Chapter 2 Application Layer

Transcription

1 Chapter 2 Application Layer Thanks and enjoy! JFK/KWR All material copyright J.F Kurose and K.W. Ross, All Rights Reserved Computer Networking: A Top Down Approach Featuring the Internet, 3 rd edition. Jim Kurose, Keith Ross Addison-Wesley, July : Application Layer 1 Chapter 2: Application layer 2.1 Principles of network applications 2.2 Web and HTTP 2.3 FTP 2.4 Electronic Mail SMTP, POP3, IMAP 2.5 DNS 2.6 P2P file sharing 2.7 Socket programming with TCP 2.8 Socket programming with UDP 2.9 Building a Web server 2: Application Layer 2 1

2 Chapter 2: Application Layer Our goals: conceptual, implementation aspects of network application protocols transport-layer service models client-server paradigm peer-to-peer paradigm learn about protocols by examining popular application-level protocols HTTP FTP SMTP / POP3 / IMAP DNS programming network applications socket API 2: Application Layer 3 Some network apps Web Instant messaging Remote login P2P file sharing Multi-user network games Streaming stored video clips Internet telephone Real-time video conference Massive parallel computing 2: Application Layer 4 2

3 Creating a network app Write programs that run on different end systems and communicate over a network. e.g., Web: Web server software communicates with browser software little software written for devices in network core network core devices do not run user application code application on end systems allows for rapid app development, propagation application transport network data link physical application transport network data link physical application transport network data link physical 2: Application Layer 5 Chapter 2: Application layer 2.1 Principles of network applications 2.2 Web and HTTP 2.3 FTP 2.4 Electronic Mail SMTP, POP3, IMAP 2.5 DNS 2.6 P2P file sharing 2.7 Socket programming with TCP 2.8 Socket programming with UDP 2.9 Building a Web server 2: Application Layer 6 3

4 Application architectures Client-server Peer-to-peer (P2P) Hybrid of client-server and P2P 2: Application Layer 7 Client-server architecture server: always-on host permanent IP address server farms for scaling clients: communicate with server may be intermittently connected may have dynamic IP addresses do not communicate directly with each other 2: Application Layer 8 4

5 Pure P2P architecture no always-on server arbitrary end systems directly communicate peers are intermittently connected and change IP addresses example: Gnutella Highly scalable But difficult to manage 2: Application Layer 9 Hybrid of client-server and P2P Napster File transfer P2P File search centralized: Peers register content at central server Peers query same central server to locate content Instant messaging Chatting between two users is P2P Presence detection/location centralized: User registers its IP address with central server when it comes online User contacts central server to find IP addresses of buddies 2: Application Layer 10 5

6 Processes communicating Process: program running within a host. within same host, two processes communicate using inter-process communication (defined by OS). processes in different hosts communicate by exchanging messages Client process: process that initiates communication Server process: process that waits to be contacted Note: applications with P2P architectures have client processes & server processes 2: Application Layer 11 Sockets process sends/receives messages to/from its socket socket analogous to door sending process shoves message out door sending process relies on transport infrastructure on other side of door which brings message to socket at receiving process host or server process socket TCP with buffers, variables controlled by app developer controlled by OS Internet host or server process socket TCP with buffers, variables API: (1) choice of transport protocol; (2) ability to fix a few parameters (lots more on this later) 2: Application Layer 12 6

7 Addressing processes For a process to receive messages, it must have an identifier A host has a unique32- bit IP address Q: does the IP address of the host on which the process runs suffice for identifying the process? Answer: No, many processes can be running on same host Identifier includes both the IP address and port numbers associated with the process on the host. Example port numbers: HTTP server: 80 Mail server: 25 More on this later 2: Application Layer 13 App-layer protocol defines Types of messages exchanged, e.g., request & response messages Syntax of message types: what fields in messages & how fields are delineated Semantics of the fields, i.e., meaning of information in fields Rules for when and how processes send & respond to messages Public-domain protocols: defined in RFCs allows for interoperability e.g., HTTP, SMTP Proprietary protocols: e.g., KaZaA 2: Application Layer 14 7

