Use GO's flag parser instead of getopt

There's only one flag, so it doesn't matter.

main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"errors"
+	"flag"
 	"fmt"
 	"log"
 	"net/http"
@@ -26,18 +27,12 @@ func errExit(err error) {
 }
 
 func main() {
-	opts, _, err := util.Getopts(os.Args, "f:")
-	if err != nil {
-		errExit(err)
-	}
+	configFile := flag.String("f", "", "config file")
+	flag.Parse()
 
-	for _, opt := range opts {
-		switch opt.Option {
-		case 'f':
-			configFiles = []string{opt.Value}
+	if len(*configFile) > 0 {
+		configFiles = []string{*configFile}
 	}
-	}
-
 	config, err := config.ParseFiles(configFiles)
 	if err != nil {
 		errExit(err)

util/getopt.go

@@ -1,122 +0,0 @@
-/*
-Copyright 2019 Drew DeVault <sir@cmpwn.com>
-
-Redistribution and use in source and binary forms, with or without
-modification, are permitted provided that the following conditions are met:
-
-1. Redistributions of source code must retain the above copyright notice, this
-list of conditions and the following disclaimer.
-
-2. Redistributions in binary form must reproduce the above copyright notice,
-this list of conditions and the following disclaimer in the documentation
-and/or other materials provided with the distribution.
-
-3. Neither the name of the copyright holder nor the names of its contributors
-may be used to endorse or promote products derived from this software without
-specific prior written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
-ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
-WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
-DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
-FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
-DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
-SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
-CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
-OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-*/
-
-package util
-
-import (
-	"fmt"
-	"os"
-)
-
-// In the case of "-o example", Option is 'o' and "example" is Value. For
-// options which do not take an argument, Value is "".
-type Option struct {
-	Option rune
-	Value  string
-}
-
-// This is returned when an unknown option is found in argv, but not in the
-// option spec.
-type UnknownOptionError rune
-
-func (e UnknownOptionError) Error() string {
-	return fmt.Sprintf("%s: unknown option -%c", os.Args[0], rune(e))
-}
-
-// This is returned when an option with a mandatory argument is missing that
-// argument.
-type MissingOptionError rune
-
-func (e MissingOptionError) Error() string {
-	return fmt.Sprintf("%s: expected argument for -%c", os.Args[0], rune(e))
-}
-
-// Getopts implements a POSIX-compatible options interface.
-//
-// Returns a slice of options and the index of the first non-option argument.
-//
-// If an error is returned, you must print it to stderr to be POSIX complaint.
-func Getopts(argv []string, spec string) ([]Option, int, error) {
-	optmap := make(map[rune]bool)
-	runes := []rune(spec)
-	for i, rn := range spec {
-		if rn == ':' {
-			if i == 0 {
-				continue
-			}
-			optmap[runes[i-1]] = true
-		} else {
-			optmap[rn] = false
-		}
-	}
-
-	var (
-		i    int
-		opts []Option
-	)
-	for i = 1; i < len(argv); i++ {
-		arg := argv[i]
-		runes = []rune(arg)
-		if len(arg) == 0 || arg == "-" {
-			break
-		}
-		if arg[0] != '-' {
-			break
-		}
-		if arg == "--" {
-			i++
-			break
-		}
-		for j, opt := range runes[1:] {
-			if optopt, ok := optmap[opt]; !ok {
-				opts = append(opts, Option{'?', ""})
-				return opts, i, UnknownOptionError(opt)
-			} else if optopt {
-				if j+1 < len(runes)-1 {
-					opts = append(opts, Option{opt, string(runes[j+2:])})
-					break
-				} else {
-					if i+1 >= len(argv) {
-						if len(spec) >= 1 && spec[0] == ':' {
-							opts = append(opts, Option{':', string(opt)})
-						} else {
-							return opts, i, MissingOptionError(opt)
-						}
-					} else {
-						opts = append(opts, Option{opt, argv[i+1]})
-						i++
-					}
-				}
-			} else {
-				opts = append(opts, Option{opt, ""})
-			}
-		}
-	}
-	return opts, i, nil
-}