The source code

    /*!
     * Ext JS Library 3.2.1
     * Copyright(c) 2006-2010 Ext JS, Inc.
     * licensing@extjs.com
     * http://www.extjs.com/license
     */
    /**
     * @class Ext.data.DataProxy
     * @extends Ext.util.Observable
     * Abstract base class for implementations which provide retrieval of unformatted data objects.
     * This class is intended to be extended and should not be created directly. For existing implementations,
     * see {@link Ext.data.DirectProxy}, {@link Ext.data.HttpProxy}, {@link Ext.data.ScriptTagProxy} and
     * {@link Ext.data.MemoryProxy}.
     * DataProxy implementations are usually used in conjunction with an implementation of {@link Ext.data.DataReader}
     * (of the appropriate type which knows how to parse the data object) to provide a block of
     * {@link Ext.data.Records} to an {@link Ext.data.Store}.
     * The parameter to a DataProxy constructor may be an {@link Ext.data.Connection} or can also be the
     * config object to an {@link Ext.data.Connection}.
     * Custom implementations must implement either the doRequest method (preferred) or the
     * load method (deprecated). See
     * {@link Ext.data.HttpProxy}.{@link Ext.data.HttpProxy#doRequest doRequest} or
     * {@link Ext.data.HttpProxy}.{@link Ext.data.HttpProxy#load load} for additional details.
     * Example 1
     *
    proxy: new Ext.data.ScriptTagProxy({
        {@link Ext.data.Connection#url url}: 'http://extjs.com/forum/topics-remote.php'
    }),
     *
     * Example 2
     *
    proxy : new Ext.data.HttpProxy({
        {@link Ext.data.Connection#method method}: 'GET',
        {@link Ext.data.HttpProxy#prettyUrls prettyUrls}: false,
        {@link Ext.data.Connection#url url}: 'local/default.php', // see options parameter for {@link Ext.Ajax#request}
        {@link #api}: {
            // all actions except the following will use above url
            create  : 'local/new.php',
            update  : 'local/update.php'
        }
    }),
     *
     * And new in Ext version 3, attach centralized event-listeners upon the DataProxy class itself!  This is a great place
     * to implement a messaging system to centralize your application's user-feedback and error-handling.
     *
    // Listen to all "beforewrite" event fired by all proxies.
    Ext.data.DataProxy.on('beforewrite', function(proxy, action) {
        console.log('beforewrite: ', action);
    });

    // Listen to "write" event fired by all proxies
    Ext.data.DataProxy.on('write', function(proxy, action, data, res, rs) {
        console.info('write: ', action);
    });

    // Listen to "exception" event fired by all proxies
    Ext.data.DataProxy.on('exception', function(proxy, type, action) {
        console.error(type + action + ' exception);
    });
     *
     * Note: These three events are all fired with the signature of the corresponding DataProxy instance event {@link #beforewrite beforewrite}, {@link #write write} and {@link #exception exception}.
     */
    Ext.data.DataProxy = function(conn){
        // make sure we have a config object here to support ux proxies.
        // All proxies should now send config into superclass constructor.
        conn = conn || {};

        // This line caused a bug when people use custom Connection object having its own request method.
        // http://extjs.com/forum/showthread.php?t=67194.  Have to set DataProxy config
        //Ext.applyIf(this, conn);

        this.api     = conn.api;
        this.url     = conn.url;
        this.restful = conn.restful;
        this.listeners = conn.listeners;

        // deprecated
        this.prettyUrls = conn.prettyUrls;

        /**
         * @cfg {Object} api
         * Specific urls to call on CRUD action methods "read", "create", "update" and "destroy".
         * Defaults to:
    api: {
        read    : undefined,
        create  : undefined,
        update  : undefined,
        destroy : undefined
    }
         *
         * The url is built based upon the action being executed [load|create|save|destroy]
         * using the commensurate {@link #api} property, or if undefined default to the
         * configured {@link Ext.data.Store}.{@link Ext.data.Store#url url}.

