command}` ?\n\n"
end
write_help_message
exit(1)
end
def parse_command(command)
case command
when '--version', '-v'
'version'
when '--help', '-h'
'help'
else
command
end
end
根据服务器命令，Rails会进一步运行以下代码，rails server将会调用server方法
def set_application_directory!
Dir.chdir(File.expand_path('../../', APP_PATH)) unless File.exist?(File.expand_path("config.ru"))
end
def server
set_application_directory!
require_command!("server")
Rails::Server.new.tap do |server|
# We need to require application after the server sets environment,
# otherwise the --environment option given to the server won't propagate.
require APP_PATH
Dir.chdir(Rails.application.root)
server.start
end
end
def require_command!(command)
require "rails/commands/#{command}"
end
如上代码首先如果当前目录config.ru不存在，会将目录切换到rails的根目录(APP_PATH是之前bin/rails文件中获得），之后会require "rails/commands/server"，然后创建Rails::Server的对象，调用tap方法启动server
rails/commands/server.rb
require 'fileutils' require 'optparse' require 'action_dispatch' require 'rails' module Rails class Server < ::Rack::Server ...... def initaialize(*) super set_environment end ...... def set_environment ENV["RAILS_ENV"] ||= options[:environment] end ...... end
fileutils和optparse是Ruby的标准库，提供文件炒作相关和解析元素的帮助方法。
action_dispatch，为actionpack/lib/action_dispatch.rb文件，ActionDispatch是Rails框架的路由组件，它增加了像路由，会话，一般中间件的功能。
当 Rails::Server.new实际上就是创建一个Rack::Server的实例再为ENV["RAILS_ENV"]赋值。
Rack::Server负责为全部的以Rack为基础的引用提供通用的server接口
Rack:lib/rack/server.rb
def initialize(options = nil) @options = options @app = options[:app] if options && options[:app] end
实际上，options参数是nil的，这个构造方法中什么都不会发生
再来看set_environment方法，在方法中并没有找到options这个局部变量，说明这是一个方法调用，其实他的方法定义在Rack::Server中，如下：
def options @options ||= parse_options(ARGV) end
然后parse_options是像这样定义的：
def parse_options(args)
options = default_options
# Don't evaluate CGI ISINDEX parameters.
# http://www.meb.uni-bonn.de/docs/cgi/cl.html
args.clear if ENV.include?("REQUEST_METHOD")
options.merge! opt_parser.parse!(args)
options[:config] = ::File.expand_path(options[:config])
ENV["RACK_ENV"] = options[:environment]
options
end
default_options：
def default_options
environment = ENV['RACK_ENV'] || 'development'
default_host = environment == 'development' ? 'localhost' : '0.0.0.0'
{
:environment => environment,
:pid => nil,
:Port => 9292,
:Host => default_host,
:AccessLog => [],
:config => "config.ru"
}
end
现在ENV中还没有REQUEST_METHOD键，所以先跳过args.clear，下面一行options merge了定义在Rack::Server中方法返回的对象的parse!方法的返回值
opt_parser:
def opt_parser Options.new end
Options这个类定义在Rack::Server中，但是在Rails::Server中被重写，重写后的parse!方法:
def parse!(args)
args, options = args.dup, {}
opt_parser = OptionParser.new do |opts|
opts.banner = "Usage: rails server [mongrel, thin, etc] [options]"
opts.on("-p", "--port=port", Integer,
"Runs Rails on the specified port.", "Default: 3000") { |v| options[:Port] = v }
...
这个方法将为那些Rails可以使用来确定服务应该怎么运行的参数设置好键。到这里initialize结束，我们跳到rails/server中require APP_PATH的地方
当require APP_PATH被执行，config/application.rb将会被加载。这个文件在你的与应用中用于更具你的需要只有的给变配置
Rails::Server#start
当config/application被加载后，server.start被调用，这个方法定义如下：
def start
print_boot_information
trap(:INT) { exit }
create_tmp_directories
log_to_stdout if options[:log_stdout]
super
...
end
private
def print_boot_information
...
puts "=> Run `rails server -h` for more startup options"
...
puts "=> Ctrl-C to shutdown server" unless options[:daemonize]
end
def create_tmp_directories
%w(cache pids sessions sockets).each do |dir_to_make|
FileUtils.mkdir_p(File.join(Rails.root, 'tmp', dir_to_make))
end
end
def log_to_stdout
wrapped_app # touch the app so the logger is set up
console = ActiveSupport::Logger.new($stdout)
console.formatter = Rails.logger.formatter
console.level = Rails.logger.level
Rails.logger.extend(ActiveSupport::Logger.broadcast(console))
end
print_boot_information这里将会是Rails启动以来第一次答应信息，start方法为INT信号创建了一个trap，所以只要你按住CTRL-C，将会退出进程。通过后面的create_tmp_directories方法，将会创建tmp/cache，tmp/session和tmp/sockets目录。之后会调用wrapped_app方法，用于在创建和分配一个ActiveSupport::Logger实例之前。
super方法将会调用Rack::Server.start这个方法，如下：
def start &blk if options[:warn] $-w = true end if includes = options[:include] $LOAD_PATH.unshift(*includes) end if library = options[:require] require library end if options[:debug] $DEBUG = true require 'pp' p options[:server] pp wrapped_app pp app end check_pid! if options[:pid] # Touch the wrapped app, so that the config.ru is loaded before # daemonization (i.e. before chdir, etc). wrapped_app daemonize_app if options[:daemonize] write_pid if options[:pid] trap(:INT) do if server.respond_to?(:shutdown) server.shutdown else exit end end server.run wrapped_app, options, &blk end
Rails应用有趣的部分就是在最后一行，server.run。这里我们再次遇到了wrapped_app方法。
wrapped_app:
def wrapped_app
@wrpped_app ||= build_app app
end
def app
@app ||= options[:builder] ? build_app_from_string : build_app_and_options_from_config
end
...
private
def build_app_and_options_from_config
if !::File.exist? options[:config]
abort "configuration #{options[:config]} not found"
end
app, options = Rack::Builder.parse_file(self.options[:config], opt_parser)
self.options.merge! options
app
end
def build_app_from_string
Rack::Builder.new_from_string(self.options[:builder])
end
option[:config]值默认是config.ru文件的位置，config.ru包含以下代码:
# This file is used by Rack-based servers to start the application.
require ::File.expand_path('../config/environment', __FILE__)
run <%= app_const %>
Rack::Builder.parse_file方法在这里获取到config.ru文件的内容然后解析他，用了下面的代码：
app = new_from_string cfgfile, config
...
def self.new_from_string(builder_script, file="(rackup)")
eval "Rack::Builder.new {\n" + builder_script + "\n}.to_app",
TOPLEVEL_BINDING, file, 0
end
Rack::Builder的初始化方法会接受一个代码块同时在Rack::Builder的一个实例中执行它。这就是大多数Rails发生的初始化过程，当执行config.ru的代码时首先会require config/environment.rb
config/environment.rb
这个文件被config.ru（rails server）和Passenger require的共同文件。
这个文件最开始require 了config/application.rb
config/application.rb
这个文件require了config/boot.rb