리눅스 네트웍 프로그래밍 (CPL-TR-09-03)

(Linux Network Programming)

i

. ,

.

,

, .

Unix Network Programming: The Sockets Networking API (R. Stevens )

API .

.

.

TCP/IP A

.

,

lnp.h B .

http://protocol.knu.ac.kr/pub/lnp.h

,

, , , , .

2009 3

ii

1. .................................................................................................................................... 1

1.1 DAYTIME CLIENT ....................................................................................................... 2

1.2 WRAPPING FUNCTIONS ............................................................................. 4

1.3 DAYTIME SERVER ....................................................................................................... 5

1.4 TCP/IP ............................................................................... 7

2. : TCP, UDP, SCTP ..................................................................................... 9

2.1 USER DATAGRAM PROTOCOL (UDP).................................................................................... 11

2.2 TRANSMISSION CONTROL PROTOCOL (TCP) .......................................................................... 11

2.3 STREAM CONTROL TRANSMISSION PROTOCOL (SCTP).............................................................. 13

2.4 TCP ................................................................................................ 13

2.5 TIME_WAIT .......................................................................................................... 18

2.6 SCTP ASSOCIATION .................................................................................... 20

2.7 .................................................................................................................... 24

2.8 CONCURRENT ......................................................................................................... 25

2.9 .......................................................................................................... 28

3. SOCKETS ............................................................................................................ 33

3.1 SOCKET ADDRESS ................................................................................................. 33

3.2 VALUE-RESULT ARGUMENTS............................................................................................... 41

3.3 BYTE ORDERING ...................................................................................................... 43

3.4 BYTE MANIPULATION ................................................................................................ 47

3.5 INET_ATON, INET_ADDR, INET_NTOA ............................................................................. 48

3.6 INET_PTON, INET_NTOP ............................................................................................. 50

4. TCP SOCKETS.................................................................................................................... 53

4.1 SOCKET ................................................................................................................. 54

4.2 CONNECT .............................................................................................................. 56

4.3 BIND .................................................................................................................... 58

iii

4.4 LISTEN .................................................................................................................. 61

4.5 ACCEPT ................................................................................................................. 66

4.6 FORK EXEC ....................................................................................................... 69

4.7 CONCURRENT ......................................................................................................... 72

4.8 CLOSE .................................................................................................................. 75

4.9 GETSOCKNAME GETPEERNAME ............................................................................... 76

5. TCP CLIENT/SERVER .................................................................................................. 77

5.1 TCP ECHO SERVER .......................................................................................................... 78

5.2 TCP ECHO CLIENT........................................................................................................... 80

5.3 .................................................................................................. 82

5.4 .......................................................................................................... 87

5.5 ................................................................................................ 100

5.6 SIGPIPE .......................................................................................................... 103

5.7 ABNORMAL SERVER TERMINATION ..................................................................................... 105

5.8 TCP ........................................................................................................... 107

5.9 USER DATA FORMAT ...................................................................................................... 109

6. I/O MULTIPLEXING: SELECT()............................................................................................ 113

6.1 I/O .................................................................................................................... 114

6.2 SELECT ................................................................................................................ 121

6.3 STR_CLI : REVISITED ................................................................................................. 127

6.4 SHUTDOWN ......................................................................................................... 129

6.5 STR_CLI : REVISITED AGAIN........................................................................................ 131

6.6 TCP ECHO : REVISITED ............................................................................................ 132

6.7 PSELECT .............................................................................................................. 135

7. SOCKET OPTIONS ........................................................................................................... 137

7.1 GETSOCKOPT SETSOCKOPT .................................................................................. 137

7.2 SOCKET OPTION ..................................................................................... 139

7.3 GENERIC SOCKET OPTIONS .............................................................................................. 144

iv

7.4 IPV4 SOCKET OPTIONS ................................................................................................... 157

7.5 IPV6 SOCKET OPTIONS ................................................................................................... 159

7.6 TCP SOCKET OPTIONS ................................................................................................... 162

7.7 SCTP SOCKET OPTIONS.................................................................................................. 166

7.8 FCNTL ................................................................................................................ 179

8. UDP SOCKETS ................................................................................................................. 182

8.1 RECVFROM SENDTO ........................................................................................... 183

8.2 UDP ECHO ......................................................................................................... 184 8.3 UDP ECHO CLIENT ........................................................................................................ 187

8.4 LOST DATAGRAM .......................................................................................................... 189

8.5 SERVER NOT RUNNING ................................................................................................... 193

8.6 UDP .......................................................................................................... 195

8.7 UDP CONNECT ................................................................................... 197

8.8 FLOW CONTROL UDP......................................................................................... 203

8.9 UDP OUTGOING INTERFACE .......................................................................... 206

9. SCTP SOCKETS ................................................................................................................ 207

9.1 INTERFACE ........................................................................................................... 208

9.2 SCTP_BINDX SCTP_BINDX .................................................................................... 213

9.3 SCTP ................................................................................................... 216

9.4 SCTP_SENDMSG ..................................................................................................... 218

9.5 SCTP_RECVMSG ..................................................................................................... 219

9.6 SCTP_OPT_INFO ..................................................................................................... 219

9.7 SCTP_PEELOFF ....................................................................................................... 220

9.8 SHUTDOWN ......................................................................................................... 221

9.9 NOTIFICATIONS............................................................................................................. 222

10. SCTP CLIENT/SERVER ............................................................................................ 228

10.1 SCTP ONE-TO-MANY STYLE STREAMING ECHO SERVER ......................................................... 229

10.2 SCTP ONE-TO-MANY STYLE STREAMING ECHO CLIENT .......................................................... 231

10.3 SCTP STREAMING ECHO CLIENT ....................................................................................... 234

v

10.4 HOL(HEAD-OF-LINE) BLOCKING ....................................................................................... 236

10.5 STREAM ...................................................................................................... 244

10.6 ....................................................................................................... 245

A. TCP/IP ............................................................................................. 247

A.1 ............................................................................................................... 248

A.2 ............................................................................................ 251

A.3 ............................................................................................................... 255

A.4 .................................................................................................... 258

A.5 ............................................................................................................... 262

A.6 INTERNET PROTOCOL (IP).................................................................................................... 263

A.7 USER DATAGRAM PROTOCOL (UDP)...................................................................................... 269

A.8 TRANSMISSION CONTROL PROTOCOL (TCP) ............................................................................ 271

A.9 STREAM CONTROL TRANSMISSION PROTOCOL (SCTP) ............................................................... 276

A.10 ..................................................................................................... 278

B. LNP.H .......................................................................................................... 282

1

1.

Client-Server .

(daemon) Client . Client

. 1.1 Client

.

Client-Server

Client ,

(layer) . TCP/IP . , Client

TCP . TCP IP(Internet Protocol) , IP

. 1.2 TCP/IP .

2

1.1 DAYTIME CLIENT

. Client TCP

, .

-------------------------------------------------------------------------- 1 #include lnp.h 2 int 3 main (int argc, char **argv) 4 { 5 int sockfd, n; 6 char revline[MAXLINE + 1]; 7 struct sockaddr_in servaddr; 8 if (argc !=2) 9 err_quit (usage: a.out ); 10 if ((sockfd = socket(AF_INET, SOCK_STREAM, 0))

3

Header

lnp.h ,

. header header

.

Command-line

command-line main .

TCP socket

socket Internet(AF_INET), stream(SOCK_STREAM) socket TCP

socket . descriptor , (connect,

read) socket . if socket , sockfd

, 0 . socket

, socket() sockets API .

socket err_sys . , error message

. err_

.

Server IP port

Internet socket address (serrvaddr) server IP port .

, bzero() , address family AF_INET

, port 13 (daytime server well-known port ) , IP command-

line (argv[1]) . , IP port

, htons("host to network short") inet_pton("presentation to numeric")

.

Server

TCP , connect() socket address

server TCP . Connect() socket address

, sizeof operator .

4

Server

Server fputs() . Server

26-byte string .

Mon May 26 20:58:40 2003

TCP segment 26 byte data . data

read() data . , TCP socket

, read() loop read 0 ( )

0 (error) loop .

exit() . descriptor

TCP socket .

1.2 WRAPPING FUNCTIONS

. socket(), inet_pton(), connect(), read(), fputs()

, err_quit(), err_sys()

.

, wrapper .

socket() (wrapping) Socket() .

sockfd = Socket (AF_INET, SOCK_STREAM, 0);

Socket() wrapper function .