         * For example:
         *
    api: {
        load :    '/controller/load',
        create :  '/controller/new',  // Server MUST return idProperty of new record
        save :    '/controller/update',
        destroy : '/controller/destroy_action'
    }

    // Alternatively, one can use the object-form to specify each API-action
    api: {
        load: {url: 'read.php', method: 'GET'},
        create: 'create.php',
        destroy: 'destroy.php',
        save: 'update.php'
    }
         *
         * If the specific URL for a given CRUD action is undefined, the CRUD action request
         * will be directed to the configured {@link Ext.data.Connection#url url}.
         *
    Note: To modify the URL for an action dynamically the appropriate API
         * property should be modified before the action is requested using the corresponding before
         * action event.  For example to modify the URL associated with the load action:
         *
    // modify the url for the action
    myStore.on({
        beforeload: {
            fn: function (store, options) {
                // use {@link Ext.data.HttpProxy#setUrl setUrl} to change the URL for *just* this request.
                store.proxy.setUrl('changed1.php');

                // set optional second parameter to true to make this URL change
                // permanent, applying this URL for all subsequent requests.
                store.proxy.setUrl('changed1.php', true);

                // Altering the proxy API should be done using the public
                // method {@link Ext.data.DataProxy#setApi setApi}.
                store.proxy.setApi('read', 'changed2.php');

                // Or set the entire API with a config-object.
                // When using the config-object option, you must redefine the entire
                // API -- not just a specific action of it.
                store.proxy.setApi({
                    read    : 'changed_read.php',
                    create  : 'changed_create.php',
                    update  : 'changed_update.php',
                    destroy : 'changed_destroy.php'
                });
            }
        }
    });
         *
         *
         */

        this.addEvents(
            /**
             * @event exception
             * Fires if an exception occurs in the Proxy during a remote request. This event is relayed
             * through a corresponding {@link Ext.data.Store}.{@link Ext.data.Store#exception exception},
             * so any Store instance may observe this event.
             * In addition to being fired through the DataProxy instance that raised the event, this event is also fired
             * through the Ext.data.DataProxy class to allow for centralized processing of exception events from all
             * DataProxies by attaching a listener to the Ext.data.Proxy class itself.
             * This event can be fired for one of two reasons:
             *
             * remote-request failed :
             * The server did not return status === 200.
             *
             * remote-request succeeded :
             * The remote-request succeeded but the reader could not read the response.
             * This means the server returned data, but the configured Reader threw an
             * error while reading the response.  In this case, this event will be
             * raised and the caught error will be passed along into this event.
             *
             *
             *
    This event fires with two different contexts based upon the 2nd
             * parameter type [remote|response].  The first four parameters
             * are identical between the two contexts -- only the final two parameters
             * differ.
             * @param {DataProxy} this The proxy that sent the request
             * @param {String} type
             * The value of this parameter will be either 'response' or 'remote'.
             *
             * 'response' :
             * An invalid response from the server was returned: either 404,
             * 500 or the response meta-data does not match that defined in the DataReader
             * (e.g.: root, idProperty, successProperty).
             *
             * 'remote' :
             * A valid response was returned from the server having
             * successProperty === false.  This response might contain an error-message
             * sent from the server.  For example, the user may have failed
             * authentication/authorization or a database validation error occurred.
             *
             *
             * @param {String} action Name of the action (see {@link Ext.data.Api#actions}.
             * @param {Object} options The options for the action that were specified in the {@link #request}.
             * @param {Object} response
             * The value of this parameter depends on the value of the type parameter:
             *
             * 'response' :
             * The raw browser response object (e.g.: XMLHttpRequest)
             *
             * 'remote' :
             * The decoded response object sent from the server.
             *
             *
             * @param {Mixed} arg
             * The type and value of this parameter depends on the value of the type parameter:
             *
             * 'response' : Error
             * The JavaScript Error object caught if the configured Reader could not read the data.
             * If the remote request returns success===false, this parameter will be null.
             *
             * 'remote' : Record/Record[]
             * This parameter will only exist if the action was a write action
             * (Ext.data.Api.actions.create|update|destroy).
             *
             *
             */
            'exception',
            /**
             * @event beforeload
             * Fires before a request to retrieve a data object.
             * @param {DataProxy} this The proxy for the request
             * @param {Object} params The params object passed to the {@link #request} function
             */
            'beforeload',
            /**
             * @event load
             * Fires before the load method's callback is called.
             * @param {DataProxy} this The proxy for the request
             * @param {Object} o The request transaction object
             * @param {Object} options The callback's options property as passed to the {@link #request} function
             */
            'load',
            /**
             * @event loadexception
             * This event is deprecated.  The signature of the loadexception event
             * varies depending on the proxy, use the catch-all {@link #exception} event instead.
             * This event will fire in addition to the {@link #exception} event.
             * @param {misc} misc See {@link #exception}.
             * @deprecated
             */
            'loadexception',
            /**
             * @event beforewrite
             * Fires before a request is generated for one of the actions Ext.data.Api.actions.create|update|destroy
             * In addition to being fired through the DataProxy instance that raised the event, this event is also fired
             * through the Ext.data.DataProxy class to allow for centralized processing of beforewrite events from all
             * DataProxies by attaching a listener to the Ext.data.Proxy class itself.
             * @param {DataProxy} this The proxy for the request
             * @param {String} action [Ext.data.Api.actions.create|update|destroy]
             * @param {Record/Record[]} rs The Record(s) to create|update|destroy.
             * @param {Object} params The request params object.  Edit params to add parameters to the request.
             */
            'beforewrite',
            /**
             * @event write
             * Fires before the request-callback is called
             * In addition to being fired through the DataProxy instance that raised the event, this event is also fired
             * through the Ext.data.DataProxy class to allow for centralized processing of write events from all
             * DataProxies by attaching a listener to the Ext.data.Proxy class itself.
             * @param {DataProxy} this The proxy that sent the request
             * @param {String} action [Ext.data.Api.actions.create|upate|destroy]
             * @param {Object} data The data object extracted from the server-response
             * @param {Object} response The decoded response from server
             * @param {Record/Record[]} rs The Record(s) from Store
             * @param {Object} options The callback's options property as passed to the {@link #request} function
             */
            'write'
        );
        Ext.data.DataProxy.superclass.constructor.call(this);

