2016年4月30日 星期六

Thread-Safety


Rack::Lock => make sure thread safe
def threadsafe!
  @preload_frameworks = true
  @cache_classes      = true
  @dependency_loading = false
  @allow_concurrency  = true
  self
end
sometimes on production rails will remove Rack::Lock => because Web server will handle it => unicorn, Fusion Passenger => single thread

puma => multi thread 
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Rails Middleware Walkthrough


ActionDispatch::Static => provide static file on public
Rack::Lock => lock the app down to a single thread
ActiveSupport::Cache::Strategy::LocalCache::Middleware => cache method based on ActiveSupport::Cache::FileStore
easy to use by Rails.cache.read or Rails.cache.write
Rack::Runtime => sets an X-Runtime response header to show spending time
Rack::MethodOverride => if set params[:_method], could reset http method, ex put, delete on form
ActionDispatch::RequestId => set unique request id
Rails::Rack::Logger => log when request start, and request end
ActionDispatch::ShowExceptions & ActionDispatch::DebugExceptions => rescue error, and custom format
ActionDispatch::RemoteIp => detect ip attack
ActionDispatch::Reloader => reload classes in development mode
ActionDispatch::Callbacks =>  We can call before or after methods on this and pass in a block which will then be triggered on each request.
ActiveRecord::ConnectionAdapters::ConnectionManagement => clear db connections
ActiveRecord::QueryCache => active record query cache
ActionDispatch::Cookies, Session::CookieStore and Flash =>  set cookie, sessions
ActionDispatch::ParamsParser => prepare params
ActionDispatch::Head => transfer head request to get
Rack::ConditionalGet and Rack::ETag => set ETag header based on the response body, conditional => if not changed, not process => only send 304

ActionDispatch::BestStandardsSupport => add recommend browser to client 
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LOG TAGGING IN RAILS

My::Application.config.log_tags = [ :uuid ]

Now you can filter the log content by a particular request ID to see all output related to a single request 
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Clickjacking



Kidnap your click, to create unexpected behavior:
ex: use invisible iframe to controller your click


user X-FRAME-OPTIONS to prevent it 
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2016年4月19日 星期二

How key-based cache expiration works




  1. The cache key is fluid part and the cache content is the fixed part
  2. key is calculated from the content
  3. when key changes, simply write the new content to new key
  4. will generate a lot of cache garbage => don’t care => Memcached will automatically evict the oldest keys first when it runs out of space
  5. You deal with dependency structure by tying the model object together on updates
  6. The caching itself then happens in the views based on partials rendering the objects in question
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2016年4月17日 星期日

ActiveRecord::Observer


callback, but not very related to model
we can use observer

class AuditObserver < ActiveRecord::Observer
  observe :account, :balance

  def after_update(record)
    AuditTrail.new(record, "UPDATED")
  end
end


Storing Observers in Rails

If you’re using Active Record within Rails, observer classes are usually stored in app/models with the naming convention of app/models/audit_observer.rb.

Configuration

In order to activate an observer, list it in the config.active_record.observers configuration setting in yourconfig/application.rb file. 
config.active_record.observers = :comment_observer, :signup_observer
Observers will not be invoked unless you define these in your application configuration. 
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2016年4月16日 星期六

how to build a virtual dom tree

如何實現一個Virtual DOM算法

  1. use javascript object to present the structure of dom, and use it to build a real dom tree, then insert to document
  2. when state updated, recreate a object tree, and then compare old tree and new tree, and record the diff
  3. use 2.) diff to 1.) real dom tree

2.1. how to compare:
1.Depth-first search for new and old tree, and add unique mark
2.diff type: REPLACE, REORDER, PROPS, TEXT

3.compare list: ex => abcdefghi =>abchdfgij 
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2016年4月10日 星期日

css 原理

 http://kb.cnblogs.com/page/125663/


from right to left effect:
DIV#divBox p span.red{color:red;} => find class ‘red’, then find span, then find p ….
in order to filter some unrelated 元素 quickly

how to optimize css

  1. 不要在ID选择器前使用标签名
    一般写法：DIV#divBox

    　　更好写法：#divBox
    　　解释：因为ID选择器是唯一的，加上div反而增加不必要的 CSS 匹配。
  2. 不要在 class 选择器前使用标签名
    一般写法：span.red
    更好写法：.red
    解释：同第一条，但如果你定义了多个.red，而且在不同的元素下是样式不一样，则不能去掉，比如你css文件中定义如下：

    　　p.red{color:red;}
　　span.red{color:#ff00ff}
    　　如果是这样定义的就不要去掉，去掉后就会混淆，不过建议最好不要这样写
  3. 尽量少使用层级关系
    一般写法：#divBoxp.red{color:red;}
    更好写法：.red{..}
  4. 使用 class 代替层级关系
    一般写法：#divBox ul li a{display:block;}
    更好写法：.block{display:block;}
  5. 在 CSS 渲染效率中 id 和 class 的效率是基本相当的
    class 会在第一次载入中被缓存，在层叠中会有更加好的效果，在根部元素采用id会具有更加好（id有微妙的速度优势）。
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how browser work








