Re: Portably disabling Nagle's algorithm for TCP

If your system actually has the constant, it will nowadays be in Socket.pm.

Query, set, unset:

use Socket qw(IPPROTO_TCP TCP_NODELAY);

sub nagle(*;$) {
    my $fh = shift;
    if (!@_) {
        return unpack("I", getsockopt($fh, IPPROTO_TCP, TCP_NODELAY) |
+|
               croak "Could not get Nagle state: $!") ? 0 : 1;
    }
    if (shift) {
        setsockopt($fh, IPPROTO_TCP, TCP_NODELAY, 0) ||
            croak "Couldn't enable Nagle's algorithm: $!";
    } else {
        setsockopt($fh, IPPROTO_TCP, TCP_NODELAY,1) ||
            croak "Couldn't disable Nagle's algorithm: $!";
    }
}
[download]

(A lot of perl code floating on the internet incorrectly uses SOL_SOCKET as level, possibly because the cookbook gets it wrong).

This functionality should only be used if it makes sense though.

Comment on Re: Portably disabling Nagle's algorithm for TCP Download Code

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Re^2: Portably disabling Nagle's algorithm for TCP by mowgli (Friar) on Jan 02, 2005 at 22:09 UTC
Thanks. How can I make sure that every system the script possibly runs on actually has that constant, though? -- mowgli	[reply]
Re^3: Portably disabling Nagle's algorithm for TCP by thospel (Hermit) on Jan 02, 2005 at 23:08 UTC
If you have a modern perl, it will always be defined in Socket.pm, whether your system actually has it or not. In case your system does not have it, calling the constant will cause it to croak with a message like "Your vendor has not defined Socket macro TCP_NODELAY". This is often what you want, so you don't have to do anything in that case. If you want to check at runtime and e.g. only turn nagle off if the constant really is there, you can check with a string eval, e.g: `# untested code use Socket qw(IPPROTO_TCP) my $has_nagle = eval "Socket::TCP_NODELAY(); 1"; ... if ($has_nagle) { setsockopt($fh, IPPROTO_TCP, Socket::TCP_NODELAY(), 1) \|\| croak "Couldn't disable Nagle's algorithm: $!"; } else { warn("Your system doesn't seem to support turning of Nagle's algor +ithm\n"); }` [download] (I also didn't try to import it in case you use a Socket.pm that doesn't even have the constant)	[reply] [d/l]
Re^4: Portably disabling Nagle's algorithm for TCP by mowgli (Friar) on Jan 03, 2005 at 17:38 UTC
Mmmm. So is it safe to assume that if Socket does not define that macro, the platform we're running on actually does not support turning of Nagle's algorithm, or are there (non-totally obscure) platforms that don't have TCP_NODELAY but support doing this by other means? -- mowgli	[reply]