8 What transport service does an app need? Data loss some apps (e.g., audio) can tolerate some loss other apps (e.g., file transfer, telnet) require 100% reliable data transfer Timing some apps (e.g., Internet telephony, interactive games) require low delay to be effective Bandwidth some apps (e.g., multimedia) require minimum amount of bandwidth to be effective other apps ( elastic apps ) make use of whatever bandwidth they get 2: Application Layer 15 Transport service requirements of common apps Application Data loss Bandwidth Time Sensitive file transfer Web documents real-time audio/video stored audio/video interactive games instant messaging no loss no loss no loss loss-tolerant loss-tolerant loss-tolerant no loss elastic elastic elastic audio: 5kbps-1Mbps video:10kbps-5mbps same as above few kbps up elastic no no no yes, 100 s msec yes, few secs yes, 100 s msec yes and no 2: Application Layer 16 8

9 Internet transport protocols services TCP service: connection-oriented: setup required between client and server processes reliable transport between sending and receiving process flow control: sender won t overwhelm receiver congestion control: throttle sender when network overloaded does not provide: timing, minimum bandwidth guarantees UDP service: unreliable data transfer between sending and receiving process does not provide: connection setup, reliability, flow control, congestion control, timing, or bandwidth guarantee Q: why bother? Why is there a UDP? 2: Application Layer 17 Internet apps: application, transport protocols Application remote terminal access Web file transfer streaming multimedia Internet telephony Application layer protocol SMTP [RFC 2821] Telnet [RFC 854] HTTP [RFC 2616] FTP [RFC 959] proprietary (e.g. RealNetworks) proprietary (e.g., Vonage,Dialpad) Underlying transport protocol TCP TCP TCP TCP TCP or UDP typically UDP 2: Application Layer 18 9

10 Chapter 2: Application layer 2.1 Principles of network applications app architectures app requirements 2.2 Web and HTTP 2.4 Electronic Mail SMTP, POP3, IMAP 2.5 DNS 2.6 P2P file sharing 2.7 Socket programming with TCP 2.8 Socket programming with UDP 2.9 Building a Web server 2: Application Layer 19 Web and HTTP First some jargon Web page consists of objects Object can be HTML file, JPEG image, Java applet, audio file, Web page consists of base HTML-file which includes several referenced objects Each object is addressable by a URL Example URL: host name path name 2: Application Layer 20 10

11 HTTP overview HTTP: hypertext transfer protocol Web s application layer protocol client/server model client: browser that requests, receives, displays Web objects server: Web server sends objects in response to requests HTTP 1.0: RFC 1945 HTTP 1.1: RFC 2068 PC running Explorer Mac running Navigator HTTP request HTTP response HTTP request HTTP response Server running Apache Web server 2: Application Layer 21 HTTP overview (continued) Uses TCP: client initiates TCP connection (creates socket) to server, port 80 server accepts TCP connection from client HTTP messages (applicationlayer protocol messages) exchanged between browser (HTTP client) and Web server (HTTP server) TCP connection closed HTTP is stateless server maintains no information about past client requests aside Protocols that maintain state are complex! past history (state) must be maintained if server/client crashes, their views of state may be inconsistent, must be reconciled 2: Application Layer 22 11

12 HTTP connections Nonpersistent HTTP At most one object is sent over a TCP connection. HTTP/1.0 uses nonpersistent HTTP Persistent HTTP Multiple objects can be sent over single TCP connection between client and server. HTTP/1.1 uses persistent connections in default mode 2: Application Layer 23 Nonpersistent HTTP Suppose user enters URL (contains text, references to 10 jpeg images) 1a. HTTP client initiates TCP connection to HTTP server (process) at on port HTTP client sends HTTP request message (containing URL) into TCP connection socket. Message indicates that client wants object somedepartment/home.index 1b. HTTP server at host waiting for TCP connection at port 80. accepts connection, notifying client 3. HTTP server receives request message, forms response message containing requested object, and sends message into its socket time 2: Application Layer 24 12

13 Nonpersistent HTTP (cont.) time 5. HTTP client receives response message containing html file, displays html. Parsing html file, finds 10 referenced jpeg objects 6. Steps 1-5 repeated for each of 10 jpeg objects 4. HTTP server closes TCP connection. 2: Application Layer 25 Response time modeling Definition of RRT: time to send a small packet to travel from client to server and back. Response time: one RTT to initiate TCP connection one RTT for HTTP request and first few bytes of HTTP response to return file transmission time total = 2RTT+transmit time initiate TCP connection RTT request file RTT file received time time time to transmit file 2: Application Layer 26 13

