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I am new to Service Workers, and have had a look through the various bits of documentation (Google, Mozilla, serviceworke.rs, Github, StackOverflow questions). The most helpful is the ServiceWorkers cookbook.
Most of the documentation seems to point to caching entire pages so that the app works completely offline, or redirecting the user to an offline page until the browser can redirect to the internet.
What I want to do, however, is store my form data locally so my web app can upload it to the server when the user's connection is restored. Which "recipe" should I use? I think it is Request Deferrer. Do I need anything else to ensure that Request Deferrer will work (apart from the service worker detector script in my web page)? Any hints and tips much appreciated.
Console errors
The Request Deferrer recipe and code doesn't seem to work on its own as it doesn't include file caching. I have added some caching for the service worker library files, but I am still getting this error when I submit the form while offline:
Console: {"lineNumber":0,"message":
"The FetchEvent for [the form URL] resulted in a network error response:
the promise was rejected.","message_level":2,"sourceIdentifier":1,"sourceURL":""}
My Service Worker
/* eslint-env es6 */
/* eslint no-unused-vars: 0 */
/* global importScripts, ServiceWorkerWare, localforage */
importScripts('/js/lib/ServiceWorkerWare.js');
importScripts('/js/lib/localforage.js');
//Determine the root for the routes. I.e, if the Service Worker URL is http://example.com/path/to/sw.js, then the root is http://example.com/path/to/
var root = (function() {
var tokens = (self.location + '').split('/');
tokens[tokens.length - 1] = '';
return tokens.join('/');
})();
//By using Mozilla’s ServiceWorkerWare we can quickly setup some routes for a virtual server. It is convenient you review the virtual server recipe before seeing this.
var worker = new ServiceWorkerWare();
//So here is the idea. We will check if we are online or not. In case we are not online, enqueue the request and provide a fake response.
//Else, flush the queue and let the new request to reach the network.
//This function factory does exactly that.
function tryOrFallback(fakeResponse) {
//Return a handler that…
return function(req, res) {
//If offline, enqueue and answer with the fake response.
if (!navigator.onLine) {
console.log('No network availability, enqueuing');
return enqueue(req).then(function() {
//As the fake response will be reused but Response objects are one use only, we need to clone it each time we use it.
return fakeResponse.clone();
});
}
//If online, flush the queue and answer from network.
console.log('Network available! Flushing queue.');
return flushQueue().then(function() {
return fetch(req);
});
};
}
//A fake response with a joke for when there is no connection. A real implementation could have cached the last collection of updates and keep a local model. For simplicity, not implemented here.
worker.get(root + 'api/updates?*', tryOrFallback(new Response(
JSON.stringify([{
text: 'You are offline.',
author: 'Oxford Brookes University',
id: 1,
isSticky: true
}]),
{ headers: { 'Content-Type': 'application/json' } }
)));
//For deletion, let’s simulate that all went OK. Notice we are omitting the body of the response. Trying to add a body with a 204, deleted, as status throws an error.
worker.delete(root + 'api/updates/:id?*', tryOrFallback(new Response({
status: 204
})));
//Creation is another story. We can not reach the server so we can not get the id for the new updates.
//No problem, just say we accept the creation and we will process it later, as soon as we recover connectivity.
worker.post(root + 'api/updates?*', tryOrFallback(new Response(null, {
status: 202
})));
//Start the service worker.
worker.init();
//By using Mozilla’s localforage db wrapper, we can count on a fast setup for a versatile key-value database. We use it to store queue of deferred requests.
//Enqueue consists of adding a request to the list. Due to the limitations of IndexedDB, Request and Response objects can not be saved so we need an alternative representations.
//This is why we call to serialize().`
function enqueue(request) {
return serialize(request).then(function(serialized) {
localforage.getItem('queue').then(function(queue) {
/* eslint no-param-reassign: 0 */
queue = queue || [];
queue.push(serialized);
return localforage.setItem('queue', queue).then(function() {
console.log(serialized.method, serialized.url, 'enqueued!');
});
});
});
}
//Flush is a little more complicated. It consists of getting the elements of the queue in order and sending each one, keeping track of not yet sent request.
