Garaday-http-cache: A Faraday Middleware That Respects HTTP Cache

Faraday Http Cache 

A Faraday middleware that respects HTTP cache, by checking expiration and validation of the stored responses.

Installation

Add it to your Gemfile:

gem 'faraday-http-cache'

Usage and configuration

You have to use the middleware in the Faraday instance that you want to, along with a suitable store to cache the responses. You can use the new shortcut using a symbol or passing the middleware class

client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache
  # or
  builder.use Faraday::HttpCache, store: Rails.cache

  builder.adapter Faraday.default_adapter
end

The middleware accepts a store option for the cache backend responsible for recording the API responses that should be stored. Stores should respond to write, read and delete, just like an object from the ActiveSupport::Cache API.

# Connect the middleware to a Memcache instance.
store = ActiveSupport::Cache.lookup_store(:mem_cache_store, ['localhost:11211'])

client = Faraday.new do |builder|
  builder.use :http_cache, store: store
  builder.adapter Faraday.default_adapter
end

# Or use the Rails.cache instance inside your Rails app.
client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache
  builder.adapter Faraday.default_adapter
end

The default store provided is a simple in memory cache that lives on the client instance. This type of store might not be persisted across multiple processes or connection instances so it is probably not suitable for most production environments. Make sure that you configure a store that is suitable for you.

The stdlib JSON module is used for serialization by default, which can struggle with unicode characters in responses in Ruby < 3.1. For example, if your JSON returns "name": "Raül" then you might see errors like:

Response could not be serialized: "\xC3" from ASCII-8BIT to UTF-8. Try using Marshal to serialize.

For full unicode support, or if you expect to be dealing with images, you can use the stdlib Marshal instead. Alternatively you could use another json library like oj or yajl-ruby.

client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache, serializer: Marshal
  builder.adapter Faraday.default_adapter
end

Strategies

You can provide a :strategy option to the middleware to specify the strategy to use.

client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache, strategy: Faraday::HttpCache::Strategies::ByVary
  builder.adapter Faraday.default_adapter
end

Available strategies are:

Faraday::HttpCache::Strategies::ByUrl

The default strategy. It Uses URL + HTTP method to generate cache keys and stores an array of request + response for each key.

Faraday::HttpCache::Strategies::ByVary

This strategy uses headers from Vary header to generate cache keys. It also uses cache to store Vary headers mapped to the request URL. This strategy is more suitable for caching private responses with the same URLs but different results for different users, like https://api.github.com/user.

Note: To automatically remove stale cache keys, you might want to use the :expires_in option.

store = ActiveSupport::Cache.lookup_store(:redis_cache_store, expires_in: 1.day, url: 'redis://localhost:6379/0')
client = Faraday.new do |builder|
  builder.use :http_cache, store: store, strategy: Faraday::HttpCache::Strategies::ByVary
  builder.adapter Faraday.default_adapter
end

Custom strategies

You can write your own strategy by subclassing Faraday::HttpCache::Strategies::BaseStrategy and implementing #write, #read and #delete methods.

Logging

You can provide a :logger option that will receive debug information based on the middleware operations:

client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache, logger: Rails.logger
  builder.adapter Faraday.default_adapter
end

client.get('https://site/api/users')
# logs "HTTP Cache: [GET users] miss, store"

Instrumentation

In addition to logging you can instrument the middleware by passing in an :instrumenter option such as ActiveSupport::Notifications (compatible objects are also allowed).

