NAME
Catalyst::View::JSON - JSON view for your data
SYNOPSIS
# lib/MyApp/View/JSON.pm
package MyApp::View::JSON;
use base qw( Catalyst::View::JSON );
1;
# configure in lib/MyApp.pm
MyApp->config({
...
'View::JSON' => {
allow_callback => 1, # defaults to 0
callback_param => 'cb', # defaults to 'callback'
expose_stash => [ qw(foo bar) ], # defaults to everything
},
});
sub hello : Local {
my($self, $c) = @_;
$c->stash->{message} = 'Hello World!';
$c->forward('View::JSON');
}
DESCRIPTION
Catalyst::View::JSON is a Catalyst View handler that returns stash data
in JSON format.
CONFIG VARIABLES
allow_callback
Flag to allow callbacks by adding "callback=function". Defaults to 0
(doesn't allow callbacks). See "CALLBACKS" for details.
callback_param
Name of URI parameter to specify JSON callback function name.
Defaults to "callback". Only effective when "allow_callback" is
turned on.
expose_stash
Scalar, List or regular expression object, to specify which stash
keys are exposed as a JSON response. Defaults to everything.
Examples configuration:
# use 'json_data' value as a data to return
expose_stash => 'json_data',
# only exposes keys 'foo' and 'bar'
expose_stash => [ qw( foo bar ) ],
# only exposes keys that matches with /^json_/
expose_stash => qr/^json_/,
Suppose you have data structure of the following.
$c->stash->{foo} = [ 1, 2 ];
$c->stash->{bar} = 2;
By default, this view will return:
{"foo":[1,2],"bar":2}
When you set "expose_stash => [ 'foo' ]", it'll return
{"foo":[1,2]}
and in the case of "expose_stash => 'foo'", it'll just return
[1,2]
instead of the whole object (hashref in perl). This option will be
useful when you share the method with different views (e.g. TT) and
don't want to expose non-irrelevant stash variables as in JSON.
no_x_json_header
no_x_json_header: 1
By default this plugin sets X-JSON header if the requested client is
a Prototype.js with X-JSON support. By setting 1, you can opt-out
this behavior so that you can do eval() by your own. Defaults to 0.
json_encoder_args
An optional hashref that supplies arguments to JSON::MaybeXS used
when creating a new object.
use_force_bom
If versions of this view older than 0.36, there was some code that
added a UTF-8 BOM marker to the end of the JSON string when the user
agent was Safari. After looking at a lot of existing code I don't
think this is needed anymore so we removed it by default. However if
this turns out to be a problem you can re enable it by setting this
attribute to true. Possible a breaking change so we offer this
workaround.
You may also override the method 'user_agent_bom_test' which
received the current request user agent string to try and better
determine if this is needed. Patches for this welcomed.
METHODS
process
Standard target of $c->forward used to prepare a response
render
The methods accepts either of the following argument signatures in order
to promote compatibility with the semi standard render method as define
in numerous Catalyst views on CPAN:
my $json_string = $c->view('JSON')->render($c, undef, $data);
my $json_string = $c->view('JSON')->render($c, $data);
Given '$data' returns the JSON serialized version, or throws and error.
OVERRIDING JSON ENCODER
By default it uses JSON::MaybeXS::encode_json to serialize perl data
structure into JSON data format. If you want to avoid this and encode
with your own encoder (like passing different options to JSON::MaybeXS
etc.), you can implement the "encode_json" method in your View class.
package MyApp::View::JSON;
use base qw( Catalyst::View::JSON );
use JSON::MaybeXS ();
sub encode_json {
my($self, $c, $data) = @_;
my $encoder = JSON::MaybeXS->new->(ascii => 1, pretty => 1, allow_nonref => 1);
$encoder->encode($data);
}
1;
ENCODINGS
NOTE Starting in release v5.90080 Catalyst encodes all text like body
returns as UTF8. It however ignores content types like application/json
and assumes that a correct JSON serializer is doing what it is supposed
to do, which is encode UTF8 automatically. In general this is what this
view does so you shoulding need to mess with the encoding flag here
unless you have some odd case.
Also, the comment about regard 'browser gotcha's' was written a number
of years ago and I can't say one way or another if those gotchas
continue to be common in the wild.
NOTE Setting this configuation has no bearing on how the actual
serialized string is encoded. This ONLY sets the content type header in
your response. By default we set the 'utf8' flag on JSON::MaybeXS so
that the string generated and set to your response body is proper UTF8
octets that can be transmitted over HTTP. If you are planning to do some
alternative encoding you should turn off this default via the
"json_encoder_args":
MyApp::View::JSON->config(
json_encoder_args => +{utf8=>0} );
NOTE In 2015 the use of UTF8 as encoding is widely standard so it is
very likely you should need to do nothing to get the correct encoding.
The following documentation will remain for historical value and
backcompat needs.
Due to the browser gotchas like those of Safari and Opera, sometimes you
have to specify a valid charset value in the response's Content-Type
header, e.g. "text/javascript; charset=utf-8".
Catalyst::View::JSON comes with the configuration variable "encoding"
which defaults to utf-8. You can change it via "YourApp->config" or even
runtime, using "component".
