In questa lezione vedremo: Fondamenti di Informatica C ex Uni/Sito...

Fondamenti di Informatica CRiccardo Cassinis 11/24/02 16:39

Lezione 15: Connettività in rete 1

Fondamenti di Informatica C

Lezione 15:Connettività in rete

11/24/02 16:39Lezione 15: Connettività in rete 2

In questa lezione vedremo:

ÎI primi rudimenti dello scambio “programmato” diinformazioni attraverso la rete

ÎUn orizzonte incredibilmente vasto


L’identificazione della macchina

ÎDue forme possibili:l Dotted quad: 192.167.20.92l 4 x 8 = 32 bit: 2564 possibili indirizzi (in teoria) =

4.294.967.296 indirizzi• Indirizzi pubblici• Indirizzi privati:

– 10.000.000.001 - 10.255.255.254– 172.016.000.001 - 172.031.255.254– 192.168.000.001 - 192.168.255.254

• Indirizzi speciali:– Broadcast– Localhost.localdomain (127.0.0.1)

l Domain Name System: zeus.ing.unibs.it


Due parole sulla struttura della rete:

Nodo

Nodo

Nodo

Nodo

Nodo

NodoNodo

Nodo

Gateway

Gateway

Name server




L’identificazione della macchina

Il package java.netl InetAddress.getByName(<nome>) ritorna un oggetto di tipo

InetAddressl InetAddress.getByName(null) ritorna un oggetto di tipo

InetAddress che si riferisce al calcolatore su cui gira ilprogramma chiamante (oppure ancheInetAddress.getByName(“localhost”)oInetAddress.getByName(“127.0.0.1”)


Le porte

ÎUn indirizzo IP non è sufficiente per identificare unserver, perché sulla stessa macchina possono esistere piùserver

ÎLe porte sono identificate da un numero a 16 bit, cheindica il servizio associato a quella porta

ÎLe porte da 1 a 1024 sono riservate al sistemaÎC’è una convenzione internazionale sull’uso delle porte:

http://www.iana.org/assignments/port-numbers


I socket (1)

l The socket is the software abstraction used torepresent the “terminals” of a connectionbetween two machines.

l For a given connection, there’s a socket on eachmachine, and you can imagine a hypothetical“cable” running between the two machines witheach end of the “cable” plugged into a socket. Ofcourse, the physical hardware and cablingbetween machines is completely unknown. Thewhole point of the abstraction is that we don’thave to know more than is necessary.


I socket (2)

ÎIn Java, you create a socket to make the connectionto the other machine, then you get anInputStream and OutputStream (or, with theappropriate converters, Reader and Writer)from the socket in order to be able to treat theconnection as an I/O stream object.

ÎThere are two stream-based socket classes: aServerSocket that a server uses to “listen” forincoming connections and a Socket that a clientuses in order to initiate a connection.




I socket (3)

ÎOnce a client makes a socket connection, theServerSocket returns (via the accept( ) method)a corresponding Socket through whichcommunications will take place on the server side.

ÎFrom then on, you have a true Socket to Socketconnection and you treat both ends the same waybecause they are the same. At this point, you usethe methods getInputStream( ) andgetOutputStream( ) to produce thecorresponding InputStream andOutputStream objects from each Socket.


Riassumendo: Client Vs. Server (1)

InetAddress addr = InetAddress.getByName("frank.ing.unibs.it");InetAddress addr = InetAddress.getByName("frank.ing.unibs.it");

ServerSocket s = new ServerSocket(PORTNUMBER); ServerSocket s = new ServerSocket(PORTNUMBER);

Socket socket = s.accept();Socket socket = s.accept();

Socket socket = new Socket(addr, PORTNUMBER);Socket socket = new Socket(addr, PORTNUMBER);

Attenzione! accept()blocca l’esecuzione del

metodo chiamante!



BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));




PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())),true);






String str = in.readLine();String str = in.readLine();

String str = in.readLine();String str = in.readLine();

out.println(str);out.println(str);

out.println(”bla bla");out.println(”bla bla");





socket.close();socket.close();

s.close();s.close();

socket.close();socket.close();


Vediamo un semplice server...

ÎQuesta non è una applet, ma non importa!


E un client che lo usi...

ÎQuesto è il client


Dove si va da qui?

ÎGet some information from that machine overthere and move it to this machine here, or viceversa. This is accomplished with basic networkprogramming.

ÎConnect to a database, which may live across anetwork. This is accomplished with Java DataBaseConnectivity (JDBC), which is an abstraction awayfrom the messy, platform-specific details of SQL(the structured query language used for mostdatabase transactions).




E inoltre...

