When I make any GET request to my shield, the only thing I get when I read the request is '\r\n'. I am sending query parameters, and when the request has been read in the past, there was the full http request.

EDIT: Could this be due to some memory issue? It seems to be fairly non-deterministic when it fails, and I have 69% of memory taken when the program starts.

SparkFun ESP8266 AT library - Demo
Jim Lindblom @ SparkFun Electronics
Original Creation Date: July 16, 2015

This example demonstrates the basics of the SparkFun ESP8266
AT library. It'll show you how to connect to a WiFi network,
get an IP address, connect over TCP to a server (as a client),
and set up a TCP server of our own.

Development environment specifics:
  IDE: Arduino 1.6.5
  Hardware Platform: Arduino Uno
  ESP8266 WiFi Shield Version: 1.0

This code is released under the MIT license.

Distributed as-is; no warranty is given.

// Library Includes //
// SoftwareSerial is required (even you don't intend on
// using it).
#include <SoftwareSerial.h> 
#include <SparkFunESP8266WiFi.h>

// WiFi Network Definitions //
// Replace these two character strings with the name and
// password of your WiFi network.
const char mySSID[] = "ssid";
const char myPSK[] = "pass";

const short out1 = 10;
const short out2 = 11;
const short out3 = 12;
const short out4 = 13;

bool on1 = false;
bool on2 = false;
bool on3 = false;
bool on4 = false;

// ESP8266Server definition //
// server object used towards the end of the demo.
// (This is only global because it's called in both setup()
// and loop()).
ESP8266Server server = ESP8266Server(80);

// HTTP Strings //
const String html = "HTTP/1.1 200 OK\r\n"
                          "Content-Type: text/html\r\n"
                          "Connection: close\r\n\r\n"
                          "<!DOCTYPE HTML>\r\n"
                          "<link rel=\"icon\" href=\"data:,\">\r\n"
                          "<a href=\"/?toggle=1\"><button>Toggle 1</button></a>\r\n"
                          "<a href=\"/?toggle=2\"><button>Toggle 2</button></a>\r\n"
                          "<a href=\"/?toggle=3\"><button>Toggle 3</button></a>\r\n"
                          "<a href=\"/?toggle=4\"><button>Toggle 4</button></a>\r\n"

// All functions called from setup() are defined below the
// loop() function. They modularized to make it easier to
// copy/paste into sketches of your own.
void setup() 
  // Set pins
  pinMode(out1, OUTPUT);
  pinMode(out2, OUTPUT);
  pinMode(out3, OUTPUT);
  pinMode(out4, OUTPUT);

  digitalWrite(out1, LOW);
  digitalWrite(out2, LOW);
  digitalWrite(out3, LOW);
  digitalWrite(out4, LOW);

  // Serial Monitor is used to control the demo and view
  // debug information.

  // initializeESP8266() verifies communication with the WiFi
  // shield, and sets it up.

  // connectESP8266() connects to the defined WiFi network.

  // displayConnectInfo prints the Shield's local IP
  // and the network it's connected to.


void loop() 

void initializeESP8266()
  // esp8266.begin() verifies that the ESP8266 is operational
  // and sets it up for the rest of the sketch.
  // It returns either true or false -- indicating whether
  // communication was successul or not.
  // true
  int test = esp8266.begin();
  if (test != true)
    Serial.println(F("Error talking to ESP8266."));
  Serial.println(F("ESP8266 Shield Present"));

void connectESP8266()
  // The ESP8266 can be set to one of three modes:
  //  1 - ESP8266_MODE_STA - Station only
  //  2 - ESP8266_MODE_AP - Access point only
  //  3 - ESP8266_MODE_STAAP - Station/AP combo
  // Use esp8266.getMode() to check which mode it's in:
  int retVal = esp8266.getMode();
  if (retVal != ESP8266_MODE_STA)
  { // If it's not in station mode.
    // Use esp8266.setMode([mode]) to set it to a specified
    // mode.
    retVal = esp8266.setMode(ESP8266_MODE_STA);
    if (retVal < 0)
      Serial.println(F("Error setting mode."));
  Serial.println(F("Mode set to station"));