14 Persistent HTTP Nonpersistent HTTP issues: requires 2 RTTs per object OS overhead for each TCP connection browsers often open parallel TCP connections to fetch referenced objects Persistent HTTP server leaves connection open after sending response subsequent HTTP messages between same client/server sent over open connection Persistent without pipelining: client issues new request only when previous response has been received one RTT for each referenced object Persistent with pipelining: default in HTTP/1.1 client sends requests as soon as it encounters a referenced object as little as one RTT for all the referenced objects 2: Application Layer 27 HTTP request message two types of HTTP messages: request, response HTTP request message: ASCII (human-readable format) request line (GET, POST, HEAD commands) header lines GET /somedir/page.html HTTP/1.1 Host: User-agent: Mozilla/4.0 Connection: close Accept-language:fr Carriage return, line feed indicates end of message (extra carriage return, line feed) 2: Application Layer 28 14

15 HTTP request message: general format 2: Application Layer 29 Uploading form input Post method: Web page often includes form input Input is uploaded to server in entity body URL method: Uses GET method Input is uploaded in URL field of request line: 2: Application Layer 30 15

16 Method types HTTP/1.0 GET POST HEAD asks server to leave requested object out of response HTTP/1.1 GET, POST, HEAD PUT uploads file in entity body to path specified in URL field DELETE deletes file specified in the URL field 2: Application Layer 31 Exemple POST POST /path/script.cgi HTTP/1.0 From: User-Agent: HTTPTool/1.0 Content-Type: application/x-www-form-urlencoded Content-Length: 32 home=cosby&favorite+flavor=flies 2: Application Layer 32 16

17 POST dans une requête POST il n'y a pas qu'un entête: les données sont dans le corps du message les données définissent des variables qui seront utilisées par le CGI l'url requise est normalement un programme la réponse HTTP est normalement la sortie d'un programme 2: Application Layer 33 HTTP response message status line (protocol status code status phrase) data, e.g., requested HTML file header lines HTTP/ OK Connection close Date: Thu, 06 Aug :00:15 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Mon, 22 Jun Content-Length: 6821 Content-Type: text/html data data data data data... 2: Application Layer 34 17

18 HTTP response status codes In first line in server->client response message. A few sample codes: 200 OK request succeeded, requested object later in this message 301 Moved Permanently requested object moved, new location specified later in this message (Location:) 400 Bad Request request message not understood by server 404 Not Found requested document not found on this server 505 HTTP Version Not Supported 2: Application Layer 35 Trying out HTTP (client side) for yourself 1. Telnet to your favorite Web server: telnet cis.poly.edu 80 Opens TCP connection to port 80 (default HTTP server port) at cis.poly.edu. Anything typed in sent to port 80 at cis.poly.edu 2. Type in a GET HTTP request: GET /~ross/ HTTP/1.1 Host: cis.poly.edu By typing this in (hit carriage return twice), you send this minimal (but complete) GET request to HTTP server 3. Look at response message sent by HTTP server! 2: Application Layer 36 18

19 Méthodes http GET C'est la méthode la plus courante pour demander une ressource. Une requête GET est sans effet sur la ressource, il doit être possible de répéter la requête sans effet. HEAD Cette méthode ne demande que des informations sur la ressource, sans demander la ressource elle-même. POST Cette méthode doit être utilisée lorsqu'une requête modifie la ressource. OPTIONS Cette méthode permet d'obtenir les options de communication d'une ressource ou du serveur en général. CONNECT Cette méthode permet d'utiliser un proxy comme un tunnel de communication. TRACE Cette méthode demande au serveur de retourner ce qu'il a reçu, dans le but de tester et effectuer un diagnostic sur la connexion. PUT Cette méthode permet d'ajouter une ressource sur le serveur. DELETE Cette méthode permet de supprimer une ressource du serveur. 2: Application Layer 37 entêtes Host Permet de préciser le site Web concerné par la requête, ce qui est nécessaire pour un serveur hébergeant plusieurs sites à la même adresse IP (name based virtual host, hôte virtuel basé sur le nom). (Obligatoire) Referer Indique l'uri du document qui a donné un lien sur la ressource demandée. Cet entête permet aux webmasters d'observer d'où viennent les visiteurs. User-Agent Indique le logiciel utilisé pour se connecter. Il s'agit généralement d'un navigateur Web ou d'un robot d'indexation. Connection connection persistante ou non Accept Cet en-tête liste les types MIME de contenu acceptés par le client. Le caractère étoile * peut servir à spécifier tous les types / sous-types. Accept-Charset Spécifie les encodages de caractères acceptés. Accept-Language Spécifie les langages acceptés. 2: Application Layer 38 19

