Does anybody know why dbus exists? I've been wracking my brain trying to come up with a usecase for dbus that isn't already covered by Unix sockets.
You want to remotely control a daemon? Use sockets. You want the daemon to respond to the client? Sockets. Want to exchange information in json? plaintext? binary data? Sockets can do it. Want to restrict access to a socket? Go ahead, change the socket's permissions. Want to prevent unauthorized programs from pretending to be someone they're not? Change the permissions of the directory containing the socket. Want network transparency? That's why we have abstract sockets.
Plenty of well-established software uses sockets. Music player daemon uses sockets. BSPWM uses sockets. Tmux uses sockets. Pipewire uses sockets. Dhcpcd uses sockets. Heck, dbus itself relies on sockets!
For developers, using sockets is easy. I once wrote a program that interfaced with BSPWM, and it was a breeze. Dbus, on the other hand, not so much. I tried writing a Python script that would contact Network Manager and check the WiFi signal strength. Right off the bat I'm using some obscure undocumented package for interfacing with dbus. What is an introspection? What is a proxy object? What is an interface? Why do I need 60 lines of (Python!) code for a seemingly trivial operation?
So why do some developers decide to use dbus when they could just use unix sockets and save a lot of hassle for themselves and others?
Easy... decoupling. You hit the pause button on your keyboard, it does not need to "know" (in code or compile time or at runtime) what your music player is, and it can still pause it. Similarly, you can write a new media player, and not have to convince 1000 different projects to support or implement your custom api. https://en.m.wikipedia.org/wiki/Enterprise_service_bus
There's nothing about dbus that makes decoupling easier, you can do it just as well with sockets. Pipewire and pulse both speak the same protocol, and they both rely on sockets, not dbus. The vast majority of the apps on my system don't know or care that they're speaking with pipewire instead of pulse. Read my comment here https://lemmy.world/comment/6284859
Did you read more than the first two words of my post? https://wiki.archlinux.org/title/MPRIS
Also, that same logic would "prove" that p2p has no value b/c you can do just as well with fixed servers and http.