The event http_cache.faraday will be published every time the middleware processes a request. In the event payload, :env contains the response Faraday env and :cache_status contains a Symbol indicating the status of the cache processing for that request:

• :unacceptable means that the request did not go through the cache at all.
• :miss means that no cached response could be found.
• :invalid means that the cached response could not be validated against the server.
• :valid means that the cached response could be validated against the server.
• :fresh means that the cached response was still fresh and could be returned without even calling the server.

client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache, instrumenter: ActiveSupport::Notifications
  builder.adapter Faraday.default_adapter
end

# Subscribes to all events from Faraday::HttpCache.
ActiveSupport::Notifications.subscribe "http_cache.faraday" do |*args|
  event = ActiveSupport::Notifications::Event.new(*args)
  cache_status = event.payload[:cache_status]
  statsd = Statsd.new

  case cache_status
  when :fresh, :valid
    statsd.increment('api-calls.cache_hits')
  when :invalid, :miss
    statsd.increment('api-calls.cache_misses')
  when :unacceptable
    statsd.increment('api-calls.cache_bypass')
  end
end

See it live

You can clone this repository, install its dependencies with Bundler (run bundle install) and execute the files under the examples directory to see a sample of the middleware usage.

What gets cached?

The middleware will use the following headers to make caching decisions:

• Vary
• Cache-Control
• Age
• Last-Modified
• ETag
• Expires

Cache-Control

The max-age, must-revalidate, proxy-revalidate and s-maxage directives are checked.

Shared vs. non-shared caches

By default, the middleware acts as a "shared cache" per RFC 2616. This means it does not cache responses with Cache-Control: private. This behavior can be changed by passing in the :shared_cache configuration option:

client = Faraday.new do |builder|
  builder.use :http_cache, shared_cache: false
  builder.adapter Faraday.default_adapter
end

client.get('https://site/api/some-private-resource') # => will be cached

Download Details:

Author: Sourcelevel
Source Code: https://github.com/sourcelevel/faraday-http-cache 
License: View license

#ruby #http #cache 

What is GEEK

Buddha Community

Garaday-http-cache: A Faraday Middleware That Respects HTTP Cache

Faraday Http Cache 

A Faraday middleware that respects HTTP cache, by checking expiration and validation of the stored responses.

Installation

Add it to your Gemfile:

gem 'faraday-http-cache'

Usage and configuration

You have to use the middleware in the Faraday instance that you want to, along with a suitable store to cache the responses. You can use the new shortcut using a symbol or passing the middleware class

client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache
  # or
  builder.use Faraday::HttpCache, store: Rails.cache

  builder.adapter Faraday.default_adapter
end

The middleware accepts a store option for the cache backend responsible for recording the API responses that should be stored. Stores should respond to write, read and delete, just like an object from the ActiveSupport::Cache API.

# Connect the middleware to a Memcache instance.
store = ActiveSupport::Cache.lookup_store(:mem_cache_store, ['localhost:11211'])

client = Faraday.new do |builder|
  builder.use :http_cache, store: store
  builder.adapter Faraday.default_adapter
end

# Or use the Rails.cache instance inside your Rails app.
client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache
  builder.adapter Faraday.default_adapter
end

The default store provided is a simple in memory cache that lives on the client instance. This type of store might not be persisted across multiple processes or connection instances so it is probably not suitable for most production environments. Make sure that you configure a store that is suitable for you.

The stdlib JSON module is used for serialization by default, which can struggle with unicode characters in responses in Ruby < 3.1. For example, if your JSON returns "name": "Raül" then you might see errors like:

Response could not be serialized: "\xC3" from ASCII-8BIT to UTF-8. Try using Marshal to serialize.

For full unicode support, or if you expect to be dealing with images, you can use the stdlib Marshal instead. Alternatively you could use another json library like oj or yajl-ruby.

client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache, serializer: Marshal
  builder.adapter Faraday.default_adapter
end

Strategies

You can provide a :strategy option to the middleware to specify the strategy to use.

client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache, strategy: Faraday::HttpCache::Strategies::ByVary
  builder.adapter Faraday.default_adapter
end

Available strategies are:

Faraday::HttpCache::Strategies::ByUrl

The default strategy. It Uses URL + HTTP method to generate cache keys and stores an array of request + response for each key.

Faraday::HttpCache::Strategies::ByVary

This strategy uses headers from Vary header to generate cache keys. It also uses cache to store Vary headers mapped to the request URL. This strategy is more suitable for caching private responses with the same URLs but different results for different users, like https://api.github.com/user.

