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yet another pass on the action controller guide

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333 railties/guides/source/action_controller_overview.textile
@@ -12,9 +12,9 @@ In this guide you will learn how controllers work and how they fit into the requ
endprologue.
-h3. What Does a Controller do?
+h3. 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 straight-forward as possible.
+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.
@@ -24,31 +24,16 @@ NOTE: For more details on the routing process, see "Rails Routing from the Outsi
h3. 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 public method with the same name as the action.
+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.
<ruby>
class ClientsController < ApplicationController
-
- # Actions are public methods
def new
end
-
- # Action methods are responsible for producing output
- def edit
- end
-
-# Helper methods are private and can not be used as actions
-private
-
- def foo
- end
-
end
</ruby>
-There's no rule saying a method on a controller has to be an action; they may well be used for other purposes such as filters, which will be covered later in this guide.
-
-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:
+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+:
<ruby>
def new
@@ -58,8 +43,9 @@ end
The "Layouts & rendering guide":layouts_and_rendering.html 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.
++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.
h3. Parameters
@@ -67,11 +53,11 @@ You will probably want to access data sent in by the user or other parameters in
<ruby>
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
+ # 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
@@ -80,24 +66,24 @@ class ClientsController < ActionController::Base
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.
+ # 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.
+ # This line overrides the default rendering behavior, which
+ # would have been to render the "create" view.
render :action => "new"
end
end
-
end
</ruby>
-h4. Hash and Array Parameters
+h4. 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:
@@ -105,7 +91,7 @@ The +params+ hash is not limited to one-dimensional keys and values. It can cont
GET /clients?ids[]=1&ids[]=2&ids[]=3
</pre>
-NOTE: The actual URL in this example will be encoded as "/clients?ids%5b%5d=1&ids%5b%5d=2&ids%5b%5b=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.
+NOTE: The actual URL in this example will be encoded as "/clients?ids%5b%5d=1&ids%5b%5d=2&ids%5b%5b=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.
@@ -120,18 +106,19 @@ To send a hash you include the key name inside the brackets:
</form>
</html>
-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]+.
+When this form is submitted, the value of +params[:client]+ will be <tt>{"name" => "Acme", "phone" => "12345", "address" => {"postcode" => "12345", "city" => "Carrot City"}}</tt>. Note the nested hash in +params[:client][:address]+.
-Note that the +params+ hash is actually an instance of HashWithIndifferentAccess from Active Support, which is a subclass of Hash that lets you use symbols and strings interchangeably as keys.
+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.
h4. 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:
<ruby>
-# ...
-map.connect "/clients/:status", :controller => "clients", :action => "index", :foo => "bar"
-# ...
+map.connect "/clients/:status",
+ :controller => "clients",
+ :action => "index",
+ :foo => "bar"
</ruby>
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".
@@ -142,16 +129,14 @@ You can set global default parameters that will be used when generating URLs wit
<ruby>
class ApplicationController < ActionController::Base
-
# The options parameter is the hash passed in to 'url_for'
def default_url_options(options)
{:locale => I18n.locale}
end
-
end
</ruby>
-These options will be used as a starting-point when generating URLs, so it's possible they'll be overridden by +url_for+. Because this method is defined in the controller, you can define it on ApplicationController so it would be used for all URL generation, or you could define it on only one controller for all URLs generated there.
+These options will be used as a starting-point when generating URLs, so it's possible they'll be overridden by +url_for+. Because this method is defined in the controller, you can define it on +ApplicationController+ so it would be used for all URL generation, or you could define it on only one controller for all URLs generated there.
h3. Session
@@ -165,9 +150,9 @@ Your application has a session for each user in which you can store small amount
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 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).
+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.
+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.
Read more about session storage in the "Security Guide":security.html.
@@ -195,7 +180,7 @@ ActionController::Base.session = {
NOTE: Changing the secret when using the CookieStore will invalidate all existing sessions.
-h4. Accessing the Session
+h4. Accessing the session
In your controller you can access the session through the +session+ instance method.
