Arduino Wifi Shield connections die after a few seconds of inactivity - arduino

Question

I have recently bought the Arduino WiFi Shield and I have updated the firmware to the latest version available.
I am using Webduino to create a kind of web service so I can check the pin's statuses and set their values to HIGH or LOW.
Everything work fine for the first seconds, however after a few seconds of inactivity, I can see the red error led turns on and later, when it recovers the connection to the network I cannot communicate again with the shield and I have to restart the Arduino board.
I have checked many posts in forums and I have seen there are more people with the same issue. Many of them talk about an issue in relation with the firmware, so it looks like there is a bug which is causing the issue.
Does anyone have an idea why it is happening? Could you point me into the right direction?
You can see my source code attached, so maybe you can see something wrong.
#include <SPI.h>
#include <WiFi.h>
#include <Streaming.h>
#define WEBDUINO_SERIAL_DEBUGGING 1
#include <WebServer.h>
#include <sha1.h>
char ssid[] = "******";
char pass[] = "******";
IPAddress ip(192,168,1,210);
int status = WL_IDLE_STATUS;
unsigned long sessionId;
#define WEBDUINO_METHOD_NOT_ALLOWED_MESSAGE "<h1>405 Requested method is not supported for resource</h1>"
#define CREDENTIALS "********"
#define PREFIX ""
#define ANALOG_PINS_AVAILABLE 5
#define DIGITAL_PINS_AVAILABLE 9
WebServer webserver(PREFIX, 80);
void welcome(WebServer &server) {
P(welcomeMsg1) = "HTTP/1.0 200 OK" CRLF;
server.printP(welcomeMsg1);
P(welcomeMsg2) =
"Content-Type: text/html" CRLF
CRLF
"<h1>Welcome to the web service</h1>";
server.printP(welcomeMsg2);
}
void httpMethodNotAllowed(WebServer &server) {
P(methodNotAllowedMsg1) = "HTTP/1.0 405 Method Not Allowed" CRLF;
server.printP(methodNotAllowedMsg1);
P(methodNotAllowedMsg2) =
"Content-Type: text/html" CRLF
CRLF
WEBDUINO_METHOD_NOT_ALLOWED_MESSAGE;
server.printP(methodNotAllowedMsg2);
}
void pinValuesJSON(WebServer &server) {
char sessionIdHeader[21];
sprintf(sessionIdHeader, "SessionId: %lu" CRLF, sessionId);
server.httpSuccess("application/json; charset=utf-8", sessionIdHeader);
server << "{";
server << "\"d2\":" << digitalRead(2) << ",";
server << "\"d3\":" << digitalRead(3) << ",";
server << "\"d5\":" << digitalRead(5) << ",";
server << "\"d6\":" << digitalRead(6);
server << "}";
}
void write(char *pin, char *value) {
if (pin[0] == 'a') {
analogWrite(strtoul(pin + 1, NULL, 10), strtoul(value, NULL, 10));
} else if (pin[0] == 'd') {
digitalWrite(strtoul(pin + 1, NULL, 10), strtoul(value, NULL, 10));
}
}
void defaultCmd(WebServer &server, WebServer::ConnectionType type, char *url_tail, bool tail_complete) {
if (server.checkCredentials(CREDENTIALS)) {
if (type == WebServer::GET) {
welcome(server);
} else {
httpMethodNotAllowed(server);
}
} else {
server.httpUnauthorized();
}
}
void pinsCmd(WebServer &server, WebServer::ConnectionType type, char *url_tail, bool tail_complete) {
#define PINLEN 5
#define VALUELEN 5
if (server.checkCredentials(CREDENTIALS)) {
if (type == WebServer::GET) {
pinValuesJSON(server);
} else if (type == WebServer::PUT) {
bool repeat;
char pin[PINLEN];
char value[VALUELEN];
do {
repeat = server.readPOSTparam(pin, PINLEN, value, VALUELEN);
write(pin, value);
} while (repeat);
pinValuesJSON(server);
}
} else {
server.httpUnauthorized();
}
}
void setup() {
randomSeed(analogRead(0));
sessionId = random(999999999);
/* Pins
* 13: SCK
* 12: MISO
* 11: MOSI
* 10: SS for WiFi
* 9: L9 (yellow) => Informational LED
* 7: Handshake between shield and Arduino
* 4: SS for SD card */
/* When SD card peripheral is not being used, it's necessary to set
pin 4 as an output and write a high to it */
pinMode(4, OUTPUT);
digitalWrite(4, HIGH);
/* Socket pins */
pinMode(2, OUTPUT);
digitalWrite(2, LOW);
pinMode(3, OUTPUT);
digitalWrite(3, LOW);
pinMode(5, OUTPUT);
digitalWrite(5, LOW);
pinMode(6, OUTPUT);
digitalWrite(6, LOW);
WiFi.config(ip);
while (status != WL_CONNECTED) {
// Connect to WPA/WPA2 network. Change this line if using open or WEP network:
status = WiFi.begin(ssid, pass);
delay(4000);
}
webserver.setDefaultCommand(&defaultCmd);
webserver.addCommand("pins", &pinsCmd);
/* start the webserver */
webserver.begin();
digitalWrite(8, HIGH);
}
void loop() {
/* process incoming connections one at a time forever */
webserver.processConnection();
}