http://www.perlmonks.org?node_id=11113183


in reply to Re^3: IO::Socket tutorial
in thread IO::Socket tutorial

I seem to have replied but forgot to post it... duh. Anyhow, I'm thinking of sticking with IO::Select and it looks very easy. I create a new Select object initialized to my TCP connection, then I can do a can_read with a timeout, and if it doesn't time out I can use ->getlines to suck up what was sent. If that's all that I was expecting {the returned stuff is terminated by a line with just a ".", as with RCS and unix-mail} I'm done, otherwise I go back and can_read again. Either I get all I needed or a can_read returns a timeout. Seems pretty easy... I can handle the recovery code when it times out. THANKS!!

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Re^5: IO::Socket tutorial
by haukex (Bishop) on Feb 20, 2020 at 00:31 UTC
    I'm thinking of sticking with IO::Select and it looks very easy. ... then I can do a can_read with a timeout, and if it doesn't time out I can use ->getlines to suck up what was sent

    No, unfortunately it's not that easy. The reason is that can_read will fire even if there's only a single byte waiting to be read, and readline and friends will still hang because it's looking for a full line, which the server might not have sent.

    srv.pl:

    use warnings; use strict; use IO::Select; use IO::Socket; my $sock = IO::Socket::INET->new( Listen=>1, ReusePort=>1, LocalAddr=>'127.0.0.1', LocalPort=>1235 ) or die "sock: $@"; my $sel = IO::Select->new($sock); while ( my @ready = $sel->can_read ) { for my $fh (@ready) { if ($fh == $sock) { my $cli = $sock->accept; print "New client\n"; $sel->add($cli); syswrite $cli, "x"; } } }

    cli.pl:

    use warnings; use strict; use Data::Dumper; use IO::Select; use IO::Socket; my $sock = IO::Socket::INET->new( PeerAddr=>'127.0.0.1', PeerPort=>1235 ) or die "sock: $@"; my $sel = IO::Select->new($sock); while ( my @ready = $sel->can_read(1) ) { for my $fh (@ready) { print "Attempting to read...\n"; # all of these hang! #print Dumper($fh->getlines); #print Dumper($fh->getline); print Dumper(scalar <$fh>); } }

    Note these aren't complete examples as they are oversimplified and lack error handling. Anyway, sure, you could implement your own routine to read the socket byte-by-byte until you've got a full line, but that's a wheel that's been re-implemented a million times (I've done it several times myself). Again: I strongly recommend you use a library that already provides this functionality!

      Thanks for the correction. I wondered how can_read and getline{s} interacted {answer: not at all}. I hear you about not reinventing the wheel and I'll look again at POE.. it seems awfully complicated for something as simple as what I need {basically *nothing* more than an unblocking read} Is there a less complicated package that provides the simple functionality I need?

      I confess that I'm a bit surprised that IO doesn't provide that facility. I could see it implementing a version of getline{} that took a timeout and gave you either the line you asked for or an error. I expect that {as you said} that functionality keeps getting reinvented, so it is a bit odd that over the years no one has added that to the IO family.

      Many many years ago I wrote a server in Perl and I had to do just as you said: the low-level sub had to read a byte at a time then assemble the response and return a complete line. I only remember it being kinda clunky but worked. And I wish I still had the code I wrote to do that :)

        <update2> Please disregard the following code example, I was pointed to Mojo::IOLoop::Stream::Role::LineBuffer which makes the implementation much nicer - many thanks to the fine people on #mojo on freenode! See this example instead. </update2>

        <update> Note that this uses the slightly lower-level API instead of the higher-level one shown at the top of Mojo::IOLoop. However, I don't yet see a easy way to use one of the existing readline modules with that interface (Mojo::IOLoop::LineReader or MojoX::LineStream, the latter has a bug and doesn't support changing the input record separator). I may have another update in a little while, we'll see. </update>

        POE.. it seems awfully complicated for something as simple as what I need {basically *nothing* more than an unblocking read} Is there a less complicated package that provides the simple functionality I need?

        Yes, I agree POE has an "interesting" interface, although once you get into it, it works well. As I mentioned, Mojolicious includes an event loop whose interface I find nicer. There's also Mojo::IOLoop::LineReader that handles the buffering and splitting of read events into lines:

        mojo_serv.pl:

        use warnings; use strict; use Data::Dump qw/dd pp/; use Mojo::IOLoop::Server; use Mojo::IOLoop::LineReader; my $server = Mojo::IOLoop::Server->new; $server->on(accept => sub { my ($serv, $handle) = @_; my $peer = $handle->peerhost.":".$handle->peerport; print $peer,": Connect\n"; my $stream = Mojo::IOLoop::LineReader->new($handle); $stream->timeout(30); $stream->on(readln => sub { my ($strm, $line) = @_; print $peer,": Got line ",pp($line),"\n"; }); $stream->on(close => sub { print $peer,": Closed\n"; $stream->stop; $stream = undef; # free reference }); $stream->on(error => sub { my ($strm, $err) = @_; warn "$peer: Error: $err"; }); $stream->start; $stream->write("Hello, client from $peer.\n"); }); $server->listen(address => '127.0.0.1', port => 3000, reuse => 1); $server->start; $server->reactor->start unless $server->reactor->is_running;

        mojo_cli.pl:

        use warnings; use strict; use Data::Dump qw/dd pp/; use Mojo::IOLoop::Client; use Mojo::IOLoop::LineReader; my $client = Mojo::IOLoop::Client->new; $client->on(connect => sub { my ($cli, $handle) = @_; print "Connect\n"; my $stream = Mojo::IOLoop::LineReader->new($handle); $stream->timeout(10); $stream->on(readln => sub { my ($strm, $line) = @_; print "Got line ",pp($line),"\n"; }); $stream->on(close => sub { print "Closed\n"; $stream->stop; $stream = undef; # free reference }); $stream->on(error => sub { my ($strm, $err) = @_; warn "Error: $err"; }); $stream->start; $stream->write("Hello, server, I am a client.\n"); }); $client->on(error => sub { my ($cli, $err) = @_; warn "Error: $err"; }); $client->connect(address => '127.0.0.1', port => 3000); $client->reactor->start unless $client->reactor->is_running;

        Here's some semi-tested client code that reads what it can. then does the inner loop for each whole line.

        # cli.pl: use strict; use warnings; use IO::Select; use IO::Socket; my $sock = IO::Socket::INET->new('127.0.0.1:1235') or die "sock: $@"; my $sel = IO::Select->new($sock); my $buffer = ''; while(@1 = $sel->can_read(2) and sysread $sock, $buffer, 4096, length +$buffer) { while( $buffer =~ s/^.*\n// ) { my $line = $&; print "got: ", $line; # or whatever processing you want here... } } die @1 ? "socket closed" : "timeout";

        If you change the read size to 1 you get the read-a-byte-at-a-time behavior.