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Action Controller Overview
In this guide you will learn how controllers work and how they fit into the request cycle in your application.
After reading this guide, you will know:
- How to follow the flow of a request through a controller.
- Why and how to store data in the session or cookies.
- How to work with filters to execute code during request processing.
- How to use Action Controller's built-in HTTP authentication.
- How to stream data directly to the user's browser.
- How to filter sensitive parameters so they do not appear in the application's log.
- How to deal with exceptions that may be raised during request processing.
What Does a Controller Do?
Action Controller is the C in MVC. After routing has determined which controller to use for a request, your controller is responsible for making sense of the request and producing the appropriate output. Luckily, Action Controller does most of the groundwork for you and uses smart conventions to make this as straightforward as possible.
For most conventional RESTful applications, the controller will receive the request (this is invisible to you as the developer), fetch or save data from a model and use a view to create HTML output. If your controller needs to do things a little differently, that's not a problem, this is just the most common way for a controller to work.
A controller can thus be thought of as a middle man between models and views. It makes the model data available to the view so it can display that data to the user, and it saves or updates data from the user to the model.
NOTE: For more details on the routing process, see Rails Routing from the Outside In.
Methods and Actions
A controller is a Ruby class which inherits from ApplicationController
and has methods just like any other class. When your application receives a request, the routing will determine which controller and action to run, then Rails creates an instance of that controller and runs the method with the same name as the action.
class ClientsController < ApplicationController
def new
end
end
As an example, if a user goes to /clients/new
in your application to add a new client, Rails will create an instance of ClientsController
and run the new
method. Note that the empty method from the example above could work just fine because Rails will by default render the new.html.erb
view unless the action says otherwise. The new
method could make available to the view a @client
instance variable by creating a new Client
:
def new
@client = Client.new
end
The Layouts & Rendering Guide explains this in more detail.
ApplicationController
inherits from ActionController::Base
, which defines a number of helpful methods. This guide will cover some of these, but if you're curious to see what's in there, you can see all of them in the API documentation or in the source itself.
Only public methods are callable as actions. It is a best practice to lower the visibility of methods which are not intended to be actions, like auxiliary methods or filters.
Parameters
You will probably want to access data sent in by the user or other parameters in your controller actions. There are two kinds of parameters possible in a web application. The first are parameters that are sent as part of the URL, called query string parameters. The query string is everything after "?" in the URL. The second type of parameter is usually referred to as POST data. This information usually comes from an HTML form which has been filled in by the user. It's called POST data because it can only be sent as part of an HTTP POST request. Rails does not make any distinction between query string parameters and POST parameters, and both are available in the params
hash in your controller:
class ClientsController < ActionController::Base
# This action uses query string parameters because it gets run
# by an HTTP GET request, but this does not make any difference
# to the way in which the parameters are accessed. The URL for
# this action would look like this in order to list activated
# clients: /clients?status=activated
def index
if params[:status] == "activated"
@clients = Client.activated
else
@clients = Client.inactivated
end
end
# This action uses POST parameters. They are most likely coming
# from an HTML form which the user has submitted. The URL for
# this RESTful request will be "/clients", and the data will be
# sent as part of the request body.
def create
@client = Client.new(params[:client])
if @client.save
redirect_to @client
else
# This line overrides the default rendering behavior, which
# would have been to render the "create" view.
render "new"
end
end
end
Hash and Array Parameters
The params
hash is not limited to one-dimensional keys and values. It can contain arrays and (nested) hashes. To send an array of values, append an empty pair of square brackets "[]" to the key name:
GET /clients?ids[]=1&ids[]=2&ids[]=3
NOTE: The actual URL in this example will be encoded as "/clients?ids%5b%5d=1&ids%5b%5d=2&ids%5b%5d=3" as "[" and "]" are not allowed in URLs. Most of the time you don't have to worry about this because the browser will take care of it for you, and Rails will decode it back when it receives it, but if you ever find yourself having to send those requests to the server manually you have to keep this in mind.
