Internet Sockets

Objectives

1. Learn how to set up for an IP Socket.

Notes

• IPV4 and IPV5 have different sockaddr structures.
• Look on 1202 and 1203 if you wish.
• Setting up the address is a bit more complex in IP.
• Fortunately they have modified the tools to make this easier.
• These use whatever resolver you have setup
  • DNS
  • files
  • /etc/nsswitch.conf
• hton* and ntoh*
  • htonl, htons, ntohl, ntohs
  • l is 32 bits, it was written a long time ago
  • s is 16 bits.
  • uint32_t htonl(uint32_t hostlong);
  • The byte order may be different on different machines.
• inet_ntop
  • network to presentation rep. Change a binary address to a string.
  • reference
  • const char *inet_ntop(int af, const void *restrict src, char dst[restrict .size], socklen_t size);
  • af: address family
  • src: the a struct * in_addr with fields filled in.
  • dst: string conversion of the network address structure
  • size: size of the struct in_addr
  • Returns pointer to dst, or null on error
  • inet_pton exists as well.
• getadderinfo
  • This function produces an array of adderesses that can be used in bind or connect.

  • int getaddrinfo(const char *restrict node,
                    const char *restrict service,
                    const struct addrinfo *restrict hints,
                    struct addrinfo **restrict res);

  • node: a host name or ip address.
  • service: the service name (/etc/services, http, https, ssh)
  • hints:
    • Fill in fields to provide "hints" as to what you are looking for.

    • struct addrinfo {
         int              ai_flags;
         int              ai_family;
         int              ai_socktype;
         int              ai_protocol;
         socklen_t        ai_addrlen;
         struct sockaddr *ai_addr;
         char            *ai_canonname;
         struct addrinfo *ai_next;
      };
                     
       The flags provide further cotroll.
               

  • res is a pointer to a list of matches.
    • The man page states you should use the first in the list unless you have a reason to do otherwise.
    • The first structure in the list holds the official name.
  • Returns a 0 on success or a error code on failure.
• Look at getAddress.cpp
• Look at dieServer.cpp
  • I just moved stuff from getAddress.cpp in.
  • And changed all relevant address type references.
• But to test
  • I need to knock mirkwood's firewall down
  • firewall-cmd --list-ports
  • firewall-cmd --add-port=10000/udp
  • firewall-cmd --remove-port=10000/udp
• Also nc -4 -u -v 147.64.242.52 10000