  // esp8266.status() indicates the ESP8266's WiFi connect
  // status.
  // A return value of 1 indicates the device is already
  // connected. 0 indicates disconnected. (Negative values
  // equate to communication errors.)
  retVal = esp8266.status();
  if (retVal <= 0)
    Serial.print(F("Connecting to "));
    // esp8266.connect([ssid], [psk]) connects the ESP8266
    // to a network.
    // On success the connect function returns a value >0
    // On fail, the function will either return:
    //  -1: TIMEOUT - The library has a set 30s timeout
    //  -3: FAIL - Couldn't connect to network.
    retVal = esp8266.connect(mySSID, myPSK);
    if (retVal < 0)
      Serial.println(F("Error connecting"));

void displayConnectInfo()
  char connectedSSID[24];
  memset(connectedSSID, 0, 24);
  // esp8266.getAP() can be used to check which AP the
  // ESP8266 is connected to. It returns an error code.
  // The connected AP is returned by reference as a parameter.
  int retVal = esp8266.getAP(connectedSSID);
  if (retVal > 0)
    Serial.print(F("Connected to: "));

  // esp8266.localIP returns an IPAddress variable with the
  // ESP8266's current local IP address.
  IPAddress myIP = esp8266.localIP();
  Serial.print(F("My IP: ")); Serial.println(myIP);

void serverSetup()
  // begin initializes a ESP8266Server object. It will
  // start a server on the port specified in the object's
  // constructor (in global area)
  Serial.print(F("Server started! Go to "));

void serverDemo()
  // available() is an ESP8266Server function which will
  // return an ESP8266Client object for printing and reading.
  // available() has one parameter -- a timeout value. This
  // is the number of milliseconds the function waits,
  // checking for a connection.
  ESP8266Client client = server.available(500);

  if (client) 
    // an http request ends with a blank line
    boolean currentLineIsBlank = true;
    String req;
    while (client.connected()) 
      if (client.available()) 
        char c = client.read();
        req += c;
        // if you've gotten to the end of the line (received a newline
        // character) and the line is blank, the http request has ended,
        // so you can send a reply
        if (c == '\n' && currentLineIsBlank) 
          if (req.indexOf("toggle=1") != -1){
            if (on1){
              Serial.println(F("TURN 1 ON"));
              digitalWrite(out1, LOW);
            else {
              Serial.println(F("TURN 1 OFF"));
              digitalWrite(out1, HIGH);
            on1 = !on1;
          else if (req.indexOf("toggle=2") != -1){
            if (on2){
              digitalWrite(out2, LOW);
              Serial.println(F("TURN 2 OFF"));
            else {
              Serial.println(F("TURN 2 ON"));
              digitalWrite(out2, HIGH);
            on2 = !on2;
          else if (req.indexOf("toggle=3") != -1){
            if (on3){
              Serial.println(F("TURN 3 OFF"));
              digitalWrite(out3, LOW);
            else {
              Serial.println(F("TURN 3 ON"));
              digitalWrite(out3, HIGH);
            on3 = !on3;
          else if (req.indexOf("toggle=4") != -1){
            if (on4){
              Serial.println(F("TURN 4 OFF"));
              digitalWrite(out4, LOW);
            else {
              Serial.println(F("TURN 4 ON"));
              digitalWrite(out4, HIGH);
            on4 = !on4;

          // send html
        if (c == '\n') 
          // you're starting a new line
          currentLineIsBlank = true;
        else if (c != '\r') 
          // you've gotten a character on the current line
          currentLineIsBlank = false;
    // give the web browser time to receive the data

    // close the connection:


// errorLoop prints an error code, then loops forever.
void errorLoop(int error)
  Serial.print(F("Error: ")); Serial.println(error);
  Serial.println(F("Looping forever."));
  for (;;)

2 Answers 2


In serverDemo() you are setting currentLineIsBlank to true. Then you are reading in each char until you get to a \n at which point you are assuming the http request has ended.

boolean currentLineIsBlank = true;

// if you've gotten to the end of the line (received a newline
// character) and the line is blank, the http request has ended,
// so you can send a reply
if (c == '\n' && currentLineIsBlank)

I think you want to set currentLineIsBlank to false to begin with ?...

  • no it's true to begin with, because if we get a \n, then we are at the end of the first blank line. If the first character is not \r or \n, then we set currentLineIsBlank = false because there is something on the line
    – holtc
    Nov 21, 2016 at 21:12
  • have you tried checking (Serial.print(c)) the value of c after reading it from client.read(); What are you seeing here as the request coming in... Nov 22, 2016 at 9:39
  • It's an issue with using String. I've made a bunch of changes to switch from String to char[], and it is working, thanks for helping
    – holtc
    Nov 22, 2016 at 16:24

It's an issue using String with arduino. I've changed to use char[] and now it is working fine.

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