Init: handle multiple httpd.listenUrl entries

Before this change:
- httpd.get() would read the last entry.
- httpd.set() would set the first entry, effectively removing one entry
  but also breaking the confiugration, as Gerrit cannot listen on two
  ports at the same time.

Now, if there are multiple httpd.listenUrl entries, init will:
- validate all the entries' syntax to be parsed as URLs (not just the
  last one), and
- print a warning that interactive mode is not supported in this case
  (when invoked without --batch), and
- most importantly, leave the entries as-is allowing Gerrit to start
  with a valid configuration.

Bug: Issue 4824
Change-Id: I57fe9fe29a0fd3399024e5c196cc889650dc6892

java/com/google/gerrit/pgm/init/InitHttpd.java

@@ -60,22 +60,67 @@ class InitHttpd implements InitStep {
   public void run() throws IOException, InterruptedException {
     ui.header("HTTP Daemon");
 
+    boolean anySsl = false;
+    // If any listenUrls are present, validate whether it can be parsed as URL.
+    String[] listenUrls = httpd.getList("listenUrl");
+    for (String listenUrl : listenUrls) {
+      if (listenUrl != null && !listenUrl.isEmpty()) {
+        try {
+          final URI u = toURI(listenUrl);
+          if (u.getScheme().startsWith("https")) {
+            anySsl = true;
+          }
+        } catch (URISyntaxException e) {
+          System.err.println(
+              String.format(
+                  "warning: invalid httpd.listenUrl entry: '%s'. Gerrit may not be able to start.",
+                  listenUrl));
+        }
+      }
+    }
+
+    if (listenUrls.length > 1) {
+      // Because we will return early here, we will warn about steps otherwise being covered.
+      if (!ui.isBatch()) {
+        System.err.println(
+            "Interactive configuration is not supported with multiple entries of "
+                + "httpd.listenUrl.");
+      }
+      if (anySsl) {
+        System.err.println(
+            "Generating self-signed SSL certificates is not supported with multiple "
+                + "entries of httpd.listenUrl.");
+      }
+      String canonicalWebUrlDefaultString = "";
+      if (listenUrls[0] != null && !listenUrls[0].isEmpty()) {
+        try {
+          canonicalWebUrlDefaultString = new URI(listenUrls[0]).toString();
+        } catch (URISyntaxException e) {
+          // Should not happen, but log it anyway
+          System.err.println(
+              String.format("warning: invalid httpd.listenUrl entry: '%s'", listenUrls[0]));
+        }
+      }
+      gerrit.string("Canonical URL", "canonicalWebUrl", canonicalWebUrlDefaultString);
+      return;
+    }
+
     boolean proxy = false;
     boolean ssl = false;
     String address = "*";
     int port = -1;
     String context = "/";
-    String listenUrl = httpd.get("listenUrl");
-    if (listenUrl != null && !listenUrl.isEmpty()) {
+
+    if (listenUrls.length > 0 && listenUrls[0] != null && !listenUrls[0].isEmpty()) {
       try {
-        final URI uri = toURI(listenUrl);
+        final URI uri = toURI(listenUrls[0]);
         proxy = uri.getScheme().startsWith("proxy-");
         ssl = uri.getScheme().endsWith("https");
-        address = isAnyAddress(new URI(listenUrl)) ? "*" : uri.getHost();
+        address = isAnyAddress(new URI(listenUrls[0])) ? "*" : uri.getHost();
         port = uri.getPort();
         context = uri.getPath();
       } catch (URISyntaxException e) {
-        System.err.println("warning: invalid httpd.listenUrl " + listenUrl);
+        System.err.println("warning: invalid httpd.listenUrl " + listenUrls[0]);
       }
     }