The Siege Can Continue

A wise internet spaceship pirate once wrote: “Whining gets you stuff. That’s why humans are at the top of the food chain.”. My Whining got me a fix that put an end to segfaults on long running scripts that react to http requests.

So I continued to add missing bits to my golfed httpd and found another good use for term:<>.

constant term:<HTTP-HEADER-404> = "HTTP/1.1 404 Not Found", "Content-Type: text/plain; charset=UTF-8", "Content-Encoding: UTF-8", "";

Without term:<> the compiler would think I wanted to substract 400 from a http header.

If you got some time to spare please write a whiny blog post about a crash that is bugging you – works like a charm.

Goto the Last Fifo

I always admired the elegance of the sysfs. You take a text and write it to a file to talk to a function running in kernel space. As soon as you know how to work with files, you can change the systems behaviour and reuse access control mechanism without any special tools. It’s very easy to script and dump (parts) of the systems state.

Linux and friends come with fifos that serve the same purpose. Create a fifo, set access rights and start reading from that pseudo-file. Very easy to do in Perl 5.

my $fifo; open($fifo, "+);
while (<$fifo>) {
    do-things-with $_;
} 

Rakudo doesn’t really know about fifos yet, as a result it doesn’t block on a read of a fifo that don’t got data anymore. After a bit of fiddeling I found a way around that problem.

      1 use v6.c;
      2
      3 # `mkfifo radio-fifo-in`
      4 # `echo "foo" > radio-fifo-in`
      5 # `echo "foo^D" > radio-fifo-in`
      6
      7 my $fifo-in = open(„radio-fifo-in“, :r);
      8
      9 LABEL: loop {
     10     react {
     11         whenever supply { .emit for $fifo-in.lines } {
     12             say .Str;
     13             last LABEL if /‚^D‘/;
     14         }
     15     }
     16 }

I learned that whenever reacts to last and will teach the docs about it later today. Luckily Perl 6 got labels so we can tell last where to goto.

UPDATE: scovit found a short expression that gets very close to the behaviour of Perl 5.

my $fifo = open("radio-fifo-in", :r);
while defined $_ = $fifo.get { .say }

We Need to Siege Moar

Alas, my attempt to avoid bugs by moving with little load was not as fruitful as I hoped.

Siegeing my tiny httpd lasted for about an hour and then the gates gave way. With dmesg the culprit was swiftly revealed.

[4361268.087988] moar[12491]: segfault at 3c8b ip 00007f86b426868b sp 00007f86aaff86b0 error 4 in libmoar.so[7f86b407b000+55d000]

A had the suspicion that close to 70000 tests will only get us the failure modes that are cought within minutes. Looks like there is quite some squashing left to do for the moar team.

Golfing httpd

I’m building a internet radio player and wanted both a curses and web interface to switch stations. Looking at the various modules in the ecosystem provided lots of options that do lots of things. I had a bug hunt in those field a while ago and didn’t like it. The amount of httpd I need is fairly small and I thought to myself: „Somebody should golf that!“. And so I did.

The objective is to have as little http as I can get away with. I want to display the names of available stations and receive a station-id to switch stations. And maybe a stop, play and record button. That can be done with with lines of text. So text/plain it is.

I can stuff channel-ids and button names into URLs. What means implementing only GET will do. Caching or other fancy stuff wont be needed, what makes the HTTP-header static. The most complex thing to do would be taking the URL apart.

That’s what I came up with:

my sub term:<now>() { DateTime.now.Instant but role :: { method Str { self.DateTime.hh-mm-ss } } };
my &BOLD = $*OUT.t ?? sub (*@s) { "\e[1m{@s.join('')}\e[0m" } !! sub (|c) { c };

constant HTTP-HEADER = "HTTP/1.1 200 OK", "Content-Type: text/plain; charset=UTF-8", "Content-Encoding: UTF-8", "";
constant term:<HTTP-HEADER-404> = "HTTP/1.1 404 Not Found", "Content-Type: text/plain; charset=UTF-8", "Content-Encoding: UTF-8", "";

react {
    whenever IO::Socket::Async.listen('0.0.0.0', 8080) -> $conn {
        note „{now} incomming connection from {$conn.peer-host}:{$conn.peer-port}“;
        my @msg = HTTP-HEADER;
        whenever $conn.Supply.lines {
            if /^GET  (<[\w„/“]>+) [„HTTP“ \d „/“ \d]? / {
                note „{now} GET $0“;
                given $0.Str {
                    @msg.push: „running since {BEGIN now} UTC“ when „/status“;

                    @msg.push: „Hello World!“ when „/“;

                    done when „/exit“
                    default {
                        @msg = HTTP-HEADER-404;
                        @msg.push: „Resource {.Str} not found.“;
                    }
                }
            }

            if /^$/ { 
                for {
                    once note .Str;
                    $conn.print(.Str ~ "\n")
                }
                $conn.close;
            }
        }
        CLOSE {
            note „{now} connection closed“;
        }
        CATCH { default { warn BOLD .^name, ': ', .Str; warn BOLD "handled in $?LINE"; } }
    }
}

The whole thing waits for a connection. Then takes the URL apart and fills an Array with lines of text. That Array is then send back to the client. A few lines of logging and error handling.

The less code there is the less ground a bug hunter has to cover. Luckily Perl 6 is very friendly to golfers.

UPDATE: Add proper handling of the http header terminator, what leads to less error handling. Also, add some more log output.

Hunting Documented Bugs

AlexDaniel came up with and Zoffix made some propaganda for a reoccuring bug hunt. This weeks pray are doc issues. In the following are detailed instructions on how to get dressed up.

zef install META6::bin
meta6 --fork-module=p6doc
cd doc
zef --deps-only install .
# you may have to add $HOME/.perl6/bin to $PATH
# edit away
git push
meta6 --pull-request --title='add t/meta.t'
# goto edit away

If you never used META6::bin you may have to do some setup.