Sockets for clients Flashcards
What are connections between?
client and the server
what is the server?
software actively listening for a connection
What is the client?
software that connects to a server
Do we need both?
yes we need both to form an active connection
benefits of TCP connections?
reliable and steam oriented connection
What do machines need to be doing?
1 needs to be listening for connection and the other needs to connect to that open port
What is the connection type?
Bi-directional
What does a protocol describe?
how the communication should happen
order bits are sent in
what individual bits mean
What is the Http protocol?
send a request and get a repsonse
simple requests are easy
What is the de facto API for TCP/IP?
Berkeley sockets
What do sockets API use?
recv(), send(), close()
do we open a connection?
no rather we create socket using socket()
which is one end of our connection and theres another socket at the other end
What does client need?
create a socket with socket()
connect to a server using connect()
transfer data using send()/recv()
close the connection using close()
How do we create socket?
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
How do we connect?
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
What needs to be done when closing connection?
both ends of connection need to close it
What are 2 approaches to convert into bytes of memory?
Big endian and little endian
What happens in big endian?
most significant byte stored at lowest memory address 12,34,56,78
What happens in little Endian?
least significant byte are stored at the lowest memory address
78,56,34,12
What is the internet standardlised as?
big endian
what do sin_port and sin_addr values need to be made sure of?
that they big endian
what is the ntohX() function?
whenever you get a value in a network you use it
it converts network byte to host byte ordering
What is the htonX() function?
whenever you set a value in a network function you use it
it converts host byte to network byte ordering
What does getaddrinfo do?
returns linked list of potential ip addresses to connect to then you can try to connect to each one
returns 0 if everything ok
what does getaddrinfo consist of?
dns hostname string
string containing service
hints
address of a PTR
what does getaddrinfo return?
return multiple addresses with multiple connection types
we can either search the linked list or provide some hints to reduce the list
what is hint provided as?
a pointer and we need to free the function as well
What do we need to be careful of when reading?
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
What does recv() do if no data available?
will block until some sent
and return 0 when connection is closed
how do we close?
both client and server must close the connection
How does it know when to close?
theres an explicit end of communication phrase in protocol
When this is sent server closes connection
When client reads it, it closes connection
