AnonymousTopicBasedPubSubCommunicationforMicroblogging/client/client.go

package client

/*
#cgo CFLAGS: -O2
#cgo LDFLAGS: -lcrypto -lm
#include "../c/dpf.h"
#include "../c/okvClient.h"
#include "../c/dpf.c"
#include "../c/okvClient.c"
*/
import "C"

import (
	"2PPS/lib"
	"bufio"
	"bytes"
	"crypto/rand"
	"crypto/sha256"
	"crypto/tls"
	"encoding/json"
	"fmt"
	"log"
	"math/big"
	mr "math/rand"
	"net"
	"os"
	"sort"
	"strconv"
	"strings"
	"sync"
	"time"
	"unsafe"

	"golang.org/x/crypto/nacl/box"
)

type tweet struct {
	Topics []string
	Text   string
}

const leader string = "127.0.0.1:4441"

//needs to be changed at leader/client at the same time
const numClients = 1000

//mylimit=8000
//sudo prlimit --nofile=$mylimit --pid $$; ulimit -n $mylimit
//for every terminal
const dataLength int = 256

//Maximum Transport Unit
const mtu int = 1100

var dbWriteSize int
var round int
var topicList []string
var archiveTopicList []string
var neededSubscriptions int
var publisherAmount int
var goodPadding int
var blocksReceived int
var timeBounds []float64
var guiTweet string

//this translates to a simulated round length of ~2h
var speedUp float64 = 7200 / ((maxTimePerRound.Seconds()) * 3)

var maxTimePerRound time.Duration = 5 * time.Second
var startTime int

var archiveInterests = make([]int, 1)
var sharedSecret [numClients][2][32]byte = createSharedSecret()

var wantsArchive = make([]byte, 1)

var leaderPublicKey *[32]byte
var followerPublicKey *[32]byte
var clientPrivateKey [numClients]*[32]byte
var clientPublicKey [numClients]*[32]byte

func main() {
	f, err := os.OpenFile("evalDataClient", os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
	if err != nil {
		log.Fatalf("error opening file: %v", err)
	}
	defer f.Close()

	log.SetOutput(f)
	log.Println("simulated Duration", speedUp)
	wg := &sync.WaitGroup{}

	for i := 0; i < numClients; i++ {
		wg.Add(1)
		go Client(i, f)
		time.Sleep(1 * time.Millisecond)
	}
	wg.Wait()
}

func Client(clientNumber int, f *os.File) {

	if clientNumber == 0 {
		getTimeBounds()
	}

	generatedPublicKey, generatedPrivateKey, err := box.GenerateKey(rand.Reader)
	if err != nil {
		panic(err)
	}
	clientPrivateKey[clientNumber] = generatedPrivateKey
	clientPublicKey[clientNumber] = generatedPublicKey

	C.initializeCipher()

	//initializes the connection to the leader
	conf := &tls.Config{
		InsecureSkipVerify: true,
	}

	leaderConn, err := tls.Dial("tcp", leader, conf)
	if err != nil {
		panic(err)
	}
	leaderConn.SetDeadline(time.Time{})

	//receives topics first so client can participate asap
	receiveTopicLists(leaderConn)

	//gets the public keys of both servers
	var tmpLeaderPubKey [32]byte
	_, err = leaderConn.Read(tmpLeaderPubKey[:])
	if err != nil {
		panic(err)
	}
	leaderPublicKey = &tmpLeaderPubKey

	var tmpFollowerPubKey [32]byte
	_, err = leaderConn.Read(tmpFollowerPubKey[:])
	if err != nil {
		panic(err)
	}
	followerPublicKey = &tmpFollowerPubKey

	//sends own public key
	writeTo(leaderConn, clientPublicKey[clientNumber][:])

	neededSubscriptionsBytes := readFrom(leaderConn, 4)
	neededSubscriptions = byteToInt(neededSubscriptionsBytes)

	startTimeBytes := readFrom(leaderConn, 4)
	startTime = byteToInt(startTimeBytes)

