user54204: I'm trying to use ESP32 + Arduino IDE to control a relay. 
I've started by using the  library and the code below.
The problem I'm having:
after clicking on the button and activating the pin, if the browser is left like this, and then the page gets refreshed by mistake, the action will be repeated.
What I thought might help, is if for any click on the button, the pin activates, and then I get a redirect back to the root of the page. so refreshing will not pose any issue.
I've searched allover the internet and could not find anything conclusive, except for this piece of code, which doesnt seem to make any difference nomatter where I place it in the main code
client.println("HTTP/1.1 307 Temporary Redirect");
client.println("Location: /");
client.println("Connection: Close");
client.println();
client.stop();

and this is the main code:
// Load Wi-Fi library
#include <WiFi.h>

// Replace with your network credentials
const char* ssid     = "WalrusnTiny";
const char* password = "994483329I";

// Set web server port number to 80
WiFiServer server(80);

// Variable to store the HTTP request
String header;

// Auxiliar variables to store the current output state
String output26State = "off";
String output27State = "off";

// Assign output variables to GPIO pins
const int output26 = 26;
const int output27 = 27;

void setup() {

  Serial.begin(115200);
  // Initialize the output variables as outputs
  pinMode(output26, OUTPUT);
  pinMode(output27, OUTPUT);
  // Set outputs to LOW
  digitalWrite(output26, LOW);
  digitalWrite(output27, LOW);

  // Connect to Wi-Fi network with SSID and password
  Serial.print("Connecting to ");
  Serial.println(ssid);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  // Print local IP address and start web server
  Serial.println("");
  Serial.println("WiFi connected.");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
  server.begin();
}




void loop(){
  WiFiClient client = server.available();   // Listen for incoming clients

  if (client) {                             // If a new client connects,
    Serial.println("New Client.");          // print a message out in the serial port
    String currentLine = "";                // make a String to hold incoming data from the client
    while (client.connected()) {            // loop while the client's connected
      if (client.available()) {             // if there's bytes to read from the client,
        char c = client.read();             // read a byte, then
        Serial.write(c);                    // print it out the serial monitor
        header += c;
        if (c == '\n') {                    // if the byte is a newline character
          // if the current line is blank, you got two newline characters in a row.
          // that's the end of the client HTTP request, so send a response:
          if (currentLine.length() == 0) {
            // HTTP headers always start with a response code (e.g. HTTP/1.1 200 OK)
            // and a content-type so the client knows what's coming, then a blank line:
            client.println("HTTP/1.1 200 OK");
            client.println("Content-type:text/html");
            client.println("Connection: close");
            client.println();

            // turns the GPIOs on and off
            if (header.indexOf("GET /26/on") >= 0) {             
              client.println();
              output26State = "on";
              digitalWrite(output26, HIGH);


            } else if (header.indexOf("GET /26/off") >= 0) {
              Serial.println("GPIO 26 off");
              output26State = "off";
              digitalWrite(output26, LOW);


            } else if (header.indexOf("GET /27/on") >= 0) {
              Serial.println("GPIO 27 on");
              output27State = "on";
              digitalWrite(output27, HIGH);


            } else if (header.indexOf("GET /27/off") >= 0) {
              Serial.println("GPIO 27 off");
              output27State = "off";
              digitalWrite(output27, LOW);
            }

            // Display the HTML web page
            client.println("<!DOCTYPE html><html>");
            client.println("<head><meta name=\"viewport\" content=\"width=device-width, initial-scale=1\">");
            client.println("<link rel=\"icon\" href=\"data:,\">");
            // CSS to style the on/off buttons 
            // Feel free to change the background-color and font-size attributes to fit your preferences
            client.println("<style>html { font-family: Helvetica; display: inline-block; margin: 0px auto; text-align: center;}");
            client.println(".button { background-color: #4CAF50; border: none; color: white; padding: 16px 40px;");
            client.println("text-decoration: none; font-size: 30px; margin: 2px; cursor: pointer;}");
            client.println(".button2 {background-color: #555555;}</style></head>");

