Sockets for clients

Question 1

What are connections between?

Answer 1

client and the server

Question 2

what is the server?

Answer 2

software actively listening for a connection

Question 3

What is the client?

Answer 3

software that connects to a server

Question 4

Do we need both?

Answer 4

yes we need both to form an active connection

Question 5

benefits of TCP connections?

Answer 5

reliable and steam oriented connection

Question 6

What do machines need to be doing?

Answer 6

1 needs to be listening for connection and the other needs to connect to that open port

Question 7

What is the connection type?

Answer 7

Bi-directional

Question 8

What does a protocol describe?

Answer 8

how the communication should happen
order bits are sent in
what individual bits mean

Question 9

What is the Http protocol?

Answer 9

send a request and get a repsonse
simple requests are easy

Question 10

What is the de facto API for TCP/IP?

Answer 10

Berkeley sockets

Question 11

What do sockets API use?

Answer 11

recv(), send(), close()

Question 12

do we open a connection?

Answer 12

no rather we create socket using socket()
which is one end of our connection and theres another socket at the other end

Question 13

What does client need?

Answer 13

create a socket with socket()
connect to a server using connect()
transfer data using send()/recv()
close the connection using close()

Question 14

How do we create socket?

Answer 14

use socket() function
tell what domain we need socket in
type of connection we want
the protocol
returns the file descriptor for created socket or -1 if errors

Question 15

How do we connect?

Answer 15

use connect() function
socket needs to be connected to other end of connection
need address of the end point
ip address of machine and port to connect to
use struct sockaddr_in to contain details

Question 16

What needs to be done when closing connection?

Answer 16

both ends of connection need to close it

Question 17

What are 2 approaches to convert into bytes of memory?

Answer 17

Big endian and little endian

Question 18

What happens in big endian?

Answer 18

most significant byte stored at lowest memory address 12,34,56,78

Question 19

What happens in little Endian?

Answer 19

least significant byte are stored at the lowest memory address
78,56,34,12

Question 20

What is the internet standardlised as?

Answer 20

big endian

Question 21

what do sin_port and sin_addr values need to be made sure of?

Answer 21

that they big endian

Question 22

what is the ntohX() function?

Answer 22

whenever you get a value in a network you use it
it converts network byte to host byte ordering

Question 23

What is the htonX() function?

Answer 23

whenever you set a value in a network function you use it
it converts host byte to network byte ordering

Question 24

What does getaddrinfo do?

Answer 24

returns linked list of potential ip addresses to connect to then you can try to connect to each one
returns 0 if everything ok

Question 25

what does getaddrinfo consist of?

Answer 25

dns hostname string
string containing service
hints
address of a PTR

Question 26

what does getaddrinfo return?

Answer 26

return multiple addresses with multiple connection types
we can either search the linked list or provide some hints to reduce the list

Question 27

what is hint provided as?

Answer 27

a pointer and we need to free the function as well

Question 28

What do we need to be careful of when reading?

Answer 28

data comes in packets so might not get all in one go so check return value of recv() to see how much was read
then check if it contains what we expect

Question 29

What does recv() do if no data available?

Answer 29

will block until some sent
and return 0 when connection is closed

Question 30

how do we close?

Answer 30

both client and server must close the connection

Question 31

How does it know when to close?

Answer 31

theres an explicit end of communication phrase in protocol
When this is sent server closes connection
When client reads it, it closes connection