-------------------------------------------------------------------------- int Socket (int family, int type, int protocol) { int n; if ( ( n = socket(family, type, protocol)) < 0) err_sys(socket error); return (n); } --------------------------------------------------------------------------

5

wrapper .

Unix/Linux API error , errno error type

, -1 . err_sys() errno

( , errno ETIMEOUT Connection timed out"

). errno . .

'E'

.

1.3 DAYTIME SERVER

1.4 Daytime Client TCP Daytime Server .

Server well-known port socket bind

bind() socket address server well-known port(daytime service

13) . Server host interface IP

INADDR_ANY interface server client .

Socket listening socket

listen() socket listening socket . TCP server socket,

bind, listen 3 listening descriptor( listenfd) . LISTENNQ

lnp.h . client kernel listening descriptor

queue .

-------------------------------------------------------------------------- 1 #include lnp.h 2 #include 3 int 4 main (int argc, char **argv) 5 { 6 int listenfd, connfd; 7 struct sockaddr_in servaddr; 8 char buff [MAXLINE]; 9 time_t ticks; 10 listenfd = Socket (AF_INET, SOCK_STREAM, 0); 11 bzero (&servaddr, sizeof(servaddr)); 12 servaddr.sin_family = AF_INET;

6

13 servaddr.sin_addr.s_addr = htonl (INADDR_ANY); 14 servaddr.sin_port = htons (13); /* daytime server */ 15 bind (listendfd, (SA *) &servaddr, sizeof (servaddr)); 16 Listen (listendfd, LISTENQ); 17 for ( ; ; ) { 18 connfd = Accept (listenfd, (SA *) NULL, NULL); 19 ticks = time(NULL); 20 snprintf (buff, sizeof (buff), %.24s\r\n, ctime(&ticks)); 21 Write (connfd, buff, strlen (buff)); 22 close (connfd); 23 } 24 } --------------------------------------------------------------------------

TCP Daytime Server

Client

server process accept() client .

TCP three-way handshake , handshake accept()

, connected descriptor descriptor . ( listening descriptor

). connected descriptor client ,

listening socket client . client

17 line loop .

library time() , 1970 1 1 0 0

0 Coordinated Universal Time(UTC)

. library ctime() .

Mon May 26 20:58:40 2003

Server close() client . TCP

. TCP FIN , FIN (ACK) .

1.4 server client

iterative server . client concurrent server

. fork() (4) client

child process . fork() thread()

pre-fork server children process .

7

Daytime Client Server .

daytimetcpcli.c daytimetcpsrv.c

1.4 TCP/IP

OSI(Open System Interconnection) model . model 7

(layer) , 1.6 Internet protocol suite layer

.

OSI , TCP/IP

8

OSI layer 2 layer system device driver networking hardware.

1500 (byte) MTU(maximum transfer unit) (Ethernet) data link

layer .

Network layer IPv4 IPv6 . Transport layer 2 TCP UDP

( 9 10 SCTP ). 1.6 TCP UDP

application transport layer IPv4, IPv6

. raw socket (ICMP raw socket ).

OSI model 3 layer application layer . Web client (browser), Telnet client,

Web server, FTP server application . Internet protocol OSI model

3 layer .

Socket programming interface application transport layer interface

. (TCP UDP socket application

). Raw socket .

1.6 . transport layer

(interface) socket API . application (: FTP, Telnet, HTTP)

4

(: data , , ). ,

TCP/IP

( (abstraction) ). API

user process 4 OS(operating system) (kernel)

. Unix/Linux OS user process kernel . socket

API .

9

2. : TCP, UDP, SCTP

TCP/IP TCP, UDP, SCTP

. client/server application TCP UDP . SCTP

VoIP(Voice over IP) (signaling) mission-critical

. TCP, UDP

SCTP .

UDP (reliability) , TCP

byte stream protocol. SCTP TCP

(message) transport level

multi-homing, multi-streaming .

, transport

protocol .

.

, TCP/IP TCP, IP .

2.1 TCP/IP .

TCP/IP

10

IPv4 IPv6 . IPv4 IPv6

AF_INET AF_INET6 . application tcpdump BSD

packet filter(BPF) datalink provider interface(DLPI) datalink

. 9 API

. traceroute program IP ICMP socket .

2.1 .

IPv4 Internet Protocol version 4. 32-bit . IPv4 TCP, UDP, SCTP, ICMP,

IGMP packet service .

IPv6

Internet Protocol version 6. IPv6 1990 IPv4

. 1990 Internet 128-bit .

IPv6 TCP, UDP, SCTP, ICMPv6 packet service .

IP" IP IP , IPv4

IPv6 .

TCP

Transmission Control Protocol. TCP

(full-duplex) byte stream . TCP socket stream socket

. TCP , .

TCP . TCP IPv4 IPv6 .

UDP

User Datagram Protocol. UDP connectionless protocol datagram socket

. UDP . TCP

UDP IPv4 IPv6 .

SCTP Stream Control Transmission Protocol. TCP , multi-homing multi-

streaming . TCP, UDP, SCTP IPv4 IPv6 .

ICMP

Internet Control Message Protocol. ICMP IP

. ping traceroute ICMP . message

user process TCP/IP networking software

. ICMPv6 ICMPv4 .

IGMP Internet Group Management Protocol. IPv4 multicasting .

ARP

Address Resolution Protocol. ARP IPv4 hardware ( Ethernet

) . ARP Ethernet, token ring, FDDI broadcast

network point-to-point network .

11

ICMPv6 Internet Control Message Protocol version 6 . ICMPv4, IGMP, ARP

.

BPF BSD Packet Filter . datalink layer

.

2.1 USER DATAGRAM PROTOCOL (UDP)

UDP transport-layer protocol. (application) UDP socket message

UDP datagram IP datagram .

UDP datagram network

. , UDP datagram

, checksum, error , .

UDP service , UDP client server

. , UDP client socket datagram

datagram . UDP server

UDP client datagram UDP socket .

2.2 TRANSMISSION CONTROL PROTOCOL (TCP)

TCP application service UDP service . TCP client

server (connection) . TCP client server data

.

TCP . TCP data

ACK(acknowledgment) . ACK TCP data

.

4~10 (network ). TCP

100% . , endpoint data

(: ) .

TCP .

12

TCP client server RTT(Round Trip Time) . RTT

network traffic TCP TCP RTT

.

TCP (error recovery) . byte data

. application 2048 byte TCP socket TCP

segment segment 1~1024 data

segment 1025~2048 data (segment TCP IP data .).

data (sequence

number) ( reordering ). data

( )

(discard) . , UDP . UDP ACK,

, RTT, timeout, . , UDP datagram

network host data .

TCP flow control . TCP data byte

. advertised window . window buffer

sender overflow . window

. Sender data window

application buffer data window . window 0

. TCP buffer data

application buffer . , UDP flow

control . UDP sender UDP receiver

datagram .

TCP (full-duplex) . application

. TCP sender, receiver

window . UDP .

13

2.3 STREAM CONTROL TRANSMISSION PROTOCOL (SCTP)

SCTP UDP, TCP service . SCTP RFC 2960 , RFC 3309

update . SCTP client server association ( TCP connection

). SCTP TCP , , flow control, data

application . SCTP (connection) association'

SCTP multi-homing . SCTP system

2 IP .

TCP SCTP message-oriented. , TCP UDP

. SCTP

multiple stream multi-streaming . stream

message stream . stream

data

TCP .

SCTP SCTP endpoint IP multi-homing .

network network . SCTP ()

SCTP association .

2.4 TCP

TCP connect(), accept(), close() TCP

TCP (state transition diagram) .

Three-Way Handshake

TCP scenario .

1) Server . socket, bind,

listen passive open .

2) Client connect() active open . TCP client

data server synchronize"(SYN) segment

. SYN IP

header, TCP header .

14

3) Server client SYN ACK data

. Server SYN segment client SYN ACK .

4) Client sever SYN ACK .

3 packet TCP three-way

handshake . 2.2 .

TCP

Client J server K . ACK

data . SYN 1byte ACK acknowledgment

SYN 1 .

TCP Connection Termination

2.3 3 segment , 4

segment .

1) application close active close . TCP

FIN segment .

2) FIN passive close . TCP FIN ACK

. FIN data .

3) application socket close. TCP FIN .

4) TCP FIN (active close ) FIN ACK .

15

TCP

FIN ACK 4 segment .

FIN data . 2, 3

segment passive close segment .

SYN FIN 1-byte (sequence number) . FIN ACK

FIN 1 .

2 3 passive close active close data

. half-close 6 shutdown .