ÎProvide services via a Web server. This isaccomplished with Java’s servlets and Java ServerPages (JSPs).

ÎExecute methods on Java objects that live onremote machines transparently, as if those objectswere resident on local machines. This isaccomplished with Java’s Remote MethodInvocation (RMI).

ÎUse code written in other languages, running onother architectures. This is accomplished using theCommon Object Request Broker Architecture(CORBA), which is directly supported by Java.


Ancora...

ÎIsolate business logic from connectivity issues,especially connections with databases includingtransaction management and security. This isaccomplished using Enterprise JavaBeans (EJBs).EJBs are not actually a distributed architecture,but the resulting applications are usually used in anetworked client-server system.

ÎEasily, dynamically, add and remove devices froma network representing a local system. This isaccomplished with Java’s Jini.


High School/Jr.High

10 PRINT "HELLO WORLD"

20 END


First year in College

program Hello(input, output) begin writeln('Hello World') end.




Senior year in College

(defun hello (print (cons 'Hello (list 'World))))


New professional

(include) <stdio.h

void main(void)

{

char *message[] = {"Hello ", "World"}; int i;

for(i = 0; i <2; ++i)

printf("%s", message[i]);

printf("\n");

}


Seasoned professional

class string { private: int size; char *ptr; public: string() : size(0), ptr(new char('\0')) {} string(const string &s) : size(s.size) { ptr = new char[size + 1]; strcpy(ptr, s.ptr); } ~string() { delete [] ptr; } friend ostream &operator <<(ostream &, const string

&); string &operator=(const char *); }; ostream &operator<<(ostream &stream, const string &s) { return(stream << s.ptr); } string &string::operator=(const char *chrs) { if (this != &chrs) {

delete [] ptr;

size = strlen(chrs);

ptr = new char[size + 1];

strcpy(ptr, chrs);

}

return(*this);

}

int main()

{ string str;

str = "Hello World";

cout << str << endl;

return(0);

}


Master Programmer

[ uuid(2573F8F4-CFEE-101A-9A9F-00AA00342820) ] library LHello { // bring in the master library importlib("actimp.tlb"); importlib("actexp.tlb"); // bring in my interfaces include "pshlo.idl" [ uuid(2573F8F5-CFEE-101A-9A9F-00AA00342820) ] cotype THello { interface IHello; interface IPersistFile; }; }; [ exe,

importheader(windows.h); importheader(ole2.h); importheader(except.hxx); importheader("pshlo.h"); importheader("shlo.hxx"); importheader("mycls.hxx"); // needed typelibs importlib("actimp.tlb"); importlib("actexp.tlb"); importlib("thlo.tlb"); [

uuid(2573F891-CFEE-101A-9A9F-00AA00342820),aggregatable

]

coclass CHello

{

cotype THello;

};

};

include "ipfix.hxx"

extern HANDLE hEvent;

class CHello : public CHelloBase

{

public:

IPFIX(CLSID_CHello);

CHello(IUnknown *pUnk);

~CHello();

HRESULT __stdcall PrintSz(LPWSTR pwszString);

private:

static int cObjRef; };

include windows.h

include ole2.h

include stdio.h

include stdlib.h

include "thlo.h"

include "pshlo.h"

include "shlo.hxx"

include "mycls.hxx"

int CHello::cObjRef = 0;

CHello::CHello(IUnknown *pUnk) : CHelloBase(pUnk)




Apprentice Hacker

/usr/local/bin/perl

$msg="Hello, world.\n";

if ($#ARGV = 0) { while(defined($arg=shift(@ARGV))) {

$outfilename = $arg;

open(FILE, "" . $outfilename) || die "Can't write $arg: $!\n";

print (FILE $msg);

close(FILE) || die "Can't close $arg: $!\n";

}

} else { print ($msg);

}

1;


Experienced Hacker

include stdio.h

define S "Hello, World\n"

main(){exit(printf(S) == strlen(S) ? 0 : 1);}


Seasoned Hacker

% cc -o a.out ~/src/misc/hw/hw.c

% a.out


Guru Hacker

% cat

Hello, world. ^D




New Manager

10 PRINT "HELLO WORLD"

20 END


Middle Manager

mail -s "Hello, world." bob@b12

Bob, could you please write me a program that prints "Hello,

world."? I need it by tomorrow.

^D


Senior Manager

% zmail jim

I need a "Hello, world." program by thisafternoon.


Chief Executive

% letter letter: Command not found. % mail To: ^X ^F ^C % help mail help: Command not found. % damn! !: Event unrecognized % logout

In questa lezione vedremo: Fondamenti di Informatica C ex Uni/Sito...

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