Fix 404 error page

Author: budulinek

README.md

@@ -97,9 +97,10 @@ You can either:
 
 Connect your Arduino to ethernet and use your web browser to access the web interface on default IP:  http://192.168.1.254
 Enjoy :-)
+
 # Settings
-  - settings marked \* are only available if ENABLE_DHCP is defined in advanced_settings.h
-  - settings marked \*\* are only available if ENABLE_EXTENDED_WEBUI is defined in advanced_settings.h
+- settings marked \* are only available if ENABLE_DHCP is defined in advanced_settings.h
+- settings marked \*\* are only available if ENABLE_EXTENDED_WEBUI is defined in advanced_settings.h
 
 ## System Info
 <img src="pics/modbus1.png" alt="modbus1" style="zoom:100%;" />

arduino-modbus-rtu-tcp-gateway/04-webserver.ino

@@ -137,12 +137,12 @@ void recvWeb(EthernetClient &client) {
   // Get the requested page from URI
   byte reqPage = PAGE_ERROR;  // requested page, 404 error is a default
   if (uri[0] == '/') {
-    if (uri[1] == '\0')  // the homepage System Info
-      reqPage = PAGE_INFO;
-    else if (!strcmp(uri + 2, ".htm")) {
-      reqPage = byte(uri[1] - 48);  // Convert single ASCII char to byte
-      if (reqPage >= PAGE_WAIT) reqPage = PAGE_ERROR;
-    } else if (!strcmp(uri, "/d.json")) {
+    if (uri[1] == '\0') {
+      reqPage = PAGE_INFO;  // Homepage
+    } else if (uri[1] >= '0' && uri[1] <= '9' && strcmp(uri + 2, ".htm") == 0) {
+      reqPage = byte(uri[1] - '0');  // Convert ASCII digit to byte
+      if (reqPage > PAGE_WAIT) reqPage = PAGE_ERROR;
+    } else if (strcmp(uri, "/d.json") == 0) {
       reqPage = PAGE_DATA;
     }
   }

arduino-modbus-rtu-tcp-gateway/05-pages.ino

@@ -15,10 +15,12 @@ void sendPage(EthernetClient &client, byte reqPage) {
   char webOutBuffer[WEB_OUT_BUFFER_SIZE];
   ChunkedPrint chunked(client, webOutBuffer, sizeof(webOutBuffer));  // the StreamLib object to replace client print
   if (reqPage == PAGE_ERROR) {
-    chunked.print(F("HTTP/1.1 404 Not Found\r\n"
-                    "\r\n"
-                    "404 Not found"));
-    chunked.end();
+    chunked.print(F(
+      "HTTP/1.1 404 Not Found\r\n"
+      "Content-Type: text/plain\r\n"
+      "Content-Length: 13\r\n\r\n"
+      "404 Not Found"));
+    chunked.flush();
     return;
   } else if (reqPage == PAGE_DATA) {
     chunked.print(F("HTTP/1.1 200\r\n"  // An advantage of HTTP 1.1 is that you can keep the connection alive

arduino-modbus-rtu-tcp-gateway/arduino-modbus-rtu-tcp-gateway.ino

@@ -26,9 +26,10 @@
                   ENABLE_EXTENDED_WEBUI and ENABLE_DHCP is set by default for Mega
   v7.3 2024-01-16 Bugfix Modbus RTU Request form, code comments
   v7.4 2024-12-16 CSS improvement, code optimization, simplify DHCP renew, better README (solution to ethernet reset issue)
+  v7.5 2025-XX-XX Fix 404 error page
 */
 
-const byte VERSION[] = { 7, 4 };
+const byte VERSION[] = { 7, 5 };
 
 #include <SPI.h>
 #include <Ethernet.h>