2.3 client active close server active close

. client active close HTTP protocol server .

TCP State Transition Diagram

TCP 2.4 (state transition diagram)

. 11 (state)

segment . , application CLOSED

active open TCP SYN SYN_SENT . TCP

SYN ACK ACK ESTABLISHED .

data .

16

TCP

ESTABLISHED . Application

(EOF: end of file) close (active close), FIN_WAIT_1 .

application ESTABLISHED FIN (passive close) CLOSE_WAIT

. client sever .

(simultaneous open) (simultaneous close, FIN

) .

17

TCP netstat 5 .

Watching the Packet

2.5 , data , TCP packet . ,

endpoint TCP .

Client MSS 536 server MSS 1460 (Ethernet MTU

) . MSS .

client server . segment

(, server 1460 ) . Server

segment ( 536 ) .

Data segment . Client ACK .

piggybacking , server

200ms ACK piggybacking . ACK

.

4 segment , active close ( client)

TIME_WAIT . .

2.5 TCP segment

segment , TCP 10 segment .

UDP 2 segment (

). UDP TCP UDP

application . TCP (congestion control)

UDP application . , application data

UDP .

18

TCP

2.5 TIME_WAIT

TCP network programming TIME_WAIT .

2.4 active close .

maximum segment lifetime(MSL) , 2MSL .

TCP MSL . RFC1122 2 , Berkeley

30 . TIME_WAIT 1 4

19

. MSL IP datagram network .

packet Internet MSL .

Packet routing . Router

router routing protocol

. routing loop loop packet .

TCP segment ,

. ( packet MSL) routing loop packet

. packet lost duplicate wandering

duplicate . TCP .

TIME_WAIT .

1. (full-duplex)

2. Network segment

2.5 client ACK

. Server FIN client ACK

FIN client . client TIME_WAIT

, client server FIN , RST(reset)

. TCP 4 segment

. TCP active close

TIME_WAIT ACK .

TIME_WAIT , 1.1.1.1 port 1500 2.2.2.2

21 TCP . IP

port . IP port

(incarnation) . TCP

. TCP TIME_WAIT

( port ) .

TCP .

20

2.6 SCTP ASSOCIATION

SCTP TCP connection-oriented association

. SCTP handshake TCP .

Four-Way Handshake

TCP scenario SCTP association . , Server

client . socket, bind, listen

passive open .

1) Client connect active open . client SCTP INIT

message server IP , sequence number association

.

2) Server IP , , initiation tag , state cookie

INIT-ACK message client . cookie

COOKIE-ECHO .

3) Client server cookie COOKIE-ECHO message .

message packet user data .

4) Server cookie client COOKIE-ACK message

association . message packet user data .

4 packet SCTP four-way handshake .

2.6 4 segment .

SCTP

21

SCTP four-way handshake cookie TCP three-way

handshake . INIT ( chunk) initiation tag(Ta) initial sequence

number(J) . Ta SCTP association

packet (SCTP verification tag

). J TCP data chunk . initiation tag(Tz),

(K) cookie C INIT-ACK chunk .

Cookie , Cookie 3 COOKIE-ECHO ,

client . TCP SYN-Flooding DoS(denial of service)

attack . SCTP four-way handshake DoS

Cookies . COOKIE-ACK SCTP association

.

Association Termination

TCP SCTP half-closed" . association

data . data queue

. 2.6 .

SCTP

SCTP initiation tag association TCP TIME_WAIT

. chunk INIT chunk INIT-ACK chunk initiation tag

. tag

. SCTP TCP .

22

SCTP State Transition Diagram

2.8 SCTP (State transition diagram) .

SCTP

chunk . ,

application CLOSED active open SCTP INIT

COOKIE-WAIT . SCTP INIT-ACK COOKIE-ECHO

COOKIE-ECHOED . SCTP COOKIE-ACK ESTABLISHED

23

. , COOKIE-ECHO COOKIE-ACK chunk chunk piggybacking

.

ESTABLISHED . application active

close (outstanding) DATA chunk SHUTDOWN-PENDING

, SHUTDOWN chunk SHUTDOWN-SENT .

ESTABLISHED SHUTDOWN (passive close), SHUTDOWN-RECEIVED

SHUTDOWN-ACK chunk . SHUTDOWN-ACK-SENT

(, release),

SHUTDOWN-COMPLETE chunk .

Watching the Packets

2.9 SCTP .

SCTP

24

client COOKIE-ECHO data chunk piggyback COOKIE-ACK server

data . COOKIE-ECHO one-to-many socket interface

application data chunk . one-to-one

socket data chunk . 9 .

SCTP chunk'. 'chunk' chunk type, chunk flags, chunk length

, DATA chunk control chunk . SCTP packet

data/control chunk .

2.7

process , transport protocol(TCP, UDP, SCTP) 16-

bit port process . TCP, UDP, SCTP

() well-known port . , FTP TCP well-

known port number 21 , TFTP(Trivial FTP) server UDP port 69 .

client ephemeral (dynamic or private) port .

client port client host .

Internet Assigned Number Authority (IANA) port . RFC

1700 . http://www.iana.org/ On-line database . Port 3

.

1) Well-known port: 0 ~ 1023. port IANA

. TCP, USP, SCTP port . ,

TCP , TCP UDP Web server port 80 .

2) Registered port: 1024 ~ 49151. IANA , IANA

list port. TCP UDP port .

, port 6000 6063 protocol X window server

, TCP .

3) Dynamic or Private port: 49152 ~ 65535. IANA port .

client port . (49152 65536 3/4 )

25

2.10 port .

Socket pair

TCP Socket pair endpoint local IP , local port, IP

, port. socket pair network TCP . SCTP

local IP , local port, IP , port .

TCP multi-homed .

endpoint IP port socket .

UDP connectionless protocol socket UDP

. Socket (bind, connect, getpeername ) ,

() . , TCP, UDP, SCTP bind() local IP

local port .

2.8 CONCURRENT

iterative server concurrent . UDP TCP

SCTP concurrent . Concurrent server server client

child process child

port ? .

server freebsd host 12.106.32.254 192.168.42.1 IP

port ( 21) passive open . 2.11

client .

26

Concurrent Server

{8:21, *:*} socket pair . Server port 21 local interface( *) bind

client . IP port *.*

. listening socket . IP port :

(HTTP ).

local IP (wildcard) . Server host

multi-homed (), server .

server . Server . local

(*) . 1 bind() socket

IP INADDR_ANY .

, client IP 206.168.112.219 host 12.106.32.254 server

active open . dynamic port 1500 . 2.12

. Client socket pair .

client

27

2.13 , server client fork()

(child process) child process client . (fork

4 .)

child process

server host listening socket connected socket .

Connected socket listening socket 21 port . Multi-homed

connected socket local IP (12.106.32.254) .

, client host client process server

. client socket dynamic port (1501) .

2.14 . Server . socket pair

socket pair , client dynamic port(1501)

.

28

client socket

TCP segment endpoint socket pair 4

. 2.14 local port(21) 3 socket

(2 connected socket 1 listening socket). {206.168.112.219, 1500}

{12.106.32.254, 21} segment child . ,

{206.168.112.219, 1501} {12.106.32.254, 21} segment child

. Port 21 segment listening socket .

2.9

network MTU . Ethernet MTU

1,500 byte. host MTU (path) MTU .

1,500byte Ethernet MTU MTU . Internet

MTU . A B B A

.

29

IP datagram , link MTU IPv4 IPv6 (fragmentation)

. . IPv4 host datagram

, IPv4 router datagram . IPv6

datagram IPv6 router datagram .

IPv4 header don't fragment"(DF) host router

. DF link MTU datagram

ICMPv4 destination unreachable, fragmentation needed but DF bit set"

error message . IPv6 router datagram DF

. IPv6 link MTU datagram ICMPv6 packet too big"

error message .

TCP data MSS(Maximum Segment Size) . MSS

. MSS link MTU IP header TCP header . 1500 byte MTU

Ethernet, IPv4 MSS 1,460 byte IPv6 MSS 1,440 byte (TCP header 20

byte, IPv4 header 20 byte, IPv6 header 40 byte ).

TCP Output

2.15 application TCP socket data .

TCP socket buffer SO_SNDBUF socket option

(7). Application write() , kernel application buffer data socket

buffer . socket buffer application buffer data

(application buffer socket buffer , socket buffer data

) process (sleep) . socket .

Application buffer byte socket buffer write()

. , TCP socket write() application buffer

. TCP data application

data . TCP

, .

