[Catalyst] FastCGI startup strangeness

[Dagfinn Ilmari Mannsåker]

"Daniel J. Luke" <dluke at geeklair.net> writes:

> I noticed today that an app I'm working on will start fine only if the
> user who is running the app can read the current directory (ie, if I'm
> starting it as a user dedicated to running the app, that user must
> have read permission on CWD).
>
> Couldn't load class (MYAPP::Script::FastCGI) because: Can't locate MYAPP/Script/FastCGI.pm:   Permission denied at /path/to/perl-5.20.0/lib/site_perl/5.20.0/Catalyst/ScriptRunner.pm line 13.
> 	Catalyst::ScriptRunner::find_script_class("Catalyst::ScriptRunner", "MYAPP", "FastCGI") called at /path/to/perl/perl-5.20.0/lib/site_perl/5.20.0/Catalyst/ScriptRunner.pm line 42
> 	Catalyst::ScriptRunner::run("Catalyst::ScriptRunner", "MYAPP", "FastCGI") called at /path/to/MYAPP/script/MYAPP_fastcgi.pl line 4
>
> strace shows the difference between a successful launch and a failed
> one is whether we get EACCESS or ENOENT when looking for
> ./MYAPP/Script/FastCGI.pm

This is due to require as of 5.18 no longer silently ignoring errors
when trying to load a module:

    require dies for unreadable files

    When require encounters an unreadable file, it now dies. It used
    to ignore the file and continue searching the directories in @INC
    [perl #113422].

https://metacpan.org/pod/perl5180delta#require-dies-for-unreadable-files

Combined with the fact that Catalyst::ScriptRunner tries to load the
optional (but in your case non-existent) MYAPP::Script::FastCGI, and
that '.' is in @INC by the default, it gives this (somewhat annoying)
behaviour.

For daemons it is generally a good idea to cd to / or some
application-specific directory before starting up, to avoid e.g. it
accidentally hanging onto a mount point.

> failure:
> stat("./MYAPP/Script/FastCGI.pmc", 0x7fffa8eba720) = -1 EACCES (Permission denied)
> stat("./MYAPP/Script/FastCGI.pm", 0x7fffa8eba660) = -1 EACCES (Permission denied)
>
> success:
> stat("./MYAPP/Script/FastCGI.pmc", 0x7fff80e76db0) = -1 ENOENT (No such file or directory)
> stat("./MYAPP/Script/FastCGI.pm", 0x7fff80e76cf0) = -1 ENOENT (No such file or directory)
>
> I didn't see this documented anywhere - am I missing some obvious reason why this behavior is desired?

-- 
"I use RMS as a guide in the same way that a boat captain would use
 a lighthouse.  It's good to know where it is, but you generally
 don't want to find yourself in the same spot." - Tollef Fog Heen