@@ -208,13 +193,14 @@ 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.
+ # 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(session[:current_user_id])
+ @_current_user ||= session[:current_user_id] &&
+ User.find(session[:current_user_id])
end
-
end
</ruby>
@@ -222,16 +208,15 @@ To store something in the session, just assign it to the key like a hash:
<ruby>
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
+ 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
</ruby>
@@ -239,14 +224,12 @@ To remove something from the session, assign that key to be +nil+:
<ruby>
class LoginsController < ApplicationController
-
# "Delete" a login, aka "log the user out"
def destroy
# Remove the user id from the session
session[:current_user_id] = nil
redirect_to root_url
end
-
end
</ruby>
@@ -258,13 +241,11 @@ The flash is a special part of the session which is cleared with each request. T
<ruby>
class LoginsController < ApplicationController
-
def destroy
session[:current_user_id] = nil
flash[:notice] = "You have successfully logged out"
redirect_to root_url
end
-
end
</ruby>
@@ -291,17 +272,19 @@ If you want a flash value to be carried over to another request, use the +keep+
<ruby>
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.
+ # 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
- flash.keep # Will persist all flash values. You can also use a key to keep
- # only that kind of value: flash.keep(:notice)
+ # 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
</ruby>
@@ -311,7 +294,6 @@ By default, adding values to the flash will make them available to the next requ
<ruby>
class ClientsController < ApplicationController
-
def create
@client = Client.new(params[:client])
if @client.save
@@ -321,17 +303,15 @@ class ClientsController < ApplicationController
render :action => "new"
end
end
-
end
</ruby>
h3. 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:
+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:
<ruby>
class CommentsController < ApplicationController
-
def new
# Auto-fill the commenter's name if it has been stored in a cookie
@comment = Comment.new(:name => cookies[:commenter_name])
@@ -342,10 +322,10 @@ class CommentsController < ApplicationController
if @comment.save
flash[:notice] = "Thanks for your comment!"
if params[:remember_name]
- # Remember the commenter's name
+ # Remember the commenter's name.
cookies[:commenter_name] = @comment.name
else
- # Don't remember, and delete the name if it has been remembered before
+ # Delete cookie for the commenter's name cookie, if any.
cookies.delete(:commenter_name)
end
redirect_to @comment.article
@@ -353,7 +333,6 @@ class CommentsController < ApplicationController
render :action => "new"
end
end
-
end
</ruby>
@@ -361,78 +340,70 @@ Note that while for session values you set the key to +nil+, to delete a cookie
h3. Filters
-Filters are methods that are run before, after or "around" a controller action. For example, one filter might check to see if the logged in user has the right credentials to access that particular controller or action. Filters are inherited, so if you set a filter on ApplicationController, it will be run on every controller in your application. A common, simple 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:
+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:
<ruby>
class ApplicationController < ActionController::Base
+ before_filter :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 # Prevents the current action from running
+ 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.
+ # 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
</ruby>
-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 (a filter which is run before the action) renders or redirects, the action will not run. If there are additional filters scheduled to run after the rendering or redirecting filter, they are also cancelled. To use this filter in a controller, use the +before_filter+ method:
-
-<ruby>
-class ApplicationController < ActionController::Base
-
- before_filter :require_login
-
-end
-</ruby>
+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. 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_filter+:
+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_filter+:
<ruby>
class LoginsController < Application
-
skip_before_filter :require_login, :only => [:new, :create]
-
end
</ruby>
-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.
+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.
-h4. After Filters and Around Filters
+h4. After filters and around filters
-In addition to the before filters, you can run filters after an action has run or both before and after. The after filter is similar to the before filter, but because the action has already been run it has access to the response data that's about to be sent to the client. Obviously, after filters can not stop the action from running. Around filters are responsible for running the action, but they can choose not to, which is the around filter's way of stopping it.
+In addition to before filters, you can run filters after an action has run or both before and after. The after filter is similar to the before filter, but because the action has already been run it has access to the response data that's about to be sent to the client. Obviously, after filters can not stop the action from running.
