The function does not work in ESP8266

[b707]

Agreed
Instead of

@arduino556665

 if (!client) {
    return;
  }
  while (!client.available()) {
    delay(1);
  }
  String request = client.readStringUntil('\r');
  client.flush();
  ...  // work with request

it would be better something like it:

 if (client  && client.available()) {
   String request = client.readStringUntil('\r');
   client.flush();
  ...  // work with request