	//setup ends above
	//while client is active he is always connected and has to participate

	for {
		//gets current phase
		phase := readFrom(leaderConn, 1)

		if phase[0] == 1 {

			//gets current dbWriteSize from leader
			dbWriteSizeBytes := readFrom(leaderConn, 4)
			dbWriteSize = byteToInt(dbWriteSizeBytes)

			//roundAsBytes := readFrom(leaderConn, 4)
			roundAsBytes := make([]byte, 4)
			_, err = leaderConn.Read(roundAsBytes)
			if err != nil {
				panic(err)
			}

			round = byteToInt(roundAsBytes)

			if clientNumber == 0 {
				fmt.Println("Round ", round)
			}

			//request virtualAddress from leader via pirQuery
			encryptedQueryLeader, encryptedQueryFollower := createAuditPIRQuery(clientNumber)
			sendQuerys(encryptedQueryLeader, encryptedQueryFollower, leaderConn, false)
			pos := receiveVirtualAddress(sharedSecret[clientNumber], leaderConn)

			tweet := getGuiTweet()
			if clientNumber == numClients-1 {
				log.Println("Round", round)
				log.Println("publisherAmount", publisherAmount)
				log.Println("goodPadding", goodPadding)
				log.Println("blocksReceived", blocksReceived)
				log.Println("goodPadding Percentage", float64(goodPadding)/float64(blocksReceived))
				publisherAmount = 0
			}

			//prep the query
			dataSize := len(tweet)
			querySize := make([]byte, 4)
			cQuerySize := C.int(byteToInt(querySize))

			var dpfQueryA *C.uchar
			var dpfQueryB *C.uchar

			C.prepQuery(C.int(pos), C.int(dbWriteSize), (*C.uchar)(&tweet[0]), C.int(dataSize), &cQuerySize, &dpfQueryA, &dpfQueryB)

			intQuerySize := int(cQuerySize) //byteToInt(querySize)

			//write the query
			queryAPlaintext := C.GoBytes(unsafe.Pointer(dpfQueryA), C.int(intQuerySize))

			//encrypts queryA and appends it to message
			var nonce [24]byte
			//fill nonce with randomness
			_, err = rand.Read(nonce[:])
			if err != nil {
				panic("couldn't get randomness for nonce!")
			}
			dpfQueryAEncrypted := box.Seal(nonce[:], queryAPlaintext, &nonce, leaderPublicKey, clientPrivateKey[clientNumber])

			//encrypts queryB and appends it to message
			queryBPlaintext := C.GoBytes(unsafe.Pointer(dpfQueryB), C.int(intQuerySize))

			//fill nonce with randomness
			_, err = rand.Read(nonce[:])
			if err != nil {
				panic("couldn't get randomness for nonce!")
			}
			dpfQueryBEncrypted := box.Seal(nonce[:], queryBPlaintext, &nonce, followerPublicKey, clientPrivateKey[clientNumber])

			//writes the dpfQuery to the leader
			dpfLengthBytes := intToByte(len(dpfQueryAEncrypted))
			writeTo(leaderConn, dpfLengthBytes)

			writeTo(leaderConn, dpfQueryAEncrypted)

			writeTo(leaderConn, dpfQueryBEncrypted)

			C.free(unsafe.Pointer(dpfQueryA))
			C.free(unsafe.Pointer(dpfQueryB))
		} else if phase[0] == 3 {
			/*
				possible Values
				0 : new client
					leader expects sharedSecrets, expects pirQuery
				1 : update needed
					leader sends topicList, performs local update of sharedSecret, expects pirQuery
				2 : no update needed
					nothing
			*/
			subPhase := readFrom(leaderConn, 1)

			var encryptedQueryLeader, encryptedQueryFollower []byte
			//first time participating
			if subPhase[0] == 0 {
				receiveTopicLists(leaderConn)
				encryptedQueryLeader, encryptedQueryFollower = createPIRQuery(int(subPhase[0]), clientNumber)
				sendQuerys(encryptedQueryLeader, encryptedQueryFollower, leaderConn, false)

