This program issues commands to an ESP8266 Wifi module in order to receive an HTML page from a website.

esp8266.ino

///////////////////////////////////////////////////////////////////////////////////////
// This program uses the ESP8266 Wifi module to access a webpage. It's an adaptation of
// the program discussed at http://hackaday.io/project/3072/instructions
// and shown here http://dunarbin.com/esp8266/retroBrowser.ino .
//
// This program was ported to the ZPUino 2.0, a softcore processor that runs on an FPGA
// and emulates an Arduino.
//
// This program works with version 00160901 of the ESP8266 firmware.
///////////////////////////////////////////////////////////////////////////////////////

#define SSID                "XESS"
#define PASS                "6a27a85603d39b7" // ESP8266 works with WPA2-PSK (AES) passwords.
//#define DEST_HOST         "retro.hackaday.com"
//#define DEST_PAGE         "/"
//#define DEST_IP           "192.254.235.21"
#define DEST_HOST           "www.xess.com"
#define DEST_PAGE           "/static/media/pages/xess_esp8266.html"
#define DEST_IP             "192.241.200.6"
#define DEST_PORT           80
#define TIMEOUT             10000 // mS
#define CONTINUE            false
#define HALT                true
#define DO_ECHO             true
#define NO_ECHO             false
#define CONNECTION_TRIES    5
#define ECHO_COMMANDS // Un-comment to echo AT+ commands to serial monitor.

// Print error message and loop stop.
void errorHalt(String msg)
{
  Serial.println(msg);
  Serial.println("HALT");
  while(true);
}

// Wait until a char is received from the ESP8266. Then return it. 
char getChar()
{
  while(Serial1.available() == false)
    ;
  return Serial1.read();
}

// Buffer used to compare strings against the output from the ESP8266.
#define CB_SIZE  20
char comp_buffer[CB_SIZE] = {0,}; // Fill buffer with string terminator.

// Get char from ESP8266 and also shift it into the comparison buffer.
char getCharAndBuffer()
{
  char b = getChar();
  char *cb_src, *cb_dst;
  cb_src = comp_buffer+1;
  cb_dst = comp_buffer;
  for(int i=1; i<CB_SIZE-1; i++)
    *cb_dst++ = *cb_src++;
  *cb_dst = b;
  return b;
}

// Compare the string against the newest contents of the buffer.
boolean cb_match(String &s)
{
  return strcmp(s, comp_buffer + CB_SIZE - 1 - s.length()) == 0; // Return true on match.
}

// Read characters from ESP8266 module and echo to serial until keyword occurs or timeout.
boolean echoFind(String keyword, boolean do_echo)
{
  // Fail if the target string has not been sent by deadline.
  unsigned long deadline = millis() + TIMEOUT;
  while(millis() < deadline)
  {
    char ch = getCharAndBuffer();
    if(do_echo)
      Serial.write(ch);
    if(cb_match(keyword))
      return true;
  }
  return false;  // Timed out
}

// Echo module output until 3 newlines encountered.
// (Used when we're indifferent to "OK" vs. "no change" responses.)
void echoSkip()
{
  echoFind("\n", DO_ECHO);        // Search for nl at end of command echo
  echoFind("\n", DO_ECHO);        // Search for 2nd nl at end of response.
  echoFind("\n", DO_ECHO);        // Search for 3rd nl at end of blank line.
}

// Send a command to the module and wait for acknowledgement string
// (or flush module output if no ack specified).
// Echoes all data received to the serial monitor.
boolean echoCommand(String cmd, String ack, boolean halt_on_fail)
{
  // Send the command to the ESP8266.
  Serial1.print(cmd);
  Serial1.write('\r'); // Append return to commands.
  
  #ifdef ECHO_COMMANDS
  Serial.println("\n\n\r--------------------------------------");
  Serial.println("COMMAND: " + cmd + "\n");
  #endif
  
  // If no ack response specified, skip all available module output.
  if (strlen(ack) == 0)
    echoSkip();
  else
  {
    // Otherwise wait for ack.
    if (!echoFind(ack, DO_ECHO))    // timed out waiting for ack string 
    {
      if (halt_on_fail)
        errorHalt(cmd + " failed");// Critical failure halt.
      else
        return false;            // Let the caller handle it.
    }
  }
  return true;                   // ack blank or ack found
}