$c->component('View::JSON')->encoding('euc-jp');
This assumes you set your stash data in raw euc-jp bytes, or Unicode
flagged variable. In case of Unicode flagged variable,
Catalyst::View::JSON automatically encodes the data into your "encoding"
value (euc-jp in this case) before emitting the data to the browser.
Another option would be to use *JavaScript-UCS* as an encoding (and pass
Unicode flagged string to the stash). That way all non-ASCII characters
in the output JSON will be automatically encoded to JavaScript Unicode
encoding like *\uXXXX*. You have to install Encode::JavaScript::UCS to
use the encoding.
CALLBACKS
By default it returns raw JSON data so your JavaScript app can deal with
using XMLHttpRequest calls. Adding callbacks (JSONP) to the API gives
more flexibility to the end users of the API: overcome the cross-domain
restrictions of XMLHttpRequest. It can be done by appending *script*
node with dynamic DOM manipulation, and associate callback handler to
the returned data.
For example, suppose you have the following code.
sub end : Private {
my($self, $c) = @_;
if ($c->req->param('output') eq 'json') {
$c->forward('View::JSON');
} else {
...
}
}
"/foo/bar?output=json" will just return the data set in "$c->stash" as
JSON format, like:
{ result: "foo", message: "Hello" }
but "/foo/bar?output=json&callback=handle_result" will give you:
handle_result({ result: "foo", message: "Hello" });
and you can write a custom "handle_result" function to handle the
returned data asynchronously.
The valid characters you can use in the callback function are
[a-zA-Z0-9\.\_\[\]]
but you can customize the behaviour by overriding the
"validate_callback_param" method in your View::JSON class.
See <http://developer.yahoo.net/common/json.html> and
<http://ajaxian.com/archives/jsonp-json-with-padding> for more about
JSONP.
NOTE For another way to enable JSONP in your application take a look at
Plack::Middleware::JSONP
INTEROPERABILITY
JSON use is still developing and has not been standardized. This section
provides some notes on various libraries.
Dojo Toolkit: Setting dojo.io.bind's mimetype to 'text/json' in the
JavaScript request will instruct dojo.io.bind to expect JSON data in the
response body and auto-eval it. Dojo ignores the server response
Content-Type. This works transparently with Catalyst::View::JSON.
Prototype.js: prototype.js will auto-eval JSON data that is returned in
the custom X-JSON header. The reason given for this is to allow a
separate HTML fragment in the response body, however this of limited use
because IE 6 has a max header length that will cause the JSON evaluation
to silently fail when reached. The recommend approach is to use
Catalyst::View::JSON which will JSON format all the response data and
return it in the response body.
In at least prototype 1.5.0 rc0 and above, prototype.js will send the
X-Prototype-Version header. If this is encountered, a JavaScript eval
will be returned in the X-JSON response header to automatically eval the
response body, unless you set *no_x_json_header* to 1. If your version
of prototype does not send this header, you can manually eval the
response body using the following JavaScript:
evalJSON: function(request) {
try {
return eval('(' + request.responseText + ')');
} catch (e) {}
}
// elsewhere
var json = this.evalJSON(request);
NOTE The above comments were written a number of years ago and I would
take then with a grain of salt so to speak. For now I will leave them in
place but not sure they are meaningful in 2015.
SECURITY CONSIDERATION
Catalyst::View::JSON makes the data available as a (sort of) JavaScript
to the client, so you might want to be careful about the security of
your data.
Use callbacks only for public data
When you enable callbacks (JSONP) by setting "allow_callback", all your
JSON data will be available cross-site. This means embedding private
data of logged-in user to JSON is considered bad.
# MyApp.yaml
View::JSON:
allow_callback: 1
sub foo : Local {
my($self, $c) = @_;
$c->stash->{address} = $c->user->street_address; # BAD
$c->forward('View::JSON');
}
If you want to enable callbacks in a controller (for public API) and
disable in another, you need to create two different View classes, like
MyApp::View::JSON and MyApp::View::JSONP, because "allow_callback" is a
static configuration of the View::JSON class.
See <http://ajaxian.com/archives/gmail-csrf-security-flaw> for more.
Avoid valid cross-site JSON requests
Even if you disable the callbacks, the nature of JavaScript still has a
possibility to access private JSON data cross-site, by overriding Array
constructor "[]".
# MyApp.yaml
View::JSON:
expose_stash: json
sub foo : Local {
my($self, $c) = @_;
$c->stash->{json} = [ $c->user->street_address ]; # BAD
$c->forward('View::JSON');
}
When you return logged-in user's private data to the response JSON, you
might want to disable GET requests (because *script* tag invokes GET
requests), or include a random digest string and validate it.
See
<http://jeremiahgrossman.blogspot.com/2006/01/advanced-web-attack-techni
ques-using.html> for more.
AUTHOR
Tatsuhiko Miyagawa <miyagawa@bulknews.net>
LICENSE
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
CONTRIBUTORS
Following people has been contributing patches, bug reports and
suggestions for the improvement of Catalyst::View::JSON.
John Wang
kazeburo
Daisuke Murase
Jun Kuriyama
Tomas Doran
SEE ALSO
Catalyst, JSON::MaybeXS, Encode::JavaScript::UCS
<http://www.prototypejs.org/learn/json>
<http://docs.jquery.com/Ajax/jQuery.getJSON>
<http://manual.dojotoolkit.org/json.html>
<http://developer.yahoo.com/yui/json/>