Lab 5 Sockets

Useful Sockets Links(courtesy of Stanford University)

Programming UNIX Sockets in C - Frequently Asked Questions http://www.softlab.ntua.gr/facilities/documentation/unix/unix-socket-faq/unix-socket-faq.html

Sockets Programming http://www.scit.wlv.ac.uk/~jphb/comms/sockets.htmlSocket Interface

http://www.netbook.cs.purdue.edu/cs363/lecture_notes/ chap22/chap22_0.html

BSD Sockets: A Quick and Dirty Primer http://world.std.com/~jimf/papers/sockets/sockets.html

Beej's Guide to Network Programming http://www.ecst.csuchico.edu/~beej/guide/netSockets Tutorial http://www.cs.rpi.edu/courses/sysprog/sockets/sock.html

Compiling Socket Code#include <netdb.h>

#include <sys/socket.h>

gcc -lsocket -lnsl -g -Wall -o foo foo.c

Outgoing Socket#include <netdb.h>#include <sys/socket.h>#define HTTP_PORT 80int main() { int our_socket; struct sockaddr_in serverAddr; struct hostent *destination;

destination = gethostbyname("ftp.redhat.com"); //Also works with “10.0.1.100” format

if(destination==NULL) { printf("No such host\n"); exit(1);

}

Two Data StructuresOne will get filled in for us..We'll have to copy info into the other...

gethostbynamestruct hostent *gethostbyname(const char *name);

People operate the Internet with names.. i.e. "www.google.com", "ftp.redhat.com"

The Internet itself operates using 32 bit numbers to identify computers. These numbers are known as Internet Protocol (IP) addresses.

gethostbyname() finds, builds and returns address of a data structure with information on the web site/ftp site with the specified name

Outgoing Socket (cont'd)//now we have to copy info from//one data structure to another//That's all these 2 lines do...serverAddr.sin_family = destination->h_addrtype;

memcpy((char *)&serverAddr.sin_addr.s_addr,destination->h_addr_list[0],destination->h_length );

What does the memcpy function do?What are its parameters?

PortsEach IP address has 65,536 "Ports" associated

with it. Some of these ports have standardized uses:

Port Use21 FTP Server (Control)22 SSH Server80 HTTP Server443 Secure HTTP (TLS/SSL)

We have to select the port number that we want to access on the server:

serverAddr.sin_port = htons(HTTP_PORT);

Outgoing Socket

serverAddr.sin_port = htons(HTTP_PORT);

//htons = 'host to network'

//remember big and little endian?

our_socket = socket(AF_INET, SOCK_STREAM, 0);

if(our_socket < 0)

{printf("cannot open socket\n");exit(1);

}

Connecting Outgoing Socketint server_response;

server_response = connect(our_socket, (struct sockaddr *) &serverAddr, sizeof(serverAddr));

if(server_response < 0) { printf("cannot connect\n"); exit(1);

}

Connect

int connect(int sockfd,

const struct sockaddr *serv_addr,

socklen_t addrlen);

Reading from Socketchar temp;int bytes_read;while (1) {

bytes_read = recv(our_socket, &temp, 1, 0);

if (bytes_read != 1) { break;}printf (“%c\n”, temp);

}

Receiving Data

Returns -1 if unsuccessful. Otherwise number of bytes read. Must pass in pointer to a buffer that you want to read in to and the size of that buffer.

size_t recv (int socket, void *buffer, size_t buffer_size, int flags)

You can cast an int to a size_t for buffer_sizeYou can set additional flags or use 0 for flags

Sending Dataint bytes_sent;char request[18]=“GET / HTTP/1.0\012\015\012\015”;

bytes_sent = send(our_socket, request, strlen(request), 0);

if (bytes_sent != strlen(request)) { printf("We didn't send the

command properly\n"); return 0;

}

Sending Data

Returns -1 if unsuccessful. Otherwise number of bytes sent. Must pass in pointer to a buffer that you want to send and the size of that buffer.

size_t send (int socket, void *buffer,

size_t buffer_size, int flags)

You can cast an int to a size_t for buffer_sizeYou can set additional flags or use 0 for flags

Closing the Socketshutdown(our_socket,SHUT_RDWR);

SHUT_RD = No more receptions;

SHUT_WR = No more transmissions;

SHUT_RDWR = No more receptions or transmissions.

Incoming Socket#define DATA_PORT 5999

int our_socket;

struct sockaddr_in localAddr;

/* Set up data socket */

localAddr.sin_family = AF_INET;

localAddr.sin_addr.s_addr = htonl(INADDR_ANY);

localAddr.sin_port = htons(DATA_PORT);

Creating Incoming Socket

our_socket = socket(AF_INET, SOCK_STREAM, 0);

Binding Incoming Addressint response;

response = bind(our_socket, (struct sockaddr *) &localAddr, sizeof(localAddr));

if(response < 0)

{ exit(1);

}

Listening for Incoming

int response, N=1;response = listen(our_socket, N);if (response != 0) {printf("Cannot listen on port\n");}

Prepare to accept connections on socket. N connectionrequests will be queued before further requests arerefused.Returns 0 on success, -1 for errors

extern int listen (int socket, int N);

Accept Incoming Socketint nsock;

nsock = accept(our_socket, 0, 0);

int accept (int listening_socket, struct sockaddr * address,socklen_t * address_length);

FTP ServerComputer10.0.1.100

Lab Computer10.0.1.X(x is a number)

Port 21 Control Connection

Data Connection

Commands

Your File