Note: To automatically remove stale cache keys, you might want to use the :expires_in option.

store = ActiveSupport::Cache.lookup_store(:redis_cache_store, expires_in: 1.day, url: 'redis://localhost:6379/0')
client = Faraday.new do |builder|
  builder.use :http_cache, store: store, strategy: Faraday::HttpCache::Strategies::ByVary
  builder.adapter Faraday.default_adapter
end

Custom strategies

You can write your own strategy by subclassing Faraday::HttpCache::Strategies::BaseStrategy and implementing #write, #read and #delete methods.

Logging

You can provide a :logger option that will receive debug information based on the middleware operations:

client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache, logger: Rails.logger
  builder.adapter Faraday.default_adapter
end

client.get('https://site/api/users')
# logs "HTTP Cache: [GET users] miss, store"

Instrumentation

In addition to logging you can instrument the middleware by passing in an :instrumenter option such as ActiveSupport::Notifications (compatible objects are also allowed).

The event http_cache.faraday will be published every time the middleware processes a request. In the event payload, :env contains the response Faraday env and :cache_status contains a Symbol indicating the status of the cache processing for that request:

• :unacceptable means that the request did not go through the cache at all.
• :miss means that no cached response could be found.
• :invalid means that the cached response could not be validated against the server.
• :valid means that the cached response could be validated against the server.
• :fresh means that the cached response was still fresh and could be returned without even calling the server.

client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache, instrumenter: ActiveSupport::Notifications
  builder.adapter Faraday.default_adapter
end

# Subscribes to all events from Faraday::HttpCache.
ActiveSupport::Notifications.subscribe "http_cache.faraday" do |*args|
  event = ActiveSupport::Notifications::Event.new(*args)
  cache_status = event.payload[:cache_status]
  statsd = Statsd.new

  case cache_status
  when :fresh, :valid
    statsd.increment('api-calls.cache_hits')
  when :invalid, :miss
    statsd.increment('api-calls.cache_misses')
  when :unacceptable
    statsd.increment('api-calls.cache_bypass')
  end
end

See it live

You can clone this repository, install its dependencies with Bundler (run bundle install) and execute the files under the examples directory to see a sample of the middleware usage.

What gets cached?

The middleware will use the following headers to make caching decisions:

• Vary
• Cache-Control
• Age
• Last-Modified
• ETag
• Expires

Cache-Control

The max-age, must-revalidate, proxy-revalidate and s-maxage directives are checked.

Shared vs. non-shared caches

By default, the middleware acts as a "shared cache" per RFC 2616. This means it does not cache responses with Cache-Control: private. This behavior can be changed by passing in the :shared_cache configuration option:

client = Faraday.new do |builder|
  builder.use :http_cache, shared_cache: false
  builder.adapter Faraday.default_adapter
end

client.get('https://site/api/some-private-resource') # => will be cached

Download Details:

Author: Sourcelevel
Source Code: https://github.com/sourcelevel/faraday-http-cache 
License: View license

#ruby #http #cache 

A Template Language That Completely Separates Structure and Logic/Ruby

Curly

Curly is a template language that completely separates structure and logic. Instead of interspersing your HTML with snippets of Ruby, all logic is moved to a presenter class.

Installing

Installing Curly is as simple as running gem install curly-templates. If you're using Bundler to manage your dependencies, add this to your Gemfile

gem 'curly-templates'

Curly can also install an application layout file, replacing the .erb file commonly created by Rails. If you wish to use this, run the curly:install generator.

$ rails generate curly:install

How to use Curly

In order to use Curly for a view or partial, use the suffix .curly instead of .erb, e.g. app/views/posts/_comment.html.curly. Curly will look for a corresponding presenter class named Posts::CommentPresenter. By convention, these are placed in app/presenters/, so in this case the presenter would reside in app/presenters/posts/comment_presenter.rb. Note that presenters for partials are not prepended with an underscore.