30

TCP

TCP data (transmission) socket buffer data

TCP . TCP data (acknowledgment)

TCP ACK TCP socket buffer . TCP

data .

TCP data MSS segment , MSS

default 536 byte . IP header

routing table IP (routing table interface

) link . IP datagram datalink

. datalink queue queue packet

protocol stack (datalink IP, IP TCP) . TCP error

segment . application .

31

UDP Output

2.16 application UDP socket data .

UDP

UDP socket buffer . UDP socket

buffer socket UDP datagram

. application socket buffer datagram EMSGSIZE

. UDP application data

buffer .

UDP datagram 8 byte header IP . IPv4 IPv6

header routing interface datagram datalink

queue (MTU ) datagram datalink queue

. TCP application data MSS UDP .

UDP socket write datagram datagram datalink

queue . queue datagram

ENOBUFS application .

32

SCTP Output

2.17 application SCTP socket data .

SCTP

SCTP TCP protocol buffer . TCP application

SO_SNDBUF buffer (7). Application write()

, kernel application buffer data socket buffer .

Application buffer byte socket buffer write .

SCTP SCTP data (transmission) socket buffer data SCTP

. SCTP socket buffer data SCTP SACK

.

33

3. SOCKETS

socket API . socket

address . : process kernel

kernel process . kernel process value-

result argument . argument .

Protocol socket address sock_

. code protocol .

3.1 SOCKET ADDRESS

socket argument socket address . protocol

suite socket address . sockaddr_

protocol suite .

IPv4 Socket Address

Internet socket address IPv4 socket address

header socketaddr_in .

struct in_addr {

in_addr_t s_addr; /* 32-bit IPv4 address */

/* network byte ordered */

};

struct sockaddr_in {

uint8_t sin_len; /* length of structure */

sa_family_t sin_family; /* AF_INET */

in_port_t sin_port; /* 16-bit TCP or UDP port number */


struct in_addr sin_addr; /* 32-bit IPv4 address */


char sin_zero[8]; /* unused */

34

socket address .

sin_len, length member OSI protocol , 4.3BSD-Reno .

sin_len , member unsigned short sin_family. vender

socket address length field , POSIX

member . uint8_t datatype. POSIX

datatype .

socket address length field .

length field , routing socket

. protocol( routing table code) socket address

routine kernel .

processt kernel socket address 4 (bind, connect, sendto,

sendmsg) Berkeley sockargs . process

socket address ,

sin_len member . Kernel process socket address

5 socket (accept, recvfrom, recvmsg, getpeername, getsockname)

process return sin_len member .

socket address length field

compile-time test . Code HAVE_SOCKADDR)SA)LEN

.

member

. socket address length field IPv6 SIN6_LEN

. IPv4 compile-time option(

_SOCKADDR_LEN) socket address length field .

.

POSIX 3 member : sin_family, sin_addr, sin_port.

POSIX member , Internet

socket address . sin_zero member

. socket address 16byte.

s_addr, sin_family, sin_port member POSIX datatype . in_addr_t datatype

35

32bit unsigned integer type , sa_family_t unsigned integer type

. length field , 8 bit unsigned integer,

16 bit unsigned tnteger.

POSIX datatype POSIX datatype .

Datatype Description Header

int8_t

uint8_t

int16_t

uint16_t

int32_t

uint32_t

Signed 8-bit integer

Unsigned 8-bit integer





sa_family_t

socklen_t

Address family of socket address structure

Length of socket address structure, normally uint32_t

in_addr_t

in_port_t

IPv4 address, normally uint32_t

TCP or UDP port, normally uint16_t

unsigned u_char, u_short, u_int, u_long datatype . POSIX

. datatype .

IPv4 TCP UDP port network byte .

member .

32-bit IPv4 address access . , serv

Internet socket address , serv.sin_addr in_addr 32-bit

IPv4 address , serv.sin_addr.s_addr in_addr_t( unsigned 32-bit

integer) 32-bit IPv4 address . , IPv4 address

. integer

.

in_addr_t sin_addr member . union

in_addr (4.2 BSD) 32-bit IPv4 address 16-bit

36

4byte access . address byte class A, B,

C . subnetting classless addressing address class

union . union

in_addr_t member in_addr .

sin_zero member . 0

. sin_zero member 0

.

non-wildcard IPv4 address bind , member 0

, member 0.

Socket address host : host

, field( , IP address port) .

(generic) Socket Address

Socket address socket reference

. socket protocol

socket address .

type . ANSI C,

: void* pointer type. socket ANSI C 1982

socket address

.

struct sockaddr {

uint8_t sa_len; sa_family sa_family; /* address family: AF_xxx value */ char sa_date[14]; /* protocol-specific address */

};

37

socket ANSI C bind prototype , socket

address :

int bind(int, struct sockaddr *, socklen_t);

socket address

protocol socket address . ,

struct sockaddr_in serv; /* IPv4 socket address structure */

/* fill in serv{} */

bind(sockfd, (struct sockaddr *) &serv, sizeof(serv));

(struct sockaddr *) , C bind

ANSI C prototype , warning: passing arg2 of bind from incompatible

pointer type, warning .

application programmer , socket address

protocol .

1 lnp.h ,

struct sockaddr SA .

kernel , socket address

kernel , struct sockaddr * .

type sa_family . application programmer

. type void* , .

38

IPv6 Socket Address

IPv6 socket address .

struct in6_addr { uint8_t s6_addr[16]; /* 128-bit IPv6 address */ /* network byte ordered */

}; #define SIN6_LEN /* required for compile-time tests */ struct sockaddr_in6 { uint8_t sin6_len; /* length of this struct (28) */ sa_family_t sin6_family; /* AF_INET6 */ in_port_t sin6_port; /* transport layer port# */ /* network byte ordered */ uint32_t sin6_flowinfo; /* flow information, undefined */ struct in6_addr sin6_addr; /* IPv6 address */ /* network byte ordered */ uint32_t sin6_scope)id; /* set of interfaces for a scope */

};

socket address length member , SIN6_LEN

.

IPv6 family AF_INET6, IPv4 family AF_INET.

member . sockaddr_in6 64-bit

, 128-bit sin6_addr member. 64-bit 64-bit data 64-bit

.

sin6_flowinfo member .

- 20bit flow label.

- 12bit .

sin6_scope_id . link-local

interface index.

39

Socket Address

socket address IPv6 socket API , struct sockaddr

. struct sockaddr , struct sockaddr_storage

socket address . sockaddr_storage

, .

struct sockaddr_storage {

uint8_t ss_len; /* length of this struct */

sa_family_t ss_family; /* address family: AF_xxx value */

/* implementation-dependent elements to provide:

* a) alignment sufficient to fulfill the alignment requirements of

* all socket address types that the system supports.

* b) enough storage to hold any type of socket address that the

* system supports.

*/

sockaddr_storage type struct sockaddr socket address

.

a) socket address ,

sockaddr_storage .

b) sockaddr_storage socket address

.

sockaddr_storage field ss_family ss_len( ) ,

. sockaddr_storage field access ss_family

socket address casting .

40

Socket Address

socket address : IPv4, IPv6,

Unix domain, datalink, storage. , socket address byte length field

. family field 1 byte . bit field

bit .

socket address

socket address , Unix domain

datalink . , socket

socket address , .

byte (4.4BSD ) .

Sockaddr_un . ( )

. , socket address (

) kernel .

sockaddr_in{} .

41

3.2 VALUE-RESULT ARGUMENTS

Socket address socket , reference

. , . .

: process kernel, .

1. , bind, connect, sendto, process kernel socket address

. socket address .

.

sturct sockaddr_in serv;

/* fill in serv{} */

connect (sockfd, (SA *) &serv, sizeof(serv));

kernel , process kernel

data . .

socket address

socket address datatype int socklen_t

chapter . POSIX socklen_t uint32_t .

42

2. 4 , accept, recvfrom, getsockname, getpeername kernel

process socket address .

socket address .

struct sockaddr_un cli; /* Unix domain */

socklen_t len;

len = sizeof(cli); /* len is a value */

getpeername(unixfd, (SA *) &cli, &len);

/* len may have changed */

, (kernel

kernel .)

( kernel process ).

value-result . .

socket address

43

process kernel socket address . 4.4

BSD , socket kernel .

, System V, socket process

. kernel protocol stack

. , , bind

connect process kernel

.

Socket address length field value-result , socket

address , kernel :

IPv4 sockaddr_in 16 IPv6 sockaddr_in 28. socket address

(, Unix sockaddr_un),

.

