AWS ip-ranges.json: Find aws prefix / CIDR block for given IP addresses

main.go

/*
find_ip search a local copy of https://docs.aws.amazon.com/general/latest/gr/aws-ip-ranges.html#aws-ip-download for a specific IP and prints the prefix.
*/
package main

import (
	"encoding/json"
	"fmt"
	"net"
	"os"
)

type IPRangesFile struct {
	Prefixes []Prefix
}

type Prefix struct {
	IPPrefix           string `json:"ip_prefix"`
	Region             string
	Service            string
	NetworkBorderGroup string
}

func loadIPRangesFile(file string) (IPRangesFile, error) {
	fp, err := os.Open(file)
	if err != nil {
		return IPRangesFile{}, err
	}
	defer fp.Close()

	var ipranges IPRangesFile
	err = json.NewDecoder(fp).Decode(&ipranges)
	return ipranges, err
}

func findPrefix(ipranges IPRangesFile, needle string) (Prefix, bool) {
	ip := net.ParseIP(needle)

	for _, prefix := range ipranges.Prefixes {
		_, cidr, err := net.ParseCIDR(prefix.IPPrefix)
		if err != nil {
			fmt.Fprintf(os.Stderr, "WARN: Ignoring prefix with invalid cidr: %s\n", prefix.IPPrefix)
			continue
		}

		if cidr.Contains(ip) {
			return prefix, true
		}
	}

	return Prefix{}, false
}

func main() {
	if len(os.Args) <= 2 {
		fmt.Fprintf(os.Stderr, "Usage: find_ip FILE IP1, [IP2, ...]\n")
		os.Exit(1)
	}

	ipranges, err := loadIPRangesFile(os.Args[1])
	if err != nil {
		fmt.Fprintf(os.Stderr, "ERROR: %v\n", err)
		os.Exit(1)
	}

	for _, ip := range os.Args[2:] {
		prefix, ok := findPrefix(ipranges, ip)

		if ok {
			fmt.Printf("%#v\n", prefix)
		} else {
			fmt.Fprintf(os.Stderr, "not found\n")
			os.Exit(1)
		}
	}
}