Java Networking

1
Java Networking

• Lecture 11

2
Introduction to Networking

• Encapsulation building data transmission

Request
Data Request
TCP Header
Request
TCP Request
IP Request
TCP Header
Request
IP Header
TCP Header
Request
IP Header
Ethernet Header
Eth Request
3
Introduction to Networking

• Data Transmission

Client
Router
Server
Request
Request
TCP Segment
TCP Segnment
IP Datagram
IP Datagram
IP Datagram
Ethernet Frame
Ethernet Frame
Ethernet Frame Ethernet Frame
Voltage (phy)?
Voltage (phy)?
Voltage Voltage
4
Introduction to Networking

• URL Uniform Resource Locator

http//www.somewhere.com8080/maps.html
protocol
Host / ip address
port
File / resource
5
Introduction to Networking

• Java runtime Exceptions

Throwable
Exception
Error
ThreadDeath
VM Error
I/O
Runtime
EOF
NullPointer
OOfMem
6
Introduction to Networking

• Java runtime Exceptions
• All exceptions caught with a try/catch block
• try
• something
• catch (someException ex)
• error something
• NOTE can have many different exceptions caught
  per try block

7
Introduction to Networking

• Java runtime Exceptions
• Major types of exceptions
• Error something failed in the JVM
• Exception normal errors in program execution
• RuntimeException null pointer oob errors
• Generating Exceptions
• Method Calls
• Runtime Exceptions
• User Generated
• Handling Exceptions
• Passing (ignore)?
• Catching

8
Introduction to Networking

• Java runtime Exceptions
• Class Throwable
• Constructors
• Throwable() - create a Throwable object
• Throwable(string) create with string message
• Methods
• fillInStackTrace()?
• printStackTrace()?
• printStackTrace(PrintStream)?
• getMessage() - get detail message

9
Introduction to Networking

• Java runtime Exceptions
• Class Throwable
• Constructors
• Throwable() - create a Throwable object
• Throwable(string) create with string message
• Methods
• fillInStackTrace()?
• printStackTrace()?
• printStackTrace(PrintStream)?
• getMessage() - get detail message

10
Introduction to Networking Example Clients

• Standards based in RFCs
• RFCs
• www.ietf.org/rfc.html
• Internet Protocol assignments
• www.iana.org
• These definitions allow developers a guide to
  what is available from other clients/servers

11
Introduction to Networking Example Clients

• DNS Client RFC 1035
• Single Header for all queries
• 16 bit fields (network byte order)?
• ID (server to bounce back to client)?
• Query/Response flags (total 16 bits)?
• QR 1 bit
• OPCODE 4 bits
• AA, TC, RD, RA 1 bit
• Z 3 bits
• RCODE 4 bits
• QDCOUNT, ANCOUNT, NSCOUNT, ARCOUNT 16 bits

0
15
ID
QR
OPCODE
AA
TZ
RD
RCODE
RA
Z
QDCOUNT
ANCOUNT
NSCOUNT
ARCOUNT
12
Introduction to Networking Example Clients

• ID 16 bits for identification
• QR bit
• 0 for query and 1 for response
• AA bit
• Set in response if Authoritative
• TC bit
• Set if truncated
• RD bit
• Set in query for recursion
• RA bit
• Set in response if recursion available
• Z bits
• Reserved (always need some extra!!!)?
• RCODE bits
• Error code in response (0 is ok)?

0
15
ID
QR
OPCODE
AA
TZ
RD
RA
Z
RCODE
QDCOUNT
ANCOUNT
NSCOUNT
ARCOUNT
13
Introduction to Networking Example Clients

• QDCOUNT, ANCOUNT, NSCOUNT, ARCOUNT
• Represent number of questions

0
15
ID
QR
OPCODE
AA
RCODE
TZ
RD
RA
Z
QDCOUNT
ANCOUNT
NSCOUNT
ARCOUNT
14
Introduction to Networking Example Clients

• Questions Each question has the same format

2
2
2
QNAME
QTYPE
QCLASS

• QNAME domain name or host name
• Name split into component labels
• e.g. www.abcdef.com - www, abcdef, com (3
  labels)?
• Each label written as a byte length, then text
• e.g. 3www6abcdef3com0 (each 1 byte)?
• Max Length of label is 63 bytes (1 for size, 1
  for 0 term)?
• QTYPE Type of resource required
• e.g. 255 all information desired
• QCLASS network class
• e.g. 1 - Internet

15
Introduction to Networking Example Clients

• Resource Records

2
2
2
2
n
n
NAME
TYPE
CLASS
TTL
RDLEN
DATA

• NAME n byte domain or host name
• TYPE unsigned short indicating type
• CLASS unsigned short indicating class
• TTL unsigned int indicating number of seconds
  TTL
• RDLEN unsigned short indicating length of DATA
• DATA n bytes of data

16
Introduction to Networking Example Clients

• Implementation (classes)?
• DNS Base defaults /etc
• DNSQuery details of hostname (request/response
  codes)?
• DNSRR Resource Records
• record.Address record package address record
• record.MailExchanger Mail Exchanger record
  (MX)?
• DNSInputStream decode data returned
• NSLookup command-line nslookup class (main)?
• Command Syntax
• Java NSLookup lthostnamegt_at_ltnameservergt
• _at_ ltnameservergt optional

17
Introduction to Networking Example Clients

• DNS Class
• Open RFC 1035
• Match Types to RFC 1035
• DNSQuery Class
• Vectors used for adding answers/etc
• Decode flags routine
• Walking through bits
• DNSInputStream
• ByteArrayInputStream used
• Ability to parse out pieces used in DNSRR
• DNSRR Class
• Superclass for all resource record classes
• record.Address
• Extends DNSRR Class