The value of params[:ids]
will now be ["1", "2", "3"]
. Note that parameter values are always strings; Rails makes no attempt to guess or cast the type.
To send a hash you include the key name inside the brackets:
<form accept-charset="UTF-8" action="/clients" method="post">
<input type="text" name="client[name]" value="Acme" />
<input type="text" name="client[phone]" value="12345" />
<input type="text" name="client[address][postcode]" value="12345" />
<input type="text" name="client[address][city]" value="Carrot City" />
</form>
When this form is submitted, the value of params[:client]
will be {"name" => "Acme", "phone" => "12345", "address" => {"postcode" => "12345", "city" => "Carrot City"}}
. Note the nested hash in params[:client][:address]
.
Note that the params
hash is actually an instance of HashWithIndifferentAccess
from Active Support, which acts like a hash that lets you use symbols and strings interchangeably as keys.
JSON/XML parameters
If you're writing a web service application, you might find yourself more comfortable on accepting parameters in JSON or XML format. Rails will automatically convert your parameters into params
hash, which you'll be able to access like you would normally do with form data.
So for example, if you are sending this JSON parameter:
{ "company": { "name": "acme", "address": "123 Carrot Street" } }
You'll get params[:company]
as { :name => "acme", "address" => "123 Carrot Street" }
.
Also, if you've turned on config.wrap_parameters
in your initializer or calling wrap_parameters
in your controller, you can safely omit the root element in the JSON/XML parameter. The parameters will be cloned and wrapped in the key according to your controller's name by default. So the above parameter can be written as:
{ "name": "acme", "address": "123 Carrot Street" }
And assume that you're sending the data to CompaniesController
, it would then be wrapped in :company
key like this:
{ :name => "acme", :address => "123 Carrot Street", :company => { :name => "acme", :address => "123 Carrot Street" }}
You can customize the name of the key or specific parameters you want to wrap by consulting the API documentation
Routing Parameters
The params
hash will always contain the :controller
and :action
keys, but you should use the methods controller_name
and action_name
instead to access these values. Any other parameters defined by the routing, such as :id
will also be available. As an example, consider a listing of clients where the list can show either active or inactive clients. We can add a route which captures the :status
parameter in a "pretty" URL:
match '/clients/:status' => 'clients#index', foo: "bar"
In this case, when a user opens the URL /clients/active
, params[:status]
will be set to "active". When this route is used, params[:foo]
will also be set to "bar" just like it was passed in the query string. In the same way params[:action]
will contain "index".
default_url_options
You can set global default parameters for URL generation by defining a method called default_url_options
in your controller. Such a method must return a hash with the desired defaults, whose keys must be symbols:
class ApplicationController < ActionController::Base
def default_url_options
{ locale: I18n.locale }
end
end
These options will be used as a starting point when generating URLs, so it's possible they'll be overridden by the options passed in url_for
calls.
If you define default_url_options
in ApplicationController
, as in the example above, it would be used for all URL generation. The method can also be defined in one specific controller, in which case it only affects URLs generated there.
Session
Your application has a session for each user in which you can store small amounts of data that will be persisted between requests. The session is only available in the controller and the view and can use one of a number of different storage mechanisms:
- ActionDispatch::Session::CookieStore - Stores everything on the client.
- ActionDispatch::Session::CacheStore - Stores the data in the Rails cache.
- @ActionDispatch::Session::ActiveRecordStore@ - Stores the data in a database using Active Record. (require
activerecord-session_store
gem). - @ActionDispatch::Session::MemCacheStore@ - Stores the data in a memcached cluster (this is a legacy implementation; consider using CacheStore instead).
All session stores use a cookie to store a unique ID for each session (you must use a cookie, Rails will not allow you to pass the session ID in the URL as this is less secure).