Add some HTML to the partial template along with some Curly components:

<!-- app/views/posts/_comment.html.curly -->
<div class="comment">
  <p>
    {{author_link}} posted {{time_ago}} ago.
  </p>

  {{body}}

  {{#author?}}
    <p>{{deletion_link}}</p>
  {{/author?}}
</div>

The presenter will be responsible for providing the data for the components. Add the necessary Ruby code to the presenter:

# app/presenters/posts/comment_presenter.rb
class Posts::CommentPresenter < Curly::Presenter
  presents :comment

  def body
    SafeMarkdown.render(@comment.body)
  end

  def author_link
    link_to @comment.author.name, @comment.author, rel: "author"
  end

  def deletion_link
    link_to "Delete", @comment, method: :delete
  end

  def time_ago
    time_ago_in_words(@comment.created_at)
  end

  def author?
    @comment.author == current_user
  end
end

The partial can now be rendered like any other, e.g. by calling

render 'comment', comment: comment
render comment
render collection: post.comments

Curly components are surrounded by curly brackets, e.g. {{hello}}. They always map to a public method on the presenter class, in this case #hello. Methods ending in a question mark can be used for conditional blocks, e.g. {{#admin?}} ... {{/admin?}}.

Identifiers

Curly components can specify an identifier using the so-called dot notation: {{x.y.z}}. This can be very useful if the data you're accessing is hierarchical in nature. One common example is I18n:

<h1>{{i18n.homepage.header}}</h1>

# In the presenter, the identifier is passed as an argument to the method. The
# argument will always be a String.
def i18n(key)
  translate(key)
end

The identifier is separated from the component name with a dot. If the presenter method has a default value for the argument, the identifier is optional – otherwise it's mandatory.

Attributes

In addition to an identifier, Curly components can be annotated with attributes. These are key-value pairs that affect how a component is rendered.

The syntax is reminiscent of HTML:

<div>{{sidebar rows=3 width=200px title="I'm the sidebar!"}}</div>

The presenter method that implements the component must have a matching keyword argument:

def sidebar(rows: "1", width: "100px", title:); end

All argument values will be strings. A compilation error will be raised if

• an attribute is used in a component without a matching keyword argument being present in the method definition; or
• a required keyword argument in the method definition is not set as an attribute in the component.

You can define default values using Ruby's own syntax. Additionally, if the presenter method accepts arbitrary keyword arguments using the **doublesplat syntax then all attributes will be valid for the component, e.g.

def greetings(**names)
  names.map {|name, greeting| "#{name}: #{greeting}!" }.join("\n")
end

{{greetings alice=hello bob=hi}}
<!-- The above would be rendered as: -->
alice: hello!
bob: hi!

Note that since keyword arguments in Ruby are represented as Symbol objects, which are not garbage collected in Ruby versions less than 2.2, accepting arbitrary attributes represents a security vulnerability if your application allows untrusted Curly templates to be rendered. Only use this feature with trusted templates if you're not on Ruby 2.2 yet.

Conditional blocks

If there is some content you only want rendered under specific circumstances, you can use conditional blocks. The {{#admin?}}...{{/admin?}} syntax will only render the content of the block if the admin? method on the presenter returns true, while the {{^admin?}}...{{/admin?}} syntax will only render the content if it returns false.

Both forms can have an identifier: {{#locale.en?}}...{{/locale.en?}} will only render the block if the locale? method on the presenter returns true given the argument "en". Here's how to implement that method in the presenter:

class SomePresenter < Curly::Presenter
  # Allows rendering content only if the locale matches a specified identifier.
  def locale?(identifier)
    current_locale == identifier
  end
end

Furthermore, attributes can be set on the block. These only need to be specified when opening the block, not when closing it:

{{#square? width=3 height=3}}
  <p>It's square!</p>
{{/square?}}

Attributes work the same way as they do for normal components.

Collection blocks

Sometimes you want to render one or more items within the current template, and splitting out a separate template and rendering that in the presenter is too much overhead. You can instead define the template that should be used to render the items inline in the current template using the collection block syntax.

