11

Java

Soc

kets

Ale

xand

er V

. Kon

stan

tinou

CS

4119

–C

ompu

ter

Net

wor

ksC

olum

bia

Uni

vers

ityS

prin

g 20

03

22

Coo

rdin

ates

TC

P, U

DP

IP

Eth

erne

t

SS

L

CO

RB

A, R

MI

App

licat

ion

IP

Eth

erne

t

TC

P, U

DP

IP

Eth

erne

t

SS

L

CO

RB

A, R

MI

App

licat

ion

App

licat

ion

Laye

r

Tra

nspo

rtLa

yer

Inte

rnet

Laye

r

Net

wor

kA

cces

sLa

yer

Soc

kets

Soc

kets

HT

TP

, FT

P, D

NS

, SM

TP

rem

oteO

bjec

t.met

hod(

arg)

33

Wha

t Are

Soc

kets

?

•P

rogr

amm

ing

abst

ract

ion

(AP

I)–

Equ

ival

ent:

File

I/O

AP

I

•N

etw

ork

serv

ice

end-

poin

t

•O

rigin

ated

as

BS

D U

NIX

con

cept

–N

ow p

art o

f mod

ern

OS

& la

ngua

ges

WW

WB

row

ser

OS

Net

wo

rkS

tack

Inte

rnet

Net

wor

kS

ervi

ceN

etw

ork

Clie

nt

AP

IP

roto

col

IP

44

File

vs.

Soc

ket A

PI

clos

e()

clos

e()

writ

e(by

tes)

writ

e(by

tes)

read

(byt

es)

read

(byt

es)

open

(des

tinat

ion)

st

ream

open

(file

nam

e)

stre

am

Net

wo

rkF

ile

Filef = new File("test");

FileInputStreamfis= new FileInputStream(f);

char c = fis.read();

fis.close();

Socket

s = new Socket("www.cs.columbia.edu", 80);

InputStreamis = s.getInputStream();

char c = is.read();

s.close();

55

Soc

ket T

ypes

•S

trea

min

gso

cket

s–

Poi

nt-t

o-po

int

–C

onne

ctio

n ba

sed

•B

i-dire

ctio

nal

–R

elia

ble,

in-o

rder

(F

IFO

)

•D

atag

ram

sock

ets

–P

oint

-to-

{poi

nt |

mul

tipoi

nt}

–C

onne

ctio

nles

s–

Non

-rel

iabl

e–

Out

-of-

orde

r de

liver

y–

Lim

ited

payl

oad

X

X

stre

am

buffe

r

66

Soc

kets

Adv

anta

ges

•C

omm

on p

rogr

amm

ing

abst

ract

ion

–S

epar

ate

the

netw

orki

ng s

tack

•A

pplic

atio

n fle

xibi

lity

–S

SL

inst

ead

of v

anill

a T

CP

–Lo

ggin

g &

per

form

ance

mea

sure

men

ts–

Tun

nelin

g

TC

PS

SL

http

brow

ser

http

sbr

owse

r

77

Java

Soc

ket A

PI O

verv

iew

Pro

toco

lT

ype

Cla

ss

TC

P s

erve

rS

trea

mja

va.n

et.S

erve

rSoc

ket

UD

P c

lient

/ser

ver

Dat

agra

mja

va.n

et.D

atag

ram

Soc

ket

SS

L cl

ient

Str

eam

java

x.ne

t.ssl

.SS

LSoc

ket

SS

L se

rver

Str

eam

java

x.ne

t.ssl

.SS

LSer

verS

ocke

t

TC

P c

lient

Str

eam

java

.net

.Soc

ket

88

Java

I/O

Str

eam

s

sock

et

Inpu

tStr

eam

/ Out

putS

trea

m

IPIP

IP

Buf

fere

d{In

put,O

utpu

t}S

trea

m

…7

4 5

6 1

3 0

…

…7

4 5

6 1

3 0

…

OS

OS

Dat

a{In

put,O

utpu

t}S

trea

m

Obj

ect{

Inpu

t, O

utpu

t)S

trea

m

{ id

=1,

des

cr=

“tes

t”}

123

“abc

”10

.1

File

I/O

File

I/O

99

Net

wor

k C

omm

unic

atio

n

•B

yte-

base

d–

Byt

e-st

ream

or

byte

-arr

ay

•P

roto

col t

ypes

–T

ext-

base

d: H

TT

P, S

MT

P, S

OA

P, …

–B

it-ba

sed:

DN

S, L

DA

P, S

NM

P …

•Is

sues

–T

ext:

enco

ding

(U

nico

de 1

6bit

8bit)

–B

it: b

yte

orde

ring

(littl

e/bi

g en

dian

)

1010

Net

wor

k P

orts

•In

tern

et h

ost a

ddre

ss–

Exa

mpl

e: 1

28.5

9.16

.1

•H

ow to

offe

r m

ultip

le s

ervi

ces?