+
+Around filters are responsible for running the action, but they can choose not to, which is the around filter's way of stopping it.
<ruby>
# Example taken from the Rails API filter documentation:
# http://api.rubyonrails.org/classes/ActionController/Filters/ClassMethods.html
class ApplicationController < Application
-
around_filter :catch_exceptions
private
-
def catch_exceptions
yield
rescue => exception
logger.debug "Caught exception! #{exception}"
raise
end
-
end
</ruby>
-h4. Other Ways to Use Filters
+h4. Other ways to use filters
While the most common way to use filters is by creating private methods and using *_filter to add them, there are two other ways to do the same thing.
@@ -440,9 +411,9 @@ The first is to use a block directly with the *_filter methods. The block receiv
<ruby>
class ApplicationController < ActionController::Base
-
- before_filter { |controller| redirect_to new_login_url unless controller.send(:logged_in?) }
-
+ before_filter do |controller|
+ redirect_to new_login_url unless controller.send(:logged_in?)
+ end
end
</ruby>
@@ -452,20 +423,16 @@ The second way is to use a class (actually, any object that responds to the righ
<ruby>
class ApplicationController < ActionController::Base
-
before_filter LoginFilter
-
end
class LoginFilter
-
def self.filter(controller)
- unless logged_in?
- controller.flash[:error] = "You must be logged in to access this section"
+ unless controller.send(:logged_in?)
+ controller.flash[:error] = "You must be logged in"
controller.redirect_to controller.new_login_url
end
end
-
end
</ruby>
@@ -475,16 +442,17 @@ The Rails API documentation has "more information on using filters":http://api.r
h3. Verification
-Verifications make sure certain criteria are met in order for a controller or action to run. They can specify that a certain key (or several keys in the form of an array) is present in the +params+, +session+ or +flash+ hashes or that a certain HTTP method was used or that the request was made using XMLHTTPRequest (Ajax). The default action taken when these criteria are not met is to render a 400 Bad Request response, but you can customize this by specifying a redirect URL or rendering something else and you can also add flash messages and HTTP headers to the response. It is described in the "API documentation":http://api.rubyonrails.org/classes/ActionController/Verification/ClassMethods.html as "essentially a special kind of before_filter".
+Verifications make sure certain criteria are met in order for a controller or action to run. They can specify that a certain key (or several keys in the form of an array) is present in the +params+, +session+ or +flash+ hashes or that a certain HTTP method was used or that the request was made using +XMLHTTPRequest+ (Ajax). The default action taken when these criteria are not met is to render a 400 Bad Request response, but you can customize this by specifying a redirect URL or rendering something else and you can also add flash messages and HTTP headers to the response. It is described in the "API documentation":http://api.rubyonrails.org/classes/ActionController/Verification/ClassMethods.html as "essentially a special kind of before_filter".
Here's an example of using verification to make sure the user supplies a username and a password in order to log in:
<ruby>
class LoginsController < ApplicationController
-
verify :params => [:username, :password],
:render => {:action => "new"},
- :add_flash => {:error => "Username and password required to log in"}
+ :add_flash => {
+ :error => "Username and password required to log in"
+ }
def create
@user = User.authenticate(params[:username], params[:password])
@@ -495,7 +463,6 @@ class LoginsController < ApplicationController
render :action => "new"
end
end
-
end
</ruby>
@@ -503,18 +470,22 @@ Now the +create+ action won't run unless the "username" and "password" parameter
<ruby>
class LoginsController < ApplicationController
-
verify :params => [:username, :password],
:render => {:action => "new"},
- :add_flash => {:error => "Username and password required to log in"},
- :only => :create # Only run this verification for the "create" action
-
+ :add_flash => {
+ :error => "Username and password required to log in"
+ },
+ :only => :create # Run only for the "create" action
end
</ruby>
h3. 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.