			}
			//updates the topic list and what client is interested in
			if subPhase[0] == 1 {

				receiveTopicLists(leaderConn)

				//updates local secret
				for index := 0; index < 2; index++ {
					sharedSecret[clientNumber][index] = sha256.Sum256(sharedSecret[clientNumber][index][:])
				}

				encryptedQueryLeader, encryptedQueryFollower = createPIRQuery(int(subPhase[0]), clientNumber)
				sendQuerys(encryptedQueryLeader, encryptedQueryFollower, leaderConn, false)

			}

			receiveTweets(sharedSecret[clientNumber], leaderConn, false, clientNumber)

			if len(archiveTopicList) > 0 {
				wantsArchive[0] = 0
			} else {
				wantsArchive[0] = 0
			}

			writeTo(leaderConn, wantsArchive)

			if wantsArchive[0] == 1 && len(archiveTopicList) > 0 {
				encryptedQueryLeader, encryptedQueryFollower = createPIRQuery(-1, clientNumber)
				sendQuerys(encryptedQueryLeader, encryptedQueryFollower, leaderConn, true)
				receiveTweets(sharedSecret[clientNumber], leaderConn, true, clientNumber)
			}

		} else {
			fmt.Println("Phase", phase)
			panic("somethin went wrong")
		}
	}
}

//creates and sends the pirQuerys for each server
func createPIRQuery(subPhase int, clientNumber int) ([]byte, []byte) {
	//later this will be taken from gui, this is only for testing
	topicsOfInterest := make([]int, 1)
	topicsOfInterest[0] = mr.Intn(10)
	archiveInterests[0] = mr.Intn(10)

	tmpNeededSubscriptions := neededSubscriptions
	if tmpNeededSubscriptions > len(topicList) {
		tmpNeededSubscriptions = len(topicList)
	}

	tmptopicsOfInterest := make([]int, len(topicsOfInterest))
	copy(tmptopicsOfInterest, topicsOfInterest)

	tmpTopicList := make([]string, len(topicList))
	copy(tmpTopicList, topicList)
	if wantsArchive[0] == 1 && subPhase == -1 {
		tmpNeededSubscriptions = len(archiveInterests)
		if tmpNeededSubscriptions > len(archiveTopicList) {
			tmpNeededSubscriptions = len(archiveTopicList)
		}
		tmptopicsOfInterest = archiveInterests //todo! take archiveInterests from gui
		tmpTopicList = archiveTopicList
	}

	//creates fake topicsOfInterest if client is boooring
	if len(tmptopicsOfInterest) < tmpNeededSubscriptions && subPhase != -1 {
		tmptopicsOfInterest = addFakeInterests(len(tmpTopicList), tmptopicsOfInterest, false)
	}

	//pirQuery [topicsOfInterest][serverAmount][topicAmount]byte
	pirQuerys := make([][][]byte, len(tmptopicsOfInterest))
	for i := range pirQuerys {
		pirQuerys[i] = make([][]byte, 2)
		for j := range pirQuerys[i] {
			pirQuerys[i][j] = make([]byte, len(tmpTopicList))
		}
	}

	//for leader
	//pirQuery will be filled with random bits
	for topic := range tmptopicsOfInterest {
		for index := range tmpTopicList {
			bit, err := rand.Int(rand.Reader, big.NewInt(2))
			if err != nil {
				panic(err)
			}
			pirQuerys[topic][0][index] = byte(bit.Int64())
		}
	}

	tmptopicsOfInterestBytes := make([]byte, len(tmpTopicList))
	for index := range tmptopicsOfInterest {
		if tmptopicsOfInterest[index] == 1 {
			tmptopicsOfInterestBytes[index] = 1
		}
	}

	for topicIndex, topic := range tmptopicsOfInterest {
		for index := range tmpTopicList {
			if topic == index {
				if pirQuerys[topicIndex][0][index] == 1 {
					pirQuerys[topicIndex][1][index] = 0
				} else {
					pirQuerys[topicIndex][1][index] = 1
				}
			} else {
				if pirQuerys[topicIndex][0][index] == 0 {
					pirQuerys[topicIndex][1][index] = 0
				} else {
					pirQuerys[topicIndex][1][index] = 1
				}
			}
		}
	}

