CSCI Computer Networking: Application Layer Programming George Blankenship. Programming George Blankenship 1

Transcription

1 CSCI 6431 Computer Networking: Application Layer Programming George Blankenship Programming George Blankenship 1

2 Lecture Outline Programming concepts PDUs and SDUs Transport Interface System-to-system to system messages General program flow WinSock (C++) Java.net API Programming George Blankenship 2

3 Programming Concepts Horizontal dialog Defined in the application design Oriented towards transactions Transaction defined by sequence of messages Vertical control Defined by the service provider (transport) Simple command set Connect to transport Send/receive data Programming George Blankenship 3

4 Horizontal Dialog Service based relationship between two peer entities At a given instant one entity is requesting a service and the other is supplying a service The request is a series of messages that that must be processed as a unit The protocol is oriented towards defining processing units Programming George Blankenship 4

5 Vertical Controls Traffic moves vertically between a communication service user and a communication service provider The service user is the application The service provider is the transport layer Provided service Open transport Send data Receive data Close transport Programming George Blankenship 5

6 Application Functions Define the location of the peer Define the bounds of a transaction Create the APDUs (Application Protocol Data Units) that define the transaction data movement Process the APDs that define the transaction data movement Use the service provider Programming George Blankenship 6

7 Server Functions Wait for the request Perform the service ACID based performance Atomic operation Consistency Isolation Durability QoS provider Programming George Blankenship 7

8 Client Functions Initiate connection Request the service End-system/end-user oriented Gather request components Transform to form expected by server Hide server functions/operation Co-operate with server to fulfill QoS requirements Programming George Blankenship 8

9 General Operation Initialize communication service Attach to service API Establish call-backs Connect to target system Wait for connections (server) Determine target address (client) Open connection (client/server) Perform application objective Programming George Blankenship 9

10 The Waiting Problem Intrinsic to communications is waiting for messages from the other side Difficult model Three solutions Blocking until a message arrives Polling for messages Call back Programming George Blankenship 10

11 Blocking Until a Message Arrives Process waits for the message Performs nothing else Does not detect missing events well If message does not arrive, process is hung If message is delayed, processing is delayed Not a good method dfor time critical i processing Programming George Blankenship 11

12 Polling for messages Process periodically checks for a message Performs other tasks between checks Solves time critical processing Polls must be more frequent than expected events Polls distract processing Polls create system overhead Programming George Blankenship 12

13 Call back Process provides API with a routine to be invoked when a message arrives Performs other tasks Message processed in call back routine Requires proper use of multithread principles i Programming George Blankenship 13

14 Communication Environment Interface Application API Communication Service Provider Communication Programming George Blankenship 14

15 Communication Service Interface API Standard set of primitives (functions) Attach connect to the API Open connect to the remote application Send send a message Receive receive a message Close disconnect from the remote application Detach disconnect from the API Programming George Blankenship 15

16 Windows Example Following code extracted from routine that uses a TCP socket to send an Written in C++ (Borland 5.02) Code is on class web site Programming George Blankenship 16

17 Windows API Defined in winsock.h (winsock2.h) Windows * Sockets 2 Application Programming Interface Programming George Blankenship 17

18 Attach Error = WSAStartup(wVersionRequested,&WinsockInfo ); wversionrequested Winsock level required MAKEWORD(level,sublevel) WinsockInfo Description of the API Programming George Blankenship 18

19 Socket System address and tcp/udp port Host:port System address Name (set of names) Gethostbyname() Table of IP addresses IP address Socket structure Programming George Blankenship 19

20 Open Socket Create the socket before opening Server side is specified Client side is defaulted Passive open (accept) Wait for connection from external system Active open (connect) Connect to an external system Programming George Blankenship 20

21 Send Error = send(socket,data,strlen(data),0); Socket is the connection to be used Data is text (byte stream) to be sent strlen(data) is number of bytes to be sent 0 is flags describing special data values Send a message using an open socket Programming George Blankenship 21

