%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%% THE MIDGARD MAGICPOINT TEMPLATE
%%
%% Copyright(c) 1999 Henri Bergius <Henri.Bergius@iki.fi>
%% 
%% A template for making MagicPoint presentations for
%% Midgard. Originally written for MagicPoint 1.06a
%% and the Midgard Workshop in October 1999.
%%
%% This version is for print usage, with white background.
%%
%% See the Midgard CVS repository for usage examples.
%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%deffont "standard"   tfont "arial.ttf",   xfont "helvetica-medium-r"
%deffont "thick"      tfont "arialbd.ttf", xfont "helvetica-bold-r"
%deffont "code"       tfont "courbd.ttf",  xfont "courier-medium-r"
%%
%% Default settings per each line numbers.
%%
%% The page settings:
%default 1 leftfill, size 2, fore "black", back "white", font "thick", bimage "background.jpg" 1024x768
%%
%% Format the header:
%default 2 size 7, vgap 70, prefix "   "
%%
%% Have a bar:
%default 3 size 2, bar "brown" 5, vgap 50
%%
%% The standard text settings:
%default 4 size 5, fore "black", vgap 50, prefix "   ", font "standard"
%%
%% Default settings that are applied to TAB-indented lines.
%%
%tab 1 size 4, vgap 40, prefix "       ", icon box "brown" 30
%tab 2 size 3, vgap 30, prefix "               ", icon arc "gray30" 30
%tab 3 size 2, vgap 30, prefix "                                  ", icon delta3 "black" 40
%%
%% Enable page caching (immediate, no effect, high speed)
%%
#%pcache 1 1 1 1
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

%center, size 4

%size 7
Introduction to Socket Programming

%right
%size 4
by Bart Trojanowski    
bart@jukie.net    

%cont, center
%image "linux-logo.png"
%size 2
December OCLUG meeting
2001-12-06

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Overview

	The Phone Analogy
	The Sockets API
	Network Byte Order
	Naming Services
	Client & Server
	Data Transfer
	Socket I/O Control
	References


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

The Phone Analogy

	"Phone number" == "IP address"
		must be predefined and known by both parties
		google.com == 216.239.33.100 as \
			555-1212 == some guy in the movie

	"Extension" == "Port number"
		also predefined and known by both parties
		port 80 == HTTP as extension 0 == operator

	"411 number directory" == "DNS"
		accessing the directory is optional; i.e. connection can be \
			made by already resolved number

	"Caller" == "client"
		client initiates the connection knowing the IP address \
			and port number 

	"Recipient" == "server"
		server listens on the specific IP address and port number \
			for new connections


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

...The Phone Analogy

	Placing a call:
%mark
		get a phone		
%again, font "code"
                              socket()
%mark, font "standard"
		select outgoing line		
%again, font "code"
                              bind()
%mark, font "standard"
		dial the number		
%again, font "code"
                              connect()
%mark, font "standard"
		talk			
%again, font "code"
                              read()/write()
%mark, font "standard"
		hang up			
%again, font "code"
                              close()
%font "standard"

	Accepting a call:
%mark
		get a phone		
%again, font "code"
                              socket()
%mark, font "standard"
		select incoming line	
%again, font "code"
                              bind()
%mark, font "standard"
		turn on the ringer		
%again, font "code"
                              listen()
%mark, font "standard"
		pickup a ringing phone	
%again, font "code"
                              accept()
%mark, font "standard"
		talk			
%again, font "code"
                              read()/write()
%mark, font "standard"
		hang up			
%again, font "code"
                              close()
%font "standard"


