Socket Programming in C

Socket Programming in CSocket Programming in C

Kyounghee Lee

[email protected]

Information and Communications Univ

ICE1230 – Computer Networks

ICUICUInformation and Communications UniversityInformation and Communications University

OutlineOutline TCP/IP introduction

– TCP/IP overview– Transport layer: TCP & UDP

Socket fundamentals– Socket address and port numbers– Network byte ordering & address conversion– Socket creation

Socket functions– Elementary TCP socket functions– TCP client-server example– Elementary UDP socket functions– UDP client-server example

Programming assignment #01– Program description– Assignment evaluation

TCP/IP IntroductionTCP/IP Introduction




Overview of TCP/IP ProtocolsOverview of TCP/IP Protocols



UDP & TCPUDP & TCP

UDP– Datagram transmission

– Connection less: delivery guarantee (X)

– Short-term relationship between client & server

TCP– Connection-oriented: reliability, packet sequence

– Flow control & congestion control

– Full-duplex

– Long-term relationship



TCP ConnectionTCP Connection

Simultaneousclose

Three-wayhandshake



TCP Client-ServerTCP Client-Server



UDP Client-ServerUDP Client-Server

UDP Client

socket()

sendto()

recvfrom()

close()

UDP Server

socket()

bind()

recvfrom()

sendto()

blocks until datagramreceived from a client

data(request)

process request

data(reply)



Common Internet ApplicationsCommon Internet Applications

Socket FundamentalsSocket Fundamentals



Socket PairSocket Pair

Socket identification– IP address + port number

TCP connection identification– Socket pair

– 4-tuple definition• IP address and port number of each endpoint• e.g.) {210.107.128.31.21, 210.107.132.195.1500}



Port numbersPort numbers

16-bit integer Differentiate a socket-related process from another Ranges

– Well-known ports (0 ~1023): assigned by IANA• e.g.) FTP (21), web server (80), …

– Registered ports (1024 ~ 49151): recommendation list• e.g.) X Window server (6000 ~ 6003)

– Dynamic or private ports (49152 ~ 65535)



Socket Address Structure (1)Socket Address Structure (1)

Generic IPv4struct sockaddr {

uint8_t sa_len;sa_family_t sa_family; /* address family: AF_XXX value */char sa_data[14]; /* protocol-specific address */

};

Posix.1gstruct in_addr {

in_addr_t s_addr; /* 32 bit IP address */ }; struct sockaddr_in {

uint8_t sin_len; /* length of structure (16) */sa_famility_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 */

};



Socket Address Structure (2)Socket Address Structure (2)

Data types in Posix.1g



Byte OrderingByte Ordering

Big & little-endian byte order

• No standard between two types



Network Byte OrderingNetwork Byte Ordering

Exchanging multi-byte data type– Two end protocol stack must agree on the order type

– IP uses big-endian byte ordering

Byte ordering functions



Byte Manipulation FunctionsByte Manipulation Functions

Berkeley-derived functions

ANSI C



Address Conversion FunctionsAddress Conversion Functions

Convert IPv4 address– Between a dotted-decimal string and its 32-bit network byte ordered

binary value



Getting an Address of a SocketGetting an Address of a Socket

Function definition

• Retrieves the address binded to a socket with its descriptor



Socket() FunctionSocket() Function

Definition

Protocol family constants & Socket type

• Protocol argument is normally set to 0 except for raw socket



Socket CreationSocket Creation

Example#include <sys/types.h>#include <sys/socket.h>….int sockfd;….sockfd = socket(AF_INET, SOCK_DGRAM, 0);….

Socket FunctionsSocket Functions



Connect() FunctionConnect() Function

Definition

• Generally cast sockaddr_in with (sockaddr *)• Variable ‘errno’ is set to the corresponding error code



Bind() FunctionBind() Function

Definition

• Specifies a port number and an IP address for a socket• Servers generally bind their well-known port when they start• Clients let the kernel choose an ephemeral port when either connect() or listen()

is called



Listen() FunctionListen() Function

Definition

Two queues in the kernel for backlog– Incomplete connection queue: SYN_RCVD state– Completed connection queue: ESTABLISHED state



Accept() FunctionAccept() Function

Definition

• Variable cliaddr is set to the corresponding client IP address and port number after a successful return



Close() FunctionClose() Function

Definition



Basic TCP Socket I/OBasic TCP Socket I/O

Read()

# include <unistd.h>

int read(int sockfd, char *ptr, size_t nbytes);

Returns: number of bytes read, -1 on error

Write()

# include <unistd.h>

int write(int sockfd, char *ptr, size_t nbytes);

Returns: number of bytes written, -1 on error



Typical I/O ExampleTypical I/O Example

int readn(int fd, void *vptr, size_t n) {size_t nleft, nread;char *ptr;

ptr = vptr;nleft = n;while(nleft > 0) {

if((nread = read(fd, ptr, nleft)) < 0) {if(errno == EINTR) nread = 0;else return –1;

} else if (nread == 0)break;

nleft -= nread;ptr += nread;

}return n;

}



TCP Server ExampleTCP Server Example

Outline for typical concurrent server



TCP Socket DescriptorTCP Socket Descriptor

Status transition

*after return from accept

*after fork()returns

*after socketclose()