	//flattens the querys to be able to send them more efficently
	messagesFlattened := make([][]byte, 2)
	//adds the sharedSecret to the first pirQuery when first time participating
	if subPhase == 0 {
		for server := 0; server < 2; server++ {
			messagesFlattened[server] = append(messagesFlattened[server], sharedSecret[clientNumber][server][:]...)
		}
	}

	for server := range messagesFlattened {
		for topic := range pirQuerys {
			messagesFlattened[server] = append(messagesFlattened[server], pirQuerys[topic][server]...)
		}
	}

	var nonce [24]byte
	_, err := rand.Read(nonce[:])
	if err != nil {
		panic("couldn't get randomness for nonce!")
	}
	encryptedQueryLeader := box.Seal(nonce[:], messagesFlattened[0], &nonce, leaderPublicKey, clientPrivateKey[clientNumber])

	_, err = rand.Read(nonce[:])
	if err != nil {
		panic("couldn't get randomness for nonce!")
	}
	encryptedQueryFollower := box.Seal(nonce[:], messagesFlattened[1], &nonce, followerPublicKey, clientPrivateKey[clientNumber])

	return encryptedQueryLeader, encryptedQueryFollower
}

func sendQuerys(encryptedQueryLeader, encryptedQueryFollower []byte, leaderConn net.Conn, getArchive bool) {
	encryptedLength := len(encryptedQueryLeader)

	//sends the pirQuerysLength to the leader
	writeTo(leaderConn, intToByte(encryptedLength))

	//sends the pirQuerys to the leader
	writeTo(leaderConn, encryptedQueryLeader)

	writeTo(leaderConn, encryptedQueryFollower)

	if getArchive {
		writeTo(leaderConn, intToByte(len(archiveInterests)))
	}
}

func receiveVirtualAddress(sharedSecret [2][32]byte, leaderConn net.Conn) int {

	virtualAddressByte := readFrom(leaderConn, 4)

	//xores the sharedSecret
	for h := 0; h < 2; h++ {
		for i := 0; i < 4; i++ {
			virtualAddressByte[i] = virtualAddressByte[i] ^ sharedSecret[h][i]
		}
	}
	return byteToInt(virtualAddressByte)
}

func receiveTweets(sharedSecret [2][32]byte, leaderConn net.Conn, getArchive bool, clientNumber int) {

	tmpNeededSubscriptions := neededSubscriptions
	if tmpNeededSubscriptions > len(topicList) {
		tmpNeededSubscriptions = len(topicList)
	}
	if getArchive {
		tmpNeededSubscriptions = len(archiveInterests)
		if tmpNeededSubscriptions > len(archiveTopicList) {
			tmpNeededSubscriptions = len(archiveTopicList)
		}
	}

	for i := 0; i < tmpNeededSubscriptions; i++ {
		if !getArchive {
			blocksReceived++
		}
		//client receives tweets
		tweetsLengthBytes := readFrom(leaderConn, 4)
		tweetsLength := byteToInt(tweetsLengthBytes)

		tweets := readFrom(leaderConn, tweetsLength)

		//expand sharedSecret so it is of right length
		expandBy := len(tweets) / 32
		expandedSharedSecrets := make([][]byte, 2)

		for i := 0; i < 2; i++ {
			for j := 0; j < expandBy; j++ {
				expandedSharedSecrets[i] = append(expandedSharedSecrets[i], sharedSecret[i][:]...)
			}
		}