For most stores, this ID is used to look up the session data on the server, e.g. in a database table. There is one exception, and that is the default and recommended session store - the CookieStore - which stores all session data in the cookie itself (the ID is still available to you if you need it). This has the advantage of being very lightweight and it requires zero setup in a new application in order to use the session. The cookie data is cryptographically signed to make it tamper-proof, but it is not encrypted, so anyone with access to it can read its contents but not edit it (Rails will not accept it if it has been edited).
The CookieStore can store around 4kB of data — much less than the others — but this is usually enough. Storing large amounts of data in the session is discouraged no matter which session store your application uses. You should especially avoid storing complex objects (anything other than basic Ruby objects, the most common example being model instances) in the session, as the server might not be able to reassemble them between requests, which will result in an error.
If your user sessions don't store critical data or don't need to be around for long periods (for instance if you just use the flash for messaging), you can consider using ActionDispatch::Session::CacheStore. This will store sessions using the cache implementation you have configured for your application. The advantage of this is that you can use your existing cache infrastructure for storing sessions without requiring any additional setup or administration. The downside, of course, is that the sessions will be ephemeral and could disappear at any time.
Read more about session storage in the Security Guide.
If you need a different session storage mechanism, you can change it in the config/initializers/session_store.rb
file:
# Use the database for sessions instead of the cookie-based default,
# which shouldn't be used to store highly confidential information
# (create the session table with "script/rails g active_record:session_migration")
# YourApp::Application.config.session_store :active_record_store
Rails sets up a session key (the name of the cookie) when signing the session data. These can also be changed in config/initializers/session_store.rb
:
# Be sure to restart your server when you modify this file.
YourApp::Application.config.session_store :cookie_store, key: '_your_app_session'
You can also pass a :domain
key and specify the domain name for the cookie:
# Be sure to restart your server when you modify this file.
YourApp::Application.config.session_store :cookie_store, key: '_your_app_session', domain: ".example.com"
Rails sets up (for the CookieStore) a secret key used for signing the session data. This can be changed in config/initializers/secret_token.rb
# Be sure to restart your server when you modify this file.
# Your secret key for verifying the integrity of signed cookies.
# If you change this key, all old signed cookies will become invalid!
# Make sure the secret is at least 30 characters and all random,
# no regular words or you'll be exposed to dictionary attacks.
YourApp::Application.config.secret_key_base = '49d3f3de9ed86c74b94ad6bd0...'
NOTE: Changing the secret when using the CookieStore
will invalidate all existing sessions.
Accessing the Session
In your controller you can access the session through the session
instance method.
NOTE: Sessions are lazily loaded. If you don't access sessions in your action's code, they will not be loaded. Hence you will never need to disable sessions, just not accessing them will do the job.
Session values are stored using key/value pairs like a hash:
class ApplicationController < ActionController::Base
private
# Finds the User with the ID stored in the session with the key
# :current_user_id This is a common way to handle user login in
# a Rails application; logging in sets the session value and
# logging out removes it.
def current_user
@_current_user ||= session[:current_user_id] &&
User.find_by_id(session[:current_user_id])
end
end
To store something in the session, just assign it to the key like a hash:
class LoginsController < ApplicationController
# "Create" a login, aka "log the user in"
def create
if user = User.authenticate(params[:username], params[:password])
# Save the user ID in the session so it can be used in
# subsequent requests
session[:current_user_id] = user.id
redirect_to root_url
end
end
end
To remove something from the session, assign that key to be nil
:
class LoginsController < ApplicationController
# "Delete" a login, aka "log the user out"
def destroy
# Remove the user id from the session
@_current_user = session[:current_user_id] = nil
redirect_to root_url
end
end
To reset the entire session, use reset_session
.
The Flash
The flash is a special part of the session which is cleared with each request. This means that values stored there will only be available in the next request, which is useful for passing error messages etc.
It is accessed in much the same way as the session, as a hash (it's a FlashHash instance).
