Arduino Uno+ESP01 module HTTP request issue - arduino

Question

I have been working with my Arduino Uno board and ESP01 module. My goal is to send an HTTP request to a remote server and fetch the last entry of a remote data base. This entry is the state of a remote toggle button which can be modified through a web page located on a remote server. I'm using AT commands.
To check the state of the toggle button HTTP requests are sent every second from Arduino Uno.
The Arduino sketch that I wrote configures the ESP01, connects it to wifi, and sends the HTTP request.
Arduino sketch:
#include <SoftwareSerial.h>
SoftwareSerial SerialESP8266(2,3); // RX, TX
String server = "someServer";
String cadena=""; //to store HTTP request
void setup() {
SerialESP8266.begin(9600);
Serial.begin(9600);
SerialESP8266.setTimeout(5000);
//checking the ESP8266 response
SerialESP8266.println("AT");
if(SerialESP8266.find("OK"))
Serial.println("AT OK");
else
Serial.println("Error on ESP8266");
//ESP8266 in STA mode.
SerialESP8266.println("AT+CWMODE=1");
if(SerialESP8266.find("OK"))
Serial.println("ESP8266 on STATION mode...");
//Connecting to wifi
SerialESP8266.println("AT+CWJAP=\"mySSID\",\"somePassword\"");
Serial.println("Connnecting...");
SerialESP8266.setTimeout(10000); //waiting for connection
if(SerialESP8266.find("OK"))
Serial.println("WIFI OK");
else
Serial.println("Unable to connect...");
SerialESP8266.setTimeout(2000);
//Disable multiple connections
SerialESP8266.println("AT+CIPMUX=0");
if(SerialESP8266.find("OK"))
Serial.println("Multiple connections disabled");
}
void loop() {
SerialESP8266.println("AT+CIPSTART=\"TCP\",\"" + server + "\",80");
//connecting to server
if(SerialESP8266.find("OK")) {
Serial.println();
Serial.println();
Serial.println();
Serial.println("Server connection successful...");
//Armamos el encabezado de la peticion http
String peticionHTTP= "GET /readLast.php";
peticionHTTP=peticionHTTP+" HTTP/1.1\r\n";
peticionHTTP=peticionHTTP+"Host: someserver\r\n\r\n";
peticionHTTP=peticionHTTP+"Host: localhost\r\n\r\n";
//Sending the length of the HTTP request
SerialESP8266.print("AT+CIPSEND=");
SerialESP8266.println(peticionHTTP.length());
//waiting for ">" for sending HTTP request
if(SerialESP8266.find(">")) {
//we can send the HTTP request when > is displayed
Serial.println("Sending HTTP request. . .");
SerialESP8266.println(peticionHTTP);
if(SerialESP8266.find("SEND OK")) {
Serial.println("HTTP request sent...:");
Serial.println();
Serial.println("On stand by...");
boolean fin_respuesta=false;
long tiempo_inicio=millis();
cadena="";
while(fin_respuesta==false) {
while(SerialESP8266.available()>0) {
char c=SerialESP8266.read();
Serial.write(c);
cadena.concat(c); //store the request string on "cadena"
}
//terminate if "cadena" length is greater than 3500
if(cadena.length()>3500) {
Serial.println("The request exceeded the maximum length...");
SerialESP8266.println("AT+CIPCLOSE");
if( SerialESP8266.find("OK"))
Serial.println("Connection terminated...");
fin_respuesta=true;
}
if((millis()-tiempo_inicio)>10000) {
//Terminate if connection time exceeded the maximum
Serial.println("Connection time exceeded...");
SerialESP8266.println("AT+CIPCLOSE");
if( SerialESP8266.find("OK"))
Serial.println("Connection terminated");
fin_respuesta=true;
}
if(cadena.indexOf("CLOSED")>0) {
Serial.println();
Serial.println("String OK, connection terminated");
fin_respuesta=true;
}
}
} else {
Serial.println("error on HTTP request.....");
}
}
} else {
Serial.println("Unable to find the server....");
}
delay(1000); //1 second delay before new loop
}
The HTTP requests (GET request) is handled by readLast.php on the server, which connects to the database and returns the last state of the toggle button. Two states are possible: encender (TURN ON) or apagar (TURN OFF).
readLast.php
<?php
$servername = "host";
$username = "user"; // username for your database
$password = "password";
$dbname = "database"; // Name of database
$now = new DateTime();
$CRLF = "\n\r";
$conn = mysqli_connect("localhost", "user", "password");
if (!$conn) {
die('Could not connect: ' . mysqli_error($conn));
}
$con_result = mysqli_select_db($conn,"database");
if(!$con_result) {
die('Could not connect to specific database: ' . mysqli_error($conn));
}
$result = mysqli_query($conn, "SELECT accion from `datatable` where id = (select MAX(id) from datatable)");
if (!$result) {
die('Invalid query: ' . mysqli_error($conn));
}
while($row = mysqli_fetch_array($result, MYSQLI_ASSOC)) {
echo "accion=" . $row["accion"];
}
mysqli_close($conn);
?>
The first HTTP request returns the state of toggle button correctly. But the next HTTP requests return BAD HTTP REQUEST:
IPD,298:HTTP/1.1 200 OK
Date: Fri, 01 Dec 2017 01:40:56 GMT
Content-Type: text/html; charset=UTF-8
Transfer-Encoding: chunked
Connection: keep-alive
Server: awex
X-Xss-Protection: 1; mode=block
X-Content-Type-Options: nosniff
X-Request-ID: cf44e42dbd53cb7cb5456e4b70e3399d
10
accion: encender
+IPD,5:0
+IPD,428:HTTP/1.1 400 Bad Request
Date: Fri, 01 Dec 2017 01:40:56 GMT
Content-Type: text/html
Content-Length: 170
Connection: close
Server: awex
X-Xss-Protection: 1; mode=block
X-Content-Type-Options: nosniff
X-Request-ID: d8ffa7b4eece5d1e88c7786fea5ace9f
<html>
<head><title>400 Bad Request</title></head>
<body bgcolor="white">
<center><h1>400 Bad Request</h1></center>
<hr><center>openresty</center>
</body>
</html>
CLOSED
What I am doing wrong?

Answer 1

I had the same problem, but was able to fix it with:
while(SerialESP8266.available()>0) {
char c=SerialESP8266.read();
Serial.write(c);
cadena.concat(c); //store the request string on "cadena"
if (cadena.length() > 50) cadena = "";
}
The problem is due to the limit of string.indexof();
Max characters supported are 170, anything larger will not work.