issues/20 If dev Live Reload port is already in use, fallback on an a…

…lternative port.

files/watch.go

@@ -19,15 +19,17 @@ package files
 import (
 	"fmt"
 	"log"
+	"net"
 	"path/filepath"
+	"strconv"
 	"time"
 
 	"github.com/jaschaephraim/lrserver"
 	"github.com/radovskyb/watcher"
 )
 
-func Watch(root string) error {
-	lr := lrserver.New(lrserver.DefaultName, lrserver.DefaultPort)
+func Watch(root string, port uint16) error {
+	lr := lrserver.New(lrserver.DefaultName, port)
 	go func() {
 		log.Fatal(lr.ListenAndServe())
 	}()
@@ -61,3 +63,32 @@ func Watch(root string) error {
 
 	return nil
 }
+
+func LiveReloadPort() uint16 {
+	port := lrserver.DefaultPort
+	for {
+		if isPortAvailable(port) {
+			break
+		}
+		// If port is already in use (e.g. another Demoit instance), then
+		// choose an alternative port
+		log.Println("\tCan't use live reload port", port, "(already in use)")
+		port++
+		if port == lrserver.DefaultPort+10 {
+			log.Fatalln("Couldn't find a live reload port after 10 attempts")
+		}
+	}
+	return port
+}
+
+func isPortAvailable(port uint16) bool {
+	portstr := strconv.Itoa(int(port))
+	conn, err := net.DialTimeout("tcp", net.JoinHostPort("", portstr), time.Second)
+	_ = err
+	if conn != nil {
+		// Connection established means "Port was already in use!"
+		conn.Close()
+		return false
+	}
+	return true
+}

handlers/step.go

@@ -21,6 +21,7 @@ import (
 	"fmt"
 	"html/template"
 	"io/ioutil"
+	"log"
 	"net/http"
 	"path/filepath"
 	"strconv"
@@ -29,6 +30,7 @@ import (
 	"github.com/dgageot/demoit/flags"
 	"github.com/dgageot/demoit/templates"
 	"github.com/gorilla/mux"
+	"github.com/jaschaephraim/lrserver"
 )
 
 // Page describes a page of the demo.
@@ -43,6 +45,11 @@ type Page struct {
 	DevMode     bool
 }
 
+// LiveReloadPort is the port used for live-reload of page contents, on change.
+// Default is 35729.
+// Can be set to an alternative value, before rendering.
+var LiveReloadPort uint16 = lrserver.DefaultPort
+
 // Step renders a given page.
 func Step(w http.ResponseWriter, r *http.Request) {
 	vars := mux.Vars(r)
@@ -63,7 +70,9 @@ func Step(w http.ResponseWriter, r *http.Request) {
 	}
 
 	step := steps[id]
-	pageTemplate, err := template.New("page").Parse(templates.Index(step.HTML))
+	pageTemplate, err := template.New("page").
+		Funcs(template.FuncMap{"lrport": func() uint16 { return LiveReloadPort }}).
+		Parse(templates.Index(step.HTML))
 	if err != nil {
 		http.Error(w, "Unable to parse page", http.StatusInternalServerError)
 		return
@@ -72,6 +81,7 @@ func Step(w http.ResponseWriter, r *http.Request) {
 	var html bytes.Buffer
 	err = pageTemplate.Execute(&html, step)
 	if err != nil {
+		log.Println(err)
 		http.Error(w, "Unable to render page", http.StatusInternalServerError)
 		return
 	}

main.go

@@ -65,7 +65,9 @@ func main() {
 }
 
 func startFileWatch(root string) {
-	log.Fatal(files.Watch(root))
+	lrport := files.LiveReloadPort()
+	handlers.LiveReloadPort = lrport
+	log.Fatal(files.Watch(root, lrport))
 }
 
 func startWebServer(r http.Handler) {

templates/index.go

@@ -39,6 +39,6 @@ func Index(content []byte) string {
       <div id="progression" style="width: calc(100vw * {{ .CurrentStep }} / {{ .StepCount }})"></div>
       </body>
       <script src="/js/demoit.js"></script>
-      {{ if .DevMode }}<script src="http://localhost:35729/livereload.js"></script>{{ end }}
+      {{ if .DevMode }}<script src="http://localhost:{{ lrport }}/livereload.js"></script>{{ end }}
     </html>`
 }