So I'm Setting up webserver with esp-01f+arduino uno. I'm using WiFiEsp library. I want to toggle led on. Pin will be given in GET request by url. Example: host.com/?ledpin=9 How can I parse it, then get 9 number?


#include "WiFiEsp.h"

// Emulate Serial1 on pins 6/7 if not present
#include "SoftwareSerial.h"
SoftwareSerial Serial1(6, 7); // RX, TX

char ssid[] = "Twim";            // your network SSID (name)
char pass[] = "12345678";        // your network password
int status = WL_IDLE_STATUS;

int ledStatus = LOW;

WiFiEspServer server(80);

// use a ring buffer to increase speed and reduce memory allocation
RingBuffer buf(8);

void setup()
  pinMode(LED_BUILTIN, OUTPUT); // initialize digital pin LED_BUILTIN as an output.
  Serial.begin(115200);   // initialize serial for debugging
  Serial1.begin(9600);    // initialize serial for ESP module
  WiFi.init(&Serial1);    // initialize ESP module

  // check for the presence of the shield
  if (WiFi.status() == WL_NO_SHIELD) {
    Serial.println("WiFi shield not present");
    // don't continue
    while (true);

  // attempt to connect to WiFi network
  while (status != WL_CONNECTED) {
    Serial.print("Attempting to connect to WPA SSID: ");
    // Connect to WPA/WPA2 network
    status = WiFi.begin(ssid, pass);

  Serial.println("You're connected to the network");

  // start the web server on port 80

void loop()
  WiFiEspClient client = server.available();  // listen for incoming clients

  if (client) {                               // if you get a client,
    Serial.println("New client");             // print a message out the serial port
    buf.init();                               // initialize the circular buffer
    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
        buf.push(c);                          // push it to the ring buffer

        // printing the stream to the serial monitor will slow down
        // the receiving of data from the ESP filling the serial buffer

        // you got two newline characters in a row
        // that's the end of the HTTP request, so send a response
        if (buf.endsWith("\r\n\r\n")) {

        // Check to see if the client request was "GET /H" or "GET /L":
        if (buf.endsWith("GET /H")) {
          Serial.println("Turn led ON");
          ledStatus = HIGH;
          digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)
        else if (buf.endsWith("GET /L")) {
          Serial.println("Turn led OFF");
          ledStatus = LOW;
          digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW

    // close the connection
    Serial.println("Client disconnected");

void sendHttpResponse(WiFiEspClient client)
  // 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");

  // the content of the HTTP response follows the header:
  client.print("The LED is ");

  client.println("Click <a href=\"/H\">here</a> turn the LED on<br>");
  client.println("Click <a href=\"/L\">here</a> turn the LED off<br>");

  // The HTTP response ends with another blank line:

void printWifiStatus()
  // print the SSID of the network you're attached to
  Serial.print("SSID: ");

  // print your WiFi shield's IP address
  IPAddress ip = WiFi.localIP();
  Serial.print("IP Address: ");

  // print where to go in the browser
  Serial.print("To see this page in action, open a browser to http://");

Details gives me only this:

GET /favicon.ico HTTP/1.1
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/76.0.3809.100 Safari/537.36
Accept: image/webp,image/apng,image/*,*/*;q=0.8
Accept-Encoding: gzip, deflate
Accept-Language: ru-RU,ru;q=0.9,en-US;q=0.8,en;q=0.7

  • 1
    First print to Serial all of the received request. Then look at it and think. How do you know that the payload is 9? What distinguishes it enough that you can always identify it in a request? What do you look for? Once you can answer these, you can then frame a more specific question to know how to implement your algorithm or just use google to find the right functions. Aug 10 '19 at 3:45
  • Can you easily say how to parse GET /pin=9? Aug 10 '19 at 4:35
  • And one more question how can I write it to serial? Aug 10 '19 at 4:36
  • I rolled back the edit. Don't change completlly a Question. Someone is maybe working on an Answer.
    – Juraj
    Aug 10 '19 at 7:55
  • OK. Thanks. Juraj Aug 10 '19 at 7:58

The answer is to use indexOf and substring functions of response String

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.