13.5  Socket-Based Data Feeds

13.5.1  Overview
      For true data feeds, wvalarmd provides a socket server which listens on 
      port 11011 of the wview server for connections. When a datafeed client 
      connects on that port, wvalarmd adds the client to the datafeed client 
      list. Then when loop data is received from wviewd, wvalarmd will write 
      the loop packet into each datafeed client's socket, preceded by a start 
      frame sequence. It is a one-way interface and the client may disconnect 
      at any time by calling "shutdown" followed by "close" to close the 
      socket. The number of active client connections is only limited by system 
      resources. The datafeed client will receive the full loop packet as 
      defined in common/datadefs.h - see the structure "LOOP_PKT".

13.5.2  Configuration
      None required for socket data feeds, just the normal PUSH_INTERVAL setup 
      described above. No alarm entries are required in wvalarm.conf for 
      datafeed clients.

13.5.2  Client Requirements
      The datafeed sockets are regular TCP/stream PF_INET sockets. The general 
      connection steps (in C) are as follows:
        
        socket (...)        // create the socket descriptor
        [setup server address and port in socckaddr_in structure]
        connect (...)
        
      The client then may add the socket descriptor to an fdset for select 
      calls, simply block on the socket for reads, however you want to design 
      it. Other programming language procedures may differ, but the general 
      approach should be the same.
      
      Normal Processing "Loop":
      
      1) Wait for data on the socket
      2) Sync to the start frame sequence: 0xF388, 0xC6A2, 0xDADA, 0xE7CF
      3) Read loop packet
      4) Process loop packet
      5) Goto #1
      
      To disconnect:
      
        shutdown (sockfd, 2)
        close (sockfd)
      
      Note: There is a handy new radlib socket API which is illustrated in the 
            sample datafeed client source code which takes care of most of the