I am communicating with the esp8266 WiFi module using Arduino. The module returns GET requests from other clients. They will be of the form

GET /101011 HTTP/1.1\r\nHost...

I wish to extract only the 101011 from the received serial data and discard the rest. I came up with this small chunk of code to test it by sending data from my laptop.

This is the code:

String s;

void setup() {


void loop() {

    s = Serial.readStringUntil(' ');
    // Discard the rest of the data . Snippet from Jeremy Blum's Blog

    while(Serial.available()>0) Serial.read(); 



Jeremy's Blog

But when I run this using the input GET /101011 HTTP/1.1\r\n the output produced is


Why is Serial.available() returning true even after reading everything? How to discard the rest of data from the serial input buffer?

  • 3
    How do you know you have read everything? Serial data is still arriving from the ESP8266 while you are clearing the buffer - and you are clearing it much faster than the data is arriving. Remember: serial data arrives s...l...o...w...l...y...
    – Majenko
    Mar 27 '16 at 11:52
  • Read this:~ hackingmajenkoblog.wordpress.com/2016/02/01/…
    – Majenko
    Mar 27 '16 at 11:52
  • @Majenko Thank you. Read your blog. Will try to implement it in my design.
    – Ray
    Mar 27 '16 at 12:02

One possible approach is to read and discard everything for a fixed time, like a second. For example:

unsigned long now = millis ();
while (millis () - now < 1000)
  Serial.read ();  // read and discard any input

I'm not a big fan of trying to "flush the input buffer". How do you know if a second is long enough? Or maybe it is too long? You are better off reading to some known delimiter.

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