18
Introduction to Networking Example Clients
public class NSLookup public static void main
(String args) if (args.length ! 1)?
throw new IllegalArgumentException
("Syntax NSLookup lthostnamegt_at_ltnameservergt")
int atIdx args0.indexOf ("_at_") String
nameServer (atIdx gt -1) ? args0.substring
(atIdx 1) "ns" String hostName (atIdx
gt -1) ? args0.substring (0, atIdx) args0
System.out.println ("Nameserver "
nameServer) System.out.println ("Request "
hostName) DNSQuery query new DNSQuery
(hostName, DNS.TYPE_ANY, DNS.CLASS_IN) try
Socket socket new Socket (nameServer,
DNS.DEFAULT_PORT) socket.setSoTimeout
(10000) sendQuery (query, socket)
getResponse (query, socket) socket.close
() printRRs (query) catch
(IOException ex) System.out.println
(ex)
19
Introduction to Networking Example Server

• Class ServerSocket
• Constructor
• ServerSocket(int port)?
• ServerSocket(int port, int backlog)?
• ServerSocket(int port, int backlog, InetAddress
  bindAddr)?
• Methods
• accept() - throws IOException
• close()?
• getInetAddress()?
• getLocalPort()?
• setSoTimeout(int timeout)?
• getSoTimeout()?
• implAccept()?
• setSocketFactory(SocketImplFactory)

20
Introduction to Networking Example Server

• Non Blocking Socket I/O
• available() - used in InputStream
• Socket Timeout Values
• Socket SO
• setSoTimeout(10)?
• Catch InterruptedIOException

21
Introduction to Networking Example Server

• Example Web Server

Errors
WebBrowser
Web Server
Static
Dynamic CGI
Network
Database
Web Service
22
Introduction to Networking Example Server
WebBrowser
Httpd
ReThread
HttpOuputStream
HttpInputStream
Network
HttpProcessor processRequest()?
main()?
HttpFile
HttpCGI
HttpClass
HttpException
HttpClassProcessor
RedirectException
CGI
Echo
23
Introduction to Networking Example Server

• Class HTTP (HTTP.java)?
• Default values and static variables
• public static final String METHOD_GET "GET"
• public static final String METHOD_POST
  "POST"
• public static final String METHOD_HEAD
  "HEAD"
• public static final int STATUS_OKAY 200
• public static final int STATUS_NO_CONTENT
  204
• public static final int STATUS_MOVED_PERMANENTLY
  301
• public static final int STATUS_MOVED_TEMPORARILY
  302
• public static final int STATUS_BAD_REQUEST
  400
• public static final int STATUS_FORBIDDEN 403
• public static final int STATUS_NOT_FOUND 404
• public static final int STATUS_NOT_ALLOWED
  405
• public static final int STATUS_INTERNAL_ERROR
  500
• public static final int STATUS_NOT_IMPLEMENTED
  501

24
Introduction to Networking Example Server

• Class Httpd
• Main class
• public static void main (String args) throws
  IOException
• ServerSocket server new ServerSocket
  (HTTP.PORT)
• while (true)
• Socket client server.accept ()
• Httpd httpd new Httpd (client)
• ReThread reThread new ReThread (httpd)
• reThread.start ()

25
Introduction to Networking Example Server

• Class HttpInputStream
• InputStream class
• public void readRequest () throws IOException
• String request readLine ()
• if (request null)?
• throw new HttpException (HTTP.STATUS_BAD_REQ
  UEST, "Null query")
• StringTokenizer parts new StringTokenizer
  (request)
• try
• parseMethod (parts.nextToken ())
• parseRequest (parts.nextToken ())
• catch (NoSuchElementException ex)
• throw new HttpException (HTTP.STATUS_BAD_REQ
  UEST, request)
• if (parts.hasMoreTokens ())?
• parseVersion (parts.nextToken ())
• else
• ..............

26
Introduction to Networking Example Server

• Class HttpFile
• Class to deal with static files
• public HttpFile (HttpInputStream in) throws
  IOException
• if (in.getMethod () HTTP.METHOD_POST)?
• throw new HttpException (HTTP.STATUS_NOT_ALL
  OWED,
• "ltTTgt"
  in.getMethod () " " in.getPath () "lt/TTgt")
• file new File (HTTP.HTML_ROOT,
  HTTP.translateFilename (in.getPath ()))
• if (in.getPath ().endsWith ("/"))?
• file new File (file, HTTP.DEFAULT_INDEX)
• if (!file.exists ())?
• throw new HttpException (HTTP.STATUS_NOT_FOU
  ND,
• "File ltTTgt"
  in.getPath () "lt/TTgt not found.")
• if (file.isDirectory ())?
• throw new RedirectException
  (HTTP.STATUS_MOVED_PERMANENTLY,
• in.getPath ()
  "/")
• if (!file.isFile () !file.canRead ())?
• throw new HttpException (HTTP.STATUS_FORBIDD
  EN, in.getPath ())

27
Introduction to Networking Example Server

• Class HttpCGI
• Class to deal with dynamic requests
• public void processRequest (HttpOutputStream
  out) throws IOException
• ReThread drain null
• try
• if (in.getMethod () ! HTTP.METHOD_POST)
• cgi jvm.exec (cgiScript.getPath (),
  env)
• cgi.getOutputStream ().close ()
• out.write (cgi.getInputStream ())
• else
• cgi jvm.exec (cgiScript.getPath (),
  env)
• drain new ReThread (this)
• drain.start ()
• out.write (cgi.getInputStream ())

28
Introduction to Networking Example Server

• Questions?