+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:
@@ -527,30 +498,26 @@ If you generate a form like this:
You will see how the token gets added as a hidden field:
-<ruby>
+<html>
<form action="/users/1" method="post">
-<div><!-- ... --><input type="hidden" value="67250ab105eb5ad10851c00a5621854a23af5489" name="authenticity_token"/></div>
-<!-- Fields -->
+<input type="hidden"
+ value="67250ab105eb5ad10851c00a5621854a23af5489"
+ name="authenticity_token"/>
+<!-- fields -->
</form>
-</ruby>
+</html>
Rails adds this token to every form that's generated using the "form helpers":form_helpers.html, 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+:
-TODO: Add line below as description
-
-Add a JavaScript variable containing the token for use with Ajax
-
-<erb>
-<%= javascript_tag "MyApp.authenticity_token = '#{form_authenticity_token}'" %>
-</erb>
+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":security.html has more about this and a lot of other security-related issues that you should be aware of when developing a web application.
-h3. The request and response Objects
+h3. 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.
+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.
-h4. The request Object
+h4. 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":http://api.rubyonrails.org/classes/ActionController/AbstractRequest.html. Among the properties that you can access on this object are:
@@ -566,11 +533,11 @@ The request object contains a lot of useful information about the request coming
* remote_ip - The IP address of the client.
* url - The entire URL used for the request.
-h5. path_parameters, query_parameters, and request_parameters
+h5. +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.
-h4. The response Object
+h4. 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.
@@ -578,12 +545,12 @@ The response object is not usually used directly, but is built up during the exe
* 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 "utf8".
+* charset - The character set being used for the response. Default is "utf-8".
* headers - Headers used for the response.
-h5. Setting Custom Headers
+h5. 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 - like "Content-Type" - automatically. If you want to add or change a header, just assign it to +headers+ with the name and value:
+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:
<ruby>
response.headers["Content-Type"] = "application/pdf"
@@ -596,49 +563,44 @@ Rails comes with two built-in HTTP authentication mechanisms:
* Basic Authentication
* Digest Authentication
-h4. HTTP Basic Authentication
+h4. 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, +authenticate_or_request_with_http_basic+.
<ruby>
class AdminController < ApplicationController
-
- USERNAME, PASSWORD = "humbaba", "5baa61e4c9b93f3f0682250b6cf8331b7ee68fd8"
+ USERNAME, PASSWORD = "humbaba", "5baa61e4"
before_filter :authenticate
- private
-
+private
def authenticate
authenticate_or_request_with_http_basic do |username, password|
- username == USERNAME && Digest::SHA1.hexdigest(password) == PASSWORD
+ username == USERNAME &&
+ Digest::SHA1.hexdigest(password) == PASSWORD
end
end
-
end
</ruby>
-With this in place, you can create namespaced controllers that inherit from AdminController. The before filter will thus be run for all actions in those controllers, protecting them with HTTP basic authentication.
+With this in place, you can create namespaced controllers that inherit from +AdminController+. The before filter will thus be run for all actions in those controllers, protecting them with HTTP basic authentication.
-h4. HTTP Digest Authentication
+h4. HTTP digest authentication
-HTTP digest authentication is superior to the basic authentication as it does not require the client to send unencrypted password over the network. Using digest authentication with Rails is quite easy and only requires using one method, +authenticate_or_request_with_http_digest+.
+HTTP digest authentication is superior to the basic authentication as it does not require the client to send 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+.
<ruby>
class AdminController < ApplicationController
-
USERS = { "lifo" => "world" }
before_filter :authenticate
- private
-
+private
def authenticate
authenticate_or_request_with_http_digest do |username|
USERS[username]
end
end
-
end
</ruby>
@@ -653,12 +615,13 @@ To stream data to the client, use +send_data+:
<ruby>
require "prawn"
class ClientsController < ApplicationController
-
- # Generate a PDF document with information on the client and return it.
- # The user will get the PDF as a file download.
+ # 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, :filename => "#{client.name}.pdf", :type => "application/pdf")
+ send_data(generate_pdf,
+ :filename => "#{client.name}.pdf",
+ :type => "application/pdf")
end
private
@@ -670,51 +633,48 @@ private
text "Email: #{client.email}"
end.render
end
-
end
</ruby>
-The +download_pdf+ action in the example above will call a private method which actually generates the file (a 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".