20 Réponses Date Moment auquel le message est généré. Server Indique quel modèle de serveur HTTP répond à la requête. Content-Length Indique la taille en octets de la ressource. Content-Type Indique le type MIME de la ressource. Expires Indique le moment après lequel la ressource devrait être considérée obsolète ; permet aux navigateurs Web de déterminer jusqu'à quand garder la ressource en mémoire cache. Last-Modified Indique la date de dernière modification de la ressource demandée. 2: Application Layer 39 Let s look at HTTP in action telnet example Ethereal example 2: Application Layer 40 20

21 CGI Common Gateway Interface exécuter du code du côté serveur Passage de paramètre par la méthode POST ou la méthode GET Variables d'environnement 2: Application Layer 41 Exemple en shell: date.cgi #!/bin/sh tmp=`/bin/date` cat <<! Content-type: text/html <HTML><HEAD><TITLE>Script Cgi</TITLE></HEAD> <BODY> <CENTER> <H1>La date courante sur le serveur est</h1> $tmp </CENTER> </BODY> </HTML>! l'url affichera la date 2: Application Layer 42 21

22 Avec un formulaire: <HTML><HEAD><TITLE>Formulaire simple</title></head> <BODY> <H2>Répondez aux questions suivantes</h2> <FORM ACTION=" METHOD=GET> Prénom : <INPUT TYPE="text" NAME=prenom SIZE=20><BR> Nom : <INPUT TYPE="text" NAME=nom SIZE=20><BR> Age : <SELECT NAME=age> <OPTION>- de 18 ans <OPTION>19 à 40 ans <OPTION>41 à 60 ans <OPTION>+ de 60 ans </SELECT><BR> <INPUT TYPE=submit VALUE="Envoyer"> <INPUT TYPE=reset VALUE="Remettre à zéro"> </FORM> </BODY> 2: Application Layer 43 Résultat par la méthode get codage des paramètres: prenom=hugues&nom=fauconnier&age= 41+%E0+60+ans le navigateur génère l'url: %E0+60+ans Avec la méthode POST prenom=hugues&nom=fauconnier&age=41 2: Application Layer 44 22

23 Traitement en perl fichier perl 2: Application Layer 45 Paramètres Les paramètres sont accessibles par l'intermédiaire de la variable d'environnement QUERY_STRING 2: Application Layer 46 23

24 Variables d'environnement SERVER_SOFTWARE Le nom et la version du serveur HTTP répondant à la requête. (Format : nom/version) SERVER_NAME Le nom d'hôte, alias DNS ou adresse IP du serveur. GATEWAY_INTERFACE La révision de la spécification CGI que le serveur utilise. (Format : CGI/révision) 2: Application Layer 47 Variables SERVER_PROTOCOL Le nom et la révision du protocole dans lequel la requête a été faite (Format : protocole/révision) SERVER_PORT Le numéro de port sur lequel la requête a été envoyée. REQUEST_METHOD La méthode utilisée pour faire la requête. Pour HTTP, elle contient généralement «GET» ou «POST». PATH_INFO Le chemin supplémentaire du script tel que donné par le client. Par exemple, si le serveur héberge le script «/cgibin/monscript.cgi» et que le client demande l'url « alors PATH_INFO contiendra «marecherche». PATH_TRANSLATED Contient le chemin demandé par le client après que les conversions virtuel physique aient été faites par le serveur. 2: Application Layer 48 24

