Merge pull request #336 from tebeka/tebeka-flags

Fun With Flags

Author: bketelsen

content/advent-2019/flag/app.go

@@ -0,0 +1,150 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"strconv"
+)
+
+var config struct {
+	port int
+	host string
+}
+
+const (
+	httpdUsage = `usage: %s httpd
+Run HTTP server
+
+Options:
+`
+	checkUsage = "usage: %s check URL\n"
+)
+
+func main() {
+	flag.Usage = func() { // [1]
+		fmt.Fprintf(flag.CommandLine.Output(), "usage: %s check|run\n", os.Args[0])
+		flag.PrintDefaults()
+	}
+	flag.Parse()
+
+	if len(os.Args) < 2 { // [2]
+		log.Fatalf("error: wrong number of arguments")
+	}
+
+	var err error
+	switch os.Args[1] { // [3]
+	case "run":
+		err = runHTTPD()
+	case "check":
+		err = checkHTTPD()
+	default:
+		err = fmt.Errorf("error: unknown command - %s", os.Args[1])
+	}
+
+	if err != nil {
+		log.Fatalf("error: %s", err)
+	}
+
+}
+
+func checkHTTPD() error {
+	fs := flag.NewFlagSet("check", flag.ContinueOnError) // [4]
+	fs.Usage = func() {
+		fmt.Fprintf(flag.CommandLine.Output(), checkUsage, os.Args[0])
+		fs.PrintDefaults()
+	}
+
+	if err := fs.Parse(os.Args[2:]); err != nil { // [5]
+		return err
+	}
+
+	if fs.NArg() != 1 {
+		return fmt.Errorf("error: wrong number of arguments")
+	}
+
+	url := fs.Arg(0) // [6]
+	resp, err := http.Get(url)
+	switch {
+	case err != nil:
+		return err
+	case resp.StatusCode != http.StatusOK:
+		return fmt.Errorf("error: bad status - %s", resp.Status)
+	}
+
+	return nil
+}
+
+func runHTTPD() error {
+	fs := flag.NewFlagSet("check", flag.ContinueOnError)
+	fs.Var(PortVar(&config.port), "port", "port to listen on")
+	fs.StringVar(&config.host, "host", config.host, "host to listen on")
+	fs.Usage = func() {
+		fmt.Fprintf(flag.CommandLine.Output(), httpdUsage, os.Args[0])
+		fs.PrintDefaults()
+	}
+
+	if err := fs.Parse(os.Args[2:]); err != nil {
+		return err
+	}
+
+	http.HandleFunc("/", handler)
+	addr := fmt.Sprintf("%s:%d", config.host, config.port)
+	fmt.Printf("server ready on %s\n", addr)
+	return http.ListenAndServe(addr, nil)
+}
+
+func PortVar(port *int) *portVar {
+	return &portVar{port}
+}
+
+type portVar struct {
+	port *int
+}
+
+func (p *portVar) String() string {
+	if p.port == nil {
+		return ""
+	}
+
+	return fmt.Sprintf("%d", *p.port)
+}
+
+func (p *portVar) Set(s string) error {
+	val, err := strconv.Atoi(s)
+	if err != nil {
+		return err
+	}
+
+	const minPort, maxPort = 1, 65535
+	if val < minPort || val > maxPort {
+		return fmt.Errorf("port %d out of range [%d:%d]", val, minPort, maxPort)
+	}
+
+	*p.port = val
+	return nil
+}
+
+func init() {
+	// Set defaults
+	s := os.Getenv("HTTPD_PORT")
+	p, err := strconv.Atoi(s)
+	if err == nil {
+		config.port = p
+	} else {
+		config.port = 8080
+	}
+
+	h := os.Getenv("HTTPD_HOST")
+	if len(h) > 0 {
+		config.host = h
+	} else {
+		config.host = "localhost"
+	}
+}
+
+func handler(w http.ResponseWriter, r *http.Request) {
+	fmt.Fprintf(w, "Hello Gophers\n")
+}

