computer betwork for forth grades, Thesis of Computer Vision

Download computer betwork for forth grades and more Thesis Computer Vision in PDF only on Docsity!

Socket Programming

15-­‐441 Computer Networks, Spring 2010

Your TAs

Lecture Today

• MoCvaCon for sockets

• What’s in a socket?

• Working with socket

• Concurrent network applicaCons

• Project 1

IdenCfy the DesCnaCon

Connection socket pair

HTTP Server

(port 80)

Client

Client socket address

Server socket address

Client host address

Server host address

FTP Server

(port 21)

• Addressing

– IP address

– hostname (resolve to IP address via DNS)

• MulCplexing

– port

Sockets

• How to use sockets

– Setup socket

• Where is the remote machine (IP address, hostname)

• What service gets the data (port)

– Send and Receive

• Designed just like any other I/O in unix

• send -­‐-­‐ write

• recv -­‐-­‐ read

– Close the socket

Step 1 – Setup Socket

• Both client and server need to setup the socket

– int socket(int domain, int type, int protocol);

• domain

– AF_INET -­‐-­‐ IPv4 (AF_INET6 for IPv6)

• type

– SOCK_STREAM -­‐-­‐ TCP

– SOCK_DGRAM -­‐-­‐ UDP

• protocol

• For example,

– int sockfd = socket(AF_INET, SOCK_STREAM, 0);

Step 2 (Server) -­‐ Binding

• Only server need to bind

– int bind(int sockfd, const struct sockaddr *my_addr,

socklen_t addrlen);

• sockfd

– file descriptor socket() returned

• my_addr

– struct sockaddr_in for IPv

– cast (struct sockaddr_in) to (struct sockaddr)

struct sockaddr_in { short sin_family; // e.g. AF_INET unsigned short sin_port; // e.g. htons(3490) struct in_addr sin_addr; // see struct in_addr, below char sin_zero[8]; // zero this if you want to }; struct in_addr { unsigned long s_addr; // load with inet_aton() };

Step 2 (Server) -­‐ Binding contd.

• addrlen

– size of the sockaddr_in

struct sockaddr_in saddr; int sockfd; unsigned short port = 80; if((sockfd=socket(AF_INET, SOCK_STREAM, 0) < 0) { // from back a couple slides printf(“Error creating socket\n”); ... } *memset(&saddr, '\0', sizeof(saddr)); // zero structure out saddr.sin_family = AF_INET; // match the socket() call saddr.sin_addr.s_addr = htonl(INADDR_ANY); // bind to any local address saddr.sin_port = htons(port); // specify port to listen on if((bind(sockfd, (struct sockaddr ) &saddr, sizeof(saddr)) < 0) { // bind! printf(“Error binding\n”); ... }

What is htonl(), htons()?

• Byte ordering

– Network order is big-­‐endian

– Host order can be big-­‐ or lidle-­‐endian

• x86 is lidle-­‐endian
• SPARC is big-­‐endian

• Conversion

– htons(), htonl() : host to network short/long

– ntohs(), ntohl() : network order to host short/long

• What need to be converted?

– Addresses

– Port

– etc.

Step 4 (Server) -­‐ Accept

• Server must explicitly accept incoming connec<ons

– int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen)

• sockfd

– again... file descriptor socket() returned

• addr

– pointer to store client address, (struct sockaddr_in *) cast to

(struct sockaddr *)

• addrlen

– pointer to store the returned size of addr, should be sizeof

(*addr)

• For example

– int isock=accept(sockfd, (struct sockaddr_in *) &caddr, &clen);

Put Server Together

struct sockaddr_in saddr, caddr; int sockfd, clen, isock; unsigned short port = 80; if((sockfd=socket(AF_INET, SOCK_STREAM, 0) < 0) { // from back a couple slides printf(“Error creating socket\n”); ... } memset(&saddr, '\0', sizeof(saddr)); // zero structure out saddr.sin_family = AF_INET; // match the socket() call saddr.sin_addr.s_addr = htonl(INADDR_ANY); // bind to any local address saddr.sin_port = htons(port); // specify port to listen on if((bind(sockfd, (struct sockaddr *) &saddr, sizeof(saddr)) < 0) { // bind! printf(“Error binding\n”); ... } if(listen(sockfd, 5) < 0) { // listen for incoming connections printf(“Error listening\n”); ... } *clen=sizeof(caddr) if((isock=accept(sockfd, (struct sockaddr ) &caddr, &clen)) < 0) { // accept one printf(“Error accepting\n”); ... }

Domain Name System (DNS)

• What if I want to send data to “www.slashdot.org”?

– DNS: Conceptually, DNS is a database collecCon of host entries

• hostname -­‐> IP address

– struct hostent *gethostbyname(const char *name);

• IP address -­‐> hostname

– struct hostent *gethostbyaddr(const char *addr, int len, int

type);

struct hostent { char *h_name; // official hostname char **h_aliases; // vector of alternative hostnames int h_addrtype; // address type, e.g. AF_INET int h_length; // length of address in bytes, e.g. 4 for IPv char **h_addr_list; // vector of addresses char *h_addr; // first host address, synonym for h_addr_list[0] };

Put Client Together

struct sockaddr_in saddr; struct hostent *h; int sockfd, connfd; unsigned short port = 80; if((sockfd=socket(AF_INET, SOCK_STREAM, 0) < 0) { // from back a couple slides printf(“Error creating socket\n”); ... } if((h=gethostbyname(“www.slashdot.org”)) == NULL) { // Lookup the hostname printf(“Unknown host\n”); ... } memset(&saddr, '\0', sizeof(saddr)); // zero structure out saddr.sin_family = AF_INET; // match the socket() call *memcpy((char ) &saddr.sin_addr.s_addr, h->h_addr_list[0], h->h_length); // copy the address saddr.sin_port = htons(port); // specify port to connect to *if((connfd=connect(sockfd, (struct sockaddr ) &saddr, sizeof(saddr)) < 0) { // connect! printf(“Cannot connect\n”); ... }

TCP Framing

• TCP does NOT guarantee message boundaries

– IRC commands are terminated by a newline

– But you may not get one at the end of read(), e.g.

• One Send “Hello\n”

• MulCple Receives “He”, “llo\n”

– If you don’t get the enCre line from one read(),

use a buffer

Client /

Server

Session

Client Server

socket socket

bind

listen

read

read write

write

Connection

request

read

close

close

EOF

open_listenfd

connect accept

open_clientfd

Revisited