–M

ailb

ox a

ppro

ach

–P

ort n

umbe

r ad

dres

sing

[1-6

5535

] (21

6 )–

Exa

mpl

e: 1

28.5

9.16

.1:T

CP

:80

IP H

ost

TC

P:8

0

TC

P:2

312

8.59

.16.

20

UD

P:5

3

http

d

nam

ed

teln

etd

Inte

rnet

1111

Exa

mpl

e: H

TT

P C

lient

:Bro

wse

r:W

WW

Ser

ver

TC

P C

on

nec

t

“GE

T /”

CR

CF

“CO

NT

EN

T-T

YP

E=t

ext/

htm

l CO

NT

EN

T-L

EN

GT

H=1

22 …

”

•T

rivia

l HT

TP

1.0

Clie

nt–

App

licat

ion-

laye

r pr

otoc

ol o

ver

TC

P

–T

ext-

base

d pr

otoc

ol

1212

HT

TP

Clie

nt (

No

Err

or H

andl

ing)

Socket

socket= new Socket(“www.cs.columbia.edu”, 80);

BufferedOutputStreamostream=

new BufferedOutputStream(socket.getOutputStream());

byte[] request = “GET /\r\n”.getBytes("ISO-8859-1");

ostream.write(request);

ostream.flush();

BufferedInputStreamistream=

new BufferedInputStream(socket.getInputStream());

byte[] buffer = new byte[4096];

intcount = istream.read(buffer);

while(count!= -1) {

System.out.print(newString(buffer, 0, count));

count = istream.read(buffer);

} socket.close();

1313

Str

eam

Soc

ket E

rror

Han

dlin

g

Socket

socket= null;

try {

socket = new Socket(“www.cs.columbia.edu”, 80);

// Perform I/O

} catch (Throwablee) {

// Application-specific error recovery

} finally{

socket.close();

}•N

etw

orks

fail!

–A

pplic

atio

ns m

ust b

e aw

are

of fa

ilure

s

•S

ocke

ts a

re s

carc

e O

S r

esou

rces

–D

on’t

rely

on

garb

age

colle

ctio

n; c

lose

() w

hen

done

!

1414

Ser

ver

Str

eam

Soc

kets

•B

ind

to p

ort (

e.g.

80)

•W

ait f

or in

com

ing

TC

P c

onne

ctio

n–

Enc

apsu

late

req

uest

as

Soc

keto

bjec

t–

Soc

ket p

air

now

com

mun

icat

e

Soc

ket

Ser

ver

Soc

ket

1. C

onne

ctne

w S

ocke

t(se

rver

, por

t)

Soc

ket

2. C

reat

e(r

etur

n to

acc

ept(

))

3. S

trea

m(b

idire

ctio

nal,

asym

met

ric)

clie

ntse

rver

1515

HT

TP

Ser

ver

(Triv

ial)

ServerSocket

server = new ServerSocket(8080);

while(active) {

Socketsocket= server.accept();

BufferedReaderreader = new BufferedReader

(new InputStreamReader

(new BufferedInputStream(socket.getInputStream())));

String request = reader.readLine();

BufferedOutputStreamostream=

new BufferedOutputStream(socket.getOutputStream());

ostream.write(“HTTP/1.0 404 HTTP NOT FOUND\r\n”);

ostream.flush();

socket.close();

} server.close();

1616

Java

Thr

eads

•W

hy p

aral

leliz

e?

–P

reve

nt b

lock

ing

from

mal

form

ed r

eque

sts

–D

eal w

ith w

ritin

g to

slo

w c

lient

s–

Inte

rleav

e pr

oces

sing

/file

rea

ding

•H

ow?

–M

ultip

le th

read

s

–S

hare

d m

emor

y–

Inte

rleav

ed e

xecu

tion

1717

Thr

eade

d S

erve

r P

atte

rnServerSocket

server =

new ServerSocket(80);

while(isActive) {

Socketsocket=

server.accept();

Handlerhandler

=new Handler(socket);

handler.start();

}

public class Handler

extendsThread{

protected final Socketsocket;

public Handler(Socketsocket) {

this.socket= socket;

} public void run() {

try {

// Protocol Impl.