22 Receive Error = recv(socket- >getsocket(),text,input_length,0); Socket->getSocket() connection to be used Text is the input buffer (byte stream) INPUT_LENGTH is the maximum number of fbytes to be received 0 is flags describing buffer Error is error flag or bytes received Receive a message using an open socket Programming George Blankenship 22

23 Close close(); Initiate a connection close Programming George Blankenship 23

24 Detach WSACleanup(); Clean up API tables Programming George Blankenship 24

25 Java API Defined in java.net.* No attach No call backs (listeners) Programming George Blankenship 25

26 Socket try {inet = InetAddress.getByName("localhost");} catch (IOException e) { trace.write("(passiveport) I/O error creating inet for "+ name+":"+integer.tostring(port)+ " ("+e.getmessage()+")"); ()+")") failed = true; // socket is unusable return; } Programming George Blankenship 26

27 Open Passive open (wait for connection) Active open (attempt to connect) Programming George Blankenship 27

28 Passive Open try {socket = new ServerSocket(port);} // try to open the listening port catch (IOException e) { trace.write("(passiveport) I/O error creating ServerSocket for "+ name+":"+integer.tostring(port)+ " ("+e.getmessage()+")"); failed = true; // socket is unusable } catch (SecurityException e) { trace.write("(passiveport) security violation creating ServerSocket for "+ name+":"+integer.tostring(port)+ " ("+e.getmessage()+")"); failed = true; // socket is unusable } Programming George Blankenship 28

29 Listening try {activesocket = socket.accept();} // start listening catch (IOException e) { // I/O error trace.write("(passiveport.open) I/O error opening port "+name+ " ("+e.getmessage()+")"); failed = true; // port is unusable return (null); } catch (SecurityException e) { // security does not allow use trace.write("(passiveport.open) security violation opening port "+name+ " ("+e (+e.getmessage()+ getmessage()+")"); ) ); failed = true; // port is unusable return (null); } Programming George Blankenship 29

30 Active Open try {socket = new Socket(inet,remotePort);} // try to open the listening port catch (UnknownHostException e) { trace.write("(activeport.open) unknown host "+name+ " ("+e (+e.getmessage()+ getmessage()+")"); ) ); failed = true; // socket is unusable return (false); } catch (IOException e) { return (false); } catch (SecurityException e) { trace.write("(activeport.open) security violation opening port"+name+ " ("+e.getmessage()+")"); failed = true; // socket is unusable return (false); } Programming George Blankenship 30

31 IO Streams try {input = new DataInputStream(socket.getInputStream());} catch (IOException e) { trace.write("(activeport.open) I/O error creating input stream "+name+ " ("+e.getmessage()+")"); failed = true; // socket is unusable return (false); } try {output = new DataOutputStream(socket.getOutputStream());} catch (IOException e) { trace.write( write("(activeport.open) open) I/O error creating output stream "+name+ " ("+e.getmessage()+")"); failed = true; // socket is unusable return (false); } Programming George Blankenship 31

32 Send try {output.writeutf(text);} catch (IOException e) { trace.write("(activeport.send) (( I/O error writing output stream "+name+ " ("+e.getmessage()+")"); close(); return (false); } Programming George Blankenship 32

33 Receive try {text = input.readutf();} catch (EOFException eof) { trace.write("(activeport.receive) I/O eof reading input stream "+name+ " ("+eof.getmessage()+")"); failed = true; // socket is unusable return null; } catch (IOException e) { trace.write("(activeport.receive) I/O error reading input stream "+name+ " ("+e (+e.getmessage()+ getmessage()+")"); ) ); close(); return null; } Programming George Blankenship 33

34 Close try {socket.close();} // actually close the port catch (IOException e) { trace.write( write("(activeport.close) close) I/O error closing port "+name+ " ("+e.getmessage()+")"); failed = true; // socket is unusable return false; } Programming George Blankenship 34

35 Reading and Thought Winsock links on class web page Java*net API Programming George Blankenship 35