Please don't. Use regex to find something that looks like an IP then build a real parser. This is madness, its's extremely hard to read and a mistake is almost impossible to spot. Not to mention that it's slow.

Just parse [0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3} using regex (for v4) and then have some code check that all the octets are valid (and store the IP as a u32).

[–] Emma_Gold_Man@lemmy.dbzer0.com 11 points 1 year ago (2 children)

And dupe check. 0.0.0.0 and 000.000.000.000 may both be valid, but they resolve the same

[–] azertyfun@sh.itjust.works 6 points 1 year ago (1 children)

Fuck that, if for whatever reason I'm writing an IP validator by hand I'm disallowing leading zeros. Parsers are very inconsistent, some will parse 010 as 10, others as 0o10 == 8 (you can try that right now with a POSIX ping). Talk about a footgun.

[–] stringere@reddthat.com 6 points 1 year ago

some will parse 010 as 10, others as 0o10 == 8

...and that's me in the fetal position, thanks.

[–] dannym@lemmy.escapebigtech.info 3 points 1 year ago* (last edited 1 year ago) (3 children)

Definitely, tho if you store it as a u32 that is fixed magically. Because 1.2.3.4 and 1.02.003.04 both map to the same number.

What I mean by storing it as a u32 is to convert it to a number, similar to how the IP gets sent over the wire, so for v4:

octet[3] | octet[2] << 8 | octet[1] << 16 | octet[0] << 24

or in more human terms:

(fourth octet) + (third octet * 256) + (second octet * 256^2) + (first octet * 256^3)

[–] Emma_Gold_Man@lemmy.dbzer0.com 2 points 1 year ago

True enough for database or dictionary storage, but a lot of times things get implemented in arrays where you still wind up with two copies of the same uint32.

[–] p1mrx@sh.itjust.works 2 points 1 year ago (1 children)

Because 1.2.3.4 and 1.02.003.04 both map to the same number.

But 10.20.30.40 and 010.020.030.040 map to different numbers. It's often best to reject IPv4 addresses with leading zeroes to avoid the decimal vs. octal ambiguity.

[–] dannym@lemmy.escapebigtech.info 2 points 1 year ago (1 children)

I don't know why anyone would write their IPs in octal, but fair point

[–] p1mrx@sh.itjust.works 2 points 1 year ago

It's not about how people write them, it's how parsers parse them. IPv4 has been around since 1982, and most parsers interpret leading zeros as octal.