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

The Sockets API
%right
... continuation of the Phone Analogy            
%left
	use "
%cont, font "code"
socket
%cont, font "standard"
" to create a phone (socket)
		must specify domain and type for new socket:
			PF_INET: IPv4  
%cont, font "thick"
domain		
%cont, font "standard", icon delta3 "gray30" 30
SOCK_DGRAM: datagram oriented (UDP 
%cont, font "thick"
type
%cont, font "standard"
)
			PF_INET6: IPv6 
%cont, font "thick"
domain		
%cont, font "standard", icon delta3 "gray30" 30
SOCK_STREAM: connection oriented (TCP 
%cont, font "thick"
type
%cont, font "standard"
)

	use "
%cont, font "code"
bind
%cont, font "standard"
" to set your extension (port) number
		this is a local setup step (plug in the phone and configure it)
		client may decide to use a dynamically allocated number
		server should set this number; there are exceptions (ftp data)

	use "
%cont, font "code"
listen
%cont, font "standard"
" to turn on the ringer
		server must start listening before any connection can be made

	use "
%cont, font "code"
accept
%cont, font "standard"
" to pick up a ringing phone
		server accepts a connection via this function call
		the IP address of the client is revealed by this call

	use "
%cont, font "code"
connect
%cont, font "standard"
" to dial the server
		the client calls this function to issue the "call"
		step is optional for datagram sockets as there is no connection


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Network Byte Order

	Internet protocols use big-endian byte ordering for multi-byte fields

	It is up to the network programmer to deal with ordering changes
		good style dictates calling byte-ordering change functions \
			even on big-endian only systems

%font "code", right, size 2
 #include <netinet/in.h>         
%font "standard", left
	"
%cont, font "code"
ntohs, ntohl
%cont, font "standard"
" - convert network to host byte order

%font "code", right, size 2
 #include <netinet/in.h>         
%font "standard", left
	"
%cont, font "code"
htons, htonl
%cont, font "standard"
" - convert host to network byte order

	Internet data is composed of 8-bit entities called octets
		today an octet is equivalent to a byte
		past systems, like the DEC-10, did not use 8-bit bytes


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Naming Services
%font "code", right, size 2
 #include <netdb.h>         
%font "standard", left
	"
%cont
%font "code"
gethostbyname
%cont
%font "standard"
" - lookup hostname in DNS, NIS, /etc/hosts, etc.
		query can be made on an dotted-decimal or host name strings
		returns all matches for query
		supports IPv4 or IPv6 (not both at the same time)

%font "code", right, size 2
 #include <netdb.h>         
%font "standard", left
	"
%cont
%font "code"
gethostbyname2
%cont
%font "standard"
" - better support for IPv6
		allows caller to specify address family to return

%font "code", right, size 2
 #include <netdb.h>         
%font "standard", left
	"
%cont
%font "code"
gethostbyaddr
%cont
%font "standard"
" - reverse lookup
		takes an address and returns the same structure as the other \
			look-up functions

%font "code", right, size 2
 #include <netdb.h>         
%font "standard", left
	"
%cont
%font "code"
getservbyname, getservbyport
%cont
%font "standard"
" - search /etc/services
		allows to locate port numbers from service names \
			and the reverse
		works for UDP and TCP protocol types

	"
%cont, font "code"
gethostbyname_r, gethostbyaddr_r 
%cont, font "standard"
" are reenterant


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

...Naming Services

%font "code", right, size 2
 #include <apra/in.h>         
%font "standard", left
	"
%cont
%font "code"
inet_aton, inet_ntoa, inet_addr
%cont
%font "standard"
" - IPv4 only
		convert between dotted-decimal string and its 32-bit network \
			byte ordered binary
		example: "1.2.3.4" <==> 0x04030201 (on a little-endian host)

%font "code", right, size 2
 #include <apra/in.h>         
%font "standard", left
	"
%cont
%font "code"
inet_pton, inet_ntop
%cont
%font "standard"
" - IPv4 and IPv6
		convert between presentation format and numeric network \
			byte ordered binary

%font "code", right, size 2
 #include <netdb.h>         
%font "standard", left
	"
%cont
%font "code"
getaddrinfo
%cont
%font "standard"
" - more informative hostname lookup
		provides a common interface to all of the services just covered
		returns an array of structures which can be used by 
%cont, font "code"
bind
%cont, font "standard"
 and 
%cont, font "code"
connect
%font "standard"

%font "code", right, size 2
 #include <netdb.h>         
%font "standard", left
	"
%cont
%font "code"
getnameinfo
%cont
%font "standard"
" - reverse of above
		takes an initialized socket address structure and uses \
			it for DNS lookup