        // Prepare the proxy api.  Ensures all API-actions are defined with the Object-form.
        try {
            Ext.data.Api.prepare(this);
        } catch (e) {
            if (e instanceof Ext.data.Api.Error) {
                e.toConsole();
            }
        }
        // relay each proxy's events onto Ext.data.DataProxy class for centralized Proxy-listening
        Ext.data.DataProxy.relayEvents(this, ['beforewrite', 'write', 'exception']);
    };

    Ext.extend(Ext.data.DataProxy, Ext.util.Observable, {
        /**
         * @cfg {Boolean} restful
         * Defaults to false.  Set to true to operate in a RESTful manner.
         *
     Note: this parameter will automatically be set to true if the
         * {@link Ext.data.Store} it is plugged into is set to restful: true. If the
         * Store is RESTful, there is no need to set this option on the proxy.
         *
    RESTful implementations enable the serverside framework to automatically route
         * actions sent to one url based upon the HTTP method, for example:
         *
    store: new Ext.data.Store({
        restful: true,
        proxy: new Ext.data.HttpProxy({url:'/users'}); // all requests sent to /users
        ...
    )}
         *
         * If there is no {@link #api} specified in the configuration of the proxy,
         * all requests will be marshalled to a single RESTful url (/users) so the serverside
         * framework can inspect the HTTP Method and act accordingly:
         *
    Method   url        action
    POST     /users     create
    GET      /users     read
    PUT      /users/23  update
    DESTROY  /users/23  delete
         *
         * If set to true, a {@link Ext.data.Record#phantom non-phantom} record's
         * {@link Ext.data.Record#id id} will be appended to the url. Some MVC (e.g., Ruby on Rails,
         * Merb and Django) support segment based urls where the segments in the URL follow the
         * Model-View-Controller approach:
         * someSite.com/controller/action/id
         *
         * Where the segments in the url are typically:
         * The first segment : represents the controller class that should be invoked.
         * The second segment : represents the class function, or method, that should be called.
         * The third segment : represents the ID (a variable typically passed to the method).
         *
         *
    Refer to {@link Ext.data.DataProxy#api} for additional information.
         */
        restful: false,