25 Variables SCRIPT_NAME Le chemin virtuel vers le script étant exécuté. Exemple : «/cgibin/script.cgi» QUERY_STRING Contient tout ce qui suit le «?» dans l'url envoyée par le client. Toutes les variables provenant d'un formulaire envoyé avec la méthode «GET» sera contenue dans le QUERY_STRING sous la forme «var1=val1&var2=val2&...». REMOTE_HOST Le nom d'hôte du client. Si le serveur ne possède pas cette information (par exemple, lorsque la résolution DNS inverse est désactivée), REMOTE_HOST sera vide. REMOTE_ADDR L'adresse IP du client. AUTH_TYPE Le type d'identification utilisé pour protéger le script (s il est protégé et si le serveur supporte l'identification). 2: Application Layer 49 Variables AUTH_TYPE Le type d'identification utilisé pour protéger le script (s il est protégé et si le serveur supporte l'identification). REMOTE_USER Le nom d'utilisateur du client, si le script est protégé et si le serveur supporte l'identification. REMOTE_IDENT Nom d'utilisateur (distant) du client faisant la requête. Le serveur doit supporter l'identification RFC 931. Cette variable devraient être utilisée à des fins de journaux seulement. CONTENT_TYPE Le type de contenu attaché à la requête, si des données sont attachées (comme lorsqu'un formulaire est envoyé avec la méthode «POST»). CONTENT_LENGTH La longueur du contenu envoyé par le client. 2: Application Layer 50 25

26 Variables HTTP_ACCEPT Les types de données MIME que le client accepte de recevoir. Exemple : text/*, image/jpeg, image/png, image/*, */* HTTP_ACCEPT_LANGUAGE Les langages dans lequel le client accepte de recevoir la réponse. Exemple : fr_ca, fr HTTP_USER_AGENT Le navigateur utilisé par le client. Exemple : Mozilla/5.0 (compatible; Konqueror/3; Linux) 2: Application Layer 51 User-server state: cookies Many major Web sites use cookies Four components: 1) cookie header line of HTTP response message 2) cookie header line in HTTP request message 3) cookie file kept on user s host, managed by user s browser 4) back-end database at Web site Example: Susan access Internet always from same PC She visits a specific e- commerce site for first time When initial HTTP requests arrives at site, site creates a unique ID and creates an entry in backend database for ID 2: Application Layer 52 26

27 Cookies: keeping state (cont.) Cookie file ebay: 8734 client usual http request msg usual http response + Set-cookie: 1678 server server creates ID 1678 for user entry in backend database Cookie file amazon: 1678 ebay: 8734 one week later: Cookie file amazon: 1678 ebay: 8734 usual http request msg cookie: 1678 usual http response msg usual http request msg cookie: 1678 usual http response msg cookiespecific action cookiespectific action access access 2: Application Layer 53 Cookies (continued) What cookies can bring: authorization shopping carts recommendations user session state (Web ) aside Cookies and privacy: cookies permit sites to learn a lot about you you may supply name and to sites search engines use redirection & cookies to learn yet more advertising companies obtain info across sites 2: Application Layer 54 27

28 Web caches (proxy server) Goal: satisfy client request without involving origin server user sets browser: Web accesses via cache browser sends all HTTP requests to cache object in cache: cache returns object else cache requests object from origin server, then returns object to client client HTTP request HTTP response HTTP request HTTP response Proxy server HTTP request HTTP response origin server client origin server 2: Application Layer 55 More about Web caching Cache acts as both client and server Typically cache is installed by ISP (university, company, residential ISP) Why Web caching? Reduce response time for client request. Reduce traffic on an institution s access link. Internet dense with caches enables poor content providers to effectively deliver content (but so does P2P file sharing) 2: Application Layer 56 28

29 Caching example Assumptions average object size = 100,000 bits avg. request rate from institution s browsers to origin servers = 15/sec delay from institutional router to any origin server and back to router = 2 sec Consequences utilization on LAN = 15% utilization on access link = 100% total delay = Internet delay + access delay + LAN delay = 2 sec + minutes + milliseconds institutional network public Internet 1.5 Mbps access link 10 Mbps LAN origin servers institutional cache 2: Application Layer 57 Caching example (cont) Possible solution increase bandwidth of access link to, say, 10 Mbps Consequences utilization on LAN = 15% utilization on access link = 15% Total delay = Internet delay + access delay + LAN delay = 2 sec + msecs + msecs often a costly upgrade institutional network public Internet 10 Mbps access link 10 Mbps LAN origin servers institutional cache 2: Application Layer 58 29

