http request in time intervals

Question

I'm doing a program that receives data from a web page every so often, but only receives the data once and then receives everything blank. I need help to receive the data every time indefinitely. I am using arduino uno with arduino etherner shield

My code:

#include <SPI.h>
#include <Ethernet.h>

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };

IPAddress ip(192, 168, 0, 177);
EthernetClient client;

int REDLed= 2;
int GREENLed= 3;
int BLUELed= 4;

void setup()
{     
  pinMode(REDLed, OUTPUT);
  pinMode(GREENLed, OUTPUT);
  pinMode(GREENLed, OUTPUT);
  Ethernet.begin(mac, ip);
  Serial.begin(9600);
  Serial.println("power up" );
  delay(3000); 
}

void loop()
{
  Serial.println("SubmitHttpRequest - started" );
  SubmitHttpRequest();
  Serial.println("SubmitHttpRequest - finished" );
  delay(10000);
}

void SubmitHttpRequest()
{
  if (client.connect(server, 80))
  {
    Serial.println("connected");
    client.println("GET /arduino/getstate.php?color=All HTTP/1.1");
    client.println("Host: cybertodo.mx");
    client.println("Connection: close");
    client.println();
  }
  else
  {
    Serial.println("connection failed");
  }
  delay(100);
  changeLed();
}

void changeLed()
{
  String content = "";
  Serial.println(client.available());
  while(client.available()!=0)
  {  
    content = content + String(char (client.read()));
  }
  Serial.println(content);
  if(content.substring(30,31)== "1")
  {
    digitalWrite(REDLed, HIGH);
  }
  else if (content.substring(30,31)== "0")
  {
    digitalWrite(REDLed, LOW);
  }

  if(content.substring(31,32)== "1")
  {
    digitalWrite(GREENLed, HIGH);
  }
  else if (content.substring(31,32)== "0")
  {
    digitalWrite(GREENLed, LOW);
  }

  if(content.substring(32,33)== "1")
  {
    digitalWrite(BLUELed, HIGH);
  }
  else if (content.substring(32,33)== "0")
  {
    digitalWrite(BLUELed, LOW);
  }
  content = "";
}

Answer 1

Immediately after making the request when reading client.available() will be 0 since no data was received yet so:

  while(client.available()!=0)
  {  
    content = content + String(char (client.read()));
  }

Will never actually run. Try something like:

unsigned long last = millis();
String content = "";

while(client.connected()) {
  int len = client.available();
  if(len > 0) {
    last = millis();

    char buff[len];
    for(int i = 0; i < len; i++) {
      buff[i] = client.read();
    }
    content += String(buff);

  } else {
    if(millis() - last > 2000) {
      client.stop();
      return;
    }
    delay(1);
  }
}

Also note if you use Connection: close on the client then you must close the connection. This example doesn't do that until 2 seconds have passed. To do this properly you'd need to also add header parsing to your client and close the connection once the amount specified in Content-Length is received.