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ruby object


  • ruby中，一切皆對象
  • 理解ruby對像模型
  • 了解ruby查找方法的方式

描述了Ruby中方法調用的過程，“向左一步進入該對象的類，然後沿著祖先鏈一直查找方法，找到方法之後，根據自身的綁定執行該方法”。 因此，對象本身只有一組綁定，而方法定義都是在類中。那麼上面說到的單件方法和類宏應該在什麼地方定義呢？單件方法肯定不能定義在類中，否則將會影響該類的所有實例對象。類本身也是對象，類的方法不能定義在自身，因為對象的方法必須定義在對象的類中，而類對象的類是Class，如果把類方法定義到Class上，那麼所有的類對像都會擁有該方法。這一切迷思的答案都來源於一個Ruby中的高級概念，Eigenclass Eigenclass在Ruby中，當調用obj.class向一個對象索要它的類的時候，編譯器並沒有告訴大家全部的真相，你得到的類並不是你看到的類，你得到的是一個對象特有的隱藏類，這就是該對象的Eigenclass，雖然Object#class方法想把關於Eigenclass的信息隱藏起來，但是，存在即存在，總會被人挖出來的。 



Eigenclass是一個類，但是是一個很特殊的類，它只能有一個實例，且不能被繼承，但是其自身可以繼承其它類。因此，所有的對像都有一個自己的Eigenclass，單件方法就定義在該對象的Eigenclass中，類宏定義在該類對象的Eigenclass中

為了區分普通類和Eigenclass，Ruby會使用“#"表明該類是一個Eigenclass。 
*一個實例對象的Eigenclass的父類是該對象的類 
*一個類對象的Eigenclass的父類是該類對象的父類的EigenClass。 


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singleton_method

singleton_method means object’s specific method

when we define method on specific object, will insert the singleton class between object and his class.
  1. puts example2. class  
  2.   
  3. class  << example2  
  4.   puts  self  
  5. end  

輸出結果：
  1. ExampleClass  
  2. #<Class:#<ExampleClass:0x28305d>>  


And if we add class method on class just like add singleton method on class 
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instance_eval 與class_eval

instance_eval’s receiver must be an instance. and if an instance call instance_eval => mean you can define this instance’s singleton_method.
and because class is a instance of Class => so class also can call instance_eval => define this class’s singleton_method => class method

class_eval’s receiver must be an class. and if class call class_eval => you can define this class’s instance_method

instance_eval must be call by instance, use to define singleton_methods

class_eval must be call by class, use to define instance_methods 
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Rails 啟動過程

1 啟動！
  1. call ruby rails in RVM folder => railties/bin/rails => require "rails/cli"
  2. railties/lib/rails/app_rails_loader.rb : find ‘bin/rails’
  3. bin/rails: require_relative '../config/boot and require 'rails/commands'
  4. config/boot.rb: setting Bundler, Gemfile
  5. rails/commands.rb: setting aliases, require 'rails/commands/commands_tasks'
  6. rails/commands/command_tasks.rb: run command, => rails/commands/server => require ‘fileutils, ‘optparse', ‘action_dispatch’, require 'rails'
  7. actionpack/lib/action_dispatch.rb: response routes
  8. rails/commands/server.rb: inherited from Rack::Server: call Rack::Server’s initialize。
  9. Rack: lib/rack/server.rb: provide interface for app on rack base, => setting options
  10. config/application.rb: app settings
  11. Rails::Server#start: still will call Rack::Server.start
  12. config/environment.rb
  13. config/application.rb => require ‘rails/all'

2 載入 Rails

  1. railties/lib/rails/all.rb
  2. config/environment.rb
  3. railties/lib/rails/application.rb: initialize!
  4. Rack: lib/rack/server.rb
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2016年4月5日 星期二

oauth 2.0 work flow



oAuth want to replace traditional user/password flow, more security.

User don’t need to provide his user/password to third party( like small game on FB), when want to play small game, 
will flow oauth work flow to get your permission to get access token to share your data with small game

U:  User (resource owner)
C:  Client (application)
A:  Authorization server
R:  Resource server

  1. C register on A, apply clientID & Secret, and also need to set redirect_url
  2. when user want to use his resource to do something, through C
  3. if not login in,
    1. 1) C set Authorization Request to U
    2. 2) U response Authorization Grant to C
    3. 3) C set Authorization Grant to A
    4. 4) A response Access Token to C
    5. 5) C use Access token to R to get resource
    6. 6) R response Protected Resource to C

some variable:
response_type => code or token, if code, have next phase authorization
                                                      if token, will response token directly
client_id => C register on A
redirect_uri => just for know response to where
scope => set protected what resources
state => any word you want to sent
code => when response_type set code, will append on redirect_uri
client_secret => C register on A
grant_type => for validate code available
access_token => use this to get api



the max different between oAuth1.0a and oAuth 2.0 is scope 






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