//Before sending a request we need to recreate it from the alternative representation stored in IndexedDB.
function flushQueue() {
//Get the queue
return localforage.getItem('queue').then(function(queue) {
/* eslint no-param-reassign: 0 */
queue = queue || [];
//If empty, nothing to do!
if (!queue.length) {
return Promise.resolve();
}
//Else, send the requests in order…
console.log('Sending ', queue.length, ' requests...');
return sendInOrder(queue).then(function() {
//Requires error handling. Actually, this is assuming all the requests in queue are a success when reaching the Network.
// So it should empty the queue step by step, only popping from the queue if the request completes with success.
return localforage.setItem('queue', []);
});
});
}
//Send the requests inside the queue in order. Waiting for the current before sending the next one.
function sendInOrder(requests) {
//The reduce() chains one promise per serialized request, not allowing to progress to the next one until completing the current.
var sending = requests.reduce(function(prevPromise, serialized) {
console.log('Sending', serialized.method, serialized.url);
return prevPromise.then(function() {
return deserialize(serialized).then(function(request) {
return fetch(request);
});
});
}, Promise.resolve());
return sending;
}
//Serialize is a little bit convolved due to headers is not a simple object.
function serialize(request) {
var headers = {};
//for(... of ...) is ES6 notation but current browsers supporting SW, support this notation as well and this is the only way of retrieving all the headers.
for (var entry of request.headers.entries()) {
headers[entry[0]] = entry[1];
}
var serialized = {
url: request.url,
headers: headers,
method: request.method,
mode: request.mode,
credentials: request.credentials,
cache: request.cache,
redirect: request.redirect,
referrer: request.referrer
};
//Only if method is not GET or HEAD is the request allowed to have body.
if (request.method !== 'GET' && request.method !== 'HEAD') {
return request.clone().text().then(function(body) {
serialized.body = body;
return Promise.resolve(serialized);
});
}
return Promise.resolve(serialized);
}
//Compared, deserialize is pretty simple.
function deserialize(data) {
return Promise.resolve(new Request(data.url, data));
}
var CACHE = 'cache-only';
// On install, cache some resources.
self.addEventListener('install', function(evt) {
console.log('The service worker is being installed.');
// Ask the service worker to keep installing until the returning promise
// resolves.
evt.waitUntil(precache());
});
// On fetch, use cache only strategy.
self.addEventListener('fetch', function(evt) {
console.log('The service worker is serving the asset.');
evt.respondWith(fromCache(evt.request));
});
// Open a cache and use `addAll()` with an array of assets to add all of them
// to the cache. Return a promise resolving when all the assets are added.
function precache() {
return caches.open(CACHE).then(function (cache) {
return cache.addAll([
'/js/lib/ServiceWorkerWare.js',
'/js/lib/localforage.js',
'/js/settings.js'
]);
});
}
// Open the cache where the assets were stored and search for the requested
// resource. Notice that in case of no matching, the promise still resolves
// but it does with `undefined` as value.
function fromCache(request) {
return caches.open(CACHE).then(function (cache) {
return cache.match(request).then(function (matching) {
return matching || Promise.reject('no-match');
});
});
}
Here is the error message I am getting in Chrome when I go offline:
(A similar error occurred in Firefox - it falls over at line 409 of ServiceWorkerWare.js)
ServiceWorkerWare.prototype.executeMiddleware = function (middleware,
request) {
var response = this.runMiddleware(middleware, 0, request, null);
response.catch(function (error) { console.error(error); });
return response;
};
this is a little more advanced that a beginner level. But you will need to detect when you are offline or in a Li-Fi state. Instead of POSTing data to an API or end point you need to queue that data to be synched when you are back on line.
This is what the Background Sync API should help with. However, it is not supported across the board just yet. Plus Safari.........
So maybe a good strategy is to persist your data in IndexedDB and when you can connect (background sync fires an event for this) you would then POST the data. It gets a little more complex for browsers that don't support service workers (Safari) or don't yet have Background Sync (that will level out very soon).
As always design your code to be a progressive enhancement, which can be tricky, but worth it in the end.
Service Workers tend to cache the static HTML, CSS, JavaScript, and image files.
I need to use PouchDB and sync it with CouchDB
Why CouchDB?