Collection blocks are opened using an asterisk:

{{*comments}}
  <li>{{body}} ({{author_name}})</li>
{{/comments}}

The presenter will need to expose the method #comments, which should return a collection of objects:

class Posts::ShowPresenter < Curly::Presenter
  presents :post

  def comments
    @post.comments
  end
end

The template within the collection block will be used to render each item, and it will be backed by a presenter named after the component – in this case, comments. The name will be singularized and Curly will try to find the presenter class in the following order:

• Posts::ShowPresenter::CommentPresenter
• Posts::CommentPresenter
• CommentPresenter

This allows you some flexibility with regards to how you want to organize these nested templates and presenters.

Note that the nested template will only have access to the methods on the nested presenter, but all variables passed to the "parent" presenter will be forwarded to the nested presenter. In addition, the current item in the collection will be passed, as well as that item's index in the collection:

class Posts::CommentPresenter < Curly::Presenter
  presents :post, :comment, :comment_counter

  def number
    # `comment_counter` is automatically set to the item's index in the collection,
    # starting with 1.
    @comment_counter
  end

  def body
    @comment.body
  end

  def author_name
    @comment.author.name
  end
end

Collection blocks are an alternative to splitting out a separate template and rendering that from the presenter – which solution is best depends on your use case.

Context blocks

While collection blocks allow you to define the template that should be used to render items in a collection right within the parent template, context blocks allow you to define the template for an arbitrary context. This is very powerful, and can be used to define widget-style components and helpers, and provide an easy way to work with structured data. Let's say you have a comment form on your page, and you'd rather keep the template inline. A simple template could look like:

<!-- post.html.curly -->
<h1>{{title}}</h1>
{{body}}

{{@comment_form}}
  <b>Name: </b> {{name_field}}<br>
  <b>E-mail: </b> {{email_field}}<br>
  {{comment_field}}

  {{submit_button}}
{{/comment_form}}

Note that an @ character is used to denote a context block. Like with collection blocks, a separate presenter class is used within the block, and a simple convention is used to find it. The name of the context component (in this case, comment_form) will be camel cased, and the current presenter's namespace will be searched:

class PostPresenter < Curly::Presenter
  presents :post
  def title; @post.title; end
  def body; markdown(@post.body); end

  # A context block method *must* take a block argument. The return value
  # of the method will be used when rendering. Calling the block argument will
  # render the nested template. If you pass a value when calling the block
  # argument it will be passed to the presenter.
  def comment_form(&block)
    form_for(Comment.new, &block)
  end

  # The presenter name is automatically deduced.
  class CommentFormPresenter < Curly::Presenter
    # The value passed to the block argument will be passed in a parameter named
    # after the component.
    presents :comment_form

    # Any parameters passed to the parent presenter will be forwarded to this
    # presenter as well.
    presents :post

    def name_field
      @comment_form.text_field :name
    end

    # ...
  end
end

Context blocks were designed to work well with Rails' helper methods such as form_for and content_tag, but you can also work directly with the block. For instance, if you want to directly control the value that is passed to the nested presenter, you can call the call method on the block yourself:

def author(&block)
  content_tag :div, class: "author" do
    # The return value of `call` will be the result of rendering the nested template
    # with the argument. You can post-process the string if you want.
    block.call(@post.author)
  end
end

Context shorthand syntax

If you find yourself opening a context block just in order to use a single component, e.g. {{@author}}{{name}}{{/author}}, you can use the shorthand syntax instead: {{author:name}}. This works for all component types, e.g.

{{#author:admin?}}
  <p>The author is an admin!</p>
{{/author:admin?}}

The syntax works for nested contexts as well, e.g. {{comment:author:name}}. Any identifier and attributes are passed to the target component, which in this example would be {{name}}.

Setting up state

Although most code in Curly presenters should be free of side effects, sometimes side effects are required. One common example is defining content for a content_for block.

If a Curly presenter class defines a setup! method, it will be called before the view is rendered:

class PostPresenter < Curly::Presenter
  presents :post

  def setup!
    content_for :title, post.title

    content_for :sidebar do
      render 'post_sidebar', post: post
    end
  end
end

Escaping Curly syntax

In order to have {{ appear verbatim in the rendered HTML, use the triple Curly escape syntax:

This is {{{escaped}}.