Let's use the act of logging out as an example. The controller can send a message which will be displayed to the user on the next request:
class LoginsController < ApplicationController
def destroy
session[:current_user_id] = nil
flash[:notice] = "You have successfully logged out."
redirect_to root_url
end
end
Note that it is also possible to assign a flash message as part of the redirection. You can assign :notice
, :alert
or the general purpose :flash
:
redirect_to root_url, notice: "You have successfully logged out."
redirect_to root_url, alert: "You're stuck here!"
redirect_to root_url, flash: { referral_code: 1234 }
The destroy
action redirects to the application's root_url
, where the message will be displayed. Note that it's entirely up to the next action to decide what, if anything, it will do with what the previous action put in the flash. It's conventional to display any error alerts or notices from the flash in the application's layout:
<html>
<!-- <head/> -->
<body>
<% flash.each do |name, msg| -%>
<%= content_tag :div, msg, class: name %>
<% end -%>
<!-- more content -->
</body>
</html>
This way, if an action sets a notice or an alert message, the layout will display it automatically.
You can pass anything that the session can store; you're not limited to notices and alerts:
<% if flash[:just_signed_up] %>
<p class="welcome">Welcome to our site!</p>
<% end %>
If you want a flash value to be carried over to another request, use the keep
method:
class MainController < ApplicationController
# Let's say this action corresponds to root_url, but you want
# all requests here to be redirected to UsersController#index.
# If an action sets the flash and redirects here, the values
# would normally be lost when another redirect happens, but you
# can use 'keep' to make it persist for another request.
def index
# Will persist all flash values.
flash.keep
# You can also use a key to keep only some kind of value.
# flash.keep(:notice)
redirect_to users_url
end
end
flash.now
By default, adding values to the flash will make them available to the next request, but sometimes you may want to access those values in the same request. For example, if the create
action fails to save a resource and you render the new
template directly, that's not going to result in a new request, but you may still want to display a message using the flash. To do this, you can use flash.now
in the same way you use the normal flash
:
class ClientsController < ApplicationController
def create
@client = Client.new(params[:client])
if @client.save
# ...
else
flash.now[:error] = "Could not save client"
render action: "new"
end
end
end
Cookies
Your application can store small amounts of data on the client — called cookies — that will be persisted across requests and even sessions. Rails provides easy access to cookies via the cookies
method, which — much like the session
— works like a hash:
class CommentsController < ApplicationController
def new
# Auto-fill the commenter's name if it has been stored in a cookie
@comment = Comment.new(author: cookies[:commenter_name])
end
def create
@comment = Comment.new(params[:comment])
if @comment.save
flash[:notice] = "Thanks for your comment!"
if params[:remember_name]
# Remember the commenter's name.
cookies[:commenter_name] = @comment.author
else
# Delete cookie for the commenter's name cookie, if any.
cookies.delete(:commenter_name)
end
redirect_to @comment.article
else
render action: "new"
end
end
end
Note that while for session values you set the key to nil
, to delete a cookie value you should use cookies.delete(:key)
.
Rendering xml and json data
ActionController makes it extremely easy to render xml
or json
data. If you generate a controller using scaffolding then it would look something like this:
class UsersController < ApplicationController
def index
@users = User.all
respond_to do |format|
format.html # index.html.erb
format.xml { render xml: @users}
format.json { render json: @users}
end
end
end
Notice that in the above case code is render xml: @users
and not render xml: @users.to_xml
. That is because if the input is not string then rails automatically invokes to_xml
.
Filters
Filters are methods that are run before, after or "around" a controller action.
Filters are inherited, so if you set a filter on ApplicationController
, it will be run on every controller in your application.
"Before" filters may halt the request cycle. A common "before" filter is one which requires that a user is logged in for an action to be run. You can define the filter method this way:
class ApplicationController < ActionController::Base
before_action :require_login
private
def require_login
unless logged_in?
flash[:error] = "You must be logged in to access this section"
redirect_to new_login_url # halts request cycle
end
end
# The logged_in? method simply returns true if the user is logged
# in and false otherwise. It does this by "booleanizing" the
# current_user method we created previously using a double ! operator.
# Note that this is not common in Ruby and is discouraged unless you
# really mean to convert something into true or false.
def logged_in?