, value-result socket address

. value-result .

select (6)

getsockopt (7)

3.3 BYTE ORDERING

2bytes 16 bit . 2bytes :

little-endian byte , address byte, big-endian byte

, address byte. .

44

Little-endian Big-endian

,

. 16bit bit bit(MSB)

bit bit(LSB) . , byte

. . host byte order

byte .

host byte order .

--------------------------------------------------------------------------

1 #include lnp.h 2 int 3 main(int argc, char **argv) 4 { 5 union { 6 short s; 7 char c[sizeof(short)]; 8 }un; 9 un.s = 0x0102; 10 printf(%s: , CPU_VENDOR_OS); 11 if(sizeof(short) == 2) { 12 if(un.c[0] == 1 && un.c[1] == 2) 13 printf(big-endian\n); 14 else if (un.c[0] == 2 && un.c[1] == 1) 15 printf(little-endian\n); 16 else 17 printf(unknown\n); 18 } else 19 printf(sizeof(short) = %d\n, sizeof(short)); 20 exit(0); 21 }

-------------------------------------------------------------------------

45

byteorder.c

short integer 2byte 0x0102 c[0]( A) c[1]( A+1) byte

order . CPU_VENDOR_OS

, CPU , OS , GNU autoconf .

.

freebsd4 % byteorder

i386-unknown-freebsd4.8: little-endian

macosx % byteorder

powerpc-apple-darwin6.6: big-endian

freebsd5 % byteorder

sparc64-unknown-freebsd5.1: big-endian

aix % byteorder

powerpc-ibm-aix5.1.0.0: big-endian

hpux % byteorder

hppa1.1-hp-hpux11.11: big-endian

linux % byteorder

i586-pc-linux-gnu: little-endian

solaris % byteorder

sparc-sun-solaris2.9: big-endian

46

16-bit byte ordering ; , 32-bit .

byte ordering .

network byte order . , TCP , 16-bit 32-

bit IP . multi-byte byte

. Internet multibyte big-endian byte

ordering .

, host byte order socket address .

byte order host byte order .

. POSIX

socket address byte field .

host byte order byte order . byte order

.

#include

uint16_t htons (uint16_t host16bitvalue);

uint32_t htonl (uint32_t host32bitvalue);

Both return : value in network byte order

uint16_t ntoh(uint16_t net16bitvalue);

uint32_t ntoh(uint32_t net32bitvalue);

Both return : value in host byte order

, h host , n network , s short , l

long . short long 4.2BSD Digital VAX . s

16-bit (TCP UDP port ) , l 32-bit (IPv4 ) .

, 64-bit Digital Alpha long 64bit . htonl ntohl 32-bit

.

, host byte order byte order (big-endian

little-endian) . host

byte order . Internet

byte ordering , null .

47

3.4 BYTE MANIPULATION

data interpreting, data C null-terminated , multibyte

. socket address ,

. IP 0 byte , C

character . (string

) str null-terminated C character .

b(byte ) 4.2BSD

socket . mem(memory )

ANSI C ANSI C

.

bzero, Berkeley-derived .

, bcopy bcmp .

#include

void bzero(void *dest, size_t nbytes);

void bcopy(const void *src, void *dest, size_t n_bytes);

void bcmp(const void *ptr1, const void *ptr2, size_t nbytes);

Returns: 0 if equal, nonzero if unequal

bzero destination byte 0 .

socket address 0 . bcopy source destination

byte . bcmp byte string .

byte string 0; 0 .

48

ANSI C .

#include

void *memset(void *dest, int c, size_t len);

void *memcpy(void *dest, const void *src, size_t nbytes);

int memcmp(const void *ptr1, const void *ptr2, size_t nbytes);

Returns: 0 if equal, 0 if unequal

memset destination byte c . memcpy bcopy

. . bcopy ,

source destination memcpy . ANSI C

memmove .

memcpy C

.

dest = src;

memcmp byte string 0 . ,

0 . ptr1 byte 0

, ptr2 byte 0 . byte unsigned chars

.

3.5 INET_ATON, INET_ADDR, INET_NTOA

.

Internet address ASCII ( ) byte ordered

binary (socket address ) .

1. inet_aton, inet_ntoa, inet_addr IPv4 dotted-decimal ( ,

206.168.112.96) 32-bit byte ordered binary .

.

49

2. inet_pton inet_ntop IPv4 IPv6 .

. .

#include

int inet_aton(const char *strptr, struct in_addr *addrptr);

Returns: 1 if string was valid, 0 on error

in_addr_t inet_addr(const char *strptr);

Returns: 32-bit binary network byte ordered IPv4 address;

INADDR_NONE if error

char *inet_ntoa(struct in_addr inaddr);

Returns: pointer to dotted-decimal string

, inet_aton strptr C character 32-bit

binary byte ordered . addrptr .

1 0 .

inet_addr , 32-bit binary byte ordered

. 232 IP addresses . (0.0.0.0

255.255.255.255), INADDR_NONE ( 32

one-bits) . dotted-decimal 255.255.255.255 (broadcast IPv4

) binary

.

, inet_addr . inet_aton .

IPv4 IPv6 .

inet_ntoa 32-bit binary byte ordered IPv4 dotted-decimal

. .

. ,

. .

.

50

3.6 INET_PTON, INET_NTOP

IPv6 . IPv4 IPv6 .

. p n presentation numeric .

ASCII socket address

.

#include

int inet_pton(int family, const char *strptr, void *addrptr);

Returns: 1 if OK, 0 if input not a valid presentation format, -1 on error

const char *inet_ntop(int family, const void *addrptr, char *strptr, size_t len);

Returns: pointer to result if OK, NULL on error

family AF_INET AF_INET6. family ,

errno EAFNOSUPPORT .

strptr .

addrptr . 1 .

family , 0 .

inet_ntop , (addrptr) (strptr). len

, .

, :

#define INET_ADDRSTRLEN 16 /* for IPv4 dotted-decimal */

#define INET6_ADDRSTRLEN 46 /* for IPv6 hex string */

len , null , null

errno ENOSPC .

inet_ntop strptr null .

. , .

51

.

IPv6 ,

.

foo.sin_addr.s_addr = inet_addr(cp);

inet_pton(AF_INET, cp, &foo.sin_addr);

ptr = inet_ntoa(foo.sin_addr);

char str[INET_ADDRSTRLEN];

ptr = inet_ntop(AF_INET, &foo.sin_addr, str, sizeof(str));

52

IPv4 inet_pton . ,

IPv4 inet_ntop .

10 int 11 inet_pton(int family, const char *strptr, void *addrptr) 12 { 13 if (family == AF_INET) { 14 struct in_addr in_val; 15 if ( inet_aton(strptr, &in_val)) { 16 memcpy(addrptr, &in_val, sizeof(struct in_addr)); 17 return (1); 18 } 19 return (0); 20 } 21 errno = EAFNOSUPPORT; 22 return (-1); 23 }

8 const char * 9 inet_ntop (int family, const void *addrptr, char *strptr, size_t

len) 10 { 11 const u_char *p = (const u_char *) addrptr; 12 if (family == AF_INET) { 13 char temp[INET_ADDRSTRLEN]; 14 snprintf(temp, sizeof(temp), %d.%d.%d.%d, p[0], p[1], p[2],

p[3]); 15 if (strlen(temp) >= len) { 16 errno = ENOSPC; 17 return (NULL); 18 } 19 strcpy(strptr, temp); 20 return (strptr); 21 } 22 errno = EAFNOSUPPORT; 23 return (NULL); 24 }

53

4. TCP SOCKETS

TCP client server socket functions

. ,

. .

client concurrency

(concurrent servers) . client connection server

fork. , fork one-process-per-client model .

4.1 TCP client server . , server

, server client . Client server request

, server request , client request .

client server end-of-file

. server client

.

TCP

54

4.1 SOCKET

#include

int socket (int family, int type, int protocol);

Returns: non-negative descriptor if OK, -1 on error

Network I/O , (IPv4, IPv6,

) socket . Family ,

4.1 . 4.2 .

argument 4.4 type

family type default 0 .

