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resolve.go
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resolve.go
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package rendezvous
import (
"bytes"
"fmt"
"io/ioutil"
"net"
"net/http"
"time"
)
type resolver interface {
// PublicIP resolves this's host public IP.
PublicIP() (net.IP, error)
}
type externalResolver struct {
url string
// Cached IP.
ip net.IP
cacheTime time.Time
cacheDuration time.Duration
}
func newExternalResolver(url string) resolver {
if url == "" {
url = "http://checkip.amazonaws.com/"
}
return &externalResolver{
url: url,
cacheDuration: 10 * time.Minute,
}
}
func (m *externalResolver) PublicIP() (net.IP, error) {
if m.needRefresh() {
if err := m.refresh(); err != nil {
return nil, err
}
}
return m.ip, nil
}
func (m *externalResolver) needRefresh() bool {
return m.ip == nil || time.Now().Sub(m.cacheTime) > m.cacheDuration
}
func (m *externalResolver) refresh() error {
ip, err := m.resolve()
if err != nil {
return err
}
m.ip = ip
m.cacheTime = time.Now()
return nil
}
func (m *externalResolver) resolve() (net.IP, error) {
resp, err := http.Get(m.url)
if err != nil {
return nil, err
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
return nil, fmt.Errorf("failed to resolve external IP address: %s", resp.Status)
}
addr, err := ioutil.ReadAll(resp.Body)
if err != nil {
return nil, err
}
return net.ParseIP(string(bytes.TrimSpace(addr))), nil
}