ip arithmetic

[lgfausak]

i create a lot of json to do configuration. typically my configurations contain ip addresses. i am new to cue, i've spent the day doing experiments and reading through all of the docs / tutorials / etc. If I wanted to use cue to create an ip address based upon a cidr + offset is that possible? something like "192.168.0.0/24" + 3 == 192.168.0.3

[NoamTD]

it's a bit convoluted, but would something like this work for you?

import "net"

#IncIP: {
    In!: net.IPv4
    Offset!: int

    _incremented: In[:3] + [In[len(In)-1]+Offset]

    Out: net.IPString(_incremented)
}

sourceIp: net.ToIP4("192.168.0.0")
withOffset: (#IncIP & {Offset: 1, In: sourceIp}).Out

output:

sourceIp: [192, 168, 0, 0]
withOffset: "192.168.0.1"

[slewiskelly]

it's a bit convoluted, but would something like this work for you?

This will fail if exceeding an octet (255).

I'm not certain that this is totally correct, but:

import (
	"math"
	"net"
	"strconv"
)

ip: (#IPAdd & {ip: "192.168.0.0", i: 256}).out

#IPAdd: {
	ip: string
	i:  uint

	out: "\(math.Floor(_out/16777216)).\(math.Floor(_out/65536) mod 256).\(math.Floor(_out/256) mod 256).\(_out mod 256)"

	_ip:  net.ToIP4(ip)
	_out: (_ip[0]*16777216 + _ip[1]*65536 + _ip[2]*256 + _ip[3]) + i
}

This is easier to implement in Go, but I'm not sure if something like this would be added to the standard library, though.

[myitcv]

but I'm not sure if something like this would be added to the standard library

This seems like a reasonable thing to support. Not least because of the problems that arise when trying to "do this by hand" as demonstrated in #3787. But generally because it seems useful enough to have cropped up here more than once.

Question: is it generally the case that a plain integer value is added? Asked another way, what should the API of such a function look like? Any good examples from the Go standard library or elsewhere?

[takonomura]

@myitcv ​Thank you for considering support for IP address arithmetic in the standard library.

Question: is it generally the case that a plain integer value is added? Asked another way, what should the API of such a function look like? Any good examples from the Go standard library or elsewhere?

In the Go standard library, there is no built-in functionality to perform arithmetic operations on IP addresses.
In cases where arithmetic operations are needed, users typically convert IP addresses into big.Int to perform arithmetic operations¹².
In contrast, Python's ipaddress module supports addition and subtraction through operator overloading, offering a more natural and intuitive interface³.

I have implemented a proof-of-concept API and created PR #3815. I look forward to feedback regarding naming conventions, interface design, and any other aspects that could improve the design.

Footnotes

1. https://github.com/kubernetes/utils/blob/24370beab75816ab1d2b33fba9e288ee667530dd/net/net.go#L55-L68 ↩

2. https://github.com/containernetworking/plugins/blob/v1.6.2/pkg/ip/cidr.go#L60-L76 ↩

3. https://docs.python.org/3/library/ipaddress.html#arithmetic-operators ↩