Protocol family

Family Description

AF_INET IPv4 protocol

AF_INET6 IPv6 protocol

AF_LOCAL Unix domain protocols

Type Description

SOCK_STREAM Stream socket

SOCK_DGRAM Datagram socket

SOCK_SEQPACKET Sequenced packet socket

SOCK_RAW Raw socket

55

family type . 4.3

. Yes .

socket family type

AF_INET AF_INET6 AF_LOCAL

SOCK_STREAM TCP|SCTP TCP|SCTP Yes

SOCK_DGRAM UDP UDP Yes

SOCK_SEQPACKET SCTP SCTP Yes

SOCK_RAW IPv4 IPv6

AF_xxx PF_xxx . AF_LOCAL AF_UNIX

. SOCK_SEQPACKET SCTP , TCP SOCK_STREAM .

Socket , file descriptor . socket

descriptor sockfd . socket descriptor , protocol family(IPv4, IPv6,

Unix) socket type(stream, datagram, raw) .

AF_xxx vs PF_xxx

AF_ prefix address family , PF_ prefix protocol_family .

, single protocol family multiple protocol family ,

PF_ AF_ .

multiple address family ,

PF_ AF_ .

, ,

. socket PF_ ,

. POSIX socket PF_ AF_ socket address structure

.

56

4.2 CONNECT

Connect TCP client TCP server client .

#include

int connect(int sockfd, const struct sockaddr *servaddr, socklen_t addrlen);

Returns: 0 if OK, -1 on error

sockfd socket socket descriptor. parameter

section3.3 socket address structure . Socket

address structure server IP port .

Client connect() bind() .

ephemeral port source IP .

TCP socket , connect TCP three-way handshake .

. .

1) client TCP SYN ETIMEDOUT .

, connect SYN , 6 , 24

. SYN 75

. .

2) Client SYN server reset(RST), server

. (, server

.) (hard error) RST ECONNREFUSED

client .

RST TCP TCP . RST

SYN , TCP

, TCP

.

57

3) client SYN destination unreachable ICMP ,

(soft error) . Client

SYN . (: 75),

ICMP EHOSTUNREACH ENETUNREACH .

destination unreachable ICMP

. ICMP . ,

15 .

1 client . daytime server

local host(127.0.0.1) .

solaris % daytimetcpcli 127.0.0.1

Sun Jul 27 22:01:51 2003

, IP .


Sun Jul 27 22:04:59 PDT 2003

, local subnet IP (192.168.1/24) host ID(100) .

, subnet host ID 100 host client host ARP ( host

), ARP .


connect error: Connection timed out

Connect . err_sys ETIMEDOUT

.

daytime server host(local router) .


connect error: Connection refused

RST .

58

IP . Tcpdump 6 hop

host ICMP .


connect error: No route to host

ETIMEDOUT , connect EHOSTUNREACH

.

TCP , connect CLOSED (socket )

SYN_SENT , ESTABLISHED . Connect ,

. connect

. connect IP ,

connect socket descriptor .

4.3 BIND

Bind local protocol address socket . 32bit IPv4

128bit IPv6 16bit TCP UDP .

#include

int bind (int sockfd, const struct sockaddr *myaddr, socklen_t addrlen);

Returns: 0 if OK,-1 on error

,

. TCP, bind IP

.

well-known port bind . TCP client server

, connect listen socket ephemeral port

. TCP client ephemeral port

59

. , TCP server ephemeral port

, server well-known .

RPC(Remote Procedure Call) server. server listening socket

ephemeral port , RPC

. client server connect ephemeral port

. UDP RPC server .

socket IP bind . IP server

. TCP client , socket IP IP

. TCP server , IP socket

.

TCP client socket IP bind . socket

interface IP source,

. TCP server socket IP bind ,

client SYN destination IP source IP .

, bind IP . 4.4

sin_addr sin_port sin6_addr sin6_port .

bind() IP

IP port

Wildcard 0 IP port

Wildcard nonzero IP , port

Local IP address 0 IP , port

Local IP address nonzero IP port

60

0 , bind ephemeral port .

wildcard IP ( IP ) socket (TCP) datagram

socket local IP . IPv4 INADDR_ANY

wildcard IP ( ) . 0. IP

.

struct sockaddr_in servaddr;

servaddr.sin_addr.s_addr = htonl (INADDR_ANY); /* wildcard */

IP 32 ( 0) IPv4 , IPv6

. 128bit IPv6 . (C

.)

.

struct sockaddr_in6 serv;

serv.sin6_addr = in6addr_any; /* wildcard */

in6addr_any IN6ADDR_ANY_INIT .

in6addr_any extern .

INADDR_ANY(0) htonl

. INADDR_

htonl() .

Bind ADDRINUSE(Address already in use). 7

SO_REUSEADDR SO_REUSEPORT socket option .

61

4.4 LISTEN

TCP server listen . socket socket active socket

. , connect client socket . Listen socket

passive socket , socket .

TCP listen socket CLOSE LISTEN .

socket .

#include

#int listen (int sockfd, int backlog);


bind accept . Backlog

, listening socket queue .

connection queue server three-way handshake

client SYN entry . socket SYN_RCVD

.

connection queue TCP three-way handshake client

entry . socket ESTABLISHED .

4.2 listening socket queue .

62

TCP listening socket Queue

Entry queue , listen socket

. . server .

4.3 queue .

TCP listening socket

Client SYN TCP queue entry three-way

handshake client SYN ACK server SYN .

entry three-way handshake (server SYN client

ACK) entry queue .

63

three-way handshake queue entry queue entry

queue queue entry

sleep .

queue .

listen backlog queue .

backlog 0 .

. .

listening socket client listening socket .

, sample code backlog 5. Busy server

1980 . Busy server

. busy HTTP server

backlog .

backlog .

, 5 backlog .

. HTTP server

server .

command-line option .

.

listen wrapper function

. LISTENQ .

64

------------------------------------------------------------------------- 137 void 138 Listen (int fd, int backlog) 139 { 140 char *ptr; 141 /* can override 2nd argument with environment variable */ 142 if ( (ptr = getenv("LISTENQ")) != NULL) 143 backlog = atoi (ptr); 144 if (listen (fd, backlog) < 0) 145 err_sys ("listen error"); 146 } -------------------------------------------------------------------------

Manual accept

server . queue

entry . busy Web server

. backlog client SYN three-way handshake

queue .

client SYN queue , SYN RST .

client TCP SYN queue

. server TCP RST , client connect

TCP .

client SYN RST "there is a server at this port but its queues are full."

.

three-way handshake server accept

server TCP socket .

4.5 backlog

. 7 backlog 5 .

65

OS backlog

backlog MacOS Linux HP-UX FreeBSD Solaris

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

1

2

3

4

5

7

8

10

11

13

14

16

17

19

20

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

1

1

3

4

6

7

9

10

12

13

15

16

18

19

21

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

1

2

4

5

6

8

10

11

13

14

16

17

19

20

22

66

4.5 ACCEPT

accept TCP server queue .

queue sleep .

#include

int accept (int sockfd, struct sockaddr *cliaddr, socklen_t *addrlen);

Returns: non-negative descriptor if OK, -1 on error

Cliaddr addrlen (client) .

Addrlen value-result argument. *addrlen cliaddr

socket address structure , , socket address

structure .

Accept , brand-new descriptor.

descriptor client TCP . Accept , accept listen

socket , accept socket . socket

. Server listen socket .

accept client socket . Server client

socket .

. socket descriptor

. client

, cliaddr addrlen null pointer . socket

listen socket server . client

identity accept null pointer .

TCP Daytime Server .

67

-------------------------------------------------------------------------- 1 #include "unp.h" 2 2 #include 3 int 4 main(int argc, char **argv) 5 { 6 int listenfd, connfd; 7 socklen_t len; 8 struct sockaddr_in servaddr, cliaddr; 9 char buff[MAXLINE]; 10 time_t ticks; 11 listenfd = Socket(AF_INET, SOCK_STREAM, 0); 12 bzero(&servaddr, sizeof(servaddr)); 13 servaddr.sin_family = AF_INET; 14 servaddr.sin_addr.s_addr = htonl(INADDR_ANY); 15 servaddr.sin_port = htons(13); /* daytime server */ 16 Bind(listenfd, (SA *) &servaddr, sizeof(servaddr)); 17 Listen(listenfd, LISTENQ); 18 for ( ; ; ) { 19 len = sizeof(cliaddr); 20 connfd = Accept(listenfd, (SA *) &cliaddr, &len); 21 printf("connection from %s, port %d\n", 22 Inet_ntop(AF_INET, &cliaddr.sin_addr, buff, sizeof(buff)), 23 ntohs(cliaddr.sin_port)); 24 ticks = time(NULL); 25 snprintf(buff, sizeof(buff), "%.24s\r\n", ctime(&ticks)); 26 Write(connfd, buff, strlen(buff)); 27 Close(connfd); 28 } 29 } --------------------------------------------------------------------------

New declarations

7-8

value-result len client

cliaddr.

