[풀스택] TCP Socket programming (1:1)

 

 

 

Network Socket

•  Network Socket is an internal endpoint for sending or receiving data within a node on a computer network.
• a representation of this endpoint in networking software (protocol stack)
• such as an entry in a table (listing communication protocol, destination, status, etc.), and
  is a form of system resource.
• 4계층을 깔고, Application 이야기한다. 
• IP 주소 + 포트 번호 -> socket address
• 4계층과 3계층은 운영체제 안에 있다.
• 소켓 프로그래밍 -> 운영체제와 이야기한다. 

 

 

 

Socket Programming

• The fundamental technology behind communications on TCP/IP networks.
• Socket provides a bidirectional communication endpoint for sending and receiving data with another socket.
• Socket connections normally run between two different computers on a local area network (LAN) or across the internet, but they can also be used for inter-process communication on a single computer.

 

 

 

Client and Server Architecture

• Socket Server
  • Any program that listens for other programs to connect to it.
  • 서버는 먼저 살아나서 listen
  • Example: Web Server, Email Server, etc.
• Socket Client
  • Any program that is designed to connect to another program.
  • Example, Web Browser, Email app on your phone,
    most all Internet games on mobile devices, etc.

 

 

 

 

Berkeley Socket API

• Application Programming Interface (API) for Internet sockets and Unix domain sockets,
  used for inter-process communication (IPC).
• It is commonly implemented as a library of linkable modules, and originated with the 4.2 BSD Unix operating system, released in 1983.
• Berkeley sockets evolved with little modification from a de facto standard into a component of the POSIX specification.

 

 

 

Berkeley Socket API Functions

•  socket()
  • creates a new socket of a certain type, identified by an integer number, and allocates system resources to it.
  • 운영체제에게 리소스 준비하라고 알려주는 기능
  • socket() -> OS, 버퍼를 만들고, 준비 등등 + 상황체크, 타이머
  • UDP는 간단하게, 가볍게 준비
• bind()
  • typically used on the server side, and associates a socket with a socket address structure,
  • i.e. a specified local IP address and a port number.
  • bind() -> 붙이는 것
    나는 이 포트 번호를 사용할거야 선언
    클라이언트 - 나에게 포트 번호를 줘
    준비된 소켓 위에, 접착제로 어플리케이션을 붙이는 것 
    아이피나 포트 등 중요한 정보를 준다. 
• listen()
  • used on the server side, and causes a bound TCP socket to enter listening state.
  • 요청을 들을 준비를 하는 것
• connect()
  • used on the client side, and assigns a free local port number to a socket.
  • In case of a TCP socket, it causes an attempt to establish a new TCP connection.
  • SYN 비트 1이 됨
  • TCP는 연결 요청 과정 있으나,
    UDP 같은 경우에는 커넥트 없음
• accept()
  • used on the server side.
  • It accepts a received incoming attempt to create a new TCP connection from the remote client, and creates a new socket associated with the socket address pair of this connection.
  • SYN에 대한 ACK
    본인의 SYN도 나감
    연결 요청을 허락하겠다. 
• send(), recv(), sendto(), and recvfrom()
  • used for sending and receiving data.
  • The standard functions write() and read() may also be used.
  • write / read - 통신과 파일 처리 등등 
  • 유닉스에서는 이를 모두 동일하게 취급했다
    파일을 연다는 개념으로 진짜 파일도 열고, 네트워크도 열고, 메모리도 열고 등등
• close()
  • causes the system to release resources allocated to a socket.
  • In case of TCP, the connection is terminated.
•  gethostbyname() and gethostbyaddr()
  • used to resolve host names and addresses. IPv4 only.
  • 도메인 - 아이피 주소
    도메인 네임 서버에 갔다오거나
    캐쉬 값을 통해 , 둘 사이를 번역
• select()
  • used to suspend, waiting for one or more of a provided list of sockets to be ready to read, ready to write, or that have errors.
  • 서버 입장에서 어떤 클라이언트 소켓을 처리할 것인지 선택
• poll()
  • used to check on the state of a socket in a set of sockets.
  • The set can be tested to see if any socket can be written to, read from or if an error occurred.
  • 읽기 전에 정보가 있는지, 상태를 체크하는 과정 
    써도 되는 건지 -> 레이어 내릴 때 터질 수 있으니깐 
• getsockopt()
  • used to retrieve the current value of a particular socket option for the specified socket.
  • 추가 옵션 세팅 과정 
• setsockopt()
  • used to set a particular socket option for the specified socket.

 

 

Berkeley Socket API Procedures for TCP

• y축 - 시간 
  서버가 먼저 살아난다.
  socket 호출 : 준비시킴
  bind : 어플이 소켓을 사용하여, 
  아이피 포트 넘버 등등 컨피그 마침
  listen 상태 (연결설정 완료)

 

• 클라이언트 - connect
  accept에 의해서 둘은 통신 관계에 들어감
  데이터를 주고 받는 관례

 

• send + recv : 병렬적으로 일어남
  둘 중 하나가 끊기를 바라면 
  클라이언트가 close - 끊기를 바람 
  : TCP Session이 끝날 뿐, 서버는 멀쩡히 살아있다.

 

• UDP 라면 연결 해제 과정 X 
  그냥 보낼 것들 보내고, 나가면 됨 

 

• 함수들이 순차적으로 호출된다.
  운영체제, 언어가 다르더라도 대동소이
  TCP UDP sample program 대충 다 비슷함

 

 

 

https://www.keil.com/pack/doc/mw6/Network/html/using_network_sockets_bsd.html

 

 

 

TCP Echo Server 

• 에러 처리 적용한 코드
• 이렇게 통신 프로그램 짜야 한다. (강한 코드)
• 상대방과 나의 관계 + 네트워크의 상황 + OS 상황
  -> 아무것도 보장할 수 없으니까

 

• try except -1
• 안정적으로 변경한 코드 
• 통신 프로그램을 짤 때 
• if -> 무조건 else 를 씀 - 뭐라도 한 줄 씀
• 불안한 통신 함수 -> 다 try except로 감싼다
• 서버 프로그램을 안정적으로 짜는 방식