How to change size of readstring() in client.read() on Arduino Ethernet?

Is there a way to use this example with TCP packets?
Because I want to login a user of a specific IP.
I dont think UDP packets can be sent through html... I didn;t find anything on google..

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

// Enter a MAC address and IP address for your controller below.
// The IP address will be dependent on your local network:
byte mac[] = {  
  0x00, 0x00, 0xAA, 0xBB, 0xCC, 0xDD };
IPAddress ip(192, 168, 10, 110);

unsigned int localPort = 8870;      // local port to listen on

// An EthernetUDP instance to let us send and receive packets over UDP
EthernetUDP Udp;

void setup() {
  // start the Ethernet and UDP:
  Ethernet.begin(mac,ip);
  Udp.begin(localPort);
}

void loop() {

  int packetSize = Udp.parsePacket();
  Serial.print("1 ");
  if(packetSize)
  {
    Serial.print("Received packet of size ");
    Serial.println(packetSize);
    Serial.print("From IP : ");

    IPAddress remote = Udp.remoteIP();
    //print out the remote connection's IP address
    Serial.print(remote);

    Serial.print(" on port : ");
    //print out the remote connection's port
    Serial.println(Udp.remotePort());
  }

}