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Socket Interfaces

Socket Interfaces. Professor Jinhua Guo CIS527 Fall 2002. What Are Sockets. A socket is an endpoint of communication to which a name can be bound. The socket interface provides access to transport protocols

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Socket Interfaces

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  1. Socket Interfaces Professor Jinhua Guo CIS527 Fall 2002

  2. What Are Sockets • A socket is an endpoint of communication to which a name can be bound. • The socket interface provides access to transport protocols • Sockets were designed to implement the client-server model for interprocess communication

  3. Sockets Domain • UNIX domain sockets are named with UNIX paths. UNIX domain sockets communicate only between processes on a single host. • Internet domain communication uses the TCP/IP suite.

  4. Socket Types • Stream sockets enable processes to communicate using TCP. • SOCK_STREAM • Datagram sockets enable processes to use UDP to communicate. • SOCK_DGRAM • Raw sockets • SOCK_RAW

  5. Socket Libraries • The socket interface routines are in a library that must be linked with the application. - libsocket.so, libsocket.a • Compile and Link - e.g. gcc main.c –o main –lsocket -lnsl

  6. Interprocess Communication (IPC) • Issues • Creating sockets • Naming (identifying) sockets • Sending/receiving data over sockets • Mechanism • UNIX system calls and library routines if ((code = syscall()) < 0) { perror(“syscall”); exit(1); }

  7. Socket Creation • s = socket(domain, type, protocol); domain: AF_INET, AF_UNIX type: SOCK_STREAM, SOCK_DGRAM, or SOCK_RAW protocol: 0 Example: s = socket(AF_INET, SOCK_STREAM, 0);

  8. Naming Sockets int bind(sd, name, namelen) int sd; struct sockaddr *name; int namelen;

  9. Socket Address • Several types of socket addresses • You will use sockaddr_in, because you use AF_INET • sockaddr_in is a C structure with 3 important fields: • sin_family • sin_addr • sin_port

  10. Internet Address and Ports • sin_addr values - four bytes e.g. esun1 is 141.215.10.123 (see /etc/hosts) - if you specify INADDR_ANY for local host address, all host address apply • sin_port values • 0 – 1024 reserved for system • well known ports are import • http is port 80 • telnet is port 23 • if you specify 0, the system picks a port

  11. Data Transfer • You can send or receive a message with the normal read and write interfaces: • - write(s, buf, sizeof buf); • - read(s, buf, sizeof buf); • You can also use send and recv: • - send(s, buf, sizeof buf, flags); • - recv(s, buf, sizeof buf, flags);

  12. Other System Calls • int connect(sd, name, namelen) • - specifies peer with which sd is to be associated • int listen(sd, backlog) • -specifies maximum backlog of connections a server will allow • int accept (sd, addr, addrlen) • extracts first connection off queue of pending connections • int close (sd) • -deletes descriptor from system tables;

  13. htonl(), htons(), ntohl(), ntohs() • convert between network byte order and host byte order • Required since some machines are big endian and others are little endian (network order is big endian) • big endian • address byte • 0 0 1 2 3 • 4 4 5 6 7 • little endian • address byte • 0 3 2 1 0 • 4 7 6 5 4 • Convert to network order before sending and back to host order after receiving

  14. Connection-Oriented Communication Using Stream Sockets

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