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Ipv4 Socket Address Structure

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 (16) */sa_family_t sin_family; /* AF_INET */

in_port_t sin_port; /* 16-bit TCP/UDP port number *//* network byte ordered */

struct in_addr sin_addr; /* 32-bit IPv4 address *//*network byte ordered*/

char sin_zero[8]; /* unused */ };

data structurenot exchanged between hosts

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struct in_addr {in_addr_t s_addr; /* 32-bit IPv4 address */


struct sockaddr_in {uint8_t sin_len; /* length of structure (16) */sa_family_t sin_family; /* AF_INET */in_port_t sin_port; /* 16-bit TCP/UDP port number */

/* network byte ordered */

struct in_addr sin_addr; /* 32-bit IPv4 address *//*network byte ordered*/

char sin_zero[8]; /* unused */ };

Generic Socket Address Structure

Passed as reference

Prior to void definition

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Generic Socket Address Structure

int bind(int, struct sockaddr *,

sock_len_t);

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Ipv6 Socket Address Structure

struct in6_addr {

uint8_t s6_addr[16]; /* 128-bit IPv6 address */


#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# */


uint32_t sin6_flowinfo; /* flow information, undefined */struct in6_addr sin6_addr; /* IPv6 address */


uint32_t sin6_scope_id; /* set of interfaces for a scope */ };

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Value-Results arguments

bind, connect, sento

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Value-Result arguments

Kernel to the process, size can change accept, recvfrom, getsockname,

getpeername

Fixed size data structure

Kernel informs howmuch information was

stored

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Socket Address Structures

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Byte ordering functions

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Internet Protocols

Network byte order big-endian

TCP Port: 16 bits

Ipv4 address: 32 bits

# include

uint16_t htons(uint16_t host16bitvalue) ;

uint32_t htonl(uint32_t host32bitvalue) ;

Both return: value in network byte order

uint16_t ntohs(uint16_t net16bitvalue) ;uint32_t ntohl(uint32_t net32bitvalue) ;

Both return: value in host byte order

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Byte manipulation function

Operates on multibyte fileds, without

interpreting the data, and without asumingthat the data is a null-terminated C string

bzero, bcopy, bcmp

memset, memcpy, memcmp

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f

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Address convertion function

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d it

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read, writelib/readn.c

1 #include "unp.h"

2 ssize_t /* Read "n" bytes from a descriptor. */

3 readn(int fd, void *vptr, size_t n)4 {

5 size_t nleft;

6 ssize_t nread;

7 char *ptr;

8 ptr = vptr;

9 nleft = n;10 while (nleft > 0) {

11 if ( (nread = read(fd, ptr, nleft)) < 0) {

12 if (errno == EINTR)

13 nread = 0; /* and call read() again */

14 else

15 return (-1);

16 } else if (nread == 0)17 break; /* EOF */

18 nleft -= nread;

19 ptr += nread;

20 }

21 return (n - nleft); /* return >= 0 */

22 }

d it

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read, writelib/writen.c

1 #include "unp.h"

2 ssize_t /* Write "n" bytes to a descriptor. */

3 writen(int fd, const void *vptr, size_t n)

4 {

5 size_t nleft;

6 ssize_t nwritten;

7 const char *ptr;

8 ptr = vptr;

9 nleft = n;

10 while (nleft > 0) {11 if ( (nwritten = write(fd, ptr, nleft))

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read, write1 # include "unp.h"

2 static int read_cnt;

3 static char *read_ptr;

4 static char read_buf[MAXLINE];5 static ssize_t

6 my_read(int fd, char *ptr)

7 {

8 if (read_cnt

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_

23 readline(int fd, void *vptr, size_t maxlen)

24 {

25 ssize_t n, rc;

26 char c, *ptr;

27 ptr = vptr;

28 for (n = 1; n < maxlen; n++) {29 if ( (rc = my_read(fd, &c)) == 1) {

30 *ptr++ = c;

31 if (c == '\n')

32 break; /* newline is stored, like fgets() */

33 } else if (rc == 0) {

34 *ptr = 0;

35 return (n - 1); /* EOF, n - 1 bytes were read */

36 } else

37 return (-1); /* error, errno set by read() */

38 }

39 *ptr = 0; /* null terminate like fgets() */

40 return (n);

41 }42 ssize_t

43 readlinebuf(void **vptrptr)

44 {

45 if (read_cnt)

46 *vptrptr = read_ptr;

47 return (read_cnt);48 }

read, write

isfdtype

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isfdtype

It checks whether the descriptor is a socket

descriptor

Socket functions for elementary TCP client server

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Socket functions for elementary TCP client-server

The socket API

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The socket API

Function socket

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

return > 0 if OK, -1 if error

Returns socket descriptor (small positive integer), similar to UNIX

file descriptor, to be used perform functions on the socket such as

read, write and close

socket

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socket

#include

int socket (int family, int type, int protocol);Returns: non-negative descriptor if OK, -1 on error

Socket Function

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Socket Function

Parameters:

family: specifies the protocol family:

AF_INET

for IPv4AF_INET6 for IPv6

AF_UNIX ouAF_LOCAL -Unix domain socket

type: specifies transport protocol:

SOCK_STREAM: stream socket for TCP

SOCK_DGRAM: datagram socket for UDP

protocol: usually set to zero

socket Function

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Combination of interest

Family Type

AF_INET SOCK_STREAM SOCK_DGRAM

AF_UNIX SOCK_STREAM SOCK_DGRAM

Exemple:sockfd = socket(AF_INET, SOCK_STREAM, 0),

creates an IPv4 socket to be used by TCP

socket Function

Connect Function

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int connect ( int sockfd, const struct

sockaddr *servaddr, int addrlen)

return 0 if OK, -1 if error,

Used for establishing a connection:three-wayhandshake

sockfd: return parameter of socket() servaddr: data structure initiated with remote

socket identifications (remote IP address, remoteport number)

For a client TCP, it is not necessary to performbind: the kernel chooses the local port ephemeralport number and the source IP number ifnecessary

Chosen in a way to avoid conflict of use of port

Connect Function

connect

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connect

errors

timeouterro ETIMEDOUT, 75 seconds,

configurable If the answer to a SYN segment is an RST one

error ECONNREFUSEDno process

listening to the port

Destination unreachable (ICMP), soft error, triesfor 75 seconds (4.4 BSD)

#include

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

Returns: 0 if OK, -1 on error

Bind Function

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int bind(int sockfd, (struct sockaddr)* myaddr, int socklen)

return 0 if OK, -1 if error

binda local protocol address given by thestructure myaddr to a socket (sockfd)

The application can let the kernel chooses the

IP address and the port number;

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If a host has more than one IP, then the kernel canchoose one

Ephemeral port numbers are chosen to avoidconflict with other socket

To let the kernel chooses the IP address theconstant INADDR_ANY should be assigned to theIP address myaddr

To let the kernel chooses an ephemeral portnumber the constant zero should be set to thecorresponding field of myaddr:

*myaddr.sin_port = 0;

*myaddr.sin_addr.s_addr = INADDR_ANY

bind

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bind

Bind performed by TCP server restricts the

socket to receiving incoming clientconnection destined only to that IP address

#include

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


bind

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No cliente, kernel faz o bind com oendereo IP da interface

Listen Function

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An active (client) socket is one that called connect com osocket, starting a 3-way handshake with a remote host;

An applications (server) which calls listen, makes anunconnected socket a passive one meaning that the kernelmust accept incoming connection requests directed to thissocket.

CLOSED LISTEN

Clients call connectwhile servers call listen followed byaccept

The backlogparameter indicates the total size of twoqueues: the complete queue (ESTABLISHED state) and the

incomplete connection queue (SYN_RVCD state)

int listen (int sockfd, (struct sockaddr) * myaddr, int backlog)

return 0 if OK, -1 if error

listen

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listen

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listen

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listen

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accept Function

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Called by a TCP server to return the next completed

connection from the front of the completed connectionqueue. If the queue is empty the process is oput to sleep

int accept (int sockfd, (struct sockaddr) * cliaddr, int * socklen)

returns nonnegative descriptor if OK, -1 if error

aadrlen is a value-result argument and it returns the size of

the structure pointed to by cliaddr, i.e., the number of bytes

stored by the kernel in the socket address structure.

fork- exec

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Fork is called once but it returns twice. The return valuetell the process whether it is a parent or a child

It returns once to the calling process (parent) with a return

value that is the process ID of the newly created process(child)

It returns once in the child, with a return value of zero (0)

All the descriptors opened by the parent before the forkare shared with the child after the fork.

connected sockts aer an accept and a fork is shared withthe

Two uses of fork: a process makes a copy of itself (fork)and a process executes another program (forke exec)

# include

pid_t fork(void);

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

fork-exec

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#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

fork-exec

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Concurrent server

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Concurrent server (iterative server)one server,

several connections. Concurrent server serves

several active connections.

Server performers a fork to create a child to

handle the client request

After accept, the server calls fork and the child

serves the client (on connfd, the connected

socket) and the parent waits for anotherconnection (on listenfd, the listening socket)

Concurrent server

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Connect returns a brand new socketdescriptor for the connection to be

established with the TCP client.

The return of a connect makes a socket a

connected socket.

On closing a socket only the specific

connection (socket) is closed, the server

remains listening to new socket connectionrequest

Concurrent server

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A close performed by the server does notimply in terminating the connection, a FYN

is sent only when the number of reference

to the descriptor in the file table is zero

when a child is created the number ofreference is incremented by one.

If a server does not close the socket none

of the children connections will be closedsince the number of reference will never

be zero and server runs out of descriptor

Concurrent server

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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 */

}

Concurrent server

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Concurrent server

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Concurrent server

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close

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SHUTDOWN used instead to force the

termination of a connection

#include

int close (int sockfd);


getsocknameand getpeername

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Returns the protocol address either local orremote

usos:

connectnot followed bybind After calling bind with 0 srgument

TCP server performs a bind in a wildcard port

#include

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

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


getsocketname and getpeername

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lib/sockfd_to_family.c

1 #include "unp.h"

2 int

3 sockfd_to_family(int sockfd)

4 {

5 struct sockaddr_storage ss;

6 socklen_t len;7 len = sizeof(ss);

8 if (getsockname(sockfd, (SA *) &ss, &len) < 0)

9 return (-1);

10 return (ss.ss_family);

11 }

TCP ports and concurrent servers

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multihomedone-or-any

any-wildcard

TCP ports and concurrent servers

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Documents

2nd Unit Ppt1