Sockets, HTTP and addressing (w1-w2)

Question 1

iPv4 is a __ bit number, written in which format?

Also, what is the range of numbers between each dot? Why?

Answer 1

32 bit number, written as dotted quad, range is up to 255 (including 0) , as 2^8 = 256.

Question 2

how many addresses available in IPv4?

Answer 2

2^32

Question 3

IPv6 has how many addresses available?

Answer 3

340 282 366 920 938 463 463 374 607 431 768 211 456

Question 4

how are IPV6 addresses formatted?

Answer 4

8 Groups of 16 bits each, each group written in hex with a colon separating the groups

Question 5

getByName is a method part of which class?

Answer 5

InetAddress class

Question 6

getByName() accomplishes what?

Answer 6

resolves address with DNS name

Question 7

getHostAddress() does what?

Answer 7

returns string containing IP address

Question 8

if given the address www.google.com, write a two line program which returns the correct IP address using InetAddress class

Answer 8

InetAddress IP = InetAddress.getByName(www.google.com);
System.out.println(name + “ : “ +
IP.getHostAddress());

Question 9

write a two line program which returns the host name, when given an IP Address

Answer 9

InetAddress IP =
InetAddress.getByName(addressIP);
System.out.println(address + “ : “ +
IP.getHostName());

Question 10

write a two line program which connects to a website, given the port and website name`

Answer 10

InetAddress IP =
InetAddress.getByName(“www.wand.net.nz”);
Socket mysocket = new Socket(IP, 443);

Question 11

Initialize a printwriter, write a line, then close the writer

Answer 11

PrintWriter out = new
PrintWriter(mysocket.getOutputStream(), true);
out.println("hello world");
out.close();

Question 12

Initialize a Buffered Reader given a socket object “socket”

Answer 12

InputStreamReader isr = new InputStreamReader(mysocket.getInputStream());
BufferedReader reader = new
BufferedReader(isr);

Question 13

initialize a serversocket on port 1234 and accept a socket connection

Answer 13

ServerSocket server = new ServerSocket(1234);
Socket client = server.accept();

Question 14

What does the InetAddress class deal with

Answer 14

deals with resolving names and addresses

Question 15

How can we write a server, so that it can accept more than one connection at a time, allowing two clients to simultaniously use the server?

Answer 15

Threads.

Question 16

How would we start a thread running in the main code?

Answer 16

ServerThread thread = new ServerThread(clientSocket);
thread.start();

Question 17

When thread.start() is called, which method begins executing code in the thread class?

Answer 17

the run() method will begin executing code

Question 18

how can we make class server{…} implement threads?

Answer 18

by extending it with threads: class server extends Thread{…}

Question 19

What is the main problem with threads? what is a partial solution to this?

Answer 19

threads do not scale, partial solution is thread pools. If a pool of size N threads gets N+1 threads, the thread number N+1 will then block until another thread is let go

Question 20

what is the problem with multiple clients accessing a server variable simultaneously? give an example

Answer 20

the server cpu might stop one process just as it is about to save some changes to a variable. then a second process starts and changes the variable. when the first process is then resumed, it will save the variable according to the first processes state, this ovverriding the second process’s changes.

Question 21

how does the synchronized keyword work

Answer 21

when changing a variable accessed by multiple users, wrap the code with the synchronize keyword in all processes to ensure the variables integrity

Question 22

what is the https:// mean at the start of urls?

Answer 22

it is the protocol used. in this case, https protocol

Question 23

break http request/response headers down into three sections

Answer 23

ASCII text header
Empty Line
Binary Data

Question 24

what is the end of the header signalled by, in the request and response

Answer 24

an empty line

Question 25

what is the end of line sequence for http, and some popular operating systems

Answer 25

\r\n same as windows
\r for mac
\n for unix

Question 26

while((rc = fis.read(buf)) != -1){
bos.write(buf, 0, rc);
}
explain every single thing going on in this while loop

Answer 26

while statement = fill up buf with as much input stream as possible, and store the length of data into rc. if no more data, this will equal -1 and exit the loop.
bos statement = writes according to bos the array, from start of the array, to end (rc)

Question 27

with a header like : String message = “HTTP/1.1 200 OK\r\n\r\n”; how would you send this header, given a buffered output stream object?

Answer 27

byte[] array = message.getBytes();

bos.write(array, 0, array.length);