go语言获取短网址真正的地址

     如果短网址跳转多次，需要特殊处理，checkRedirect函数会执行多次，返回的error类型会被包装成url.Error类型，在GET方法的返回值里面可以对这个error做接口查询，获取返回值，然后对这个返回值做需要的处理。google group上别人的讨论： https://groups.google.com/forum/#!topic/golang-china/RLdLq-pP6Hk

    这种方法有一个需要注意的地方，当redictrect中途出错的时候，返回的也是url.Error类型, 程序里面要处理这种情况：

(*url.Error)(0x11a2c580)(Get http://refer.ly/aSpT: dial tcp 23.21.175.217:80: ConnectEx tcp: A connection attempt failed because the connected party did not properly respond aftera period of time, or established connection failed because connected host has failed to respond.)

package main

import (
	"fmt"
	"net/http"
	"net/url"
	//"reflect"
	"errors"
)

var redirectCount int = 0

func myRedirect(req *http.Request, via []*http.Request) (e error) {
	redirectCount++	
	if redirectCount == 2 {
        //if strings.Index(str, "baidu") != -1 {
		//value := reflect.TypeOf(*req)	
		//fmt.Print((value.Field(1).Name))
		//fmt.Println(req.URL.String())
		redirectCount = 0
		return errors.New(req.URL.String())

	}
	return 

}

func main() {
	client := &http.Client{CheckRedirect: myRedirect}
	response, err := client.Get("http://t.co/R9iYVHVy52")
	if err != nil {
		if e, ok:= err.(*url.Error); ok && e.Err != nil {
			remoteUrl := e.URL	
			//fmt.Println(e.Err)
			fmt.Println(remoteUrl)
		}
	}
	defer response.Body.Close()
}

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