		//xors the received messge into the message to display
		for i := 0; i < 2; i++ {
			lib.Xor(expandedSharedSecrets[i][:], tweets)
		}

		index := strings.Index(string(tweets), ";;")

		if index != -1 {

			textArr := strings.Split(string(tweets), ";;;")
			text := textArr[:len(textArr)-1]

			if text[1] != "" {
				text[1] = text[1][1:]

			}
			ok := strings.Contains(text[0], text[1])
			if !ok {
				goodPadding++
			}

		} else if index == -1 && tweets[0] != 0 {
			fmt.Println("error")
			fmt.Println("round", round, string(tweets), "length", len(tweets))
			return
		}
	}
}

//creates a shared secret for each server
func createSharedSecret() [numClients][2][32]byte {
	var tmpSharedSecret [numClients][2][32]byte
	for i := 0; i < numClients; i++ {
		for j := 0; j < 2; j++ {
			_, err := rand.Read(tmpSharedSecret[i][j][:])
			if err != nil {
				panic("couldn't get randomness for sharedSecret!")
			}
		}
	}

	return tmpSharedSecret
}

func createAuditPIRQuery(clientNumber int) ([]byte, []byte) {
	//pirQuery [serverAmount][dbWriteSize]byte
	pirQuerys := make([][]byte, 2)
	for i := range pirQuerys {
		pirQuerys[i] = make([]byte, dbWriteSize)
	}

	//for leader
	//pirQuery will be filled with random bits
	for index := range pirQuerys[0] {
		bit := mr.Intn(2)
		pirQuerys[0][index] = byte(bit)
	}
	copy(pirQuerys[1], pirQuerys[0])

	//the positon the virtual address will be taken from
	pos := mr.Intn(dbWriteSize)
	pirQuerys[0][pos] = 1
	pirQuerys[1][pos] = 0

	//flattens the querys to be able to send them more efficently
	messagesFlattened := make([][]byte, 2)
	//adds the sharedSecret to the pirQuery
	for server := 0; server < 2; server++ {
		messagesFlattened[server] = append(messagesFlattened[server], sharedSecret[clientNumber][server][:]...)
	}

	for server := 0; server < 2; server++ {
		messagesFlattened[server] = append(messagesFlattened[server], pirQuerys[server][:]...)
	}

	var nonce [24]byte
	_, err := rand.Read(nonce[:])
	if err != nil {
		panic("couldn't get randomness for nonce!")
	}
	encryptedQueryLeader := box.Seal(nonce[:], messagesFlattened[0], &nonce, leaderPublicKey, clientPrivateKey[clientNumber])

	_, err = rand.Read(nonce[:])
	if err != nil {
		panic("couldn't get randomness for nonce!")
	}
	encryptedQueryFollower := box.Seal(nonce[:], messagesFlattened[1], &nonce, followerPublicKey, clientPrivateKey[clientNumber])

	return encryptedQueryLeader, encryptedQueryFollower
}

//generates a topicOfInterest array with random values
func addFakeInterests(max int, topicsOfInterest []int, doAuditing bool) []int {
	tmpNeededSubscriptions := neededSubscriptions
	if tmpNeededSubscriptions > len(topicList) {
		tmpNeededSubscriptions = len(topicList)
	}

	faketopicsOfInterest := make([]int, tmpNeededSubscriptions)
	maxInt := max

	//fills the array with unique random ascending values ranging from 0 to max
	for i := 0; i < tmpNeededSubscriptions; i++ {
		faketopicsOfInterest[i] = mr.Intn(maxInt)

		for j := 0; j < i; j++ {
			if faketopicsOfInterest[i] == faketopicsOfInterest[j] {
				i--
				break
			}
		}
	}

	if doAuditing {
		sort.Ints(faketopicsOfInterest)
		return faketopicsOfInterest
	}