!!current_user
end
end
The method simply stores an error message in the flash and redirects to the login form if the user is not logged in. If a "before" filter renders or redirects, the action will not run. If there are additional filters scheduled to run after that filter, they are also cancelled.
In this example the filter is added to ApplicationController
and thus all controllers in the application inherit it. This will make everything in the application require the user to be logged in in order to use it. For obvious reasons (the user wouldn't be able to log in in the first place!), not all controllers or actions should require this. You can prevent this filter from running before particular actions with skip_before_action
:
class LoginsController < ApplicationController
skip_before_action :require_login, only: [:new, :create]
end
Now, the LoginsController
's new
and create
actions will work as before without requiring the user to be logged in. The :only
option is used to only skip this filter for these actions, and there is also an :except
option which works the other way. These options can be used when adding filters too, so you can add a filter which only runs for selected actions in the first place.
After Filters and Around Filters
In addition to "before" filters, you can also run filters after an action has been executed, or both before and after.
"After" filters are similar to "before" filters, but because the action has already been run they have access to the response data that's about to be sent to the client. Obviously, "after" filters cannot stop the action from running.
"Around" filters are responsible for running their associated actions by yielding, similar to how Rack middlewares work.
For example, in a website where changes have an approval workflow an administrator could be able to preview them easily, just apply them within a transaction:
class ChangesController < ActionController::Base
around_action :wrap_in_transaction, only: :show
private
def wrap_in_transaction
ActiveRecord::Base.transaction do
begin
yield
ensure
raise ActiveRecord::Rollback
end
end
end
end
Note that an "around" filter also wraps rendering. In particular, if in the example above, the view itself reads from the database (e.g. via a scope), it will do so within the transaction and thus present the data to preview.
You can choose not to yield and build the response yourself, in which case the action will not be run.
Other Ways to Use Filters
While the most common way to use filters is by creating private methods and using *_action to add them, there are two other ways to do the same thing.
The first is to use a block directly with the *_action methods. The block receives the controller as an argument, and the require_login
filter from above could be rewritten to use a block:
class ApplicationController < ActionController::Base
before_action do |controller|
redirect_to new_login_url unless controller.send(:logged_in?)
end
end
Note that the filter in this case uses send
because the logged_in?
method is private and the filter is not run in the scope of the controller. This is not the recommended way to implement this particular filter, but in more simple cases it might be useful.
The second way is to use a class (actually, any object that responds to the right methods will do) to handle the filtering. This is useful in cases that are more complex and can not be implemented in a readable and reusable way using the two other methods. As an example, you could rewrite the login filter again to use a class:
class ApplicationController < ActionController::Base
before_action LoginFilter
end
class LoginFilter
def self.filter(controller)
unless controller.send(:logged_in?)
controller.flash[:error] = "You must be logged in"
controller.redirect_to controller.new_login_url
end
end
end
Again, this is not an ideal example for this filter, because it's not run in the scope of the controller but gets the controller passed as an argument. The filter class has a class method filter
which gets run before or after the action, depending on if it's a before or after filter. Classes used as around filters can also use the same filter
method, which will get run in the same way. The method must yield
to execute the action. Alternatively, it can have both a before
and an after
method that are run before and after the action.
Request Forgery Protection
Cross-site request forgery is a type of attack in which a site tricks a user into making requests on another site, possibly adding, modifying or deleting data on that site without the user's knowledge or permission.
The first step to avoid this is to make sure all "destructive" actions (create, update and destroy) can only be accessed with non-GET requests. If you're following RESTful conventions you're already doing this. However, a malicious site can still send a non-GET request to your site quite easily, and that's where the request forgery protection comes in. As the name says, it protects from forged requests.
The way this is done is to add a non-guessable token which is only known to your server to each request. This way, if a request comes in without the proper token, it will be denied access.
