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// Released under the MIT/X11 license
// http://www.opensource.org/licenses/mit-license.php
"use strict";
var Request = require("request").Request;
var xhrMod = require("xhr");
// Initialize myStorage if we don't have it.
var myStorage = require("simple-storage").storage;
if (!myStorage.cachedRequest) {
myStorage.cachedRequest = {};
}
// https://bugzilla.mozilla.org/582760 is still alive
var debugOption = true;
function debug(str) {
if (debugOption) {
console.log(str);
}
}
/**
* Decorating cached response object with a bit of additional
* functionality.
*/
function CachedResponse (url) {
if (!myStorage.cachedRequest[url]) {
myStorage.cachedRequest[url] = {};
this.url = url;
this.text = null;
this.status = "";
this.statusText = "";
this.headers = {};
}
else {
var storedResponse = myStorage.cachedRequest[url];
this.url = url;
this.text = storedResponse.text;
this.status = storedResponse.status;
this.statusText = storedResponse.statusText;
this.headers = storedResponse.headers;
}
}
/**
* getter returning object from this.text
* (so we don't save essentially the same object same)
*
* @return Object from this.text, if this.text isn't JSONable,
* return null
*/
CachedResponse.prototype.__defineGetter__("json", function() {
try {
return JSON.parse(this.text);
}
catch (ex) {
if (ex instanceof SyntaxError) {
return null;
} else {
throw ex;
}
}
});
/**
* save the current object's values to myStorage.
*/
CachedResponse.prototype.saveCached = function() {
var storedResponse = myStorage.cachedRequest[this.url];
storedResponse.text = this.text;
storedResponse.status = this.status;
storedResponse.statusText = this.statusText;
storedResponse.headers = this.headers;
};
/**
* getter returning Last-Modified header as a Date object.
*
* @return Date when this has Last-Modified header, or null otherwise
*/
CachedResponse.prototype.__defineGetter__("lastModified", function() {
if (this.headers && (this.headers.hasOwnProperty("Last-Modified"))) {
return new Date(this.headers["Last-Modified"]);
}
return null;
});
/**
* Emulates Request object, but caches the result for speedier access,
* and protection when the remote site is down.
*
* @opts Object with properties same as Request
*
* Limitations: does only GET requests, so it doesn't even have
* .post(), .get() or any other methods.
* Contrary to Request() opts can have onError callback, and
* getExpiredAnyway property to allow using expired cached value,
* if the remote connection returns error.
*/
exports.CachedRequest = function CachedRequest(opts) {
var crStorage = new CachedResponse(opts.url);
var req = new xhrMod.XMLHttpRequest();
req.open("HEAD", opts.url, true);
req.onreadystatechange = function () {
if (req.readyState == 4) {
if(req.status == 200) {
var curETag = req.getResponseHeader("ETag");
var curLastModified = new Date(req.getResponseHeader("Last-Modified"));
if (crStorage && crStorage.headers &&
((curETag == crStorage.headers.eTag) ||
(curLastModified <= crStorage.lastModified))) {
debug("Loading from cache!");
// use cached values
}
else { // cache is not up-to-date
new Request({
url: opts.url,
onComplete: function(resp) {
if (resp.status == 200) {
debug("Too old cache! Reloaded");
crStorage.headers = resp.headers;
crStorage.text = resp.text;
crStorage.status = resp.status;
crStorage.statusText = resp.statusText;
crStorage.saveCached();
}
else {
// If we cannot get response from the real URL,
// we may be happy with getting our fix from
// anywhere, including (possibly) expired cache
if (opts.getExpiredAnyway && crStorage && crStorage.text) {
debug("Nothing better to do! Returning expired cache.");
}
else {
// We definitively lost, just call .onComplete
// with what we have.
opts.onComplete({
text: resp.text,
json: null,
status: resp.status,
statusText: resp.statusText,
headers: resp.headers
});
// to avoid call opts.onComplete below
return ;
}
}
}
}).get();
}
opts.onComplete(crStorage);
}
}
};
req.send();
};
//vim: set ts=2 et sw=2 textwidth=80:
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