使用 URL Shortener API 时，runtime error: invalid memory address or nil pointer dereference
1、参考网址：https://github.com/unknwon/the-way-to-go_ZH_CN/blob/master/eBook/09.11.md 。通过浏览 http://localhost:8080/ 的页面来测试。在 Shorten this 中输入：http://www.destandaard.be ，点击：Give me the short URL。一直加载中，直至超时。如图1
图1
2、查看终端输出，报错：runtime error: invalid memory address or nil pointer dereference。如图2
图2
PS E:\wwwroot\go\the-way-to-go\package> go run urlshortener.go
2020/09/07 19:52:23 http: panic serving 127.0.0.1:55417: runtime error: invalid memory address or nil pointer dereference
goroutine 34 [running]:
net/http.(*conn).serve.func1(0xc000282000)
c:/go/src/net/http/server.go:1767 +0x140
panic(0x957240, 0xe59f20)
c:/go/src/runtime/panic.go:679 +0x1c0
main.short(0xac7dc0, 0xc0002ac1c0, 0xc00029a100)
E:/wwwroot/go/the-way-to-go/package/urlshortener.go:42 +0x18d
net/http.HandlerFunc.ServeHTTP(0xa2e470, 0xac7dc0, 0xc0002ac1c0, 0xc00029a100)
c:/go/src/net/http/server.go:2007 +0x4b
net/http.(*ServeMux).ServeHTTP(0xe6f740, 0xac7dc0, 0xc0002ac1c0, 0xc00029a100)
c:/go/src/net/http/server.go:2387 +0x1c4
net/http.serverHandler.ServeHTTP(0xc000264000, 0xac7dc0, 0xc0002ac1c0, 0xc00029a100)
c:/go/src/net/http/server.go:2802 +0xab
net/http.(*conn).serve(0xc000282000, 0xac8b00, 0xc00025c080)
c:/go/src/net/http/server.go:1890 +0x87c
created by net/http.(*Server).Serve
c:/go/src/net/http/server.go:2927 +0x395
2020/09/07 19:52:29 http: panic serving 127.0.0.1:55418: runtime error: invalid memory address or nil pointer dereference
goroutine 20 [running]:
net/http.(*conn).serve.func1(0xc0002b4000)
c:/go/src/net/http/server.go:1767 +0x140
panic(0x957240, 0xe59f20)
c:/go/src/runtime/panic.go:679 +0x1c0
main.short(0xac7dc0, 0xc00030c000, 0xc0002b0100)
E:/wwwroot/go/the-way-to-go/package/urlshortener.go:42 +0x18d
net/http.HandlerFunc.ServeHTTP(0xa2e470, 0xac7dc0, 0xc00030c000, 0xc0002b0100)
c:/go/src/net/http/server.go:2007 +0x4b
net/http.(*ServeMux).ServeHTTP(0xe6f740, 0xac7dc0, 0xc00030c000, 0xc0002b0100)
c:/go/src/net/http/server.go:2387 +0x1c4
net/http.serverHandler.ServeHTTP(0xc000264000, 0xac7dc0, 0xc00030c000, 0xc0002b0100)
c:/go/src/net/http/server.go:2802 +0xab
net/http.(*conn).serve(0xc0002b4000, 0xac8b00, 0xc000266080)
c:/go/src/net/http/server.go:1890 +0x87c
created by net/http.(*Server).Serve
c:/go/src/net/http/server.go:2927 +0x395
2020/09/07 19:52:40 http: panic serving 127.0.0.1:55438: runtime error: invalid memory address or nil pointer dereference
goroutine 14 [running]:
net/http.(*conn).serve.func1(0xc00011a820)
c:/go/src/net/http/server.go:1767 +0x140
panic(0x957240, 0xe59f20)
c:/go/src/runtime/panic.go:679 +0x1c0
main.short(0xac7dc0, 0xc0002640e0, 0xc000244200)
E:/wwwroot/go/the-way-to-go/package/urlshortener.go:42 +0x18d
net/http.HandlerFunc.ServeHTTP(0xa2e470, 0xac7dc0, 0xc0002640e0, 0xc000244200)
c:/go/src/net/http/server.go:2007 +0x4b
net/http.(*ServeMux).ServeHTTP(0xe6f740, 0xac7dc0, 0xc0002640e0, 0xc000244200)
c:/go/src/net/http/server.go:2387 +0x1c4
net/http.serverHandler.ServeHTTP(0xc000264000, 0xac7dc0, 0xc0002640e0, 0xc000244200)
c:/go/src/net/http/server.go:2802 +0xab
net/http.(*conn).serve(0xc00011a820, 0xac8b00, 0xc00004d280)
c:/go/src/net/http/server.go:1890 +0x87c
created by net/http.(*Server).Serve
c:/go/src/net/http/server.go:2927 +0x395
exit status 2
PS E:\wwwroot\go\the-way-to-go\package>
3、查看 Go 文件，urlshortener.go。为了代码的简洁我们并没有检测返回的错误状态，但是在真实的生产环境的应用中一定要做检测。打开网址：http://goo.gl ，发现到 2019年3月30日，URL Shortener API 已经停止支持。如图3
图3
package main
import (
"fmt"
"net/http"
"text/template"
"google.golang.org/api/urlshortener/v1"
)
func main() {
http.HandleFunc("/", root)
http.HandleFunc("/short", short)
http.HandleFunc("/long", long)
http.ListenAndServe("localhost:8080", nil)
}
// the template used to show the forms and the results web page to the user
var rootHtmlTmpl = template.Must(template.New("rootHtml").Parse(`
<html><body>
<h1>URL SHORTENER</h1>
{{if .}}{{.}}<br /><br />{{end}}
<form action="/short" type="POST">
Shorten this: <input type="text" name="longUrl" />
<input type="submit" value="Give me the short URL" />
</form>
<br />
<form action="/long" type="POST">
Expand this: http://goo.gl/<input type="text" name="shortUrl" />
<input type="submit" value="Give me the long URL" />
</form>
</body></html>
`))
func root(w http.ResponseWriter, r *http.Request) {
rootHtmlTmpl.Execute(w, nil)
}
func short(w http.ResponseWriter, r *http.Request) {
longUrl := r.FormValue("longUrl")
urlshortenerSvc, _ := urlshortener.New(http.DefaultClient)
url, _ := urlshortenerSvc.Url.Insert(&urlshortener.Url{LongUrl:
longUrl,}).Do()
rootHtmlTmpl.Execute(w, fmt.Sprintf("Shortened version of %s is : %s",
longUrl, url.Id))
}
func long(w http.ResponseWriter, r *http.Request) {
shortUrl := "http://goo.gl/" + r.FormValue("shortUrl")
urlshortenerSvc, _ := urlshortener.New(http.DefaultClient)
url, err := urlshortenerSvc.Url.Get(shortUrl).Do()
if err != nil {
fmt.Println("error: %v", err)
return
}
rootHtmlTmpl.Execute(w, fmt.Sprintf("Longer version of %s is : %s",
shortUrl, url.LongUrl))
}
4、对于希望迁移到 FDL 的开发人员，请参阅我们的迁移指南。点击链接：our migration guide。由使用 URL Shortener 改为使用 Firebase 动态链接。如图4
图4
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