How do messengers work?

Question

Database

Hello, tell us and give links to information and books about how instant messengers work. Interested in the full cycle, from sending a message by a user to delivery to another user. When encryption occurs, how the message gets to the right user, and so on.
Books on networks, information transfer, encryption, and other things that take place are appropriate.
Thank you.
PS This is my first question, if I wrote something wrong, please let me know.

Answer 1

Encryption? Few people bother.
You can read about encryption separately. This is its own branch of knowledge.
Read, for example, the description of the Jabber protocol. Everything is detailed there.

Answer 2

tell and give links to information and books about how instant messengers work.

How can you even talk in general about “how messengers work”, if there are many of these messengers today, and they work in completely different ways?

Answer 3

Interested in full cycle

Here you can do different things:
- pear-to-pear, in this case, the server is needed only for people to find each other. Well, or you can contrive and then the server is not needed at all. In this case, clients connect to each other and send messages directly.
- the usual model of messaging through a shared server. The easiest option. Everything connects to one server, which acts as a message router. Each message has an identifier from where and where it wants to be delivered. Further, I think the algorithm will be clear to you.
Looking at what level to do it. You can encrypt yourself at the application level (it’s very difficult and you have to read a lot of smart books and it’s advisable to unlearn the desired specialty at the university), or you can trust the system TLS, then the entire operating system handles, but of course it’s not so secure because SSL certificates can be compromised.
Books... look here for questions on computer networks, I think you will find a list of references.

Answer 4

https://xmpp.org/xmpp-protocols/rfcs/
https://xmpp.org/xmpp-protocols/xmpp-extensions/
Полное описание протокола XMPP. Ну а если нужно подробнее - то уже исходники ejabberd2 и какого-нибудь клиента.
Как работают проприетарные мессенджеры никто вам не расскажет. А если расскажет - то догадки или то, что выяснили по косвенным признакам.