build: fix race in doc/articles/wiki test

The original test would open a local port and then immediately close it
and use the port number in subsequent tests. Between the port being closed
and reused by the later process, it could be opened by some other program
on the machine.

Changed the test to run the server process directly and have it save the
assigned port to a text file to be used by client processes.

Fixes #5564.

LGTM=adg
R=golang-codereviews, gobot, adg
CC=golang-codereviews
https://golang.org/cl/72290043

doc/articles/wiki/Makefile

@@ -4,7 +4,7 @@
 
 all: index.html
 
-CLEANFILES=get.bin final-test.bin a.out
+CLEANFILES=get.bin final.bin a.out
 
 clean:
 	rm -f $(CLEANFILES)

doc/articles/wiki/final.go

@@ -5,12 +5,19 @@
 package main
 
 import (
+	"flag"
 	"html/template"
 	"io/ioutil"
+	"log"
+	"net"
 	"net/http"
 	"regexp"
 )
 
+var (
+	addr = flag.Bool("addr", false, "find open address and print to final-port.txt")
+)
+
 type Page struct {
 	Title string
 	Body  []byte
@@ -81,8 +88,24 @@ func makeHandler(fn func(http.ResponseWriter, *http.Request, string)) http.Handl
 }
 
 func main() {
+	flag.Parse()
 	http.HandleFunc("/view/", makeHandler(viewHandler))
 	http.HandleFunc("/edit/", makeHandler(editHandler))
 	http.HandleFunc("/save/", makeHandler(saveHandler))
+
+	if *addr {
+		l, err := net.Listen("tcp", "127.0.0.1:0")
+		if err != nil {
+			log.Fatal(err)
+		}
+		err = ioutil.WriteFile("final-port.txt", []byte(l.Addr().String()), 0644)
+		if err != nil {
+			log.Fatal(err)
+		}
+		s := &http.Server{}
+		s.Serve(l)
+		return
+	}
+
 	http.ListenAndServe(":8080", nil)
 }

doc/articles/wiki/test.bash

@@ -7,7 +7,7 @@ set -e
 wiki_pid=
 cleanup() {
 	kill $wiki_pid
-	rm -f test_*.out Test.txt final-test.bin final-test.go a.out get.bin
+	rm -f test_*.out Test.txt final.bin final-port.txt a.out get.bin
 }
 trap cleanup 0 INT
 
@@ -19,13 +19,25 @@ if [ "$1" == "-all" ]; then
 fi
 
 go build -o get.bin get.go
-addr=$(./get.bin -addr)
-sed s/:8080/$addr/ < final.go > final-test.go
-go build -o final-test.bin final-test.go
-(./final-test.bin) &
+go build -o final.bin final.go
+(./final.bin --addr) &
 wiki_pid=$!
 
-./get.bin --wait_for_port=5s http://$addr/edit/Test > test_edit.out
+l=0
+while [ ! -f ./final-port.txt ]
+do
+	l=$(($l+1))
+	if [ "$l" -gt 5 ]
+	then
+		echo "port not available within 5 seconds"
+		exit 1
+		break
+	fi
+	sleep 1
+done
+
+addr=$(cat final-port.txt)
+./get.bin http://$addr/edit/Test > test_edit.out
 diff -u test_edit.out test_edit.good
 ./get.bin -post=body=some%20content http://$addr/save/Test > test_save.out
 diff -u test_save.out test_view.good # should be the same as viewing