Golang - check if IP address is in a network

The Go net package includes the following functions:

• ParseCIDR: takes a string representing an IP/mask and returns an IP and an IPNet
• IPNet.Contains: checks whether an IP is in a network

This should cover your needs.

Based on Zoyd's feedback...

https://play.golang.org/p/wdv2sPetmt

package main

import (
    "fmt"
    "net"
)

func main() {

    A := "172.17.0.0/16"
    B := "172.17.0.2/16"

    ipA,ipnetA,_ := net.ParseCIDR(A)
    ipB,ipnetB,_ := net.ParseCIDR(B)

    fmt.Println("Network address A: ", A)
    fmt.Println("IP address      B: ", B)
    fmt.Println("ipA              : ", ipA)
    fmt.Println("ipnetA           : ", ipnetA)
    fmt.Println("ipB              : ", ipB)
    fmt.Println("ipnetB           : ", ipnetB)


    fmt.Printf("\nDoes A (%s) contain: B (%s)?\n", ipnetA, ipB)

    if ipnetA.Contains(ipB) {
        fmt.Println("yes")
    } else {
        fmt.Println("no")
    }

}

Based on tgogos's answer:

package main

import (
    "fmt"
    "net"
)

func main() {
    A := "172.17.0.0/16"
    B := "172.17.0.2"

    _, ipnetA, _ := net.ParseCIDR(A)
    ipB := net.ParseIP(B)

    fmt.Printf("\nDoes A (%s) contain: B (%s)?\n", ipnetA, ipB)

    if ipnetA.Contains(ipB) {
        fmt.Println("yes")
    } else {
        fmt.Println("no")
    }
}