CouchDB is a NoSQL database consisting of a number of Documents
created with JSON.
It has versioning (each document has a _rev
property with the last modified date)
It can be synchronised with
PouchDB, a local JavaScript application that stores data in local
storage via the browser using IndexedDB. This allows us to create
offline applications.
The two databases are both “master” copies of
the data.
PouchDB is a local JavaScript implementation of CouchDB.
I still need a better answer than my partial notes towards a solution!
Yes, this type of service worker is the correct one to use for saving form data offline.
I have now edited it and understood it better. It caches the form data, and loads it on the page for the user to see what they have entered.
It is worth noting that the paths to the library files will need editing to reflect your local directory structure, e.g. in my setup:
importScripts('/js/lib/ServiceWorkerWare.js');
importScripts('/js/lib/localforage.js');
The script is still failing when offline, however, as it isn't caching the library files. (Update to follow when I figure out caching)
Just discovered an extra debugging tool for service workers (apart from the console): chrome://serviceworker-internals/. In this, you can start or stop service workers, view console messages, and the resources used by the service worker.
To use Events API for Slack App development, there is a setting for "Events API Request URLs" as described in doc:
In the Events API, your Events API Request URL is the target location
where all the events your application is subscribed to will be
delivered, regardless of the team or event type.
There is a UI for changing the URL "manually" at api.slack.com under
"Event Subscriptions" section in settings. There is also url_verification event after changing the Request URL described here.
My question - Is there an API call (method) so I can update the endpoint (Request URL) from my server code?
For example, in Facebook API there is a call named subscriptions where I can change webhook URL after initial setup - link
Making a POST request with the callback_url, verify_token, and object
fields will reactivate the subscription.
PS. To give a background, this is needed for development using outbound tunnel with dynamic endpoint URL, e.g. ngrok free subscription. By the way, ngrok is referenced in sample "onboarding" app by slack here
Update. I checked Microsoft Bot Framework, and they seems to use RTM (Real Time Messaging) for slack which doesn't require Request URL setup, and not Events API. Same time, e.g. for Facebook they (MS Bot) instruct me to manually put their generated URL to webhook settings of a FB app, so there is no automation on that.
Since this question was originally asked, Slack has introduced app manifests, which enable API calls to change app configurations. This can be used to update URLs and other parameters, or create/delete apps.
At the time of writing, the manifest / manifest API is in beta:
Beta API — this API is in beta, and is subject to change without the usual notice period for changes.
so the this answer might not exactly fit the latest syntax as they make changes.
A programatic workflow might look as follows:
Pull a 'template' manifest from an existing version of the application, with most of the settings as intended (scopes, name, etc.)
Change parts of the manifest to meet the needs of development
Verify the manifest
Update a slack app or create a new one for testing
API List
Basic API list
Export a manifest as JSON: apps.manifest.export
Validate a manifest JSON: apps.manifest.validate
Update an existing app: apps.manifest.update
Create a new app from manifest: apps.manifest.create
Delete an app: apps.manifest.delete
Most of these API requests are Tier 1 requests, so only on the order of 1+ per minute.
API Access
You'll need to create and maintain "App Configuration Tokens". They're created in the "Your Apps" dashboard. More info about them here.