} finally {

socket.close();

}}

}

1818

Dat

agra

m S

ocke

ts

•C

onne

ctio

nles

s

•U

nrel

iabl

e•

Lim

ited

payl

oad

–T

heor

etic

al 6

5508

byt

es–

Pra

ctic

al 5

12 b

ytes

(IE

TF

RF

C)

•W

hen

to u

se–

Sim

ple

requ

est-

resp

onse

pro

toco

l–

Sm

all r

eque

sts/

repl

ies

(fit

in d

atag

ram

)–

Sta

tele

ss/r

e-en

tran

t ser

vers

–R

eal-t

ime

stre

amin

g

Fra

gmen

tatio

n

1919

UD

P C

lient

Exa

mpl

eDatagramSocketsocket = new DatagramSocket();

byte[] data = "hello world".getBytes();

DatagramPacketpacket = new DatagramPacket

(data,

data.length,

InetAddress.getByName("localhost"),

1234);

socket.send(packet);

data = "followupcall".getBytes();

packet.setData(data);

socket.send(packet);

2020

UD

P S

erve

r E

xam

ple

DatagramSocketsocket = new DatagramSocket(1234);

byte[] buffer = new byte[512];

DatagramPacketpacket =

new DatagramPacket(buffer, buffer.length);

while(true) {

socket.receive(packet);

String msg=

new String(packet.getData(), 0, packet.getLength()));

System.out.println(newjava.util.Date() + ": " + msg);

packet.setLength(buffer.length); // !!! Necessary !!!

}

2121

Mul

ticas

t

•O

ne-t

o-m

any

tran

smis

sion

–S

peci

al r

ange

of I

P a

ddre

sses

•22

4.0.

0.0

–23

9.25

5.25

5.25

5

•S

ame

sock

et A

PI a

s U

DP

•N

ot u

nive

rsal

ly a

vaila

ble

2222

SS

L S

ocke

ts

•S

ecur

e co

mm

unic

atio

ns–

Laye

red

over

TC

P

•D

rop-

in r

epla

cem

ent (

subc

lass

es)

–S

ocke

t S

SLS

ocke

t–

Ser

verS

ocke

tS

SLS

erve

rSoc

ket

•K

ey m

anag

emen

t–keytool

com

man

d-lin

e ut

ility

–C

reat

es p

ublic

/priv

ate

keys

•S

tore

d in

“ke

ysto

res”

–Ja

va V

M in

voca

tion

with

key

stor

ein

fo

2323

Non

-Blo

ckin

g Ja

va I/

O

•T

hrea

d sc

alin

g is

sues

–E

.g. H

TT

P s

erve

r w

ith 1

000s

con

nect

ions

•JD

K 1

.4 in

trod

uced

non

-blo

ckin

g I/O

–P

erfo

rm a

ll pr

oces

sing

in o

ne th

read

–ja

va.n

io.*

pac

kage

2424

Soc

ket F

AQ

s

•W

rong

hos

t/por

t/pro

toco

l–

E.g

“loca

lhos

t”, “

127.

0.0.

1”, “

ww

w”

vs. “

ww

w.fo

o.co

m”

•Ig

norin

g I/O

exc

eptio

ns

•S

trea

ms:

–flu

sh()

whe

n do

ne–

use

buffe

red

read

er/s

trea

m–

clos

e co

nnec

tions

whe

n do

ne

•D

atag

ram

s–

pack

et.s

etLe

ngth

() b

efor

e re

use

–T

est i

n lo

ssy

envi

ronm

ent

2525

Soc

ket F

AQ

s(2

)

•W

ait-

fore

ver

–U

se S

ocke

t.set

SoT

imeo

ut()

–C

atch

Inte

rrup

tedI

OE

xcep

tion

•B

yte-

alig

nmen

t iss

ues

–N

etw

ork

byte

ord

er

•S

ecur

ity r

estr

ictio

ns (

appl

ets)

•U

nix

rest

ricts

non

-roo

t ser

vers

to p

orts

>10

24

2626

Adv

ance

d Is

sues

•T

hrea

d po

ols

–R

esou

rce

man

agem

ent

•B

indi

ng to

spe

cific

inte

rfac

es–

Bin

ding

to a

spe

cific

inte

rfac

e (s

ecur

ity)

•S

win

g ap

plic

atio

ns–

Sw

ing

is s

ingl

e th

read

ed

–N

etw

ork

oper

atio

ns in

non

-Sw

ing

thre

ad–

Use

Sw

ingU

tiliti

es.in

voke

Late

r()