February 2021 - dancer-users - lists.preshweb.co.uk

Debugging sessions
by Nikola Mitev 29 Jun '23

29 Jun '23

Hi all, I have an annoyingly intermittent problem where on successful authentication the session info disappears and the user is endlessly redirected to the login page. It happens about once a month on a site with 10-20 logins daily. Once it happens to a user, it keeps happening for that user only. A restart of the app usually fixes the issue, and I am yet to see someone who had this problem to report it again at a later stage. Had about 10 cases so far in total. The cookie is generated on accessing the login page, stored in the browser and sent with the login POST request so I can verify cookies are enabled. The user is then authenticated, data added to the session including an 'authenticated' flag and they are redirected to their dashboard. Right before the redirection the session data is present. They make a request for the dashboard following the redirect, this triggers a session authenticated check which fails as no data is available for the session. They are then redirected for authentication and so on in a loop. If I restart the app the issue vanishes. hook before => sub { # <snip> if (!session('authenticated')) { forward '/login'; } } post '/login' => sub { # user authentication and session storage here, then the debug code and the redirecton: my $authenticated = session('authenticated'); $log->info("User authenticated ($authenticated), redirecting to $target_route"); return redirect $target_route; }; I don't have an explicit check on cookie size - not sure how to check it doesn't exceed 4K - but find it unlikely this is the issue. If that was the problem it should be happening persistently for a user regardless of restarts etc? Hope all this makes sense, I am looking for general advice on how to troubleshoot this but any ideas at all will be very much appreciated. Nik

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Designing a route for a long survey
by Richard Reina 20 Feb '21

20 Feb '21

I have a friend who needs me to develop a page which is a long survey, There is some skip logic needed, for example, if users birthday is before x date skip to question 5, if answer to question 12 is 'no' skip to question 16, but nothing too complicated. I nevertheless am struggling with how to design such a route and was wondering if anyone perhaps knew of any similar examples. Rciahrd

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passing client/socket error from server to dancer app
by Paul Clements 15 Feb '21

15 Feb '21

I asked a similar question a few weeks ago, and am circling back because I am still in need of a solution. As it turns out, without a way to handle client/socket disconnect, I am having trouble finding a suitable working combination of Dancer2/PSGI Server. I've tried several, and while Twiggy does give an error (SIGPIPE) on client disconnect, my app is not AnyEvent- (or even thread-) based, so the forking servers (e.g., Starman) are a better fit (without rewriting substantial amounts of code). At this point, I'm wondering if a fairly simple change to Dancer2 might be acceptable. It's a minimal change, but gives the Dancer2 app a way to know when a client disconnect has occurred in a "delayed" handler. Specifically, it turns out that many/most servers return "undef" from their write routines once the socket is closed. So, the idea is to allow that information to pass back to the app: diff --git a/lib/Dancer2/Core/DSL.pm b/lib/Dancer2/Core/DSL.pm index fd29ac74..9adb3e28 100644 --- a/lib/Dancer2/Core/DSL.pm +++ b/lib/Dancer2/Core/DSL.pm @@ -329,7 +329,7 @@ sub content { eval { $Dancer2::Core::Route::WRITER->write(@_); - 1; + # use write's return code instead # 1; } or do { my $error = $@ || 'Zombie Error'; $Dancer2::Core::Route::ERROR_HANDLER It doesn't seem like the constant 1 return code from "content" is something that anyone would be relying on, so changing it shouldn't hurt (?), but would provide a way to get the error information back to the app, e.g.: my $client_ok = content $data; if (!defined($client_ok)) { # something's wrong! Thanks, Paul

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The most important Dancer Plugins
by Gabor Szabo 13 Feb '21