You don't need to escape the closing }}.

Comments

If you want to add comments to your Curly templates that are not visible in the rendered HTML, use the following syntax:

{{! This is some interesting stuff }}

Presenters

Presenters are classes that inherit from Curly::Presenter – they're usually placed in app/presenters/, but you can put them anywhere you'd like. The name of the presenter classes match the virtual path of the view they're part of, so if your controller is rendering posts/show, the Posts::ShowPresenter class will be used. Note that Curly is only used to render a view if a template can be found – in this case, at app/views/posts/show.html.curly.

Presenters can declare a list of accepted variables using the presents method:

class Posts::ShowPresenter < Curly::Presenter
  presents :post
end

A variable can have a default value:

class Posts::ShowPresenter < Curly::Presenter
  presents :post
  presents :comment, default: nil
end

Any public method defined on the presenter is made available to the template as a component:

class Posts::ShowPresenter < Curly::Presenter
  presents :post

  def title
    @post.title
  end

  def author_link
    # You can call any Rails helper from within a presenter instance:
    link_to author.name, profile_path(author), rel: "author"
  end

  private

  # Private methods are not available to the template, so they're safe to
  # use.
  def author
    @post.author
  end
end

Presenter methods can even take an argument. Say your Curly template has the content {{t.welcome_message}}, where welcome_message is an I18n key. The following presenter method would make the lookup work:

def t(key)
  translate(key)
end

That way, simple ``functions'' can be added to the Curly language. Make sure these do not have any side effects, though, as an important part of Curly is the idempotence of the templates.

Layouts and content blocks

Both layouts and content blocks (see content_for) use yield to signal that content can be inserted. Curly works just like ERB, so calling yield with no arguments will make the view usable as a layout, while passing a Symbol will make it try to read a content block with the given name:

# Given you have the following Curly template in
# app/views/layouts/application.html.curly
#
#   <html>
#     <head>
#       <title>{{title}}</title>
#     </head>
#     <body>
#       <div id="sidebar">{{sidebar}}</div>
#       {{body}}
#     </body>
#   </html>
#
class ApplicationLayout < Curly::Presenter
  def title
    "You can use methods just like in any other presenter!"
  end

  def sidebar
    # A view can call `content_for(:sidebar) { "some HTML here" }`
    yield :sidebar
  end

  def body
    # The view will be rendered and inserted here:
    yield
  end
end

Rails helper methods

In order to make a Rails helper method available as a component in your template, use the exposes_helper method:

class Layouts::ApplicationPresenter < Curly::Presenter
  # The components {{sign_in_path}} and {{root_path}} are made available.
  exposes_helper :sign_in_path, :root_path
end

Testing

Presenters can be tested directly, but sometimes it makes sense to integrate with Rails on some levels. Currently, only RSpec is directly supported, but you can easily instantiate a presenter:

SomePresenter.new(context, assigns)

context is a view context, i.e. an object that responds to render, has all the helper methods you expect, etc. You can pass in a test double and see what you need to stub out. assigns is the hash containing the controller and local assigns. You need to pass in a key for each argument the presenter expects.

Testing with RSpec

In order to test presenters with RSpec, make sure you have rspec-rails in your Gemfile. Given the following presenter:

# app/presenters/posts/show_presenter.rb
class Posts::ShowPresenter < Curly::Presenter
  presents :post

  def body
    Markdown.render(@post.body)
  end
end

You can test the presenter methods like this:

# You can put this in your `spec_helper.rb`.
require 'curly/rspec'

# spec/presenters/posts/show_presenter_spec.rb
describe Posts::ShowPresenter, type: :presenter do
  describe "#body" do
    it "renders the post's body as Markdown" do
      assign(:post, double(:post, body: "**hello!**"))
      expect(presenter.body).to eq "<strong>hello!</strong>"
    end
  end
end

Note that your spec must be tagged with type: :presenter.

Examples

Here is a simple Curly template – it will be looked up by Rails automatically.