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

The Client

	The simple client:
%font "code", size 2, vgap 5
        int main (void)
        {
            int                  sock;
            struct sockaddr_in   serv_addr;
            
            sock = socket (AF_INET, SOCK_STREAM, 0);
            
            serv_addr.sin_family = AF_INET;
            serv_addr.sin_port = htons (110);	/* pop3 client */
            inet_aton ("127.0.0.1", &serv_addr.sin_addr);
            
            connect (sock, &serv_addr, sizeof (serv_addr));
            
            ...
            
            close (sock);
        }

%font "standard"
	Common client tasks:
		create a socket
		optionally bind to a local port
		create a server socket structure
		connect to server
		communicate
		close the server socket


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

The Server

	The simple server:
%font "code", size 2, vgap 5
        int main (void)
        {
            int                  serv, cli, cli_len;
            struct sockaddr_in   serv_addr, cli_addr;
            
            serv = socket (AF_INET, SOCK_STREAM, 0);
            
            serv_addr.sin_family = AF_INET;
            serv_addr.sin_port = htons (110);       /* pop3 server */
            serv_addr.sin_addr.s_addr = htonl (INADDR_ANY);
            bind (serv, &serv_addr, sizeof (serv_addr));
            listen (serv, 5);
            
            for (;;) {
                cli_len = sizeof (cli_addr);
                cli = accept (serv, &cli_addr, &cli_len);
                ...
                close (cli);
            }
            close (serv);
        }

%font "standard"
	Common server tasks:
		create a socket
		create a server socket structure and bind on it
		start listening for connections
		accept client connections
		communicate and close client socket
		close the server socket


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

...The Server (concurrent clients)

	Multi-threaded
		one server thread handles all accepts
		the server thread creates a new agent thread for each client accepted
		agents handle requests for their specific clients

	Select / Poll
		one process solution using the select or poll system calls
		process alternates between the server and client sockets


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

...The Server (select)

%font "code", size 2, vgap 5
        int main (void)
        {
            int sock_fd[MAX_TO_HANDLE], sock_num=0, fd_max=0, i;
            fd_set rfds;
            
            fd_max = sock_fd[sock_num++] = socket (AF_INET, SOCK_STREAM, 0);
            /* setup the socket */
            ...

            FD_ZERO (&rfds);
            FD_SET (sock_fd[0], &rfds);
            for (;;) {

                select (fd_max + 1, &rfds, NULL, NULL, NULL);
                if (FD_ISSET (sock_fd[0], &rfds)) {
                    sock_fd[sock_num] = accept (sock_fd[0], NULL, NULL);
                    if (fd_max < sock_fd[sock_num])
                        fd_max = sock_fd[sock_num];
                    sock_num++;
                }
                FD_SET (sock_fd[0], &rfds);

                for (i=1; i<sock_num; i++) {
                    if (FD_ISSET (sock_fd[i], &rfds)) {
                        /* do something with this client */
                        ...
                    }
                    FD_SET (sock_fd[i], &rfds);
                }
            }
        }
%font "standard"

	select does not scale - poll is a more suitable replacement


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Data Transfer

	Datagram transfer
		mainly used by UDP and other non-stream protocols
		can be used for stream protocols but there is no benefit
		client and server use "
%cont, font "code"
recv/recvfrom/recvmsg
%cont, font "standard"
" and "
%cont, font "code"
send/sendto/sendmsg
%cont, font "standard"
" to communicate over the socket

	Unbuffered transfer
		can be used by any protocol (UDP, TCP, etc)
		client and server use "
%cont, font "code"
read
%cont, font "standard"
" and "
%cont, font "code"
write
%cont, font "standard"
" to communicate over the socket
		this is no different if the file-descriptor was opened with "
%cont, font "code"
open
%cont, font "standard"
"
		most of the standard "
%cont, font "code"
ioctl
%cont, font "standard"
" calls function as if the socket was a file-descriptor

