Re: network time service, non-blocking?

[david kerns]

On Wed, May 11, 2022 at 1:39 AM Petr Slansky <slansky@gmail.com> wrote:

> Hello Gawk,
>
> this is not real bug report, it is something like a feedback. I use gawk
> 4.1.4.
>
> I tried to use gawk for some network service, to report progress of data
> processed from pipeline to websocket but I think I cannot do that because
> gawk doesn't support non-blocking sockets. To illustrate that, I use
> example with simple time service, similar to
>
> https://www.gnu.org/software/gawk/manual/gawkinet/html_node/Setting-Up.html#Setting-Up
>
> $ cat timesrv.awk
> # Time server
> BEGIN {
>   service = "/inet/tcp/8888/0/0";
>   while (1) {
>      time = strftime();
>      print time;
>      print time |& service;
>      close(service);
>   }
> }
>
> # run it
> $ gawk -f timeserv.awk
>
> # other terminal
> $ sleep 45; date; curl http://localhost:8888
>
> The problem of this server is that it reports "old" time. It samples time
> to a variable and it waits for an incoming connection from a client, then
> it reports time and samples new time. When clients don't connect
> frequently, they get wrong (old) time.
>
> Is there a way, to check if client connected to listening socket? Open
> server socket, do some other tasks and from time to time check if client is
> connected; when client is connected, serve fresh data otherwise continue to
> process data. It is possible that I cannot use gawk for my task and I have
> to use Python, Go or other tool.
>
> Petr
>

you should be using the awk-help mailing list for this question ...

since you are using curl/http to connect (ie have lots of incoming data to
indicate a new connection)
just make the blocking read at the top of the loop:

# Time server
BEGIN {
  service = "/inet/tcp/8888/0/0";
  while (1) {
     service |& getline; # wait for new request
     time = strftime();
     print time;
     print time |& service;
     close(service);
  }
}

this code still only returns the time, (in a non machine friendly format)
and not a valid http reply, but that's beyond the scope of the OP