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?
I will conveniently avoid any dbus talk, because the why is not so interesting as the how and direct you to this path
/var/run/wpa_supplicant. You would probably sendSCAN_RESULTSon the socket, you could also initiate aSCANfirst to include the strength of stations you're not connected to. If you want deeper access to wireless, you use netlink to communicate with the kernel (see/usr/include/linux/nl80211.h) and poke someNL80211_STA_INFOs.. or the other direction (everything is a file) you just parse/proc/net/wirelesswithout any special permissions for the current signal strength.Oh.. and btw dbus has a simple binary protocol underneath all the XML/interface fluff and uses a UNIX socket.