            // Web Page Heading
            client.println("<body><h1>ESP32 Web Server</h1>");
            // Display current state, and ON/OFF buttons for GPIO 26  
            client.println("<p>GPIO 26 - State " + output26State + "</p>");
            // If the output26State is off, it displays the ON button       
            if (output26State=="off") {
              client.println("<p><a href=\"/26/on\"><button class=\"button\">ON</button></a></p>");
            } else {
              client.println("<p><a href=\"/26/off\"><button class=\"button button2\">OFF</button></a></p>");
            } 

            // Display current state, and ON/OFF buttons for GPIO 27  
            client.println("<p>GPIO 27 - State " + output27State + "</p>");
            // If the output27State is off, it displays the ON button       
            if (output27State=="off") {
              client.println("<p><a href=\"/27/on\"><button class=\"button\">ON</button></a></p>");
            } else {
              client.println("<p><a href=\"/27/off\"><button class=\"button button2\">OFF</button></a></p>");
            }
            client.println("</body></html>");

            // The HTTP response ends with another blank line
            client.println();
            // Break out of the while loop
            break;
          } else { // if you got a newline, then clear currentLine
            currentLine = "";
          }
        } else if (c != '\r') {  // if you got anything else but a carriage return character,
          currentLine += c;      // add it to the end of the currentLine
        }
      }
    }
    // Clear the header variable

    header = "";
    // Close the connection



    Serial.println("Client disconnected.");
    Serial.println("");
  }
}

Any help would be greatly appreciated.
Thank you in advance.

user54204: Solved:
Just needed to add this code to every button press,
 client.print("<HEAD>");
 client.print("<meta http-equiv=\"refresh\" content=\"0;url=/\">");
 client.print("</head>");


54204: <p>I'm trying to use ESP32 + Arduino IDE to control a relay. </p>

<p>I've started by using the  library and the code below.</p>

<p>The problem I'm having:</p>

<p>after clicking on the button and activating the pin, if the browser is left like this, and then the page gets refreshed by mistake, the action will be repeated.</p>

<p>What I thought might help, is if for any click on the button, the pin activates, and then I get a redirect back to the root of the page. so refreshing will not pose any issue.</p>

<p>I've searched allover the internet and could not find anything conclusive, except for this piece of code, which doesnt seem to make any difference nomatter where I place it in the main code</p>

<pre><code>client.println("HTTP/1.1 307 Temporary Redirect");
client.println("Location: /");
client.println("Connection: Close");
client.println();
client.stop();
</code></pre>

<p>and this is the main code:</p>

<pre><code>// Load Wi-Fi library
#include &lt;WiFi.h&gt;

// Replace with your network credentials
const char* ssid     = "WalrusnTiny";
const char* password = "994483329I";

// Set web server port number to 80
WiFiServer server(80);

// Variable to store the HTTP request
String header;

// Auxiliar variables to store the current output state
String output26State = "off";
String output27State = "off";

// Assign output variables to GPIO pins
const int output26 = 26;
const int output27 = 27;

void setup() {

  Serial.begin(115200);
  // Initialize the output variables as outputs
  pinMode(output26, OUTPUT);
  pinMode(output27, OUTPUT);
  // Set outputs to LOW
  digitalWrite(output26, LOW);
  digitalWrite(output27, LOW);

  // Connect to Wi-Fi network with SSID and password
  Serial.print("Connecting to ");
  Serial.println(ssid);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  // Print local IP address and start web server
  Serial.println("");
  Serial.println("WiFi connected.");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
  server.begin();
}




void loop(){
  WiFiClient client = server.available();   // Listen for incoming clients

  if (client) {                             // If a new client connects,
    Serial.println("New Client.");          // print a message out in the serial port
    String currentLine = "";                // make a String to hold incoming data from the client
    while (client.connected()) {            // loop while the client's connected
      if (client.available()) {             // if there's bytes to read from the client,
        char c = client.read();             // read a byte, then
        Serial.write(c);                    // print it out the serial monitor
        header += c;
        if (c == '\n') {                    // if the byte is a newline character
          // if the current line is blank, you got two newline characters in a row.
          // that's the end of the client HTTP request, so send a response:
          if (currentLine.length() == 0) {
            // HTTP headers always start with a response code (e.g. HTTP/1.1 200 OK)
            // and a content-type so the client knows what's coming, then a blank line:
            client.println("HTTP/1.1 200 OK");
            client.println("Content-type:text/html");
            client.println("Connection: close");
            client.println();