Example NodeJS Code
const axios = require('axios');
// Change these values:
const TEMPLATE_APP_ID = 'ABC1234XYZ';
const PUBLIC_URL = 'https://www.example.com/my/endpoint';
let access = {
slackConfigToken: "xoxe.xoxp-1-MYTOKEN",
slackConfigRefreshToken: "xoxe-1-MYREFRESHTOKEN",
slackConfigTokenExp: 1648550283
};
// Helpers ------------------------------------------------------------------------------------------------------
// Get a new access token with the refresh token
async function refreshTokens() {
let response = await axios.get(`https://slack.com/api/tooling.tokens.rotate?refresh_token=${access.slackConfigRefreshToken}`);
if (response.data.ok === true) {
access.slackConfigToken = response.data.token;
access.slackConfigRefreshToken = response.data.refresh_token;
access.slackConfigTokenExp = response.data.exp;
console.log(access);
} else {
console.error('> [error] The token could not be refreshed. Visit https://api.slack.com/apps and generate tokens.');
process.exit(1);
}
}
// Get an app manifest from an existing slack app
async function getManifest(applicationID) {
const config = {headers: { Authorization: `Bearer ${access.slackConfigToken}` }};
let response = await axios.get(`https://slack.com/api/apps.manifest.export?app_id=${applicationID}`, config);
if (response.data.ok === true) return response.data.manifest;
else {
console.error('> [error] Invalid could not get manifest:', response.data.error);
process.exit(1);
}
}
// Create a slack application with the given manifest
async function createDevApp(manifest) {
const config = {headers: { Authorization: `Bearer ${access.slackConfigToken}` }};
let response = await axios.get(`https://slack.com/api/apps.manifest.create?manifest=${encodeURIComponent(JSON.stringify(manifest))}`, config);
if (response.data.ok === true) return response.data;
else {
console.error('> [error] Invalid could not create app:', response.data.error);
process.exit(1);
}
}
// Verify that a manifest is valid
async function verifyManifest(manifest) {
const config = {headers: { Authorization: `Bearer ${access.slackConfigToken}` }};
let response = await axios.get(`https://slack.com/api/apps.manifest.validate?manifest=${encodeURIComponent(JSON.stringify(manifest))}`, config);
if (response.data.ok !== true) {
console.error('> [error] Manifest did not verify:', response.data.error);
process.exit(1);
}
}
// Main ---------------------------------------------------------------------------------------------------------
async function main() {
// [1] Check token expiration time ------------
if (access.slackConfigTokenExp < Math.floor(new Date().getTime() / 1000))
// Token has expired. Refresh it.
await refreshTokens();
// [2] Load a manifest from an existing slack app to use as a template ------------
const templateManifest = await getManifest(TEMPLATE_APP_ID);
// [3] Update URLS and data in the template ------------
let devApp = { name: 'Review App', slashCommand: '/myslashcommand' };
templateManifest.settings.interactivity.request_url = `${PUBLIC_URL}/slack/events`;
templateManifest.settings.interactivity.message_menu_options_url = `${PUBLIC_URL}/slack/events`;
templateManifest.features.slash_commands[0].url = `${PUBLIC_URL}/slack/events`;
templateManifest.oauth_config.redirect_urls[0] = `${PUBLIC_URL}/slack/oauth_redirect`;
templateManifest.settings.event_subscriptions.request_url = `${PUBLIC_URL}/slack/events`;
templateManifest.display_information.name = devApp.name;
templateManifest.features.bot_user.display_name = devApp.name;
templateManifest.features.slash_commands[0].command = devApp.slashCommand;
// [5] Verify that the manifest is still valid ------------
await verifyManifest(templateManifest);
// [6] Create our new slack dev application ------------
devApp.data = await createDevApp(templateManifest);
console.log(devApp);
}
main();
Hope this helps anyone else looking to update Slack applications programatically.
No, such a method does not exist in the official documentation. There might be an unofficial method - there are quite a few of them actually - but personally I doubt it.
But you don't need this feature for developing Slack apps. Just simulate the POST calls from Slack on your local dev machine with a script and then do a final test together with Slack on your webserver on the Internet.
How can i get previouse url without magic and in backend?
Now i get it through policies:
module.exports = function(req, res, next) {
if (!req.session.previouseUrls) {
req.session.previouseUrls = [];
}
req.session.previouseUrl = req.session.currentUrl || "/";
req.session.currentUrl = req.url;
req.session.previouseUrls.push(req.session.previouseUrl);
next();
};
but it's uncomfortable. Can i get previouse Url from backend simpler?
If you need to know the history (or just previous page) of the user's page requests purely on the client-side, could you query native HTML5 History?
..or if you need to support older browsers, maybe History.js?
I would be concerned with how you're doing it now for 2 reasons:
It's going to start filling up your session store. This may not be a big issue if you have short-lives sessions or not many users.
It could record not just traditional page views "clicks" but any request. Unless you're very carful about scoping this policy you may end up adding an Ajax call that goes through this policy check and you probably didn't intend for that.
I'm trying to integrate Medium blogging into an app by showing some cards with posts images and links to the original Medium publication.
