Socket functions

• Open (client)
  • sd = socket(family, type, proto);
  • bind(sd, localaddr, len);
  • connect(sd, serveraddr, len);

• Open (server)
  • sd = socket(family, type, proto);
  • bind(sd, localaddr, len);
  • listen(sd, queuesize);
  • sd2 = accept(sd, clientaddr, len);

• Close
  • close(sd);

• Write
  • write(sd, data, len);
  • send(sd, data, len, flags);
  • sendto(sd, data, len, flags, destaddr, len);
  • sendmsg(sd, msgstruct, flags);

• read
  • read(sd, buf, len);
  • recv(sd, buf, len, flags);
  • recvfrom(sd, buf, flags, len, srcaddr, len);
  • recvmsg(sd, msgstruct, flags);
• additional system calls used
  • gethostbyname(hostname)
  • getprotobyname(protocolname)
  • htonl(hostnumber)
  • htons(portnumber)

Using Sockets

• Connection-Oriented - TCP ( point to point )
  • Open a client connection
    • sd = socket(PF_INET, SOCK_STREAM, PROTO_TCP);
      • create buffers and OS table entries to track connection
    • bind(sd, localaddr, len);
      • specify the local connection point (optional)
    • connect(sd, serveraddr, len);
      • initiate a connection
      • serveraddr may not go out of scope
  • Open a server
    • sd = socket(family, type, proto);
      • create buffers and OS table entries to track connection
    • bind(sd, localaddr, len);
      • specify the local connection point for listening
      • localaddr may not go out of scope
    • listen(sd, queuesize);
      • create a queue for incoming (SYN) packets and attach to network
      • allows receipt of new requests while processing existing one(s)
    • sd2 = accept(sd, clientaddr, len);
      • pull next connection request from the queue
      • uses new descriptor for I/O so the original can keep listening
      • clientaddr may not go out of scope
  • Write (server and/or client)
    • write(sd, data, len);
    • send(sd, data, len, flags);
      • either works to send data through the network
      • send is used mustly on non-Unix systems
  • Read (server and/or client)
    • read(sd, buf, len);
    • recv(sd, buf, len, flags);
      • either works to receive data through the network
      • recv is used mustly on non-Unix systems
  • Close (server and client)
    • close(sd);
    • closesocket(sd);
      • closesocket used mostly on non-Unix systems

  
  

• Connectionless - UDP model ( broadcast )
  • doesn't follow strict client/server model
  • send/receive instead of read/write
  • don't need bind/accept/connect but still uses socket call

  • Sender
    • sd = socket(PF_INET, SOCK_DGRAM, PROTO_UDP);
    • sendto(sd, data, len, flags, destaddr, len);
    • (or sendmsg(sd, msgstruct, flags);)

  • Receiver
    • sd = socket(PF_INET, SOCK_DGRAM, PROTO_UDP);
    • recvfrom(sd, buf, flags, len, srcaddr, len);
    • (or recvmsg(sd, msgstruct, flags);)




Telnet always makes a pretty good client, just give it the host and port.