13 Feb '21

Hi, When making improvements to Dancer2 it is important to notice if a plugin breaks and either make the change in a different way or notify the author of the plugin regarding the upcoming breaking change. In order to help with this, in the GitHub Actions configuration I've added the testing of some of the plugins. Specifically: Dancer2::Plugin::Auth::HTTP::Basic::DWIW Dancer2::Plugin::Minion Dancer2::Template::Handlebars Dancer2::Session::Cookie See https://github.com/PerlDancer/Dancer2/blob/master/.github/workflows/ci.yml However I assume these are not the only popular plugins. So I wonder, which other plugins do you use? Gabor

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How to add application-specific config values to config.yml? and the environments/* files?
by Gabor Szabo 09 Feb '21

09 Feb '21

e.g. My applications uses some external system and I'd like to read its URL and the token I need to access it from some config file. I looked at the generated config files, and the only solution I could come up with is to put it under "plugins" like this: plugins: MyApp: url: http://galaxy.com/ token: 42 I don't really like it. What is the recommended way to do it? Gabor

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Help with the dancer2 command
by Gabor Szabo 08 Feb '21

08 Feb '21

I think running the dancer2 command is quite unclear: dancer2 <command> [-?h] [long options...] -? -h --help show help Available commands: commands: list the application's commands help: display a command's help screen gen: create new Dancer2 application But if I run "dancer2 -h" as I think everyone would expect to get more help, I just get back the same thing. Only "dancer2 gen" gives me what I was looking for. What do you think? Gabor

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Perl Dancer live coding
by Gabor Szabo 07 Feb '21

07 Feb '21

Hi, Recently I started to do a lot of live coding and learning while streaming it via Twitch. So far it worked out really well for me as it makes me focus a lot more than when I write on my own. It is also really nice to interact with other people and get their advice even if I don't always follow it. I hear such live sessions are also really good for the people who watch them. It is a great way to learn many things that you can only learn by watching someone else. I am new to this, but I see other programmers with more than 200 people watching while they write code. Today I am going to have such a live steamed session in which I am going to build a small Dancer-based web application to be a front-end to run CI jobs on GitLab. I am going to start at 18:00 UTC but you can join later as well. https://www.twitch.tv/szabgab If you are interested, but cannot make it this time, I'd still invite you to follow me on Twitch and set it up to send you notifications when I start to stream. I plan to steam quit often in the coming weeks. Gabor

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http_throw and Dancer2
by Paul Clements 06 Feb '21

06 Feb '21

I've been trying for a while now to figure out the best way to handle exceptions with Dancer2. I like the simplicity of http_throw. However, I've not been able to get that to work successfully with Dancer2 without this workaround: https://pastebin.com/wLsUBJhN (The test shows a PSGI app with HTTPExceptions enabled, which allows proper use of http_throw. It also shows a sample Dancer2 app with my workaround to allow use of http_throw.) Basically, it appears that Dancer2 wants to intercept any exception and rethrow it as 500 (Internal Server Error) without some hacky hook code to intercept the exception and re-apply it later. Has anyone dealt with this issue? Is there a better way to handle this (some middleware or config option)? Thanks, Paul

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BUG? client disconnect not handled in delayed route
by Paul Clements 03 Feb '21

03 Feb '21

Hi, I've been having trouble getting the server (tried the default PSGI one and Starman) to notice when a client disconnects from a delayed route handler. Long story short, I was able to finally debug this down to the content subroutine in DSL.pm. With the change below, I'm now able to detect and properly handle a disconnect (in my case, I'm just hitting ^C on a client curl session). My question is: Does this seem like a proper fix (should I prepare a PR), or is there a better way to handle this? - Paul --- $ diff -pu git/Dancer2/lib/Dancer2/Core/DSL.pm . --- git/Dancer2/lib/Dancer2/Core/DSL.pm 2020-12-31 11:21:47.490454726 -0500 +++ ./DSL.pm 2021-01-23 11:07:47.464438846 -0500 @@ -328,7 +328,8 @@ sub content { } eval { - $Dancer2::Core::Route::WRITER->write(@_); + my $res = $Dancer2::Core::Route::WRITER->write(@_); + die "Write Error\n" if (!defined($res)); 1; } or do { my $error = $@ || 'Zombie Error';

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