external html path configuration for interstitial (#716)

endpoints/publicProxy/config.go

@@ -23,6 +23,7 @@ type Config struct {
 
 type InterstitialConfig struct {
 	Enabled           bool
+	HtmlPath          string
 	UserAgentPrefixes []string
 }
 

endpoints/publicProxy/http.go

@@ -180,7 +180,7 @@ func shareHandler(handler http.Handler, pcfg *Config, key []byte, ctx ziti.Conte
 									_, zrokOkErr := r.Cookie("zrok_interstitial")
 									if skip == "" && zrokOkErr != nil {
 										logrus.Debugf("forcing interstitial for '%v'", r.URL)
-										interstitialUi.WriteInterstitialAnnounce(w)
+										interstitialUi.WriteInterstitialAnnounce(w, pcfg.Interstitial.HtmlPath)
 										return
 									}
 								}

endpoints/publicProxy/interstitialUi/handler.go

@@ -3,19 +3,35 @@ package interstitialUi
 import (
 	"github.com/sirupsen/logrus"
 	"net/http"
+	"os"
 )
 
-func WriteInterstitialAnnounce(w http.ResponseWriter) {
-	if data, err := FS.ReadFile("index.html"); err == nil {
-		w.WriteHeader(http.StatusOK)
-		n, err := w.Write(data)
-		if n != len(data) {
-			logrus.Errorf("short write")
-			return
+var externalFile []byte
+
+func WriteInterstitialAnnounce(w http.ResponseWriter, htmlPath string) {
+	if htmlPath != "" && externalFile == nil {
+		if data, err := os.ReadFile(htmlPath); err == nil {
+			externalFile = data
+		} else {
+			logrus.Errorf("error reading external interstitial file '%v': %v", htmlPath, err)
 		}
-		if err != nil {
-			logrus.Error(err)
-			return
+	}
+	var htmlData = externalFile
+	if htmlData == nil {
+		if data, err := FS.ReadFile("index.html"); err == nil {
+			htmlData = data
+		} else {
+			logrus.Errorf("error reading embedded interstitial html 'index.html': %v", err)
 		}
 	}
+	w.WriteHeader(http.StatusOK)
+	n, err := w.Write(htmlData)
+	if n != len(htmlData) {
+		logrus.Errorf("short write")
+		return
+	}
+	if err != nil {
+		logrus.Error(err)
+		return
+	}
 }