30 Caching example (cont) Install cache suppose hit rate is.4 Consequence 40% requests will be satisfied almost immediately 60% requests satisfied by origin server utilization of access link reduced to 60%, resulting in negligible delays (say 10 msec) total avg delay = Internet delay + access delay + LAN delay =.6*(2.01) secs + milliseconds < 1.4 secs institutional network public Internet 1.5 Mbps access link 10 Mbps LAN origin servers institutional cache 2: Application Layer 59 Conditional GET Goal: don t send object if cache has up-to-date cached version cache: specify date of cached copy in HTTP request If-modified-since: <date> server: response contains no object if cached copy is upto-date: HTTP/ Not Modified cache HTTP request msg If-modified-since: <date> HTTP response HTTP/ Not Modified HTTP request msg If-modified-since: <date> HTTP response HTTP/ OK <data> server object not modified object modified 2: Application Layer 60 30

31 Compléments Javascript Code qui s'exécute du côté du client calcul local contrôle d'une zone de saisie affichage d'alerte fenêtres menus etc.. Balise : <SCRIPT languge="javascript1.2"> le code... </SCRIPT> 2: Application Layer 61 Exemple: bonjour <HTML><HEAD> <TITLE>Très facile</title> </HEAD> <SCRIPT language="javascript1.2"> function bonjour() { alert ("Bonjour madame, bonjour monsieur"); } </SCRIPT> <BODY bgcolor="white" onload="bonjour();"> <H1>Bonjour</H1> </BODY></HTML> 2: Application Layer 62 31

32 Un peu plus: minicalcul HTML> <HEAD> <TITLE>Petit calcul</title> </HEAD> <BODY bgcolor='white'> <script language='javascript1.2' src='calcul.js'></script> <script language='javascript1.2' src='fenetre.js'></script> <script language='javascript1.2' src='ctrl.js'></script> <CENTER><H1>Calcul</H1></CENTER> Un petit exemple de formulaire. <P> Création d'une <A href='#a' onclick='affichedoc();'>fenêtre avec JavaScript</A> 2: Application Layer 63 Suite <FORM ACTION='Simul.html' METHOD='POST' NAME='Simul'> <CENTER> <TABLE BORDER=3> <TR><TD>Argument 1 <TD> <INPUT TYPE='TEXT' SIZE=20 NAME='arg1' onchange='calcul();'></tr> <TR><TD>* Argument 2 <TD> <INPUT TYPE='TEXT' SIZE=20 NAME='arg2' onchange='calcul();'> </TR> <TR><TD>Résultat= <TD> <INPUT TYPE='TEXT' SIZE=20 NAME='res' > </TR> </TABLE> <INPUT TYPE='BUTTON' VALUE='Vérifier' onclick='ctrl();'> <INPUT TYPE='RESET' VALUE='Effacer tout' onclick=' if (!confirm("vraiment vous voulez effacer?")) exit;'> </CENTER> </FORM> </BODY> </HTML> 2: Application Layer 64 32

33 Fichiers js ctrl.js calcul function ctrl() { if (isnan(window.document.simul.res.value )) { alert ("Valeur incorrecte : " + document.simul.res.value + "?"); document.forms[0].res.focus(); } } function calcul() { v1=document.forms[0].arg1.value; v2=document.forms[0].arg2.value; document.forms[0].res.value = v2*v1 ; } 2: Application Layer 65 suite et fin fenetre.js function affichedoc() { options = "width=300,height=200"; fenetre = window.open('','mu',options); } fenetre.document.open(); manuel = "<HTML><HEAD><TITLE>Documentation</TITLE></HEAD>" + "<BODY bgcolor='white'>" + "Il n'y a pas besoin d'aide " + " c'est facile." + " Bonne chance!</body></html>"; fenetre.document.write(manuel); fenetre.document.close(); 2: Application Layer 66 33

34 Compléments: php php est un langage de script pour les serveurs webs de nombreuses fonctions permettent de traiter les requêtes http ici on est du côté du serveur 2: Application Layer 67 Exemple simple <HTML> <HEAD> <TITLE>Exemple très simple</title> </HEAD> <BODY> <H1>Exemple</H1> le <?php echo Date ("j/m/y à H:i:s");?> <P> <?php echo "Client :". $_SERVER['HTTP_USER_AGENT']. "<BR>"; echo "Adresse IP client:".$_server['remote_addr']."<br>"; echo "Server: ". $_SERVER['SERVER_NAME'];?> </BODY></HTML> 2: Application Layer 68 34

