golang url parsing pitfalls

package main

import (
    "fmt"
    "log"
    "net/url"
    "os"
)

// The URL library parse function  https://golang.org/pkg/net/url/#Parse
// silently fails to parse a URL that does not include a scheme
// This means that you are turned a paritally formed or ill-formed URL object
// => If you include a port number, your domain will be assigned to scheme
// => If you include only a path, your domain/path will all be considered path
// => In all cases, hostname is left blank

/* Testing how AUTHN_URL is parsed, run these:
   AUTHN_URL=host.domain.com      go run urlparse.go
   AUTHN_URL=host.domain.com:2112 go run urlparse.go
   AUTHN_URL=host.domain.com:2112/syrinx go run urlparse.go
   AUTHN_URL=host.domain.com/syrinx      go run urlparse.go

   AUTHN_URL=https://host.domain.com go run urlparse.go
   AUTHN_URL=http://host.domain.com:2112/syrinx go run urlparse.go
*/

// Note that if you change to using "ParseRequestURI",
// you will get an error when parsing
func lookupURL(name string) (*url.URL, error) {
    if val, ok := os.LookupEnv(name); ok {
        return url.Parse(val)
    }
    return nil, nil
}

func readenv(name string) (string) {
    if val, ok := os.LookupEnv(name); ok {
        return val
    }
    return ""
 }

func main() {
   fmt.Printf("\nUnparsed URL from ENV: %s\n", readenv("AUTHN_URL"))

    parsedURL, err := lookupURL("AUTHN_URL")
    if err != nil {
        log.Fatalln(err)
    }
    fmt.Printf("Parsed URL Scheme    : %s\n", parsedURL.Scheme)
    fmt.Printf("Parsed URL Hostname  : %s\n", parsedURL.Hostname())
    fmt.Printf("Parsed URL Port      : %s\n", parsedURL.Port())
    fmt.Printf("parsed URL Path      : %s\n", parsedURL.EscapedPath())
    fmt.Printf("parsed URL as string : %s\n\n", parsedURL.String())
}