        /**
         * Redefines the Proxy's API or a single action of an API. Can be called with two method signatures.
         * If called with an object as the only parameter, the object should redefine the entire API, e.g.:
    proxy.setApi({
        read    : '/users/read',
        create  : '/users/create',
        update  : '/users/update',
        destroy : '/users/destroy'
    });

         * If called with two parameters, the first parameter should be a string specifying the API action to
         * redefine and the second parameter should be the URL (or function if using DirectProxy) to call for that action, e.g.:
    proxy.setApi(Ext.data.Api.actions.read, '/users/new_load_url');

         * @param {String/Object} api An API specification object, or the name of an action.
         * @param {String/Function} url The URL (or function if using DirectProxy) to call for the action.
         */
        setApi : function() {
            if (arguments.length == 1) {
                var valid = Ext.data.Api.isValid(arguments[0]);
                if (valid === true) {
                    this.api = arguments[0];
                }
                else {
                    throw new Ext.data.Api.Error('invalid', valid);
                }
            }
            else if (arguments.length == 2) {
                if (!Ext.data.Api.isAction(arguments[0])) {
                    throw new Ext.data.Api.Error('invalid', arguments[0]);
                }
                this.api[arguments[0]] = arguments[1];
            }
            Ext.data.Api.prepare(this);
        },

        /**
         * Returns true if the specified action is defined as a unique action in the api-config.
         * request.  If all API-actions are routed to unique urls, the xaction parameter is unecessary.  However, if no api is defined
         * and all Proxy actions are routed to DataProxy#url, the server-side will require the xaction parameter to perform a switch to
         * the corresponding code for CRUD action.
         * @param {String [Ext.data.Api.CREATE|READ|UPDATE|DESTROY]} action
         * @return {Boolean}
         */
        isApiAction : function(action) {
            return (this.api[action]) ? true : false;
        },

        /**
         * All proxy actions are executed through this method.  Automatically fires the "before" + action event
         * @param {String} action Name of the action
         * @param {Ext.data.Record/Ext.data.Record[]/null} rs Will be null when action is 'load'
         * @param {Object} params
         * @param {Ext.data.DataReader} reader
         * @param {Function} callback
         * @param {Object} scope The scope (this reference) in which the callback function is executed. Defaults to the Proxy object.
         * @param {Object} options Any options specified for the action (e.g. see {@link Ext.data.Store#load}.
         */
        request : function(action, rs, params, reader, callback, scope, options) {
            if (!this.api[action] && !this.load) {
                throw new Ext.data.DataProxy.Error('action-undefined', action);
            }
            params = params || {};
            if ((action === Ext.data.Api.actions.read) ? this.fireEvent("beforeload", this, params) : this.fireEvent("beforewrite", this, action, rs, params) !== false) {
                this.doRequest.apply(this, arguments);
            }
            else {
                callback.call(scope || this, null, options, false);
            }
        },

        /**
         * Deprecated load method using old method signature. See {@doRequest} for preferred method.
         * @deprecated
         * @param {Object} params
         * @param {Object} reader
         * @param {Object} callback
         * @param {Object} scope
         * @param {Object} arg
         */
        load : null,

        /**
         * @cfg {Function} doRequest Abstract method that should be implemented in all subclasses.  Note: Should only be used by custom-proxy developers.
         * (e.g.: {@link Ext.data.HttpProxy#doRequest HttpProxy.doRequest},
         * {@link Ext.data.DirectProxy#doRequest DirectProxy.doRequest}).
         */
        doRequest : function(action, rs, params, reader, callback, scope, options) {
            // default implementation of doRequest for backwards compatibility with 2.0 proxies.
            // If we're executing here, the action is probably "load".
            // Call with the pre-3.0 method signature.
            this.load(params, reader, callback, scope, options);
        },