            // turns the GPIOs on and off
            if (header.indexOf("GET /26/on") &gt;= 0) {             
              client.println();
              output26State = "on";
              digitalWrite(output26, HIGH);


            } else if (header.indexOf("GET /26/off") &gt;= 0) {
              Serial.println("GPIO 26 off");
              output26State = "off";
              digitalWrite(output26, LOW);


            } else if (header.indexOf("GET /27/on") &gt;= 0) {
              Serial.println("GPIO 27 on");
              output27State = "on";
              digitalWrite(output27, HIGH);


            } else if (header.indexOf("GET /27/off") &gt;= 0) {
              Serial.println("GPIO 27 off");
              output27State = "off";
              digitalWrite(output27, LOW);
            }

            // Display the HTML web page
            client.println("&lt;!DOCTYPE html&gt;&lt;html&gt;");
            client.println("&lt;head&gt;&lt;meta name=\"viewport\" content=\"width=device-width, initial-scale=1\"&gt;");
            client.println("&lt;link rel=\"icon\" href=\"data:,\"&gt;");
            // CSS to style the on/off buttons 
            // Feel free to change the background-color and font-size attributes to fit your preferences
            client.println("&lt;style&gt;html { font-family: Helvetica; display: inline-block; margin: 0px auto; text-align: center;}");
            client.println(".button { background-color: #4CAF50; border: none; color: white; padding: 16px 40px;");
            client.println("text-decoration: none; font-size: 30px; margin: 2px; cursor: pointer;}");
            client.println(".button2 {background-color: #555555;}&lt;/style&gt;&lt;/head&gt;");

            // Web Page Heading
            client.println("&lt;body&gt;&lt;h1&gt;ESP32 Web Server&lt;/h1&gt;");
            // Display current state, and ON/OFF buttons for GPIO 26  
            client.println("&lt;p&gt;GPIO 26 - State " + output26State + "&lt;/p&gt;");
            // If the output26State is off, it displays the ON button       
            if (output26State=="off") {
              client.println("&lt;p&gt;&lt;a href=\"/26/on\"&gt;&lt;button class=\"button\"&gt;ON&lt;/button&gt;&lt;/a&gt;&lt;/p&gt;");
            } else {
              client.println("&lt;p&gt;&lt;a href=\"/26/off\"&gt;&lt;button class=\"button button2\"&gt;OFF&lt;/button&gt;&lt;/a&gt;&lt;/p&gt;");
            } 

            // Display current state, and ON/OFF buttons for GPIO 27  
            client.println("&lt;p&gt;GPIO 27 - State " + output27State + "&lt;/p&gt;");
            // If the output27State is off, it displays the ON button       
            if (output27State=="off") {
              client.println("&lt;p&gt;&lt;a href=\"/27/on\"&gt;&lt;button class=\"button\"&gt;ON&lt;/button&gt;&lt;/a&gt;&lt;/p&gt;");
            } else {
              client.println("&lt;p&gt;&lt;a href=\"/27/off\"&gt;&lt;button class=\"button button2\"&gt;OFF&lt;/button&gt;&lt;/a&gt;&lt;/p&gt;");
            }
            client.println("&lt;/body&gt;&lt;/html&gt;");

            // The HTTP response ends with another blank line
            client.println();
            // Break out of the while loop
            break;
          } else { // if you got a newline, then clear currentLine
            currentLine = "";
          }
        } else if (c != '\r') {  // if you got anything else but a carriage return character,
          currentLine += c;      // add it to the end of the currentLine
        }
      }
    }
    // Clear the header variable

    header = "";
    // Close the connection



    Serial.println("Client disconnected.");
    Serial.println("");
  }
}
</code></pre>

<p>Any help would be greatly appreciated.
Thank you in advance.</p>
 54204: <p>Solved:</p>

<p>Just needed to add this code to every button press,</p>

<pre><code> client.print("&lt;HEAD&gt;");
 client.print("&lt;meta http-equiv=\"refresh\" content=\"0;url=/\"&gt;");
 client.print("&lt;/head&gt;");
</code></pre>
