webpush | webpush , Encryption Utilities for Web Push protocol | Notification library

I have put some push notifications in my code, in order to someone to be notified when an action is made. I made the back end with lib.net.webpush 3.1.0 with .net 4.5.2 in C#. So far, the notification system is working very well, but there is something I can't succeed : Within my service worker file (sw.js), using Angular 9, i want, when someone received the notification, that when a user click on it, he is redirect to the page from which it was sent.

first i made it like it (as i read in the doc):

I'd like to make web push with c#. In the backend I use web-push-csharp. I try to test it with postman before pass the API to frontend developer but I get this error.

"Message": "An error has occurred.", "ExceptionMessage": "The best overloaded method match for 'WebPush.WebPushClient.SendNotificationAsync(WebPush.PushSubscription, string, System.Collections.Generic.Dictionary)' has some invalid arguments", "ExceptionType": "Microsoft.CSharp.RuntimeBinder.RuntimeBinderException",

The error comes from payload in the json body because when I replace it with a simple string , the error is gone.

This is the json body in postman:

I've installed django-webpush in my project and put {% webpush_header %} in the part of my HTML template as instructed, however I am getting an error:

I installed web push :

Please explain to me how webpush work in TCP/IP network layers (especially layer 4-5).

I understand that HTTP is stateless protocol:

• the protocol is opening TCP / layer 4 connection,
• 'state' is 'made to work' with cookie/session,
• then client send HTTP request (plaintext/compressed "HTTP/1.1 /url/here ... Content-Length: ..."),
• then server respond with HTTP request (plaintext/compressed "200 OK ... ..."),

Therefore it's understandable that for a user behind NAT to be able to view webpage of a remote host (because the user behind NAT is the one initiating the connection); but the webserver cannot initiate TCP connection with the client (browser process).

However there are some exceptions like 'websocket' where client (browser) initiate a connection, then leave it open (elevate to just TCP, not HTTP anymore). In this architecture, webserver may send / initiate sending message to client (for example "you have new chat message" notification).

What I don't understand is the new term 'webpush'.

• I observed that it can send notification from server to client/browser (from user, it 'feels' like the server is the one initiating the connection)
• webpush can send notification anytime, even when browser is closed / not opened yet (as when the device was just freshly turned on), or when it's just connected to internet

How does it work? How do they accomplish this? Previously I think that:

• either a javascript in a page is continously (ex: 5 second interval) checking if there's a new notification in server,
• or a javascript initiate a websocket (browser initiate/open TCP connection) and keep it alive, when server need to send something, it's sent from webserver to client/browser through this connection

Is this correct? Or am I missing something? Since both of my guess above won't work behind NAT'd network

Is Firebase web notification also this kind of webpush?

I have searched the internet for explanation on what make it work on client side, but there seems only explanation on 'how to send webpush', 'how to market your product with webpush', those articles only explain the server side (communication of app server with push service server) or articles about marketing.

Also, I'm interested in understanding what application layer protocol they're running on (as in what text/binary data the client/server send to each other), if it's not HTTP

I have node.js with express backend with some endpoints, all works fine testing with curl or postman, but on my client-side with angular on the http.post request i get the response correctly, but no cookie is saved. I've tried changing my localhost dns, after some try i'm ended up using 127.0.0.1:4200 client and 127.0.0.1:3000 backend.

backend code:

I'm trying to run a 'node.js' server for push notification. But I received an error instead. This was picked up on a tutorial for adding push notification using SwPush to PWA on Angular.

Do I need to place the Public key somewhere?? I had generated public and private keys using "web-push generate-vapid-keys".

Server.js script:

When a user create a subscription through the PushManager.subscribe(), given the applicationServerKey (VAPID public key), it creates a valid subscription the contents of which can be sent and stored in the database. The content sent to the database looks something like the following:

I use firebase_messaging for push notifications and to send the messages I use POST requests.

When sending messages to FCM token it all works properly, but when sending them to topic (I basically modified the request I use for token messages) they won't get delivered.

I checked and the topic is correct and on physical Android device I'm correctly subscripted to that topic, as when sending a topic message from FCM console it gets delivered immediately. Can you spot what I'm doing wrong here?

Many thanks.