// Data packets have the format "+IPD,0,1024:lwkjfwsnv....". This routine gets
// the second number preceding the ":" that indicates the number of characters 
// in the packet.
int getPacketLength()
{
  while(getChar() != ',')
    ;
  char len[10];
  for(int i=0; i<10; i++)
  {
    char c = getChar();
    if(c == ':')
    {
      len[i] = 0; // Terminate string.
      break;
    }
    len[i] = c;
  }
  return atoi(len);
}

// Echo a received Wifi packet to the PC.
void echoPacket()
{
  if(echoFind("+IPD,", NO_ECHO))
  {
    for(int l = getPacketLength(); l>0; l--)
      Serial.write(getChar());
  }
}

// Connect to the specified wireless network.
boolean connectWiFi(String ssid, String pwd)
{
  String cmd = "AT+CWJAP=\"" + ssid + "\",\"" + pwd + "\"";
  if (echoCommand(cmd, "OK", CONTINUE)) // Join Access Point
  {
    Serial.println("\nConnected to WiFi.");
    return true;
  }
  else
  {
    Serial.println("\nConnection to WiFi failed.");
    return false;
  }
}

// Establish a TCP link to a given IP address and port.
boolean establishTcpLink(String ip, int port)
{
  String cmd = "AT+CIPSTART=0,\"TCP\",\"" + ip + "\"," + port;
  return echoCommand(cmd, "OK", HALT);
}

// Request a page from an HTTP server.
boolean requestPage(String host, String page, int port)
{
  // Create raw HTTP request for web page.
  String http_req = "GET " + page + " HTTP/1.1\r\nHost: " + host + ":" + port + "\r\n\r\n";
  
  // Ready the module to receive raw data.
  String cmd = "AT+CIPSEND=0,";
  cmd = cmd + http_req.length(); // Tell the ESP8266 how long the coming HTTP request is.
  if (!echoCommand(cmd, ">", CONTINUE))
  {
    echoCommand("AT+CIPCLOSE", "", CONTINUE);
    errorHalt("Connection timeout");
  }
  
  // Send the raw HTTP request.
  return echoCommand(http_req, "OK", CONTINUE);
}


HardwareSerial esp8266(2); // Find the ZPUino serial port connected to the ESP8266.

void setup()  
{
  Serial.begin(115200);  // Initialize serial port to the PC.

  Serial1 = esp8266; // Rename the ESP8266 serial port to something more standard.
  // Initialize the serial port to the ESP8266, but also assign the RX & TX lines
  // to specific pins of the ZPUino FPGA. Obviously, this part is not needed when
  // using a standard Arduino.
  Serial1.begin(115200, TX(3), RX(17));
  
  // Wait for a keypress from the PC before running the demo.
  while(!Serial.available())
    ;
  Serial.read();

  Serial.println("\n\n\n\r----------- ESP8266 Demo -----------\n\n");

  echoCommand("AT+RST",      "ready", HALT);      // Reset the module.  
  echoCommand("AT+GMR",      "OK",    CONTINUE);  // Show module's firmware ID. 
  echoCommand("AT+CWMODE=1", "",      CONTINUE);  // Set module into station mode.
  echoCommand("AT+CIPMUX=1", "OK",    CONTINUE);  // Allow multiple connections. Necessary for TCP link.

  delay(2000);  // Let things settle down for a bit...

  echoCommand("AT+CWLAP", "OK", HALT);       // Scan for available access points.

  // Connect to the Wifi.
  for(int i=1; i<=CONNECTION_TRIES; i++)
  {
    if(connectWiFi(SSID, PASS))
      break;
    if(i == CONNECTION_TRIES)
      errorHalt("Connection failed");
  }

  delay(4000);  // Let the link stabilize.

  echoCommand("AT+CIFSR", "", HALT);      // Show the IP address assigned by the access point.
}


void loop() 
{
  establishTcpLink(DEST_IP, DEST_PORT);
    
  delay(2000);  // Once again, let the link stabilize.
  
  // Show the connection status.
  echoCommand("AT+CIPSTATUS", "OK", HALT);
  
  // Request a page from an HTTP server.
  requestPage(DEST_HOST, DEST_PAGE, DEST_PORT);
  
  // Loop forever echoing data received over the Wifi from the HTTP server.
  while(true)
    echoPacket();
      
  errorHalt("ONCE ONLY");
}

where is Serial1 defined? Arduino IDE gives me 'Serial1' was not declared in this scope