Accept connection and print client's address

19-23

len socket address structure cliaddr pointer len

pointer accept . Socket address structure 32 IP

ASCII inet_ntop ,

16 ntohs .

68

.


Thu Sep 11 12:44:00 2003


Thu Sep 11 12:44:09 2003

IP (127.0.0.1) IP (192.168.1.20)

. .

solaris # daytimetcpsrv1

connection from 127.0.0.1, port 43388

connection from 192.168.1.20, port 43389

IP . Daytime client bind

outgoing interface source IP

section 4.4 . source IP

IP . Solaris ephemeral port

43388 43389 .

shell prompt # . 13 reserved port

. bind .

69

4.6 FORK EXEC

(concurrent server) fork

. .

#include

pid_t fork(void);

Returns: 0 in child, process ID of child in parent, -1 on error

fork (process) child process .

(parent) .

(child) ID . return value parent child

.

Fork child parent ID 0 child

parent getppid parent ID .

parent ID

ID return value . ID fork return

value .

Fork descriptor fork

. , accept fork

. connected socket . connected socket

. fork .

.

. .

. Fork

fork (

) exec( ) . shell

.

70

exec . (

exec .) exec

main . ID . exec

.

exec

(a) () () ,

(b) pointer ,

(c) , .

#include

int execl (const char *pathname, const char *arg0, ... /* (char *) 0 */ );

int execv (const char *pathname, char *const argv[]);

int execle (const char *pathname, const char *arg0, ...

/* (char *) 0, char *const envp[] */ );

int execve (const char *pathname, char *const argv[], char *const envp[]);

int execlp (const char *filename, const char *arg0, ... /* (char *) 0 */ );

int execvp (const char *filename, char *const argv[]);

All six return: -1 on error, no return on success

caller . main

. 4.4 . execve

execve .

71

EXEC

.

1. exec ,

pointer .

pointer argv . argv null pointer

. .

2. filename argument . PATH

. Execlp execvp filename argument (/)

PATH . pathname

argument .

3. environment pointer .

environ environment list

. environment list . Pointer envp

null pointer .

72

4.7 CONCURRENT

iterative server. daytime server .

,

. (concurrent)

fork .

(concurrent) .

pid_t pid; int listenfd, connfd; listenfd = Socket( ... ); /* fill in sockaddr_in{} with server's well-known port */ Bind(listenfd, ... ); Listen(listenfd, LISTENQ); for ( ; ; ) { connfd = Accept (listenfd, ... ); /* probably blocks */ if( (pid = Fork()) == 0) { Close(listenfd); /* child closes listening socket */ doit(connfd); /* process the request */ Close(connfd); /* done with this client */ exit(0); /* child terminates */ } Close(connfd); /* parent closes connected socket */ }

accept , fork .

(connfd connected socket) .

(listenfd listening socket) connected socket

.

doit .

, connected socket close. exit

close . open descriptor

. close .

2 TCP close FIN

. connfd close

73

? reference count .

Reference count file table entry , open descriptor

. socket , listenfd file table entry reference

count 1 . accept , connfd file table entry reference

count 1 . fork descriptor

file table entry reference count 2 . connfd

reference count 2 1 . Reference count 0

descriptor . connfd .

. 4.5 accept

(block)

.

Accept()

accept , 4.6 . connfd

. connected socket .

Accept()

74

(concurrent) fork . 4.7 fork

.

fork()

descriptor listenfd connfd .

connected socket listening socket . 4.8 .

parent child

.

listening socket accept .

75

4.8 CLOSE

close TCP .

#include

int close (int sockfd);


TCP close

. socket descriptor . , read write

. TCP queue .

TCP .

Descriptor Reference Counts

(concurrent) connected socket close descriptor

reference count . reference count 0 close

TCP . connected

socket (concurrent) .

TCP FIN , close shutdown (6 ).

accept connected socket close

. descriptor .

descriptor .

. connected socket

, reference count 2 1 connected socket

1 . TCP .

76

4.9 GETSOCKNAME GETPEERNAME

local protocol address (getsockname), getpeername

foreign protocol address .

#include

int getsockname(int sockfd, struct sockaddr *localaddr, socklen_t *addrlen);

int getpeername(int sockfd, struct sockaddr *peeraddr, socklen_t *addrlen);

Both return: 0 if OK, -1 on error

value-result . localaddr

peeraddr socket address structure .

IP

. domain name .

.

bind TCP connect getsockname

local IP local .

0( local ) bind getsockname

local .

address family getsockname .

IP bind TCP (accept )

getsockname local IP .

socket descriptor argument connected socket .

77

5. TCP CLIENT/SERVER

TCP / .

.

1. .

2. .

3. .

5.1 / .

Echo Client/Server

, full-

duplex TCP . fgets fputs .

, TCP/IP TCP UDP

. .

/ .

/ .

.

(

.) .

78

5.1 TCP ECHO SERVER

(concurrent) .

-------------------------------------------------------------------------- 1 #include "lnp.h" 2 int 3 main(int argc, char **argv) 4 { 5 int listenfd, connfd; 6 pid_t childpid; 7 socklen_t clilen; 8 struct sockaddr_in cliaddr, servaddr; 9 listenfd = Socket (AF_INET, SOCK_STREAM, 0); 10 bzero(&servaddr, sizeof(servaddr)); 11 servaddr.sin_family = AF_INET; 12 servaddr.sin_addr.s_addr = htonl (INADDR_ANY); 13 servaddr.sin_port = htons (SERV_PORT); 14 Bind(listenfd, (SA *) &servaddr, sizeof(servaddr)); 15 Listen(listenfd, LISTENQ); 16 for ( ; ; ) { 17 clilen = sizeof(cliaddr); 18 connfd = Accept(listenfd, (SA *) &cliaddr, &clilen); 19 if ( (childpid = Fork()) == 0) { /* child process */ 20 Close(listenfd); /* close listening socket */ 21 str_echo(connfd); /* process the request */ 22 exit (0); 23 } 24 Close(connfd); /* parent closes connected socket */ 25 } 26 } --------------------------------------------------------------------------

Create socket, bind server's well-known port

9-15

TCP . (INADDR_ANY) well

known port . Wildcard address

local interface . listen listening

socket .

Wait for client connection to complete

17-18 accept .

79

Concurrent server

19-24

fork

. Section 4.8 listening socket connected

socket . str_echo (

) .

str_echo . ,

.

-------------------------------------------------------------------------- 1 #include "unp.h" 2 void 3 str_echo(int sockfd) 4 { 5 ssize_t n; 6 char buf[MAXLINE]; 7 again: 8 while ( (n = read(sockfd, buf, MAXLINE) ) > 0) 9 Writen(sockfd, buf, n); 10 if (n < 0 && errno == EINTR) 11 goto again; 12 else if (n < 0) 13 err_sys("str_echo: read error"); 14 } --------------------------------------------------------------------------

Read a buffer and echo the buffer

8-9

writen .

(the normal scenario), FIN readline 0

. , str_echo , .

80

5.2 TCP ECHO CLIENT

TCP Echo main .

-------------------------------------------------------------------------- 1 #include "unp.h" 2 int 3 main(int argc, char **argv) 4 { 5 int sockfd; 6 struct sockaddr_in servaddr; 7 if (argc != 2) 8 err_quit("usage: tcpcli "); 9 sockfd = Socket(AF_INET, SOCK_STREAM, 0); 10 bzero(&servaddr, sizeof(servaddr)); 11 servaddr.sin_family = AF_INET; 12 servaddr.sin_port = htons(SERV_PORT); 13 Inet_pton(AF_INET, argv[1], &servaddr.sin_addr); 14 Connect(sockfd, (SA *) &servaddr, sizeof(servaddr)); 15 str_cli(stdin, sockfd); /* do it all */ 16 exit(0); 17 } --------------------------------------------------------------------------

.

Create socket, fill in Internet socket address structure

9-13

TCP , internet socket address structure IP

. IP command-line argument , well known

port(SERV_PORT) unp.h .

Connect to server

14-15

connect . str_cli() .

81

str_cli() . ,

, , .

