This post is part of the notes I took while preparing for and during the migration of https://perlmonks.org behind a CDN. I mostly publish these notes so that I can find them again later.

There are situations where I don't want to override the DNS resolution for my complete system, but still connect to specific machines pretending a DNS name resolves to them. Examples are SSL certificate checking, and various firewall configurations. Especially while migrating a site behind a CDN or when setting up s site beh[nd a reverse proxy or Wireguard, I want to inspect and compare the results of queries to the different machines.

For these examples, assume that 10.0.0.1 is the machine serving the website perlmonks.org as the origin. The public DNS resolves to a pool of CDN machines somewhere else, but we want to debug what the original source is serving. The original machine also wants to be accessed as perlmonks.org over SSL.

Override curl name resolution

This is documented in the curl manpage

curl --resolve perlmonks.org:443:10.0.0.1 https://...

Override Firefox name resolution

Open the Firefox browser console with Ctrl+Shift+J . You should be able to enter Javascript there; If not, enable "Debugging Tools für Browser-Chrome" in the normal browser console settings (F12 , then F1 yeah, CUI standards be damned ). Then enter the name/IP pair for name resolution. This persists until you restart Firefox.

const gOverride = Cc["@mozilla.org/network/native-dns-override;1"].getService(Ci.nsINativeDNSResolverOverride);
gOverride.addIPOverride("perlmonks.org", "10.0.0.1");

Override LWP::UserAgent DNS name resolution

For LWP::UserAgent there is no general mechanism, but monkeypatching LWP::Protocol::https works. To also make SNI work, you should additionally pass in the SSL_hostname explicitly to the SSL options. I'm not sure why this is necessary, as the code in LWP::Protocol::https extracts the hostname from the request URL, but this made the difference for me between 421 Misdirected Request and 200 OK with Fastly :

our $force_peeraddr;
around 'LWP::Protocol::http::_extra_sock_opts' => sub {
        my $orig = shift;
        die unless wantarray;
        my @rv = $orig->(@_);
        push @rv, PeerAddr => $force_peeraddr if defined $force_peeraddr;
        return @rv;
};
around 'LWP::Protocol::https::_get_sock_info' => sub {
        my $orig = shift;
        my ($self, $res, $sock) = @_;
        my $cert = $sock->get_peer_certificate;
        my @san = $cert->peer_certificate('subjectAltNames');
        use Data::Dumper; warn Dumper \@san;
        while (@san) {
                my ($type_id, $value) = splice @san, 0, 2;
                $res->push_header("Client-SSL-Cert-SubjectAltName"
                        => "$type_id: $value");
        }
        $orig->(@_);
};

$force_peeraddr = '10.0.0.1';

my $ua = LWP::UserAgent->new(
    ssl_opts => {
        verify_hostname => 0,
        SSL_hostname => 'perlmonks.org', # for SNI
    },
    timeout => 60,
);

Override Chrome name resolution

It seems that this is not possible.

Override wget name resolution

It seems that this is not possible.

I really like live-editing documents. Interactively seeing the results of your edits makes editing more fun. For tools made by others, this would mean WYSIWYG, but for tools made by (and for) myself, I prefer the approach of editing a text file and having the conversion process kick off automatically on every file save.

For some reason, I mostly prefer editing text in a plain/small editor as ASCII. My markup needs are usually restricted to bold and italics, with a sprinkling of images and links. I don't have particular layout needs - most of that is covered by a template.

The main idea is to have two programs, one program for editing (commonly, a text editor) and one program for converting and displaying the rendered file. Instead of having a program that does the display and editing for one or more file formats, this separation allows me to use the convenient text editor that I've customized to my liking instead of a built-in text editor. It also allows me to add arbitrary intermediate steps to convert from the source to the display.

This idea is nothing new - the Emacs Flymake mode does recompilation (and other recreation) in the background whenever a source file changes as well.

With File::ChangeNotify ( and Linux::Inotify2 on Linux, respectively File::ChangeNotify::ReadDirectoryChanges for Windows, writing such tools that auto-update the viewer whenever the source file changes is really easy.

One of the programs that implement this idea is live-edit.pl.

live-edit.pl

This program runs make whenever a file in a given directory or its subdirectories changes. The Makefile should contain the rules to regenerate the interesting content. The default rules are only for converting LaTeX files into PDF:

# This is the default Makefile to be used by the asset reloader
# if no Makefile is found in the current directory

OPEN=xdg-open
MAYBE_OPEN=perl /home/corion/Projekte/App-LiveEdit/scripts/maybe-open.pl

.PHONY: all

all: .pdf

.pdf.tex:
    pdflatex -interaction=batchmode "$<"
    $(MAYBE_OPEN) "$@"

make solves the problem backwards, given a file that I want, regenerate everything intermediate. live-edit.pl solves the problem forwards, given a file that changed, regenerate everything that depends on it. Maybe live-edit.pl should be named ekam instead.

maybe-open.pl - this is an offshoot program that opens a file using xdg-open if no process is running with the file name on its command line. Highly convenient for launching a .pdf file once in its viewer.

It's weird but currently I draw most of my programming satisfaction from using (and enhancing) App::sqldisplay. It is a simplistic app that allows me to write and display SQL queries against a spreadsheet. I mostly use it to do the accounting for the Perl club. But doing that made doing the books much more fun actually.

Here I edit a cell in the spreadsheet, and the SQL query in the browser automatically updates and highlights the changed rows:

Also, I've now started exploring HTMX for that, and it works surprisingly well for the use case I have, removing 20+ lines of code in favour of 1 line of configuration and small Perl-side code changes.

The one thing I don't like about HTMX is that for every component of your page that you want to update individually, you need to create an HTTP accessible endpoint. But for push notifications, you can just push the new HTML instead, which is good enough.

But "even" with this hobby project, I see feature creep, as just today I thought about exporting the collection of queries as an Excel sheet. And the UI now has tabs, just like an Excel sheet and I wonder if I should keep an Excel sheet/spreadsheet for data entry or just (also) write my own editing UI. But writing an editing UI is makework for little gain. I would want it to have mostly Excel-like UI, keyboard bindings and autofill.

Last week, the Perl community came together for the 28th German Perl Workshop. This year, it was held at the Heilandskirche in Berlin Moabit. Excitingly, we had the nave for the presentations.

While the name is still German Perl Workshop, we now draw attendees from all over the globe. Presenters came from India, the US and various European countries. Maybe it is time to announce it as a more international conference again.

Bringing the infrastructure to a Perl Workshop is a lot of additional hardware that we hopefully won't need, like looong HDMI cables, various adapters to HDMI, a bundle extension cords and duct tape of the non-Perl variant. Lee also brought the EPO recording set for recording the presentations. The set came back with me from Berlin, as its main use is nowadays recording the talks at a German Perl Workshop for later publication.

Organizing a conference usually means that my attention is divided between running the event, chatting with attendees and giving a presentation or two. Luckily other members of Frankfurt.pm and other long-time attendees are always there to lend a hand.

Over the years, we have organized the German Perl Workshop many times. Local organizers for 2027 already stepped up. Next year, we aim for the city of Hannover. We don't have the contract for a venue signed, so watch https://www.perl-workshop.de/news for announcements.

Such an event can't happen without the sponsors who support us financially. Let me quickly show their logos here:

... which are meaningless internet points, but Anthropic only recognize projects with 5k+ Github stars for their Open Source program. Of course, you can also apply and try for a manual review. But maybe we should push the stars of the Perl repository up a bit in this popularity contest...

Of course, a free 6-month Claude Max subscription isn't all that great, but if Github stars are a measure...