From Medium API docs I can see how to retrieve publications and create posts, but it doesn't mention retrieving posts. Is retrieving posts/stories for a user currently possible using the Medium's API?
The API is write-only and is not intended to retrieve posts (Medium staff told me)
You can simply use the RSS feed as such:
https://medium.com/feed/#your_profile
You can simply get the RSS feed via GET, then if you need it in JSON format just use a NPM module like rss-to-json and you're good to go.
Edit:
It is possible to make a request to the following URL and you will get the response. Unfortunately, the response is in RSS format which would require some parsing to JSON if needed.
https://medium.com/feed/#yourhandle
⚠️ The following approach is not applicable anymore as it is behind Cloudflare's DDoS protection.
If you planning to get it from the Client-side using JavaScript or jQuery or Angular, etc. then you need to build an API gateway or web service that serves your feed. In the case of PHP, RoR, or any server-side that should not be the case.
You can get it directly in JSON format as given beneath:
https://medium.com/#yourhandle/latest?format=json
In my case, I made a simple web service in the express app and host it over Heroku. React App hits the API exposed over Heroku and gets the data.
const MEDIUM_URL = "https://medium.com/#yourhandle/latest?format=json";
router.get("/posts", (req, res, next) => {
request.get(MEDIUM_URL, (err, apiRes, body) => {
if (!err && apiRes.statusCode === 200) {
let i = body.indexOf("{");
const data = body.substr(i);
res.send(data);
} else {
res.sendStatus(500).json(err);
}
});
});
Nowadays this URL:
https://medium.com/#username/latest?format=json
sits behind Cloudflare's DDoS protection service so instead of consistently being served your feed in JSON format, you will usually receive instead an HTML which is suppose to render a website to complete a reCAPTCHA and leaving you with no data from an API request.
And the following:
https://medium.com/feed/#username
has a limit of the latest 10 posts.
I'd suggest this free Cloudflare Worker that I made for this purpose. It works as a facade so you don't have to worry about neither how the posts are obtained from source, reCAPTCHAs or pagination.
Full article about it.
Live example. To fetch the following items add the query param ?next= with the value of the JSON field next which the API provides.
const MdFetch = async (name) => {
const res = await fetch(
`https://api.rss2json.com/v1/api.json?rss_url=https://medium.com/feed/${name}`
);
return await res.json();
};
const data = await MdFetch('#chawki726');
To get your posts as JSON objects
you can replace your user name instead of #USERNAME.
https://api.rss2json.com/v1/api.json?rss_url=https://medium.com/feed/#USERNAME
With that REST method you would do this: GET https://api.medium.com/v1/users/{{userId}}/publications and this would return the title, image, and the item's URL.
Further details: https://github.com/Medium/medium-api-docs#32-publications .
You can also add "?format=json" to the end of any URL on Medium and get useful data back.
Use this url, this url will give json format of posts
Replace studytact with your feed name
https://api.rss2json.com/v1/api.json?rss_url=https://medium.com/feed/studytact
I have built a basic function using AWS Lambda and AWS API Gateway if anyone is interested. A detailed explanation is found on this blog post here and the repository for the the Lambda function built with Node.js is found here on Github. Hopefully someone here finds it useful.
(Updating the JS Fiddle and the Clay function that explains it as we updated the function syntax to be cleaner)
I wrapped the Github package #mark-fasel was mentioning below into a Clay microservice that enables you to do exactly this:
Simplified Return Format: https://www.clay.run/services/nicoslepicos/medium-get-user-posts-new/code
I put together a little fiddle, since a user was asking how to use the endpoint in HTML to get the titles for their last 3 posts:
https://jsfiddle.net/h405m3ma/3/
You can call the API as:
curl -i -H "Content-Type: application/json" -X POST -d '{"username":"nicolaerusan"}' https://clay.run/services/nicoslepicos/medium-get-users-posts-simple
You can also use it easily in your node code using the clay-client npm package and just write:
Clay.run('nicoslepicos/medium-get-user-posts-new', {"profile":"profileValue"})
.then((result) => {
// Do what you want with returned result
console.log(result);
})
.catch((error) => {
console.log(error);
});
Hope that's helpful!