	//adds unique and new random numbers to topicOfInterests until length is satisfied
	for _, number := range faketopicsOfInterest {
		if !inList(number, topicsOfInterest) {
			topicsOfInterest = append(topicsOfInterest, number)
		}
		if len(topicsOfInterest) == tmpNeededSubscriptions {
			break
		}
	}

	sort.Ints(topicsOfInterest)

	return topicsOfInterest
}

func inList(number int, list []int) bool {
	for _, element := range list {
		if element == number {
			return true
		}
	}
	return false
}

func receiveTopicLists(leaderConn net.Conn) {
	for i := 0; i < 2; i++ {
		topicListLength := readFrom(leaderConn, 4)

		recTopicList := readFrom(leaderConn, byteToInt(topicListLength))

		var tmpTopicList []string
		arrayReader := bytes.NewReader(recTopicList[:])
		json.NewDecoder(arrayReader).Decode(&tmpTopicList)
		if i == 0 {
			topicList = tmpTopicList
		} else {
			archiveTopicList = tmpTopicList
		}
	}
}

func SetGuiTweet(tweet string) {
	guiTweet = tweet
}

func getGuiTweet() []byte {

	if guiTweet == "" {
		tweet := make([]byte, dataLength)
		return tweet
	}

	var tweet []byte
	var topics []byte
	var text []byte

	tweetArray := strings.Split(guiTweet, "#")
	text = []byte(tweetArray[0])

	tweetArray = tweetArray[1:]
	for _, elem := range tweetArray {
		topics = append(topics, []byte(elem)[:]...)
		topics = append(topics, []byte(",")[0])
	}

	topics = topics[:len(topics)-1]

	tweet = append(tweet, topics...)
	tweet = append(tweet, []byte(";")[0])
	tweet = append(tweet, text...)
	tweet = append(tweet, []byte(";;")[:]...)

	//adds padding
	length := dataLength - len(tweet)
	padding := make([]byte, length)
	rand.Read(padding)
	tweet = append(tweet, padding...)

	publisherAmount++
	guiTweet = ""
	return tweet

}
func getRealTweet(clientNumber int) []byte {

	fUserList, err := os.Open("/home/simon/goCode/tweets/userList")
	if err != nil {
		panic(err)
	}

	defer fUserList.Close()

	currentLine := 0

	scanner := bufio.NewScanner(fUserList)
	userID := ""

	for scanner.Scan() {
		if currentLine == clientNumber {
			userID = scanner.Text()
			break
		}
		currentLine++
	}

	if userID == "" {
		panic("no userID picked")
	}

	fTweets, err := os.Open("/home/simon/goCode/tweets/userTweets/" + userID)
	if err != nil {
		panic(err)
	}

	defer fTweets.Close()

	scanner = bufio.NewScanner(fTweets)

	lowerBound := timeBounds[round-1]
	upperBound := timeBounds[round]

	var tweet []byte

	for scanner.Scan() {

		//skips round 1, cause of 90% publisher rate
		if round == 1 {
			break
		}

		lineArr := strings.Split(scanner.Text(), ", \"hashtags\"")
		lineArr = strings.Split(lineArr[0], ": ")
		lineArr = strings.Split(lineArr[1], " \"")

		timestamp, _ := strconv.Atoi(lineArr[0])

		//transforms timestamp to current time
		timestamp -= 1351742400
		timestamp += startTime

		if float64(timestamp) > lowerBound && float64(timestamp) < upperBound {
			lineArr = strings.Split(scanner.Text(), "[\"")
			line := lineArr[1]
			lineArr = strings.Split(line, "\"]")
			line = lineArr[0]
			lineArr = strings.Split(line, ",")
			line = strings.Join(lineArr, "")
			topicLine := strings.Split(line, "\"")

			var topics []byte
			for index, topic := range topicLine {
				if index%2 == 1 {
					continue
				}
				if len(topics)+len(topic) > dataLength-10 {
					break
				}
				topics = append(topics, []byte(topic)[:]...)
				topics = append(topics, []byte(",")[0])

			}

			if len(topics) == 0 {
				break
			}
			topics = topics[:len(topics)-1]

			tweet = append(tweet, topics...)
			tweet = append(tweet, []byte(";")[0])

			r := mr.New(mr.NewSource(time.Now().UnixNano()))
			num := r.Intn(10000)
			if num == 0 {
				num = 1
			}
			tweet = append(tweet, []byte(strconv.Itoa(num) + ";;")[:]...)

