My brain has issues with this kind of form. It prevents me from reading words in a fifo manner. I now need to backtrack, because the 'no' negates the word before.
Port 0: The Port That Does Not Exist (acid.vegas)
39 pointsby NewCzech6 hours ago15 comments
OptionOfT 7 minutes ago
> And asking for port 0 needs no privileges.
fosco 16 minutes ago
greggsy 4 hours ago
I saw the URL and immediately thought it was about Acid Pro DAW or Vegas video editor is used to use back in the early 00’s.
99harry 2 hours ago
Sometimes I have scripts that automatically assign ports starting from 30000. How would that work? Would I have to bind to port 0 multiple times until I randomly get a port in that range?
0bytes 2 hours ago
I’m not exactly sure if that’s the question, but the range can be set. Here’s the Linux solution: https://tldp.org/LDP/solrhe/Securing-Optimizing-Linux-RH-Edi...
FreeBSD has net.inet.ip.portrange
99harry an hour ago
That might not quite fit my use case. My AI-generated scripts probably won't modify system-level configuration files to change the port range
Zambyte 23 minutes ago
... do you not have a say in the matter?
_flux 37 minutes ago
I'm not quite sure what a script assigning ports actually does, but if I need an app to bind a port in some port range, I just start binding ports starting from 30000 until it succeeds.
If it's in a script then that might be difficult, but a racy approximation could be to loop e.g. listening socat with different ports for finding the free port. (Or maybe: parse output of ss.) But if the port use is separate from the port binding, then it might still be busy once the time to rebind it comes.
embedding-shape 4 hours ago
I'm not sure how I'd do acceptance/E2E testing without the magic of port 0. As long as you have a way of capturing what port it ended up using (which most languages are able to out of the box more or less), parallelizing testing workloads becomes such a breeze without having to manage ports and all that jazz, just fire everything up with N parallism and let the OS figure out what the free ports are, pass the references down and stuff just works. Thanks Linux :)
Joker_vD an hour ago
And then there is OpenSSH...
joker@joker:~$ ssh localhost -D 127.0.0.1:0
Bad dynamic forwarding specification '127.0.0.1:0'
joker@joker:~$ ssh localhost -D 127.0.0.1:9999
ssh: connect to host localhost port 22: Connection refused
joker@joker:~$ ssh localhost -L 127.0.0.1:0:localhost:8080
Bad local forwarding specification '127.0.0.1:0:localhost:8080'
joker@joker:~$ ssh localhost -L 127.0.0.1:9999:localhost:8080
ssh: connect to host localhost port 22: Connection refused
wolrah 42 minutes ago
> I'm not sure how I'd do acceptance/E2E testing without the magic of port 0.
Same as anything else, an explicit flag to achieve the same "just give me a port" functionality as this "magic number" does without resulting in the documented unpredictable behavior around a technically legitimate port number.
As the article points out, most if not all of the services exposed on port 0 seem to be accidental and likely resulted from people assuming this magic behavior applies everywhere instead of just to one specific API.
embedding-shape 17 minutes ago
> Same as anything else
Yeah, obviously I'm a programmer so I'm well aware it's technically possible, it was a bit of an exaggeration to explain how much value I feel I get from it.
> most if not all of the services exposed on port 0 seem to be accidental
No program actually end up "exposed on port 0", if it's not supported it won't be able to create a listener on that port, AFAIK. Most yeah, all no. P2P software commonly leverage port 0, and other "discover<>connect" types of software. But I'd agree that it's most likely accidental if outside of those niches.
justsomehnguy 31 minutes ago
I have a feeling what sometimes :0 is interpreted as a 'first listening'. But Occam says what most of the time it's just 'DNAT dst port ANY to :80' or whatever, no magik.
skinfaxi 6 hours ago
Seems hugged?