How to Check if an IP Address is Within a Specific Range in Go?

Checking IP Address Range in Go/GoLang

When working with IP addresses in Go, you may encounter the need to determine if a given IP address falls within a specific range. This task is made simple and efficient with Go's built-in functions.

To check if an IP address is in a range, follow these steps:

1. Convert IP Addresses to Bytes:

Convert the range start and end IP addresses, as well as the input IP address, to byte slices using the net.ParseIP function. This function returns an IP type, which is a bigendian byte slice representation of the IP address.

2. Compare Byte Slices:

Use bytes.Compare to compare the byte slices of the input IP address and the range start and end IP addresses. This function returns an integer indicating the relative ordering of the byte slices:

• If bytes.Compare(input, start) >= 0, the input IP address is greater than or equal to the start of the range.
• If bytes.Compare(input, end) <= 0, the input IP address is less than or equal to the end of the range.

Example Code:

The following code demonstrates how to check if an IP address is in a range using bytes.Compare:

package main

import (
    "bytes"
    "fmt"
    "net"
)

var (
    ip1 = net.ParseIP("216.14.49.184")
    ip2 = net.ParseIP("216.14.49.191")
)

func check(ip string) bool {
    trial := net.ParseIP(ip)
    if trial.To4() == nil {
        fmt.Printf("%v is not an IPv4 address\n", trial)
        return false
    }
    if bytes.Compare(trial, ip1) >= 0 && bytes.Compare(trial, ip2) <= 0 {
        fmt.Printf("%v is between %v and %v\n", trial, ip1, ip2)
        return true
    }
    fmt.Printf("%v is NOT between %v and %v\n", trial, ip1, ip2)
    return false
}

func main() {
    check("1.2.3.4")
    check("216.14.49.185")
    check("1::16")
}
In this example, the check function first tries to parse the input IP address. If it's not a valid IPv4 address, it returns an error message. Otherwise, it compares the byte slices of the input IP address with the start and end IP addresses of the range using bytes.Compare. It then prints the result and returns a boolean indicating whether the input IP address is in the range.
By utilizing bytes.Compare, Go provides an efficient and straightforward way to check if an IP address is within a specified range, making it a valuable tool for IP address manipulation tasks.

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