helloserver: add basic hello world web server

We want to revive golang.org/x/example as a test case for an experiment with a 'gonew' command. This CL adds a basic "hello, world" web server as golang.org/x/example/helloserver. Change-Id: Icf76c756f7b256285d4c5e6a33655996597eb2da Reviewed-on: https://go-review.googlesource.com/c/example/+/513997 Auto-Submit: Russ Cox <rsc@golang.org> TryBot-Result: Gopher Robot <gobot@golang.org> Run-TryBot: Russ Cox <rsc@golang.org> Reviewed-by: Cameron Balahan <cbalahan@google.com>
2023-07-28 15:06:57 -04:00 · 2023-07-28 15:06:57 -04:00 · 3dc2413024
--- a/helloserver/go.mod
+++ b/helloserver/go.mod
@ -0,0 +1,4 @@
+module golang.org/x/example/helloserver
+
+go 1.19
+
--- a/helloserver/server.go
+++ b/helloserver/server.go
@ -0,0 +1,75 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Hello is a simple hello, world demonstration web server.
+//
+// It serves version information on /version and answers
+// any other request like /name by saying "Hello, name!".
+//
+// See golang.org/x/example/outyet for a more sophisticated server.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"html"
+	"log"
+	"net/http"
+	"os"
+	"runtime/debug"
+	"strings"
+)
+
+func usage() {
+	fmt.Fprintf(os.Stderr, "usage: helloserver [options]\n")
+	flag.PrintDefaults()
+	os.Exit(2)
+}
+
+var (
+	greeting = flag.String("g", "Hello", "Greet with `greeting`")
+	addr     = flag.String("addr", "localhost:8080", "address to serve")
+)
+
+func main() {
+	// Parse flags.
+	flag.Usage = usage
+	flag.Parse()
+
+	// Parse and validate arguments (none).
+	args := flag.Args()
+	if len(args) != 0 {
+		usage()
+	}
+
+	// Register handlers.
+	// All requests not otherwise mapped with go to greet.
+	// /version is mapped specifically to version.
+	http.HandleFunc("/", greet)
+	http.HandleFunc("/version", version)
+
+	log.Printf("serving http://%s\n", *addr)
+	log.Fatal(http.ListenAndServe(*addr, nil))
+}
+
+func version(w http.ResponseWriter, r *http.Request) {
+	info, ok := debug.ReadBuildInfo()
+	if !ok {
+		http.Error(w, "no build information available", 500)
+		return
+	}
+
+	fmt.Fprintf(w, "<!DOCTYPE html>\n<pre>\n")
+	fmt.Fprintf(w, "%s\n", html.EscapeString(info.String()))
+}
+
+func greet(w http.ResponseWriter, r *http.Request) {
+	name := strings.Trim(r.URL.Path, "/")
+	if name == "" {
+		name = "Gopher"
+	}
+
+	fmt.Fprintf(w, "<!DOCTYPE html>\n")
+	fmt.Fprintf(w, "Hello, %s!\n", html.EscapeString(name))
+}