content/advent-2019/flag/go.mod

@@ -0,0 +1,3 @@
+module main
+
+go 1.13

content/advent-2019/flag/httpd-var.go

@@ -0,0 +1,93 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"strconv"
+)
+
+var config struct {
+	port int
+	host string
+}
+
+const (
+	usage = `usage: %s
+Run HTTP server
+
+Options:
+`
+)
+
+func main() {
+	flag.Var(PortVar(&config.port), "port", "port to listen on")
+	flag.StringVar(&config.host, "host", config.host, "host to listen on")
+	flag.Usage = func() {
+		fmt.Fprintf(flag.CommandLine.Output(), usage, os.Args[0])
+		flag.PrintDefaults()
+	}
+	flag.Parse()
+
+	http.HandleFunc("/", handler)
+	addr := fmt.Sprintf("%s:%d", config.host, config.port)
+	fmt.Printf("server ready on %s\n", addr)
+	if err := http.ListenAndServe(addr, nil); err != nil {
+		log.Fatalf("error: %s", err)
+	}
+}
+
+func PortVar(port *int) *portVar {
+	return &portVar{port}
+}
+
+type portVar struct {
+	port *int
+}
+
+func (p *portVar) String() string {
+	if p.port == nil {
+		return ""
+	}
+
+	return fmt.Sprintf("%d", *p.port)
+}
+
+func (p *portVar) Set(s string) error {
+	val, err := strconv.Atoi(s)
+	if err != nil {
+		return err
+	}
+
+	const minPort, maxPort = 1, 65535
+	if val < minPort || val > maxPort {
+		return fmt.Errorf("port %d out of range [%d:%d]", val, minPort, maxPort)
+	}
+
+	*p.port = val
+	return nil
+}
+
+func init() {
+	// Set defaults
+	s := os.Getenv("HTTPD_PORT")
+	p, err := strconv.Atoi(s)
+	if err == nil {
+		config.port = p
+	} else {
+		config.port = 8080
+	}
+
+	h := os.Getenv("HTTPD_HOST")
+	if len(h) > 0 {
+		config.host = h
+	} else {
+		config.host = "localhost"
+	}
+}
+
+func handler(w http.ResponseWriter, r *http.Request) {
+	fmt.Fprintf(w, "Hello Gophers\n")
+}

content/advent-2019/flag/httpd.go

@@ -0,0 +1,63 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"strconv"
+)
+
+var config struct { // [1]
+	port int
+	host string
+}
+
+const (
+	usage = `usage: %s
+Run HTTP server
+
+Options:
+`
+)
+
+func main() {
+	flag.IntVar(&config.port, "port", config.port, "port to listen on")    // [2]
+	flag.StringVar(&config.host, "host", config.host, "host to listen on") // [3]
+	flag.Usage = func() {                                                  // [4]
+		fmt.Fprintf(flag.CommandLine.Output(), usage, os.Args[0])
+		flag.PrintDefaults()
+	}
+	flag.Parse() // [5]
+
+	http.HandleFunc("/", handler)
+	addr := fmt.Sprintf("%s:%d", config.host, config.port)
+	fmt.Printf("server ready on %s\n", addr)
+	if err := http.ListenAndServe(addr, nil); err != nil {
+		log.Fatalf("error: %s", err)
+	}
+
+}
+
+func init() { // [6]
+	// Set defaults
+	s := os.Getenv("HTTPD_PORT")
+	p, err := strconv.Atoi(s)
+	if err == nil {
+		config.port = p
+	} else {
+		config.port = 8080
+	}
+
+	h := os.Getenv("HTTPD_HOST")
+	if len(h) > 0 {
+		config.host = h
+	} else {
+		config.host = "localhost"
+	}
+}
+
+func handler(w http.ResponseWriter, r *http.Request) {
+	fmt.Fprintf(w, "Hello Gophers\n")
+}