how do i redirect an HTTP request?

my code is for a watering system and executes its primary function just fine. i can surf to the URL, click on a relay and select it to add water.

my only issue is accounting for user error. if user does an accidental refresh, a second unwanted watering event could occur, which is bad.

The issue is that following selection, the user’s URL get’s updated to the relay call

    http://192.168.1.12/SWITCH=2

a simple redirect following the call would fix the issue, landing it on

    http://192.168.1.12

instead. then an accidental refresh would do no harm.

I tried

    client.println("Location: /");

in many places in my code but no redirect ever happened. I could have been doing it wrong.

example code:

    if (request.indexOf("/SWITCH=0") != -1){
        digitalWrite(switchPin0, LOW);
        digitalWrite(statusLed, LOW);   // blink led
        delay(1);
        digitalWrite(statusLed, HIGH);
        //set water pump time here
        delay(8000);
        digitalWrite(switchPin0, HIGH);
        value = HIGH;
        ++switch0;
        client.println("Location: /"); //where i think it should go, but fails
      } else if (request.indexOf("/SWITCH=1") != -1){
        digitalWrite(switchPin1, LOW);
        digitalWrite(statusLed, LOW);   // blink led
        delay(1);
        digitalWrite(statusLed, HIGH);
        //set water pump time here
        delay(8000);
        digitalWrite(switchPin1, HIGH);
        value = HIGH;
        ++switch1;
        client.println("Location: /");
        
    }

actual code:

    //note, when you write to low, you turn the switchport on. It's backwards for some reason
    #include <ESP8266WiFi.h>
    #define statusLed 2   // built-in led for the ESP8266-12
    
    const char* ssid = "myssid";
    const char* password = "mypass";
     
    int switchPin0 = 16;
    int switchPin1 = 5;
    int switch0;
    int switch1;
    
    WiFiServer server(80);
     
    void setup() {
      Serial.begin(115200);
      delay(10);
     
      pinMode(statusLed, OUTPUT);
      pinMode(switchPin0, OUTPUT);
      pinMode(switchPin1, OUTPUT);
     
      digitalWrite(switchPin0, HIGH);
      digitalWrite(switchPin1, HIGH);
    
      // Connect to WiFi network
      Serial.println();
      Serial.println();
      Serial.print("Connecting to ");
      Serial.println(ssid);
     
      WiFi.begin(ssid, password);
     
      while (WiFi.status() != WL_CONNECTED) {
        delay(500);
        Serial.print(".");
      }
      digitalWrite(statusLed, HIGH);
      Serial.println("");
      Serial.println("WiFi connected");
     
      // Start the server
      server.begin();
      Serial.println("Server started");
     
      // Print the IP address
      Serial.print("Use this URL : ");
      Serial.print("http://");
      Serial.print(WiFi.localIP());
      Serial.println("/");
     
    }
     
    void loop() {
      // Check if a client has connected
      WiFiClient client = server.available();
      if (!client) {
        return;
      }
     
      // Wait until the client sends some data
      Serial.println("new client");
      while(!client.available()){
        delay(1);
      }
     
      // Read the first line of the request
      String request = client.readStringUntil('\r');
      Serial.println(request);
    
      client.flush();
    
      // Match the request
     
      int value = HIGH;
     if (request.indexOf("/SWITCH=0") != -1){
        digitalWrite(switchPin0, LOW);
        digitalWrite(statusLed, LOW);   // blink led
        delay(1);
        digitalWrite(statusLed, HIGH);
        //set water pump time here
        delay(8000);
        digitalWrite(switchPin0, HIGH);
        value = HIGH;
        ++switch0;
      } else if (request.indexOf("/SWITCH=1") != -1){
        digitalWrite(switchPin1, LOW);
        digitalWrite(statusLed, LOW);   // blink led
        delay(1);
        digitalWrite(statusLed, HIGH);
        //set water pump time here
        delay(8000);
        digitalWrite(switchPin1, HIGH);
        value = HIGH;
        ++switch1;
      } else {
        //reserved
      }
     
      // Return the response
      client.println("HTTP/1.1 200 OK");
      client.println("Content-Type: text/html");
      client.println(""); //  do not forget this one
      client.println("<!DOCTYPE HTML>");
      client.println("<html>");
     
      client.print("Switch pin is now: ");
     
      client.println("

");
      client.println("Switch 0");
      client.println("Click <a href=\"/SWITCH=0\">here</a>  to send a measured amount
");
      client.println("Number of times plant 0 has been fed is ");
      client.println(switch0);
      client.println("

");
      client.println("Switch 1");
      client.println("Click <a href=\"/SWITCH=1\">here</a>  to send a measured amount
");
      client.println("Number of times plant 1 has been fed is ");
      client.println(switch1);
      client.println("

");
      client.println("
");
      client.println("</html>");
     
      delay(1);
      Serial.println("Client disconnected");
      Serial.println("");
      digitalWrite(statusLed, LOW);   // blink led
      delay(1);
      digitalWrite(statusLed, HIGH);
     
    }

How do i redirect my landing page post selection? or a better solution?

List of things that do not work:

writing location after the content does not work

    client.println("Content-Type: text/html");
    client.println("Location: /");

Throwing the RFC at me, does not work.

thank you for your reply. unfortunately it does not clarify much for me.

i have never attempted POST on an arduino. i was pretty sure I was doing GET but i am not familiar with it outside of php that does everything for you, making situations like this more difficult. this is why i was going with Location:, it was a hypothetical cheat to work with GET.

POST would actually help me because my next task is to add a second parameter. my next issue.

I only work with the ESP8266Webserver.h and with that it is fairly straightforward.

I just found that and playing with it now.

Disregard this post. Any question I have from here will be completely different.

Thank you