go - Golang "net/http" Error: undefined: DetectContentType -

the "net/http" package implements function detectcontenttype

http://golang.org/pkg/net/http/#detectcontenttype

but when try use it, error undefined: detectcontenttype

package main  import (     "fmt"     "io/ioutil"     "log"     "net/http" )  func main() {     res, err := http.get("http://www.google.com/robots.txt")     if err != nil {         log.fatal(err)     }      robots, err := ioutil.readall(res.body)     res.body.close()     if err != nil {         log.fatal(err)     }      filetype := detectcontenttype(robots)          fmt.println("filetype: ", filetype) } 

https://play.golang.org/p/wjduu8xx-5

what doing wrong?

it part of "net/http" package therefore have write,

http.detectcontenttype(robots) 

note if wanted use function in way change import statement such:

import (    ...    . "net/http" )