Add url redirect (#8970)

* added getAvailableVersion(), moved _httpClientTimeout and _followRedirects to protected, added enum HTTPUpdateError

* auto numbering of HTTPUpdateError enum

* added getAvailableVersion(), debug output current current Sketch MD5

* Revert "added getAvailableVersion(), debug output current current Sketch MD5"

This reverts commit 60d2c77.

* Revert "auto numbering of HTTPUpdateError enum"

This reverts commit 61785b2.

* Revert "added getAvailableVersion(), moved _httpClientTimeout and _followRedirects to protected, added enum HTTPUpdateError"

This reverts commit cec84ed.

* add redirect function

* enhanced redirect() by cache control and client stop

* updated redirect() comment

* replaced redirect() API calls in examples

* server.client().stop() not needed, redirect() does this

libraries/DNSServer/examples/CaptivePortalAdvanced/handleHttp.ino

@@ -27,9 +27,7 @@ void handleRoot() {
 boolean captivePortal() {
   if (!isIp(server.hostHeader()) && server.hostHeader() != (String(myHostname) + ".local")) {
     Serial.println("Request redirected to captive portal");
-    server.sendHeader("Location", String("http://") + toStringIp(server.client().localIP()), true);
-    server.send(302, "text/plain", "");  // Empty content inhibits Content-length header so we have to close the socket ourselves.
-    server.client().stop();              // Stop is needed because we sent no content length
+    server.redirect(String("http://") + toStringIp(server.client().localIP()));
     return true;
   }
   return false;
@@ -91,12 +89,7 @@ void handleWifiSave() {
   Serial.println("wifi save");
   server.arg("n").toCharArray(ssid, sizeof(ssid) - 1);
   server.arg("p").toCharArray(password, sizeof(password) - 1);
-  server.sendHeader("Location", "wifi", true);
-  server.sendHeader("Cache-Control", "no-cache, no-store, must-revalidate");
-  server.sendHeader("Pragma", "no-cache");
-  server.sendHeader("Expires", "-1");
-  server.send(302, "text/plain", "");  // Empty content inhibits Content-length header so we have to close the socket ourselves.
-  server.client().stop();              // Stop is needed because we sent no content length
+  server.redirect("wifi");
   saveCredentials();
   connect = strlen(ssid) > 0;  // Request WLAN connect with new credentials if there is a SSID
 }

libraries/DNSServer/examples/NAPTCaptivePortal/PortalRedirectHttp.ino

@@ -36,13 +36,11 @@ void sendPortalRedirect(String path, String targetName) {
     If the "Location" header element works the HTML stuff is never seen.
   */
   // https://tools.ietf.org/html/rfc7231#section-6.4.3
-  server.sendHeader("Location", path, true);
-  addNoCacheHeader();
   String reply = FPSTR(portalRedirectHTML);
   reply.reserve(reply.length() + 2 * path.length() + 80);
   reply.replace("{t}", targetName);
   reply.replace("{1}", path);
-  server.send(302, "text/html", reply);
+  server.redirect(path, reply);
 }
 
 #endif  // LWIP_FEATURES && !LWIP_IPV6

libraries/ESP8266WebServer/examples/WebServer/WebServer.ino

@@ -43,8 +43,7 @@ void handleRedirect() {
 
   if (!LittleFS.exists(url)) { url = "/$update.htm"; }
 
-  server.sendHeader("Location", url, true);
-  server.send(302);
+  server.redirect(url);
 }  // handleRedirect()
 
 

libraries/ESP8266WebServer/src/ESP8266WebServer.h

@@ -207,6 +207,30 @@ class ESP8266WebServerTemplate
     sendContent(emptyString);
   }
 
+  /**
+   * @brief  Redirect to another URL, e.g.
+   *   webserver.on("/index.html", HTTP_GET, []() { webserver.redirect("/"); });
+   * There are 3 points of redirection here:
+   *   1) "Location" element in the header
+   *   2) Disable client caching
+   *   3) HTML "content" element to redirect
+   * If the "Location" header element works the HTML content is never seen.
+   * https://tools.ietf.org/html/rfc7231#section-6.4.3
+   * @param  url URL to redirect to
+   * @param  content Optional redirect content
+   */
+  void redirect(const String& url, const String& content = emptyString) {
+    sendHeader(F("Location"), url, true);
+    sendHeader(F("Cache-Control"), F("no-cache, no-store, must-revalidate"));
+    sendHeader(F("Pragma"), F("no-cache"));
+    sendHeader(F("Expires"), F("-1"));
+    send(302, F("text/html"), content);  // send 302: "Found"
+    if (content.isEmpty()) {
+      // Empty content inhibits Content-length header so we have to close the socket ourselves.
+      client().stop();  // Stop is needed because we sent no content length
+    }
+  }
+
   // Whether other requests should be accepted from the client on the
   // same socket after a response is sent.
   // This will automatically configure the "Connection" header of the response.