If you generate a form like this:
<%= form_for @user do |f| %>
<%= f.text_field :username %>
<%= f.text_field :password %>
<% end %>
You will see how the token gets added as a hidden field:
<form accept-charset="UTF-8" action="/users/1" method="post">
<input type="hidden"
value="67250ab105eb5ad10851c00a5621854a23af5489"
name="authenticity_token"/>
<!-- fields -->
</form>
Rails adds this token to every form that's generated using the form helpers, so most of the time you don't have to worry about it. If you're writing a form manually or need to add the token for another reason, it's available through the method form_authenticity_token
:
The form_authenticity_token
generates a valid authentication token. That's useful in places where Rails does not add it automatically, like in custom Ajax calls.
The Security Guide has more about this and a lot of other security-related issues that you should be aware of when developing a web application.
The Request and Response Objects
In every controller there are two accessor methods pointing to the request and the response objects associated with the request cycle that is currently in execution. The request
method contains an instance of AbstractRequest
and the response
method returns a response object representing what is going to be sent back to the client.
The request
Object
The request object contains a lot of useful information about the request coming in from the client. To get a full list of the available methods, refer to the API documentation. Among the properties that you can access on this object are:
Property of request |
Purpose |
---|---|
host | The hostname used for this request. |
domain(n=2) | The hostname's first n segments, starting from the right (the TLD). |
format | The content type requested by the client. |
method | The HTTP method used for the request. |
get?, post?, patch?, put?, delete?, head? | Returns true if the HTTP method is GET/POST/PATCH/PUT/DELETE/HEAD. |
headers | Returns a hash containing the headers associated with the request. |
port | The port number (integer) used for the request. |
protocol | Returns a string containing the protocol used plus "://", for example "http://". |
query_string | The query string part of the URL, i.e., everything after "?". |
remote_ip | The IP address of the client. |
url | The entire URL used for the request. |
path_parameters
, query_parameters
, and request_parameters
Rails collects all of the parameters sent along with the request in the params
hash, whether they are sent as part of the query string or the post body. The request object has three accessors that give you access to these parameters depending on where they came from. The query_parameters
hash contains parameters that were sent as part of the query string while the request_parameters
hash contains parameters sent as part of the post body. The path_parameters
hash contains parameters that were recognized by the routing as being part of the path leading to this particular controller and action.
The response
Object
The response object is not usually used directly, but is built up during the execution of the action and rendering of the data that is being sent back to the user, but sometimes - like in an after filter - it can be useful to access the response directly. Some of these accessor methods also have setters, allowing you to change their values.
Property of response |
Purpose |
---|---|
body | This is the string of data being sent back to the client. This is most often HTML. |
status | The HTTP status code for the response, like 200 for a successful request or 404 for file not found. |
location | The URL the client is being redirected to, if any. |
content_type | The content type of the response. |
charset | The character set being used for the response. Default is "utf-8". |
headers | Headers used for the response. |
Setting Custom Headers
If you want to set custom headers for a response then response.headers
is the place to do it. The headers attribute is a hash which maps header names to their values, and Rails will set some of them automatically. If you want to add or change a header, just assign it to response.headers
this way:
response.headers["Content-Type"] = "application/pdf"
Note: in the above case it would make more sense to use the content_type
setter directly.
HTTP Authentications
Rails comes with two built-in HTTP authentication mechanisms:
- Basic Authentication
- Digest Authentication
HTTP Basic Authentication
HTTP basic authentication is an authentication scheme that is supported by the majority of browsers and other HTTP clients. As an example, consider an administration section which will only be available by entering a username and a password into the browser's HTTP basic dialog window. Using the built-in authentication is quite easy and only requires you to use one method, http_basic_authenticate_with
.
class AdminController < ApplicationController
http_basic_authenticate_with name: "humbaba", password: "5baa61e4"
end
With this in place, you can create namespaced controllers that inherit from AdminController
. The filter will thus be run for all actions in those controllers, protecting them with HTTP basic authentication.