<!-- app/views/posts/show.html.curly -->
<h1>{{title}}<h1>
<p class="author">{{author}}</p>
<p>{{description}}</p>

{{comment_form}}

<div class="comments">
  {{comments}}
</div>

When rendering the template, a presenter is automatically instantiated with the variables assigned in the controller or the render call. The presenter declares the variables it expects with presents, which takes a list of variables names.

# app/presenters/posts/show_presenter.rb
class Posts::ShowPresenter < Curly::Presenter
  presents :post

  def title
    @post.title
  end

  def author
    link_to(@post.author.name, @post.author, rel: "author")
  end

  def description
    Markdown.new(@post.description).to_html.html_safe
  end

  def comments
    render 'comment', collection: @post.comments
  end

  def comment_form
    if @post.comments_allowed?
      render 'comment_form', post: @post
    else
      content_tag(:p, "Comments are disabled for this post")
    end
  end
end

Caching

Caching is handled at two levels in Curly – statically and dynamically. Static caching concerns changes to your code and templates introduced by deploys. If you do not wish to clear your entire cache every time you deploy, you need a way to indicate that some view, helper, or other piece of logic has changed.

Dynamic caching concerns changes that happen on the fly, usually made by your users in the running system. You wish to cache a view or a partial and have it expire whenever some data is updated – usually whenever a specific record is changed.

Dynamic Caching

Because of the way logic is contained in presenters, caching entire views or partials by the data they present becomes exceedingly straightforward. Simply define a #cache_key method that returns a non-nil object, and the return value will be used to cache the template.

Whereas in ERB you would include the cache call in the template itself:

<% cache([@post, signed_in?]) do %>
  ...
<% end %>

In Curly you would instead declare it in the presenter:

class Posts::ShowPresenter < Curly::Presenter
  presents :post

  def cache_key
    [@post, signed_in?]
  end
end

Likewise, you can add a #cache_duration method if you wish to automatically expire the fragment cache:

class Posts::ShowPresenter < Curly::Presenter
  ...

  def cache_duration
    30.minutes
  end
end

In order to set any cache option, define a #cache_options method that returns a Hash of options:

class Posts::ShowPresenter < Curly::Presenter
  ...

  def cache_options
    { compress: true, namespace: "my-app" }
  end
end

Static Caching

Static caching will only be enabled for presenters that define a non-nil #cache_key method (see Dynamic Caching.)

In order to make a deploy expire the cache for a specific view, set the version of the view to something new, usually by incrementing by one:

class Posts::ShowPresenter < Curly::Presenter
  version 3

  def cache_key
    # Some objects
  end
end

This will change the cache keys for all instances of that view, effectively expiring the old cache entries.

This works well for views, or for partials that are rendered in views that themselves are not cached. If the partial is nested within a view that is cached, however, the outer cache will not be expired. The solution is to register that the inner partial is a dependency of the outer one such that Curly can automatically deduce that the outer partial cache should be expired:

class Posts::ShowPresenter < Curly::Presenter
  version 3
  depends_on 'posts/comment'

  def cache_key
    # Some objects
  end
end

class Posts::CommentPresenter < Curly::Presenter
  version 4

  def cache_key
    # Some objects
  end
end

Now, if the version of Posts::CommentPresenter is bumped, the cache keys for both presenters would change. You can register any number of view paths with depends_on.

Curly integrates well with the caching mechanism in Rails 4 (or Cache Digests in Rails 3), so the dependencies defined with depends_on will be tracked by Rails. This will allow you to deploy changes to your templates and have the relevant caches automatically expire.

Thanks

Thanks to Zendesk for sponsoring the work on Curly.

Contributors

• Daniel Schierbeck (@dasch)
• Benjamin Quorning (@bquorning)
• Jeremy Rodi (@medcat)
• Alisson Cavalcante Agiani (@thelinuxlich)
• Łukasz Niemier (@hauleth)
• Cristian Planas (@Gawyn)
• Steven Davidovitz (@steved)

Build Status

---

Author: zendesk
Source code: https://github.com/zendesk/curly

#ruby   #ruby-on-rails 

Caching In WordPress: What You Need to Learn?

