dwayne · July 31, 2015 20:57 · Jul 31, 2015
diff --git a/0-how-cookies-work.md b/0-how-cookies-work.md
@@ -0,0 +1,26 @@
+I will use the simple Sinatra application below to explain.
+
+First, we run the app.
+
+```
+$ ruby app.rb
+```
+
+This launches a server at `localhost:4567`.
+
+1. Open your browser at `http://localhost:4567`.
+2. Enter your name, say Dwayne, and click **Set**.
+3. Doing so causes your browser to send a **POST** request to **/set** with **name=Dwayne**.
+4. The corresponding route handler then "sets a cookie" under the name **name** with value **Dwayne**.
+5. What really happens is that the **Set-Cookie** header is set with **name=Dwayne**.
+6. The redirect is executed causing a `303 status` and at least the **Set-Cookie** and **Location** headers to be sent to the browser.
+7. The browser stores the cookie and will send it via the **COOKIE** header with any subsequent request, which happens to be now.
+8. You see, the 303 redirect causes the browser to immediately make another request to the URL given in the **Location** header, **/**. Hence, the cookie information will be sent along.
+9. The corresponding route handler then fetches the relevant cookie and displays the appropriate message.
+
+**References**
+
+- [My HTTP Cookies Bookmarks](https://pinboard.in/search/u:dwaynecrooks?query=http-cookies)
+- [Rack `response.set_cookie`](http://www.rubydoc.info/github/rack/rack/master/Rack/Response#set_cookie-instance_method)
+- [Rack `request.cookies`](http://www.rubydoc.info/github/rack/rack/master/Rack/Request#cookies-instance_method)
+- [Where does Google Chrome store cookies in Linux?](http://stackoverflow.com/q/1841901/391924)
diff --git a/1-app-Gemfile.rb b/1-app-Gemfile.rb
@@ -0,0 +1,4 @@
+source 'https://rubygems.org'
+
+gem 'sinatra'
+gem 'thin'
diff --git a/1-app-app.rb b/1-app-app.rb
@@ -0,0 +1,11 @@
+require 'sinatra'
+
+get '/' do
+  @name = request.cookies['name'] || 'world'
+  erb :index
+end
+
+post '/set' do
+  response.set_cookie('name', params[:name])
+  redirect to('/')
+end
diff --git a/1-app-views-index.erb b/1-app-views-index.erb
@@ -0,0 +1,11 @@
+<p>
+  Hello, <%= @name %>!
+</p>
+
+<form action="/set" method="POST">
+  <label>
+    What's your name?<br>
+    <input type="text" name="name">
+  </label>
+  <button type="submit">Set</button>
+</form>
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