Functions for ConcurrencyFunctions for Concurrency

‘exec’ functions

Difference in 6 functions is– whether the file to execute is specified by a filename or pathname– whether the arguments are passed one by one or array of pointers– whether the environment of the calling process is passed or whether new

environment is specified



Simple TCP Server Example (1)Simple TCP Server Example (1)

TCP echo server



Simple TCP Server Example (2)Simple TCP Server Example (2)

‘str_echo’ function



Simple TCP Client ExampleSimple TCP Client Example

TCP echo client



Basic UDP Socket I/O (1)Basic UDP Socket I/O (1)

sendto()

# include <sys/socket.h>

int sendto(int s, const void *msg, int len, unsigned int flags, const struct sockaddr *to, int tolen);

Returns: number of bytes sent, -1 on error

recvfrom()

# include <sys/socket.h>

int recvfrom(int s, void *buf, int len, unsigned int flags, struct sockaddr *from, int *fromlen);

Returns: number of bytes received, -1 on error



Basic UDP Socket I/O (2)Basic UDP Socket I/O (2)

“flags” for socket I/O functions– Either 0 or formed by logically OR’ing one or more of the constants shown in the

following table

Remark– MSG_DONTROUTE: destination is in the local network– MSG_OOB: message has higher priority than in-band data– MSG_PEEK: let the received data seem to be still available to be read (do not discard

from the queue)– MSG_WAITALL:tell to kernel not to return until the request number of bytes have been

read

Flags Description recvfrom sendto

MSG_DONTROUTE

MSG_DONTWAIT

MSG_OOB

MSG_PEEK

MSG_WAITALL

Bypass routing table lookup

Socket operation is non-blocking

Send or receive out of band data

Peek at incoming message

Wait for all the data

•

•

•

•

•

•

•



Simple UDP Server ExampleSimple UDP Server Example#include <sys/socket.h>#include <sys/types.h>

int main(int argc, char **argv){ int sockfd, n, len; char msg[80]; struct sockaddr_in servaddr, cliaddr;

sockfd = socket(AF_INET, SOCK_DGRAM, 0);

bzero(&servaddr, sizeof(servaddr)); servaddr.sin_family = AF_INET; servaddr.sin_addr.s_addr = htonl(INADDR_ANY); servaddr.sin_port = htons(1500);

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

len = sizeof(cliaddr); while(1) { n = recvfrom(sockfd, msg, 80, 0, (struct sockaddr *)&cliaddr, &len); sendto(sockfd, msg, n, 0, (struct sockaddr *)&cliaddr, len); }}



Simple UDP Client Example (1)Simple UDP Client Example (1)#include <sys/socket.h>#include <sys/types.h>#include <string.h>

int main(int argc, char **argv){ int sockfd, n; char sendline[80], recvline[80]; struct sockaddr_in servaddr;

if(argc != 2) { printf(“Usage: uecho <IP address>\n”); exit(0); }

sockfd = socket(AF_INET, SOCK_DGRAM, 0);

bzero(&servaddr, sizeof(servaddr)); servaddr.sin_family = AF_INET; servaddr.sin_addr.s_addr = inet_addr(argv[1]); servaddr.sin_port = htons(1500);



Simple UDP Client Example (2)Simple UDP Client Example (2) while(gets(sendline) != NULL) { sendto(sockfd, sendline, strlen(sendline), 0, (struct sockaddr *)&servaddr, sizeof(servaddr);

n = recvfrom(sockfd, recvline, 80, 0, NULL, NULL);

puts(recvline); }}

Programming Assignment Programming Assignment #01#01



Program DescriptionProgram Description Baseball game

– User finds three blind numbers (1~9) given by server (e.g. 7 5 9)– User tries 12 times and server replies with X ball Y strike

(e.g. 2 5 7 1 ball & 1 strike)– If a user finds the sequence of 3 numbers before 12 tries, win!

Requirements– Multi-client support (concurrent server)– Both TCP and UDP socket should be used * UDP: request of game start (designated port, 9000), reply to the request (user full or accept with port number for connecting) * TCP: user tries & server replies for game proceeding– Use C or C++ language on UNIX/LINUX systems



Assignment Evaluation (1)Assignment Evaluation (1)

Due date– Mar 21, 11:00 PM– Late submission will be assessed a penalty of 10% for a day

Submission– Implementation report– Full source codes– Send an email to TA ([email protected])

Evaluation factors– Originality (‘S’ or ‘F’)– Operability (40)– Readability (30)– Efficiency (30)

Recommended reference– “UNIX Network Programming”, W. R.Stevens, Prentice Hall



Assignment Evaluation (2)Assignment Evaluation (2)

Implementation Report– Your name and affiliation– Assignment objective

– Program functionality– Program design– Implementation environment (platform, OS, programming library, etc.)– Results

• How to compile/execute your program• Display the execution results that you have tested• Pros and cons of your implementation

– MS Word or PDF file with name of “studentID.doc” or “studentID.pdf” Source codes

– Detailed comments

– Including a ‘Makefile’– All the files should be compressed with a ‘tar’ or ‘zip’ program– The compressed file should be named with “studentID.*”

Socket Programming in C

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