tests/serve/serve.go: use a kernel-assigned port

When firing up a minimal server to serve up content so that we can
retrieve it using HTTP, make it possible to let the kernel assign us
which port to use, so that the script that's calling us doesn't have to
make a(n occasionally bad) guess.

Signed-off-by: Nalin Dahyabhai <[email protected]>

Author: nalind

tests/helpers.bash

@@ -40,9 +40,23 @@ function setup() {
 function starthttpd() {
     pushd ${2:-${TESTDIR}} > /dev/null
     go build -o serve ${TESTSDIR}/serve/serve.go
-    HTTP_SERVER_PORT=$((RANDOM+32768))
-    ./serve ${HTTP_SERVER_PORT} ${1:-${BATS_TMPDIR}} &
+    portfile=$(mktemp)
+    if test -z "${portfile}"; then
+        echo error creating temporaty file
+        exit 1
+    fi
+    ./serve ${1:-${BATS_TMPDIR}} 0 ${portfile} &
     HTTP_SERVER_PID=$!
+    waited=0
+    while ! test -s ${portfile} ; do
+        sleep 0.1
+        if test $((++waited)) -ge 300 ; then
+            echo test http server did not start within timeout
+            exit 1
+        fi
+    done
+    HTTP_SERVER_PORT=$(cat ${portfile})
+    rm -f ${portfile}
     popd > /dev/null
 }
 

tests/serve/serve.go

@@ -1,10 +1,14 @@
 package main
 
 import (
+	"context"
+	"io/ioutil"
 	"log"
+	"net"
 	"net/http"
 	"os"
 	"path/filepath"
+	"strconv"
 )
 
 func sendThatFile(basepath string) func(w http.ResponseWriter, r *http.Request) {
@@ -30,11 +34,40 @@ func sendThatFile(basepath string) func(w http.ResponseWriter, r *http.Request)
 
 func main() {
 	args := os.Args
-	if len(args) < 3 {
-		log.Fatal("requires listening port and subdirectory path")
+	if len(args) < 2 {
+		log.Fatal("requires subdirectory path [and optional port [and optional port file name]]")
+	}
+	basedir := args[1]
+	port := "0"
+	if len(args) > 2 {
+		port = args[2]
 	}
-	port := args[1]
-	basedir := args[2]
 	http.HandleFunc("/", sendThatFile(basedir))
-	log.Fatal(http.ListenAndServe(":"+port, nil))
+	server := http.Server{
+		Addr: ":" + port,
+		BaseContext: func(l net.Listener) context.Context {
+			if tcp, ok := l.Addr().(*net.TCPAddr); ok {
+				if len(args) > 3 {
+					f, err := ioutil.TempFile(filepath.Dir(args[3]), filepath.Base(args[3]))
+					if err != nil {
+						log.Fatalf("%v", err)
+					}
+					tempName := f.Name()
+					bytes := []byte(strconv.Itoa(tcp.Port))
+					if n, err := f.Write(bytes); err != nil || n != len(bytes) {
+						if err != nil {
+							log.Fatalf("%v", err)
+						}
+						log.Fatalf("short write: %d != %d", n, len(bytes))
+					}
+					f.Close()
+					if err := os.Rename(tempName, args[3]); err != nil {
+						log.Fatalf("rename: %v", err)
+					}
+				}
+			}
+			return context.Background()
+		},
+	}
+	log.Fatal(server.ListenAndServe())
 }