Firefox Hacks [Electronic resources] نسخه متنی

Hack 66. Work with Mozilla XML-RPC Services

Want web service scripting, but
don''''t need SOAP''''s complexity? Use
XML-RPC.

XML-RPC is a way for
you to run methods on a server from a remote client. All commands and
responses are formatted as XML. It''''s similar to SOAP
[Hack #65], and both are intended
to solve the same sorts of problems. However, XML-RPC is a much
simpler protocol.

XML-RPC was developed by UserLand Software. The specification is at http://www.xmlrpc.com/spec.

There are two major differences between
XML-RPC and SOAP. First, XML-RPC has only
eight data types: int, boolean,
string, double,
dateTime.iso8601, base64,
array, and struct, whereas SOAP
has many more data types and more can be added via XML Schema.
Second, XML-RPC has no standardized discovery mechanisms, such as
SOAP''''s WSDL or UDDI.

You might find that XML-RPC''''s
"limitations" make it easier to
learn than SOAP. With fewer requirements, it''''s
easier to make your code work, and there are fewer things that can go
wrong.

XML-RPC is widely deployed on web services across the Internet. Most
weblog publishing software, for example, includes support for at
least one of the major external editor
protocols: Blogger API, MetaWeblog API, or Movable Type (mt) API.

6.10.1. Locate XML-RPC in Firefox

Firefox supports
XML-RPC
in the chrome. Your extensions can use XML-RPC to pass commands and
data back and forth between Firefox and any web service with a
published XML-RPC specification.

H5

XML-RPC used in the chrome has no security
restrictions. Scripts can talk to any server. At the time of writing,
Firefox''''s native XML-RPC service is not yet
available to ordinary web pages.

This limitation is bound to change eventually, because of
XML-RPC''''s similarity to SOAP, which is available to
scripts in web pages. If you need to use XML-RPC in a web page, there
are some free, cross-platform XML-RPC libraries on the Web, written
in JavaScript. One oft-used example is Scott
Andrew''''s XML-RPC JavaScript Message Builder,
available at http://www.scottandrew.com/xml-rpc/.

The XML-RPC component that comes with Firefox is slightly imperfect.
It''''s easy to fix, but until the official component
has been fixed, its bug will have implications for any chrome
extension you create (for distribution) that uses XML-RPC. You will
either have to provide your own implementation of XML-RPC or include
the fixed version we''''re about
to describe. The latter option might require that your
extension''''s license be compatible with the Mozilla
Public License. You don''''t have to worry about this
for hacking your own copy of Firefox.

To fix the bug:

Download /image/library/english/10055_nsXmlRpcClient.js
to a file on disk.

Exit Firefox.

Open the Components folder in the Firefox
installation area and move the existing
nsXmlRpcClient.js file to a safe place.

Move the new file you downloaded in Step one to the
Components folder.

Restart Firefox.

Without this fix, most XML-RPC calls will generate errors.

6.10.2. Create an XUL Test File

Since we need to work from within the security of the chrome,
we''''ll create a small
XUL extension that uses a testing
service provided by XML-RPC.com (http://www.xmlrpc.com). Their server has a
function called
examples.getStateList. It expects a list of numbers between
1 and 50 and returns a string that contains a comma-separated list of
the names of the U.S. states that were specified. States are numbered
by their date of acceptance to the Unionoldest first.

Our interface needs are minor: a text field to enter some state
numbers, a text field to display the results, and a button to run the
XML-RPC call. Create an
XUL file named
xml-rpc.xul with the following contents:

<?xml version="1.0"?>
<?xml-stylesheet href=" type="text/css"?>
<!DOCTYPE window>
<window title="XML-RPC States" 
xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
style="width: 4in; height: 1.5in;">
<script type="application/x-javascript" src="/image/library/english/10055_xml-rpc.js" />
<vbox flex="1" style="margin: 8px;">
<text value="Enter a state code:"/>
<hbox>
<textbox flex="1" rows="1" id="statecodes"/>
<button label="List States" onclick="listStates( )"/>
</hbox>
<text value="States:"/>
<hbox flex="1">
<textbox flex="1" id="states" multiline="true"/>
</hbox>
</vbox>
</window>

H5

Just as with SOAP and WSDL, your best bet when scripting with
XML-RPC is to create a proxy object
to hide the communication details from the rest of your script.

This will also make it much easier to switch from XML-RPC to SOAP or some other protocol, should you ever choose to do so.

Create a file named /image/library/english/10055_xml-rpc.js with the
following contents:

const Cc = Components.classes;
const Ci = Components.interfaces;
var statesProxy = {
_xmlRpcClient: null,
get xmlrpc( ) {
if ( ! this._xmlRpcClient ) {
this._xmlRpcClient = Cc["@mozilla.org/xml-rpc/client;1"]
.createInstance( Ci.nsIXmlRpcClient );
}
return this._xmlRpcClient;
},
invoke: function( call, aParams, cb ) {
this.xmlrpc.init( "http://www.xmlrpc.com/RPC2" );
var Listener = {
onResult: function( client, ctxt, result ) {
// assumes result is string
window[ cb ]( result.QueryInterface( Ci.nsISupportsCString ).data );
},
onFault: function( client, ctxt, fault ) { },
onError: function( client, ctxt, status, errorMsg ) { }
};
this.xmlrpc.asyncCall( Listener, null, call, aParams, aParams.length );
},
listStates: function( aStateNums ) {
var xmlrpc = this.xmlrpc;
var stateList = xmlrpc.createType( xmlrpc.ARRAY, {} );
var stateCode;
for ( var i = 0; i < aStateNums.length; i++ ) {
stateCode = xmlrpc.createType( xmlrpc.INT, {} );
stateCode.data = aStateNums[ i ] - 0;
stateList.AppendElement( stateCode );
}
var params = new Array( stateList );
this.invoke( "examples.getStateList", params, "listStatesCallback" );
}
};
function listStates( ) {
var sList = document.getElementById( "statecodes" ).value;
var aStateNums = sList.split( /[, ]+/ );
statesProxy.listStates( aStateNums );
}
function listStatesCallback( result ) {
document.getElementById( "states" ).value = result;
}

H5

Create an extension [Hack #88] and
move the XUL and JavaScript file into its content folder. Assuming
that the name of your extension is xmlrpc, you
can then run your test with the URL Figure 6-10.

<>Figure 6-10. The final, working version of the XML-RPC test file

Seth Dillingham