1. Reference URL: https://github.com/unknwon/the-way-to-go_ZH_CN/blob/master/eBook/09.11.md . Test by browsing the page at http://localhost:8080/ . Enter http://www.destandaard.be in Shorten this, and click Give me the short URL. It keeps loading until it times out. See Figure 1.
2. Check the terminal output, which reports the error: runtime error: invalid memory address or nil pointer dereference. See Figure 2.
Plaintext
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. Review the Go file, urlshortener.go. For code simplicity, we did not check the returned error status, but this check must be performed in a real production environment application. Open the URL: http://goo.gl , and find that the URL Shortener API stopped being supported as of March 30, 2019. See Figure 3.
Go
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(`
URL SHORTENER
{{if .}}{{.}}{{end}}
Shorten this:
Expand this: http://goo.gl/
`))
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. For developers who want to migrate to FDL, please refer to our migration guide. Click the link: our migration guide. Change from using URL Shortener to using Firebase Dynamic Links. See Figure 4.
