Go 通过IP查询城市

• 条件
• 答案

现有一堆IP，每个IP有对应的城市，给一个IP，查询到对应的城市

package main

import (
	"bytes"
	"encoding/binary"
	"net"
)

type IpRange struct {
	Begin uint32
	End   uint32
	City  string
}

type IpData []*IpRange

func (id *IpData) Length() int {
	return len(*id)
}

func ip2Long(ip string) uint32 {
	var long uint32

	binary.Read(bytes.NewBuffer(net.ParseIP(ip).To4()), binary.BigEndian, &long)

	return long
}

func getCity(ip string, list IpData) string {
	head, tail := 0, list.Length()-1

	il := ip2Long(ip)
	if il <= 0 {
		return ""
	}

	for head <= tail {
		mid := head + (tail-head)/2

		ir := list[mid]

		if ir.Begin <= il && ir.End >= il {
			return ir.City
		} else if ir.Begin > il {
			tail = mid - 1
		} else {
			head = mid + 1
		}
	}

	return ""
}