35 Résultat Exemple le 8/11/2006 à 15:54:29 Client :Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1;.NET CLR ; InfoPath.1) Adresse IP client: Server: localhost 2: Application Layer 69 Reçu par le client <HTML> <HEAD> <TITLE>Exemple très simple</title> </HEAD> <BODY> <H1>Exemple</H1> le 8/11/2006 à 15:54:29 <P> Client :Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1;.NET CLR ; InfoPath.1)<BR>Adresse IP client: <br>server: localhost </BODY></HTML> 2: Application Layer 70 35

36 Php On est ici côté serveur: les balises <?php> <?> sont interprétées par le serveur (apache par exemple) et servent à générer la page html reçu par le client Mais surtout php permet d'accéder aux variables d'environnement d'utiliser de nombreuses fonctionsalités sessions, paramètres etc. Php sert souvent d'interface pour MySql serveur simple de bases de données 2: Application Layer 71 Php pas de typage ni de déclaration des variables $v est remplacé par la valeur de v (et permet aussi l'affectation) echo "$v"; constantes define("pi, ); types des variables numériques $i=1; $v=3.14; chaînes de caractères (expressions régulières) $nom="hugues"; ',",{} 2: Application Layer 72 36

37 php tableaux indicés $tab[0]="un"; $tab=array("un","deux","trois"); associatifs $m=array("un"=>"one", "deux"=>"two"); $m["trois"]="three"; next() prev() key() current do {echo "Clé=key($m).Valeur= current($m)"} while(next($mes)); foreach($m as $cle =>$val) {echo "Clé=$cle.Valeur=$val";} 2: Application Layer 73 Php structures de contrôles if if else while do while for foreach break, continue 2: Application Layer 74 37

38 fonctions function Nom([$arg1, $arg2,...]) { corps } passage par valeur (et pas références &) exemples function Add($i,$j){ $somme= $i + $j; return $somme; } function Add($i,$j,&$somme){ $somme= $i + $j; } 2: Application Layer 75 divers variables automatiques (locales) statiques (comme en C) globales classes et objets 2: Application Layer 76 38

39 Pour le serveur tableaux associatifs prédéfinis $_SERVER: environnement serveur REQUEST_METHOD QUERY_STRING CONTENT_LENGTH SERVER_NAME PATH_INFO HTTP_USER_AGENT REMOTE_ADDR REMOTE_HOST REMOTE_USER REMOTE_PASSWORD 2: Application Layer 77 Suite Autres tableaux $_ENV : environnement système $_COOKIE $_GET $_POST $_FILES $_REQUEST (variables des 4 précédents $_SESSION $GLOBALS les variables globales du scritp 2: Application Layer 78 39

40 Cookies et php <?php // Est-ce que le Cookie existe? if (isset($_cookie['compteur'])) { $message = "Vous êtes déjà venu {$_COOKIE['compteur']} fois ". "me rendre visite<br>\n"; // On incrémente le compteur $valeur = $_COOKIE['compteur'] + 1; } else { // Il faut créer le cookie avec la valeur 1 $message = "Bonjour, je vous envoie un cookie<br>\n"; $valeur = 1; } // Envoi du cookie SetCookie ("compteur", $valeur);?> 2: Application Layer 79 Cookies et php (fin) <HTML><HEAD> <TITLE>Les cookies</title> </HEAD> <BODY> <H1>Un compteur d'accès au site avec cookie</h1> <?php echo $message;?> </BODY></HTML> 2: Application Layer 80 40

41 En utilisant les sessions <?php // La fonction session_start fait tout le travail session_start();?> <HTML><HEAD> <TITLE>Les cookies</title> </HEAD> <BODY> <H1>Un compteur d'accès au site avec Session</H1> 2: Application Layer 81 Fin <?php if (!isset($_session['cp'])) { $_SESSION['cp']=1; echo "C'est la première fois, votre id est:".session_id()."<br>"; } else{ $_SESSION['cp']++; echo "C'est votre ".$_SESSION['cp']." n-ième connexion"; if($_session['cp']>10){ echo "on vous a trop vu"."<br>"; session_destroy(); } }?> </BODY></HTML> 2: Application Layer 82 41

42 session session_start() session_destroy() session_id() on peut associer des variables à la session par le tableau associatif $_SESSION elle sera accessible à chaque session_start() jusqu'au session_destroy() pour toute connexion qui fournit le session_id(). 2: Application Layer 83 42