HTTP Digest Authentication
HTTP digest authentication is superior to the basic authentication as it does not require the client to send an unencrypted password over the network (though HTTP basic authentication is safe over HTTPS). Using digest authentication with Rails is quite easy and only requires using one method, authenticate_or_request_with_http_digest
.
class AdminController < ApplicationController
USERS = { "lifo" => "world" }
before_action :authenticate
private
def authenticate
authenticate_or_request_with_http_digest do |username|
USERS[username]
end
end
end
As seen in the example above, the authenticate_or_request_with_http_digest
block takes only one argument - the username. And the block returns the password. Returning false
or nil
from the authenticate_or_request_with_http_digest
will cause authentication failure.
Streaming and File Downloads
Sometimes you may want to send a file to the user instead of rendering an HTML page. All controllers in Rails have the send_data
and the send_file
methods, which will both stream data to the client. send_file
is a convenience method that lets you provide the name of a file on the disk and it will stream the contents of that file for you.
To stream data to the client, use send_data
:
require "prawn"
class ClientsController < ApplicationController
# Generates a PDF document with information on the client and
# returns it. The user will get the PDF as a file download.
def download_pdf
client = Client.find(params[:id])
send_data generate_pdf(client),
filename: "#{client.name}.pdf",
type: "application/pdf"
end
private
def generate_pdf(client)
Prawn::Document.new do
text client.name, align: :center
text "Address: #{client.address}"
text "Email: #{client.email}"
end.render
end
end
The download_pdf
action in the example above will call a private method which actually generates the PDF document and returns it as a string. This string will then be streamed to the client as a file download and a filename will be suggested to the user. Sometimes when streaming files to the user, you may not want them to download the file. Take images, for example, which can be embedded into HTML pages. To tell the browser a file is not meant to be downloaded, you can set the :disposition
option to "inline". The opposite and default value for this option is "attachment".
Sending Files
If you want to send a file that already exists on disk, use the send_file
method.
class ClientsController < ApplicationController
# Stream a file that has already been generated and stored on disk.
def download_pdf
client = Client.find(params[:id])
send_file("#{Rails.root}/files/clients/#{client.id}.pdf",
filename: "#{client.name}.pdf",
type: "application/pdf")
end
end
This will read and stream the file 4kB at the time, avoiding loading the entire file into memory at once. You can turn off streaming with the :stream
option or adjust the block size with the :buffer_size
option.
If :type
is not specified, it will be guessed from the file extension specified in :filename
. If the content type is not registered for the extension, application/octet-stream
will be used.
WARNING: Be careful when using data coming from the client (params, cookies, etc.) to locate the file on disk, as this is a security risk that might allow someone to gain access to files they are not meant to.
TIP: It is not recommended that you stream static files through Rails if you can instead keep them in a public folder on your web server. It is much more efficient to let the user download the file directly using Apache or another web server, keeping the request from unnecessarily going through the whole Rails stack.
RESTful Downloads
While send_data
works just fine, if you are creating a RESTful application having separate actions for file downloads is usually not necessary. In REST terminology, the PDF file from the example above can be considered just another representation of the client resource. Rails provides an easy and quite sleek way of doing "RESTful downloads". Here's how you can rewrite the example so that the PDF download is a part of the show
action, without any streaming:
class ClientsController < ApplicationController
# The user can request to receive this resource as HTML or PDF.
def show
@client = Client.find(params[:id])
respond_to do |format|
format.html
format.pdf { render pdf: generate_pdf(@client) }
end
end
end
In order for this example to work, you have to add the PDF MIME type to Rails. This can be done by adding the following line to the file config/initializers/mime_types.rb
:
Mime::Type.register "application/pdf", :pdf
NOTE: Configuration files are not reloaded on each request, so you have to restart the server in order for their changes to take effect.