------------------------------------------------------------------------- 1 #include "unp.h" 2 void 3 str_cli(FILE *fp, int sockfd) 4 { 5 char sendline[MAXLINE], recvline[MAXLINE]; 6 while (Fgets(sendline, MAXLINE, fp) != NULL) { 7 Writen(sockfd, sendline, strlen (sendline)); 8 if (Readline(sockfd, recvline, MAXLINE) == 0) 9 err_quit("str_cli: server terminated prematurely"); 10 Fputs(recvline, stdout); 11 } 12 } -------------------------------------------------------------------------

Read a line, write to server

6-7

fgets , writen .

Read echoed line from server, write to standard output

8-10

readline fput .

Return to main

11-12

fget null pointer . end-of-file(EOF)

. Fgets wrapper

Fgets end-of-file null pointer .

82

5.3

Normal Startup

TCP ( main str_echo, str_cli, readline, witen

150), .

( ,

, ) .

(boundary conditions) TCP/IP ,

.

linux background .

linux % tcpserv01 &

[1] 17870

, socket, bind, listen, accept accept . (

.) , listening socket

netstat .

linux % netstat -a

Active Internet connections (servers and established)

Proto Recv-Q Send-Q Local Address Foreign Address State

tcp 0 0 *:9877 *:* LISTEN

(the heading) .

. Listening socket

a flag .

. (wildcard) local IP 9877 local

LISTEN . Netstat IP 0(INADDR_ANY, the wildcard) 0

(asterisk) .

83

IP 127.0.0.1(loopback)

. normal(non-loopback) IP .

linux % tcpcli01 127.0.0.1

socket connect , TCP three-way handshake

. Three-way handshake , connect

accept . .

1. str_cli . fgets .

2. accept , fork str_echo .

readline , readline read , read

.

3. , accept

.

.

Three_way handshake , ,

. Three-way handshake

connect , accept .

accept connect RTT .

, -

.

netstat TCP .

linux % netstat -a

Active Internet connections (servers and established)

Proto Recv-Q Send-Q Local Address Foreign Address State

tcp 0 0 local host:9877 localhost:42758 ESTABLISHED

tcp 0 0 local host:42758 localhost:9877 ESTABLISHED

tcp 0 0 *:9877 *:* LISTEN

84

ESTABLISHED local 9877 .

ESTABLISHED local 42758 .

.

ps .

linux % ps -t pts/6 -o pid,ppid,tty,stat,args,wchan

PID PPID TT STAT COMMAND WCHAN

22038 22036 pts/6 S -bash wait4

17870 22038 pts/6 S ./tcpserv01 wait_for_connect

19315 17870 pts/6 S ./tcpserv01 tcp_data_wait

19314 22038 pts/6 S ./tcpcli01 127.0 read_chan

. PID PPID

. PPID PID tcpserv01

tcpserv01 . PPID shell.

STAT S, .

, WCHAN . Linux accept

connect wait_for_connect,

tcp_data_wait, terminal I/O read_chain .

WCHAN .

85

Normal Termination

.

linux % tcpcli01 127.0.0.1

hello, world

hello, world

good bye

good bye

^D

echo , EOF (Control-D)

. netstat .

linux % netstat -a | grep 9877

tcp 0 0 *:9877 *:* LISTEN

tcp 0 0 localhost:42758 localhost:9877 TIME_WAIT

(local 42758) TIME_WAIT listening socket

.( netstat grep

well-known port , the heading line .)

.

1. EOF , fgets null pointer str_cli() .

2. str_cli main () , exit .

3. open descriptors

. FIN , TCP ACK

. TCP .

CLOSE_WAIT , FIN_WAIT_2 .

4. TCP FIN , readline() readline

0 . str_echo main .

5. exit .

86

6. descriptors . connected socket

TCP .

FIN ACK. .

TIME_WAIT .

7. SIGCHLD

.

. . ps

.

linux % ps -t pts/6 -o pid,ppid,tty,stat,args,wchan

PID PPID TT STAT COMMAND WCHAN

22038 22036 pts/6 S -bash read_chan

17870 22038 pts/6 S ./tcpserv01 wait_for_connect

19315 17870 pts/6 Z [tcpserv01

87

5.4

A.

. software

interruption . .

.

( )

SIGCHLD

.

action disposition . Sigaction()

disposition disposition .

. signal handler

, . SIGKILL SIGSTOP

. .

. ,

void handler(int signo);

. , sigaction

. SIGIO, SIGPOLL

.

disposition SIG_IGN . SIGKILL

SIGSTOP .

disposition SIG_DFL disposition .

,

working directory . disposition

. SIGCHLD .

88

Signal() Function

POSIX disposition sigaction .

. disposition

signal .

pointer SIG_IGN SIG_DFL .

signal POSIX . POSIX

sigaction . , POSIX sigaction

signal . .

-------------------------------------------------------------------------- 1 #include "lnp.h" 2 Sigfunc * 3 signal (int signo, Sigfunc *func) 4 { 5 struct sigaction act, oact; 6 act.sa_handler = func; 7 sigemptyset (&act.sa_mask); 8 act.sa_flags = 0; 9 if (signo == SIGALRM) { 10 #ifdef SA_INTERRUPT 11 act.sa_flags |= SA_INTERRUPT; /* SunOS 4.x */ 12 #endif 13 } else { 14 #ifdef SA_RESTART 15 act.sa_flags |= SA_RESTART; /* SVR4, 4.4BSD */ 16 #endif 17 } 18 if (sigaction (signo, &act, &oact) < 0) 19 return (SIG_ERR); 20 return (oact.sa_handler); 21 } --------------------------------------------------------------------------

Simplify function prototype using typedef

2-3

signal .

void (*signal (int signo, void (*func) (int))) (int);

89

lnp.h Sigfunc .

typedef void Sigfunc(int);

signal handler , (void).

.

Sigfunc *signal (int signo, Sigfunc *func);

pointer ,

.

Set handler

6 sigaction sa_handler func .

Set signal mask for handler

7

POSIX signal handler .

. Sa_mask signal handler

. POSIX handler

.

Set SA_RESTART flag

8-17

SA_RESTART optional flag. , interrupted system

.( interrupted system

.) SIGALRM SA_RESTART flag(

) . (SIGALRM Section 14.2

,

.) SunOS 4.x

interrupted system . flag complement

SA_INTERRUPT . flag SIGALRM flag

.

90

Call sigaction

18-20

sigaction signal action .

signal .

POSIX Signal Semantics

POSIX .

signal handler .

signal handler . signal handler

sigaction sa_mask .

sa_mask ,

.

. queue .

.

91

B. SIGCHLD

.

ID (CPU , ) .

,

ID 1(init ) , .

(, init wait) COMMAND

.

Handling Zombies

. ,

. fork

wait . SIGCHLD signal handler

signal handler wait .

listen signal handler .

Signal (SIGCHLD, sig_chld);

fork . signal

handler .

-------------------------------------------------------------------------- 1 #include "unp.h" 2 void 3 sig_chld(int signo) 4 { 5 pid_t pid; 6 int stat; 7 pid = wait(&stat); 8 printf("child %d terminated\", pid); 9 return; 10 } -------------------------------------------------------------------------

92

Solaris 9 signal

.

solaris % tcpserv02 & start server in background

[2] 16939

solaris % tcpcli01 127.0.0.1 then start client in foreground

hi there we type this

hi there and this is echoed

^D we type our EOF character

child 16942 terminated output by printf in signal handler

accept error: Interrupted system call

main function aborts

.

1. EOF . TCP FIN

ACK .

2. FIN readline EOF . .

3. SIGCHLD accept . sig_chld(signal

handler) , wait PID printf .

4. disposition(accept ) ,

accept EINTR(interrupted system ) .

.

signal ,

. Solaris 9

C signal interrupted system

. SA_RESTART flag signal

. interrupted system .

4.4BSD signal

interrupted system accept .

93

signal handler return void

. return statement

.

Handling Interrupted System Calls

accept disposition

. , return .

. , accept

. echo

read(readline) . disposition

. caller .

disposition

signal handler EINTR .

interrupted system .

( SIGCHLD ), disposition EINTR

. POSIX SA_RESTART flag

can some . SA_RESTART flag

interrupted system .

, Berkeley-derived implementations select

accept recvfrom .

accept accept , for

.

for ( ; ; ) { clilen = sizeof (cliaddr); if ( (connfd = accept (listenfd, (SA *) &cliaddr, &clilen)) < 0) { if (errno == EINTR) continue; /* back to for () */ else err_sys ("accept error"); }

94

wrapper Accept accept .

. interrupted system

. read, write, select, open accept .

connect. EINTR

.

. connect

select .

C. wait waitpid

wait .

#include

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리눅스 네트웍 프로그래밍 (CPL-TR-09-03)