	Buffered stream transfer
		seldom used
		client and server use "
%cont, font "code"
fdopen
%cont, font "standard"
" to convert a socket into a "
%cont, font "code"
FILE
%cont, font "standard"
" pointer
		then client and server use "
%cont, font "code"
fread
%cont, font "standard"
" and "
%cont, font "code"
fwrite
%cont, font "standard"
" to communicate over the socket
		functions like "
%cont, font "code"
fprintf
%cont, font "standard"
" and "
%cont, font "code"
fscanf
%cont, font "standard"
" can be used directly on the "
%cont, font "code"
FILE
%cont, font "standard"
" pointer
		this type functions similarly to a "
%cont, font "code"
FILE
%cont, font "standard"
" opened with "
%cont, font "code"
fopen
%cont, font "standard"
"

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Socket I/O Control

%font "code", right, size 2
 #include <sys/types.h>        
 #include <sys/socket.h>        
%font "standard", left
	"
%cont, font "code"
getsockopt
%cont, font "standard"
" and "
%cont, font "code"
setsockopt
%cont, font "standard"
"
		manipulate options associated with a socket
		each function takes a protocol level and option to access as \
				parameters
		for example this call allows the port of a bound socket \
			to be reused quickly:
%font "code", size 3
       getsockopt (s, SOL_SOCKET, SO_REUSEPORT, &value);
%font "standard"
		some other useful values include:
			SOL_SOCKET, SO_SNDBUF - set send buffer
			SOL_SOCKET, SO_RCVBUF - set receive buffer
			IPPROTO_IP, IP_TOS - set TOS field in IP header
			IPPROTO_IP, IP_TTL - set TTL field in IP header
			IPPROTO_TCP, TCP_MAXRT - set maximum retransmit time
			IPPROTO_TCP, TCP_MAXSEG - set maximum segment size
			IPPROTO_TCP, TCP_KEEPALIVE - set number of seconds \
				between TCP keep-alive probes

	Useful "
%cont, font "code"
ioctl
%cont, font "standard"
" calls for sockets
		"
%cont, font "code"
ioctl
%cont, font "standard"
" calls can be made on sockets just in the same way as on file descriptors
		some interesting ioctls include:
			FIONREAD - get the amount of unread data in \
				receive buffer
			TIOCOUTQ - get the amount of unsent data in \
				send buffer
			SIOCGSTAMP - get timestamp of last packet \
				received
			FIOASYNC - change to asynchronous I/O mode \
				(non blocking event driven interaction)


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

References

	Books:
		UNIX Network Programming Vol I, by W. Richard Stevens
			2nd Ed, 1998, Prentice Hall
			this is a fantastic book by an amazing author; \
			never hesitate to purchase any book by this man; \
			sadly he is no longer with us

	Man pages:
		Socket specific system calls:
			socket(2)
			bind(2)
			listen(2)
			accept(2)
			connect(2)
			getsockopt(2)
			recv(2)
			sned(2)
		Relevant system calls:
			read(2)
			write(2)
			ioctl(2)
		Information about socket configuration:
			socket(7)
			ip(7)
			tcp(7)


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

...References (on the web)

	BSD Sockets: A Quick And Dirty Primer
		http://ftp.std.com/homepages/jimf/sockets.html

	An Introduction to Socket Programming
		http://www.uwo.ca/its/doc/courses/notes/socket/index.html

	UNIX Network Programming
		http://www-net.cs.umass.edu/ntu_socket/

	Beej's Guide to Network Programming Beej's Guide to Network Programming
		http://www.ecst.csuchico.edu/~beej/guide/net/

	Spencer's Socket Site
		http://www.lowtek.com/sockets/

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

...References (even more on the web)

	Introduction to Socket Programming
		http://www.linuxgazette.com/issue47/bueno.html

	Linux Network Programming (a magazine column)
		http://www2.linuxjournal.com/lj-issues/issue46/2333.html
		http://www2.linuxjournal.com/lj-issues/issue47/2335.html
		http://www2.linuxjournal.com/lj-issues/issue48/2336.html

	BSD Sockets Programming Tutorial
		http://www.ecst.csuchico.edu/~chafey/prog/sockets/sinfo1.html

	UNIX Socket FAQ
		http://www.lcg.org/sock-faq/

	Socket Programming in C (examples)
		http://pont.net/socket/