Check this One you will get all info about your own post........
mediumController.getBlogs = (req, res) => {
parser('https://medium.com/feed/#profileName', function (err, rss) {
if (err) {
console.log(err);
}
var stories = [];
for (var i = rss.length - 1; i >= 0; i--) {
var new_story = {};
new_story.title = rss[i].title;
new_story.description = rss[i].description;
new_story.date = rss[i].date;
new_story.link = rss[i].link;
new_story.author = rss[i].author;
new_story.comments = rss[i].comments;
stories.push(new_story);
}
console.log('stories:');
console.dir(stories);
res.json(200, {
Data: stories
})
});
}
I have created a custom REST API to retrieve the stats of a given post on Medium, all you need is to send a GET request to my custom API and you will retrieve the stats as a Json abject as follows:
Request :
curl https://endpoint/api/stats?story_url=THE_URL_OF_THE_MEDIUM_STORY
Response:
{
"claps": 78,
"comments": 1
}
The API responds within a reasonable response time (< 2 sec), you can find more about it in the following Medium article.
I want to prefix URLs which match my patterns. When I open a new tab in Firefox and enter a matching URL the page should not be loaded normally, the URL should first be modified and then loading the page should start.
Is it possible to modify an URL through a Mozilla Firefox Addon before the page starts loading?
Browsing the HTTPS Everywhere add-on suggests the following steps:
Register an observer for the "http-on-modify-request" observer topic with nsIObserverService
Proceed if the subject of your observer notification is an instance of nsIHttpChannel and subject.URI.spec (the URL) matches your criteria
Create a new nsIStandardURL
Create a new nsIHttpChannel
Replace the old channel with the new. The code for doing this in HTTPS Everywhere is quite dense and probably much more than you need. I'd suggest starting with chrome/content/IOUtils.js.
Note that you should register a single "http-on-modify-request" observer for your entire application, which means you should put it in an XPCOM component (see HTTPS Everywhere for an example).
The following articles do not solve your problem directly, but they do contain a lot of sample code that you might find helpful:
https://developer.mozilla.org/en/Setting_HTTP_request_headers
https://developer.mozilla.org/en/XUL_School/Intercepting_Page_Loads
Thanks to Iwburk, I have been able to do this.
We can do this my overriding the nsiHttpChannel with a new one, doing this is slightly complicated but luckily the add-on https-everywhere implements this to force a https connection.
https-everywhere's source code is available here
Most of the code needed for this is in the files
IO Util.js
ChannelReplacement.js
We can work with the above files alone provided we have the basic variables like Cc,Ci set up and the function xpcom_generateQI defined.
var httpRequestObserver =
{
observe: function(subject, topic, data) {
if (topic == "http-on-modify-request") {
var httpChannel = subject.QueryInterface(Components.interfaces.nsIHttpChannel);
var requestURL = subject.URI.spec;
if(isToBeReplaced(requestURL)) {
var newURL = getURL(requestURL);
ChannelReplacement.runWhenPending(subject, function() {
var cr = new ChannelReplacement(subject, ch);
cr.replace(true,null);
cr.open();
});
}
}
},
get observerService() {
return Components.classes["#mozilla.org/observer-service;1"]
.getService(Components.interfaces.nsIObserverService);
},
register: function() {
this.observerService.addObserver(this, "http-on-modify-request", false);
},
unregister: function() {
this.observerService.removeObserver(this, "http-on-modify-request");
}
};
httpRequestObserver.register();
The code will replace the request not redirect.
While I have tested the above code well enough, I am not sure about its implementation. As far I can make out, it copies all the attributes of the requested channel and sets them to the channel to be overridden. After which somehow the output requested by original request is supplied using the new channel.
P.S. I had seen a SO post in which this approach was suggested.
You could listen for the page load event or maybe the DOMContentLoaded event instead. Or you can make an nsIURIContentListener but that's probably more complicated.
Is it possible to modify an URL through a Mozilla Firefox Addon before the page starts loading?
YES it is possible.
Use page-mod of the Addon-SDK by setting contentScriptWhen: "start"
Then after completely preventing the document from getting parsed you can either
fetch a different document from the same domain and inject it in the page.
after some document.URL processing do a location.replace() call
Here is an example of doing 1. https://stackoverflow.com/a/36097573/6085033