        /**
         * @cfg {Function} onRead Abstract method that should be implemented in all subclasses.  Note: Should only be used by custom-proxy developers.  Callback for read {@link Ext.data.Api#actions action}.
         * @param {String} action Action name as per {@link Ext.data.Api.actions#read}.
         * @param {Object} o The request transaction object
         * @param {Object} res The server response
         * @fires loadexception (deprecated)
         * @fires exception
         * @fires load
         * @protected
         */
        onRead : Ext.emptyFn,
        /**
         * @cfg {Function} onWrite Abstract method that should be implemented in all subclasses.  Note: Should only be used by custom-proxy developers.  Callback for create, update and destroy {@link Ext.data.Api#actions actions}.
         * @param {String} action [Ext.data.Api.actions.create|read|update|destroy]
         * @param {Object} trans The request transaction object
         * @param {Object} res The server response
         * @fires exception
         * @fires write
         * @protected
         */
        onWrite : Ext.emptyFn,
        /**
         * buildUrl
         * Sets the appropriate url based upon the action being executed.  If restful is true, and only a single record is being acted upon,
         * url will be built Rails-style, as in "/controller/action/32".  restful will aply iff the supplied record is an
         * instance of Ext.data.Record rather than an Array of them.
         * @param {String} action The api action being executed [read|create|update|destroy]
         * @param {Ext.data.Record/Ext.data.Record[]} record The record or Array of Records being acted upon.
         * @return {String} url
         * @private
         */
        buildUrl : function(action, record) {
            record = record || null;

            // conn.url gets nullified after each request.  If it's NOT null here, that means the user must have intervened with a call
            // to DataProxy#setUrl or DataProxy#setApi and changed it before the request was executed.  If that's the case, use conn.url,
            // otherwise, build the url from the api or this.url.
            var url = (this.conn && this.conn.url) ? this.conn.url : (this.api[action]) ? this.api[action].url : this.url;
            if (!url) {
                throw new Ext.data.Api.Error('invalid-url', action);
            }

            // look for urls having "provides" suffix used in some MVC frameworks like Rails/Merb and others.  The provides suffice informs
            // the server what data-format the client is dealing with and returns data in the same format (eg: application/json, application/xml, etc)
            // e.g.: /users.json, /users.xml, etc.
            // with restful routes, we need urls like:
            // PUT /users/1.json
            // DELETE /users/1.json
            var provides = null;
            var m = url.match(/(.*)(\.json|\.xml|\.html)$/);
            if (m) {
                provides = m[2];    // eg ".json"
                url      = m[1];    // eg: "/users"
            }
            // prettyUrls is deprectated in favor of restful-config
            if ((this.restful === true || this.prettyUrls === true) && record instanceof Ext.data.Record && !record.phantom) {
                url += '/' + record.id;
            }
            return (provides === null) ? url : url + provides;
        },

        /**
         * Destroys the proxy by purging any event listeners and cancelling any active requests.
         */
        destroy: function(){
            this.purgeListeners();
        }
    });

    // Apply the Observable prototype to the DataProxy class so that proxy instances can relay their
    // events to the class.  Allows for centralized listening of all proxy instances upon the DataProxy class.
    Ext.apply(Ext.data.DataProxy, Ext.util.Observable.prototype);
    Ext.util.Observable.call(Ext.data.DataProxy);

    /**
     * @class Ext.data.DataProxy.Error
     * @extends Ext.Error
     * DataProxy Error extension.
     * constructor
     * @param {String} message Message describing the error.
     * @param {Record/Record[]} arg
     */
    Ext.data.DataProxy.Error = Ext.extend(Ext.Error, {
        constructor : function(message, arg) {
            this.arg = arg;
            Ext.Error.call(this, message);
        },
        name: 'Ext.data.DataProxy'
    });
    Ext.apply(Ext.data.DataProxy.Error.prototype, {
        lang: {
            'action-undefined': "DataProxy attempted to execute an API-action but found an undefined url / function.  Please review your Proxy url/api-configuration.",
            'api-invalid': 'Recieved an invalid API-configuration.  Please ensure your proxy API-configuration contains only the actions from Ext.data.Api.actions.'
        }
    });