+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".
-h4. Sending Files
+h4. Sending files
-If you want to send a file that already exists on disk, use the +send_file+ method. This is usually not recommended, but can be useful if you want to perform some authentication before letting the user download the file.
+If you want to send a file that already exists on disk, use the +send_file+ method.
<ruby>
class ClientsController < ApplicationController
-
- # Stream a file that has already been generated and stored on disk
+ # Stream a file that has already been generated and stored on disk.
def download_pdf
client = Client.find(params[:id])
- send_data("#{RAILS_ROOT}/files/clients/#{client.id}.pdf", :filename => "#{client.name}.pdf", :type => "application/pdf")
+ send_data("#{RAILS_ROOT}/files/clients/#{client.id}.pdf",
+ :filename => "#{client.name}.pdf",
+ :type => "application/pdf")
end
-
end
</ruby>
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.
-WARNING: Be careful when using (or just don't use) "outside" data (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 see.
+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 see.
-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. Although if you do need the request to go through Rails for some reason, you can set the +:x_sendfile+ option to true, and Rails will let the web server handle sending the file to the user, freeing up the Rails process to do other things. Note that your web server needs to support the +X-Sendfile+ header for this to work, and you still have to be careful not to use user input in a way that lets someone retrieve arbitrary files.
+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. Although if you do need the request to go through Rails for some reason, you can set the +:x_sendfile+ option to true, and Rails will let the web server handle sending the file to the user, freeing up the Rails process to do other things. Note that your web server needs to support the +X-Sendfile+ header for this to work.
-h4. RESTful Downloads
+h4. 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:
<ruby>
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) }
+ format.pdf { render :pdf => generate_pdf(@client) }
end
end
-
end
</ruby>
@@ -728,19 +688,17 @@ NOTE: Configuration files are not reloaded on each request, so you have to resta
Now the user can request to get a PDF version of a client just by adding ".pdf" to the URL:
-<ruby>
+<shell>
GET /clients/1.pdf
-</ruby>
+</shell>
h3. Parameter Filtering
-Rails keeps a log file for each environment (development, test, and production) 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. The +filter_parameter_logging+ method can be used to filter out sensitive information from the log. It works by replacing certain values in the +params+ hash with "[FILTERED]" as they are written to the log. As an example, let's see how to filter all parameters with keys that include "password":
+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. The +filter_parameter_logging+ method can be used to filter out sensitive information from the log. It works by replacing certain values in the +params+ hash with "[FILTERED]" as they are written to the log. As an example, let's see how to filter all parameters with keys that include "password":
<ruby>
class ApplicationController < ActionController::Base
-
filter_parameter_logging :password
-
end
</ruby>
@@ -748,29 +706,30 @@ The method works recursively through all levels of the +params+ hash and takes a
h3. 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:
+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.
-h4. The Default 500 and 404 Templates
+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:
+
+h4. 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.
-h4. rescue_from
+h4. +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.
-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.
+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.
+Here's how you can use +rescue_from+ to intercept all +ActiveRecord::RecordNotFound+ errors and do something with them.
<ruby>
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
</ruby>
@@ -778,20 +737,16 @@ Of course, this example is anything but elaborate and doesn't improve on the def
<ruby>
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_filter :check_authorization
@@ -801,19 +756,19 @@ class ClientsController < ApplicationController
end
private
-
# If the user is not authorized, just throw the exception.
def check_authorization
raise User::NotAuthorized unless current_user.admin?
end
-
end
</ruby>
-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":http://m.onkey.org/2008/7/20/rescue-from-dispatching on the subject for more information.
+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":http://m.onkey.org/2008/7/20/rescue-from-dispatching on the subject for more information.
h3. Changelog
"Lighthouse Ticket":http://rails.lighthouseapp.com/projects/16213-rails-guides/tickets/17
+* February 17, 2009: Yet another proofread by Xavier Noria.
+
* November 4, 2008: First release version by Tore Darell
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