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    SocketProgramming 3

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    api-3802795
    Socket programming uses a client-server model where the client initiates contact with the server to request a service. The application programming interface (API) defines functions for processes to communicate via sockets. Key functions include socket(), bind(), listen(), accept(), connect(), send(), recv(), which are used to set up the socket, bind addresses, listen for connections, accept connections, connect sockets, and send/receive data. Network byte order and utility functions help with address conversions and additional socket operations.

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    SocketProgramming 3

    Uploaded by

    api-3802795
    128 views20 pages
    Socket programming uses a client-server model where the client initiates contact with the server to request a service. The application programming interface (API) defines functions for processes to communicate via sockets. Key functions include socket(), bind(), listen(), accept(), connect(), send(), recv(), which are used to set up the socket, bind addresses, listen for connections, accept connections, connect sockets, and send/receive data. Network byte order and utility functions help with address conversions and additional socket operations.

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    Socket programming uses a client-server model where the client initiates contact with the server to request a service. The application programming interface (API) defines functions for processes to communicate via sockets. Key functions include socket(), bind(), listen(), accept(), connect(), send(), recv(), which are used to set up the socket, bind addresses, listen for connections, accept connections, connect sockets, and send/receive data. Network byte order and utility functions help with address conversions and additional socket operations.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    128 views20 pages

    SocketProgramming 3

    Uploaded by

    api-3802795
    Socket programming uses a client-server model where the client initiates contact with the server to request a service. The application programming interface (API) defines functions for processes to communicate via sockets. Key functions include socket(), bind(), listen(), accept(), connect(), send(), recv(), which are used to set up the socket, bind addresses, listen for connections, accept connections, connect sockets, and send/receive data. Network byte order and utility functions help with address conversions and additional socket operations.

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    Socket Programming

    Srinidhi Varadarajan
    Client-server paradigm
    Client:
    application
    transport
     initiates contact with server network
    data link
    (“speaks first”) physical

     typically requests service request


    from server,
     for Web, client is
    implemented in browser; for
    e-mail, in mail reader
    reply
    Server:
     provides requested service application
    transport
    to client network
    data link
    physical
     e.g., Web server sends
    requested Web page, mail
    server delivers e-mail
    Application Layer Programming

    API: application programming interface


     defines interface between application and
    transport layer

     sockets: Internet API


    – two processes communicate by sending data
    into socket, reading data out of socket
    Socket Interface. What is it?
     Gives a file system like abstraction to the
    capabilities of the network.

     Each transport protocol offers a set of


    services. The socket API provides the
    abstraction to access these services

     The API defines function calls to create,


    close, read and write to/from a socket.
    Socket Abstraction
     The socket is the basic abstraction for network
    communication in the socket API
    – Defines an endpoint of communication for a process
    – Operating system maintains information about the
    socket and its connection
    – Application references the socket for sends, receives,
    etc.

    Network
    Process Process
    A B

    Ports (Sockets)
    What do you need for socket communication ?

     Basically 4 parameters
    – Source Identifier (IP address)
    – Source Port
    – Destination Identifier
    – Destination Port

     In the socket API, this information is


    communicated by binding the socket.
    Creating a socket
    int socket(int domain, int type, int protocol)

    Protocol Family: Usually


    PF_INET or UNSPEC
    PF_UNIX

    Communication
    semantics:
    SOCK_STREAM or
    SOCK_DGRAM

    The call returns a integer identifier called a


    handle
    Binding a socket
    int bind (int socket, struct sockaddr *address, int addr_len)

     This call is executed by:


    – Server in TCP and UDP

     It binds the socket to the specified address. The


    address parameter specifies the local component
    of the address, e.g. IP address and UDP/TCP port
    Socket Descriptors
     Operatingsystem maintains a set of
    socket descriptors for each process
    – Note that socket descriptors are shared
    by threads
     Three data structures
    – Socket descriptor table
    – Socket data structure
    – Address data structure
    Socket Descriptors
    Socket Socket Data
    Descriptor Structure
    Table proto family:
    0: PF_INET
    Address Data
    1: service: Structure
    2: SOCK_STREAM
    address family:
    .. local address:
    . AF_INET
    remote address: host IP:
    128.173.88.85
    ..
    . port:
    80
    TCP Server Side: Listen
    int listen (int socket, int backlog)

     This server side call specifies the number


    of pending connections on the given
    socket.

     When the server is processing a


    connection, “backlog” number of
    connections may be pending in a queue.
    TCP Server Side: Passive Open
    int accept (int socket, struct sockaddr *address, int *addr_len)

     This call is executed by the server.

     The call does not return until a remote


    client has established a connection.

     When it completes, it returns a new socket


    handle corresponding to the just-
    established connection
    TCP Client Side: Active Open
    int connect (int socket, struct sockaddr *address, int *addr_len)

     This call is executed by the client. *address


    contains the remote address.

     The call attempts to connect the socket to a


    server. It does not return until a connection has
    been established.

     When the call completes, the socket “socket” is


    connected and ready for communication.
    Sockets: Summary
     Client:
    int socket(int domain, int type, int protocol)
    int connect (int socket, struct sockaddr *address, int addr_len)

     Server:
    int socket(int domain, int type, int protocol)
    int bind (int socket, struct sockaddr *address, int addr_len)
    int listen (int socket, int backlog)
    int accept (int socket, struct sockaddr *address, int *addr_len)
    Message Passing
     int send (int socket, char *message, int msg_len, int
    flags) (TCP)
     int sendto (int socket, void *msg, int len, int
    flags, struct sockaddr * to,
    int tolen ); (UDP)
     int write(int socket, void *msg, int len); /* TCP */

     int recv (int socket, char *buffer, int buf_len, int


    flags) (TCP)
     int recvfrom(int socket, void *msg, int len, int
    flags, struct sockaddr *from, int
    *fromlen); (UDP)
     int read(int socket, void *msg, int len); (TCP)
    Summary of Basic Socket Calls
    CLIENT Connect SERVER
    (3-way handshake)
    connect() accept()

    new connection
    write() Data read()

    read() Data write()

    close() close()
    Network Byte Order
     Network byte order is most-significant
    byte first
     Byte ordering at a host may differ
     Utility functions
    – htons(): Host-to-network byte order for a short
    word (2 bytes)
    – htonl(): Host-to-network byte order for a long
    word (4 bytes)
    – ntohs(): Network-to-host byte order for a short
    word
    – ntohl(): Network-to-host byte order for a long
    word
    Some Other “Utility” Functions
     gethostname() -- get name of local host
     getpeername() -- get address of remote
    host
     getsockname() -- get local address of
    socket
     getXbyY() -- get protocol, host, or service
    number using known number, address, or
    port, respectively
     getsockopt() -- get current socket options
     setsockopt() -- set socket options
     ioctl() -- retrieve or set socket information
    Some Other “Utility” Functions
     inet_addr() -- convert “dotted”
    character string form of IP address to
    internal binary form
     inet_ntoa() -- convert internal binary
    form of IP address to “dotted”
    character string form
    Address Data Structures
    struct sockaddr {
    u_short sa_family; // type of address
    char sa_data[14]; // value of address
    }

     sockaddr is a generic address structure

    struct sockaddr_in {
    u_short sa_family; // type of address (AF_INET)
    u_short sa_port; // protocol port number
    struct in_addr sin_addr; // IP address
    char sin_zero[8]; // unused (set to zero)
    }
     sockaddr_in is specific instance for the Internet address
    family

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