WordPress caching has nothing new to showcase in this context. WordPress websites also run on a specific server system and you have to make sure these servers work well for user engagement. So caching can help your website server work effectively to serve too many visitors collectively. The commonly requested items can be converted into varied copies that the website server doesn’t want to showcase every time to every website visitor. Classification of Caching is usually divided into two kinds. The Client-Side Caching & the Server Side Caching. Where client-side caching has nothing to do with your website, Server Side Caching is usually its opposite. Read more on https://bit.ly/3rbqvVh

#caching plugins #server side caching #client side caching #wordpress websites #wordpress caching

How Django Middleware Works?

How Django Middleware Works?

 April 25, 2021  Deepak@321  0 Comments

Welcome to my Blog, in this article we learn about How Django Middleware Works?

Django Middleware is a lightweight, low-level plugin system that modifies Django’s input and output. It is a framework that integrates Django for the processing of queries and answers. You can use middleware if you want to change the request object.

Django maintains a list of middleware for each project. Middleware allows you to edit requests from the browser before they reach Django, and to view the response from the view before they reach the browser. The middleware is applied in the same order as it is added to the list in the Django settings. If a new Django project has added a number of middlewares, in most cases they cannot be removed. Middleware is a checkmark that modifies the Django query and response objects.

In order for middleware to play a role, it is dependent on other middleware. For example, AuthenticationMiddleware stores the authenticated user session and executes the SessionMiddleware.

#django #django middleware #django middleware works #how django middleware works #structure of middleware in django

Mid: Middleware for HTTP Services in Go

Mid - Assorted middleware for HTTP services.

This is mid, a collection of useful middleware for HTTP services.

Err

The Err function turns a func(http.ResponseWriter, *http.Request) error into an http.Handler, allowing handler functions to return errors in a more natural fashion. These errors result in the handler producing an HTTP 500 status code, but CodeErr and Responder allow you to control this behavior (see below). A nil return produces a 200, or a 204 (“no content”) if no bytes were written to the response object.

Usage:

func main() {
  http.Handle("/foo", Err(fooHandler))
  http.ListenAndServe(":8080", nil)
}

func fooHandler(w http.ResponseWriter, req *http.Request) error {
  if x := req.FormValue("x"); x != "secret password" {
    return CodeErr{C: http.StatusUnauthorized}
  }
  fmt.Fprintf(w, "You know the secret password")
  return nil
}

JSON

The JSON function turns a func(context.Context, X) (Y, error) into an http.Handler, where X is the type of a parameter into which the HTTP request body is automatically JSON-unmarshaled, and Y is the type of a result that is automatically JSON-marshaled into the HTTP response. Any error is handled as with Err (see above). All parts of the func signature are optional: the context.Context parameter, the X parameter, the Y result, and the error result.

Usage:

func main() {
  // Parses the request body as a JSON-encoded array of strings,
  // then sorts, re-encodes, and returns that array.
  http.Handle("/bar", JSON(barHandler))

  http.ListenAndServe(":8080", nil)
}

func barHandler(inp []string) []string {
  sort.Strings(inp)
  return inp
}

CodeErr and Responder

CodeErr is an error type suitable for returning from Err- and JSON-wrapped handlers that can control the HTTP status code that gets returned. It contains an HTTP status code field and a nested error.

Responder is an interface (implemented by CodeErr) that allows an error type to control how Err- and JSON-wrapped handlers respond to the pending request.

ResponseWrapper

ResponseWrapper is an http.ResponseWriter that wraps a nested http.ResponseWriter and also records the status code and number of bytes sent in the response.

Trace

The Trace function wraps an http.Handler and decorates the context.Context in its *http.Request with any “trace ID” string found in the request header.

Log

The Log function wraps an http.Handler with a function that writes a simple log line on the way into and out of the handler. The log line includes any “trace ID” found in the request’s context.Context.

Author: Bobg
Source Code: https://github.com/bobg/mid 
License: MIT license

#go #golang #middleware #http