			//adds padding
			length := dataLength - len(tweet)
			padding := make([]byte, length)
			rand.Read(padding)
			tweet = append(tweet, padding...)

			publisherAmount++
			return tweet
		}
	}

	tweet = make([]byte, dataLength)

	return tweet
}

func getTimeBounds() {
	timeBounds = make([]float64, 10000)
	timeBounds[0] = float64(time.Now().Unix())

	for index := range timeBounds {
		if index == 0 {
			continue
		}
		timeBounds[index] = timeBounds[index-1] + speedUp*(3*maxTimePerRound.Seconds()+2)
	}
}

func getRandomTweet(clientNumber int) []byte {
	var tweet []byte

	r := mr.New(mr.NewSource(time.Now().UnixNano()))

	maxTopics := r.Intn(6)
	if maxTopics == 0 {
		maxTopics = 1
	}
	maxInt := 100
	topicNumbers := make([]int, maxTopics)
	//fills the array with unique random ascending values ranging from 0 to maxInt
	for i := 0; i < maxTopics; i++ {
		topicNumbers[i] = mr.Intn(maxInt)

		for j := 0; j < i; j++ {
			if topicNumbers[i] == topicNumbers[j] {
				i--
				break
			}
		}
	}

	sort.Ints(topicNumbers)
	var topics []byte

	topicIndex := 0
	for i := 0; i < len(topicNumbers)*2; i++ {
		if i%2 == 0 {
			topics = append(topics, byte(topicNumbers[topicIndex]))
			topicIndex++
		} else if i != (len(topicNumbers)*2)-1 {
			topics = append(topics, []byte(",")[0])
		}
	}

	topics = append(topics, []byte(";")[0])

	num := r.Intn(100)
	if num == 0 {
		num = 1
	}

	text := []byte(strconv.Itoa(num) + ";")
	tweet = append(tweet, topics...)
	tweet = append(tweet, text...)
	tweet = append(tweet, []byte(";")[0])

	//adds padding
	length := dataLength - len(tweet)
	padding := make([]byte, length)
	rand.Read(padding)
	tweet = append(tweet, padding...)

	return tweet
}

//sends the array to the connection
func writeTo(connection net.Conn, array []byte) {
	remainingLength := len(array)
	for remainingLength > 0 {
		if remainingLength >= mtu {
			_, err := connection.Write(array[:mtu])
			if err != nil {
				panic(err)
			}
			array = array[mtu:]
			remainingLength -= mtu
		} else {
			_, err := connection.Write(array)
			if err != nil {
				panic(err)
			}
			remainingLength = 0
		}
	}
}

//reads an array which is returned and of size "size" from the connection
func readFrom(connection net.Conn, size int) []byte {
	var array []byte
	remainingSize := size
	for remainingSize > 0 {
		var err error
		toAppend := make([]byte, mtu)
		if remainingSize > mtu {
			_, err = connection.Read(toAppend)
			array = append(array, toAppend...)
			remainingSize -= mtu
		} else {
			_, err = connection.Read(toAppend[:remainingSize])
			array = append(array, toAppend[:remainingSize]...)
			remainingSize = 0

		}
		if err != nil {
			panic(err)
		}
	}

	return array
}

func intToByte(myInt int) (retBytes []byte) {
	retBytes = make([]byte, 4)
	retBytes[3] = byte((myInt >> 24) & 0xff)
	retBytes[2] = byte((myInt >> 16) & 0xff)
	retBytes[1] = byte((myInt >> 8) & 0xff)
	retBytes[0] = byte(myInt & 0xff)
	return
}

func byteToInt(myBytes []byte) (x int) {
	x = int(myBytes[3])<<24 + int(myBytes[2])<<16 + int(myBytes[1])<<8 + int(myBytes[0])
	return
}