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// Copyright 2006 The Closure Library Authors. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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//      http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS-IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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/**
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 * @fileoverview
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 * DataSource implementation that uses XMLHttpRequest as transport, with
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 * response as valid JSON.
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 *
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 * Response can have unexecutable starting/ending text to prevent inclusion
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 * using <script src="...">
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 *
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 */
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goog.provide('goog.ds.JsXmlHttpDataSource');
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goog.require('goog.Uri');
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goog.require('goog.ds.DataManager');
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goog.require('goog.ds.FastDataNode');
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goog.require('goog.ds.LoadState');
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goog.require('goog.ds.logger');
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goog.require('goog.events');
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goog.require('goog.json');
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goog.require('goog.log');
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goog.require('goog.net.EventType');
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goog.require('goog.net.XhrIo');
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/**
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 * Similar to JsonDataSource, with using XMLHttpRequest for transport
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 * Currently requires the result be a valid JSON.
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 *
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 * @param {(string|goog.Uri)} uri URI for the request.
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 * @param {string} name Name of the datasource.
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 * @param {string=} opt_startText Text to expect/strip before JS response.
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 * @param {string=} opt_endText Text to expect/strip after JS response.
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 * @param {boolean=} opt_usePost If true, use POST. Defaults to false (GET).
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 *
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 * @extends {goog.ds.FastDataNode}
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 * @constructor
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 * @final
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 */
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goog.ds.JsXmlHttpDataSource = function(
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    uri, name, opt_startText, opt_endText, opt_usePost) {
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  goog.ds.FastDataNode.call(this, {}, name, null);
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  if (uri) {
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    this.uri_ = new goog.Uri(uri);
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    this.xhr_ = new goog.net.XhrIo();
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    this.usePost_ = !!opt_usePost;
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    goog.events.listen(
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        this.xhr_, goog.net.EventType.COMPLETE, this.completed_, false, this);
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  } else {
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    this.uri_ = null;
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  }
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  this.startText_ = opt_startText;
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  this.endText_ = opt_endText;
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};
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goog.inherits(goog.ds.JsXmlHttpDataSource, goog.ds.FastDataNode);
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/**
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 * Delimiter for start of JSON data in response.
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 * null = starts at first character of response
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 * @type {string|undefined}
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 * @private
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 */
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goog.ds.JsXmlHttpDataSource.prototype.startText_;
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/**
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 * Delimiter for end of JSON data in response.
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 * null = ends at last character of response
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 * @type {string|undefined}
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 * @private
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 */
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goog.ds.JsXmlHttpDataSource.prototype.endText_;
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/**
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 * Gets the state of the backing data for this node
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 * @return {goog.ds.LoadState} The state.
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 * @override
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 */
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goog.ds.JsXmlHttpDataSource.prototype.getLoadState = function() {
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  return this.loadState_;
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};
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/**
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 * Sets the request data. This can be used if it is required to
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 * send a specific body rather than build the body from the query
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 * parameters. Only used in POST requests.
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 * @param {string} data The data to send in the request body.
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 */
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goog.ds.JsXmlHttpDataSource.prototype.setQueryData = function(data) {
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  this.queryData_ = data;
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};
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/**
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 * Load or reload the backing data for this node.
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 * Fires the JsonDataSource
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 * @override
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 */
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goog.ds.JsXmlHttpDataSource.prototype.load = function() {
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  goog.log.info(
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      goog.ds.logger, 'Sending JS request for DataSource ' +
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          this.getDataName() + ' to ' + this.uri_);
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  if (this.uri_) {
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    if (this.usePost_) {
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      var queryData;
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      if (!this.queryData_) {
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        queryData = this.uri_.getQueryData().toString();
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      } else {
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        queryData = this.queryData_;
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      }
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      var uriNoQuery = this.uri_.clone();
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      uriNoQuery.setQueryData(null);
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      this.xhr_.send(String(uriNoQuery), 'POST', queryData);
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    } else {
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      this.xhr_.send(String(this.uri_));
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    }
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  } else {
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    this.loadState_ = goog.ds.LoadState.NOT_LOADED;
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  }
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};
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/**
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 * Called on successful request.
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 * @private
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 */
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goog.ds.JsXmlHttpDataSource.prototype.success_ = function() {
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  goog.ds.DataManager.getInstance().fireDataChange(this.getDataName());
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};
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/**
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 * Completed callback. Loads data if successful, otherwise sets
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 * state to FAILED
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 * @param {goog.events.Event} e Event object, Xhr is target.
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 * @private
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 */
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goog.ds.JsXmlHttpDataSource.prototype.completed_ = function(e) {
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  if (this.xhr_.isSuccess()) {
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    goog.log.info(
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        goog.ds.logger, 'Got data for DataSource ' + this.getDataName());
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    var text = this.xhr_.getResponseText();
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    // Look for start and end token and trim text
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    if (this.startText_) {
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      var startpos = text.indexOf(this.startText_);
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      text = text.substring(startpos + this.startText_.length);
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    }
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    if (this.endText_) {
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      var endpos = text.lastIndexOf(this.endText_);
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      text = text.substring(0, endpos);
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    }
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    // Parse result.
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    try {
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      var jsonObj = goog.json.parse(text);
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      this.extendWith(jsonObj);
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      this.loadState_ = goog.ds.LoadState.LOADED;
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    } catch (ex) {
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      // Invalid JSON.
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      this.loadState_ = goog.ds.LoadState.FAILED;
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      goog.log.error(goog.ds.logger, 'Failed to parse data: ' + ex.message);
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    }
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    // Call on a timer to avoid threading issues on IE.
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    goog.global.setTimeout(goog.bind(this.success_, this), 0);
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  } else {
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    goog.log.info(
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        goog.ds.logger,
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        'Data retrieve failed for DataSource ' + this.getDataName());
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    this.loadState_ = goog.ds.LoadState.FAILED;
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  }
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};
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