Now the user can request to get a PDF version of a client just by adding ".pdf" to the URL:
GET /clients/1.pdf
Log Filtering
Rails keeps a log file for each environment in the log
folder. These are extremely useful when debugging what's actually going on in your application, but in a live application you may not want every bit of information to be stored in the log file.
Parameters Filtering
You can filter certain request parameters from your log files by appending them to config.filter_parameters
in the application configuration. These parameters will be marked [FILTERED] in the log.
config.filter_parameters << :password
Redirects Filtering
Sometimes it's desirable to filter out from log files some sensible locations your application is redirecting to.
You can do that by using the config.filter_redirect
configuration option:
config.filter_redirect << 's3.amazonaws.com'
You can set it to a String, a Regexp, or an array of both.
config.filter_redirect.concat ['s3.amazonaws.com', /private_path/]
Matching URLs will be marked as '[FILTERED]'.
Rescue
Most likely your application is going to contain bugs or otherwise throw an exception that needs to be handled. For example, if the user follows a link to a resource that no longer exists in the database, Active Record will throw the ActiveRecord::RecordNotFound
exception.
Rails' default exception handling displays a "500 Server Error" message for all exceptions. If the request was made locally, a nice traceback and some added information gets displayed so you can figure out what went wrong and deal with it. If the request was remote Rails will just display a simple "500 Server Error" message to the user, or a "404 Not Found" if there was a routing error or a record could not be found. Sometimes you might want to customize how these errors are caught and how they're displayed to the user. There are several levels of exception handling available in a Rails application:
The Default 500 and 404 Templates
By default a production application will render either a 404 or a 500 error message. These messages are contained in static HTML files in the public
folder, in 404.html
and 500.html
respectively. You can customize these files to add some extra information and layout, but remember that they are static; i.e. you can't use RHTML or layouts in them, just plain HTML.
rescue_from
If you want to do something a bit more elaborate when catching errors, you can use rescue_from
, which handles exceptions of a certain type (or multiple types) in an entire controller and its subclasses.
When an exception occurs which is caught by a rescue_from
directive, the exception object is passed to the handler. The handler can be a method or a Proc
object passed to the :with
option. You can also use a block directly instead of an explicit Proc
object.
Here's how you can use rescue_from
to intercept all ActiveRecord::RecordNotFound
errors and do something with them.
class ApplicationController < ActionController::Base
rescue_from ActiveRecord::RecordNotFound, with: :record_not_found
private
def record_not_found
render text: "404 Not Found", status: 404
end
end
Of course, this example is anything but elaborate and doesn't improve on the default exception handling at all, but once you can catch all those exceptions you're free to do whatever you want with them. For example, you could create custom exception classes that will be thrown when a user doesn't have access to a certain section of your application:
class ApplicationController < ActionController::Base
rescue_from User::NotAuthorized, with: :user_not_authorized
private
def user_not_authorized
flash[:error] = "You don't have access to this section."
redirect_to :back
end
end
class ClientsController < ApplicationController
# Check that the user has the right authorization to access clients.
before_action :check_authorization
# Note how the actions don't have to worry about all the auth stuff.
def edit
@client = Client.find(params[:id])
end
private
# If the user is not authorized, just throw the exception.
def check_authorization
raise User::NotAuthorized unless current_user.admin?
end
end
NOTE: Certain exceptions are only rescuable from the ApplicationController
class, as they are raised before the controller gets initialized and the action gets executed. See Pratik Naik's article on the subject for more information.
Force HTTPS protocol
Sometime you might want to force a particular controller to only be accessible via an HTTPS protocol for security reasons. You can use the force_ssl
method in your controller to enforce that:
class DinnerController
force_ssl
end
Just like the filter, you could also pass :only
and :except
to enforce the secure connection only to specific actions:
class DinnerController
force_ssl only: :cheeseburger
# or
force_ssl except: :cheeseburger
end
Please note that if you find yourself adding force_ssl
to many controllers, you may want to force the whole application to use HTTPS instead. In that case, you can set the config.force_ssl
in your environment file.