Geoip2 - golang golang source code analysis

https://github.com/oschwald/geoip2-golang用来解析

[GeoLite2](http://dev.maxmind.com/geoip/geoip2/geolite2/)

and [GeoIP2](http://www.maxmind.com/en/geolocation_landing)Database a kit.类似于nginx的https://github.com/leev/ngx_http_geoip2_module

GeoIP2What's the use of the database？我们可以根据ip来获取ipResponse of regional location and do relevant business：

1,简单的cdn,根据ipGeographic information is redirected to the appropriatecdn服务器

2,Do business fixed area block,比如：Don't give the Japanese customers

3,做国际化,According to the different places for different language services.

For example, we commonly used online toolshttps://github.com/zu1k/nali 其实就用到了geoip2-golang这个包来解析GeoIP2数据.下面,We see this package should be how to use：

package main

import (
  "fmt"
  "log"
  "net"

  "github.com/oschwald/geoip2-golang"
)

func main() {
  db, err := geoip2.Open("./GeoLite2-City.mmdb")
  if err != nil {
    log.Fatal(err)
  }
  defer db.Close()
  // If you are using strings that may be invalid, check that ip is not nil
  ip := net.ParseIP("180.101.49.12") //120.24.37.249
  record, err := db.City(ip)
  if err != nil {
    log.Fatal(err)
  }
  fmt.Printf("Portuguese (BR) city name: %v\n", record.City.Names["zh-CN"])
  fmt.Printf("English subdivision name: %v\n", record.Subdivisions[0].Names["en"])
  fmt.Printf("Russian country name: %v\n", record.Country.Names["en"])
  fmt.Printf("ISO country code: %v\n", record.Country.IsoCode)
  fmt.Printf("Time zone: %v\n", record.Location.TimeZone)
  fmt.Printf("Coordinates: %v, %v\n", record.Location.Latitude, record.Location.Longitude)
  // Output:
  // Portuguese (BR) city name: Londres
  // English subdivision name: England
  // Russian country name: Великобритания
  // ISO country code: GB
  // Time zone: Europe/London
  // Coordinates: 51.5142, -0.0931
}

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非常简单,加载GeoLite2-City.mmdb数据库,解析ip地址,通过ipAddress loading city information.

接着,我们详细分析下geoip2-golang这个包的源码.Its source code is very simple only a file：

reader.go

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调用了maxminddbData analysis packagegithub.com/oschwald/maxminddb-golang来做 数据的解析,Just do a layer on the interface encapsulation,And the corresponding geographic data format（企业、城市、国家、AnonymousIP、Domain、ISP）的定义.

比如城市信息：

// The City struct corresponds to the data in the GeoIP2/GeoLite2 City
// databases.
type City struct {
  City struct {
    GeoNameID uint              `maxminddb:"geoname_id"`
    Names     map[string]string `maxminddb:"names"`
  } `maxminddb:"city"`
  Continent struct {
    Code      string            `maxminddb:"code"`
    GeoNameID uint              `maxminddb:"geoname_id"`
    Names     map[string]string `maxminddb:"names"`
  } `maxminddb:"continent"`
  Country struct {
    GeoNameID         uint              `maxminddb:"geoname_id"`
    IsInEuropeanUnion bool              `maxminddb:"is_in_european_union"`
    IsoCode           string            `maxminddb:"iso_code"`
    Names             map[string]string `maxminddb:"names"`
  } `maxminddb:"country"`
  Location struct {
    AccuracyRadius uint16  `maxminddb:"accuracy_radius"`
    Latitude       float64 `maxminddb:"latitude"`
    Longitude      float64 `maxminddb:"longitude"`
    MetroCode      uint    `maxminddb:"metro_code"`
    TimeZone       string  `maxminddb:"time_zone"`
  } `maxminddb:"location"`
  Postal struct {
    Code string `maxminddb:"code"`
  } `maxminddb:"postal"`
  RegisteredCountry struct {
    GeoNameID         uint              `maxminddb:"geoname_id"`
    IsInEuropeanUnion bool              `maxminddb:"is_in_european_union"`
    IsoCode           string            `maxminddb:"iso_code"`
    Names             map[string]string `maxminddb:"names"`
  } `maxminddb:"registered_country"`
  RepresentedCountry struct {
    GeoNameID         uint              `maxminddb:"geoname_id"`
    IsInEuropeanUnion bool              `maxminddb:"is_in_european_union"`
    IsoCode           string            `maxminddb:"iso_code"`
    Names             map[string]string `maxminddb:"names"`
    Type              string            `maxminddb:"type"`
  } `maxminddb:"represented_country"`
  Subdivisions []struct {
    GeoNameID uint              `maxminddb:"geoname_id"`
    IsoCode   string            `maxminddb:"iso_code"`
    Names     map[string]string `maxminddb:"names"`
  } `maxminddb:"subdivisions"`
  Traits struct {
    IsAnonymousProxy    bool `maxminddb:"is_anonymous_proxy"`
    IsSatelliteProvider bool `maxminddb:"is_satellite_provider"`
  } `maxminddb:"traits"`
}

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先看下open函数

func Open(file string) (*Reader, error) {
  reader, err := maxminddb.Open(file)
  if err != nil {
    return nil, err
  }
  dbType, err := getDBType(reader)
  return &Reader{reader, dbType}, err
}

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它调用了 maxminddb.Open返回了一个Reader

type Reader struct {
  mmdbReader   *maxminddb.Reader
  databaseType databaseType
}

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Reader上定义了City,County等函数

func (r *Reader) City(ipAddress net.IP) (*City, error) {
  if isCity&r.databaseType == 0 {
    return nil, InvalidMethodError{"City", r.Metadata().DatabaseType}
  }
  var city City
  err := r.mmdbReader.Lookup(ipAddress, &city)
  return &city, err
}

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These functions are just formmdbReader.Lookup做了简单的封装.