[sr-dev] [kamailio/kamailio] app_perl: Ignore __DIE__ signals that come from eval blocks (#2745)

### Description

If possible, I would like that the `kamailio/src/modules/app_perl/lib/perl/Kamailio.pm` file does not generate error messages to the system log files, which are not actual errors and are caused by `eval` blocks of third-party Perl modules that my code depends on.

To illustrate the current setup, let's consider the following:

- In file `/etc/kamailio/kamailio_52.cfg` ```perl modparam( "app_perl", "filename", "/opt/myprogram/perllib/MyKamailio.pm" ) ```

- In file `/opt/myprogram/perllib/MyKamailio.pm`: ```perl use Crypt::JWT qw( decode_jwt encode_jwt ); ```

- It happens that `Crypt::JWT` depends on `CryptX`, which in turn needs a `JSON::XS` implementation, which could be either `Cpanel::JSON::XS` or `JSON::XS`or `JSON::PP`, in that order of preference. That need is resolved at runtime, as we can see in the following code fragment taken from the file at https://github.com/DCIT/perl-CryptX/blob/master/lib/CryptX.pm: ```perl BEGIN { if (eval { require Cpanel::JSON::XS }) { Cpanel::JSON::XS->import(qw(encode_json decode_json)); $has_json = 1; } elsif (eval { require JSON::XS }) { JSON::XS->import(qw(encode_json decode_json)); $has_json = 2; } elsif (eval { require JSON::PP }) { JSON::PP->import(qw(encode_json decode_json)); $has_json = 3; } else { $has_json = 0; } } ```

- In my system, `Cpanel::JSON::XS` is not installed because it is not needed. I could install it, but unfortunately that module intermittently causes a segmentation fault, as described in the issue report at https://github.com/rurban/Cpanel-JSON-XS/issues/179.

### Expected behavior

I would expect two things:

- The operating system log files, like `/var/log/syslog`, adds only entries like the following ones after restarting Kamailio:

May 25 14:30:06 myserver systemd[1]: kamailio.service: Succeeded. May 25 14:30:06 myserver systemd[1]: Stopped Kamailio server. May 25 14:30:06 myserver systemd[1]: Starting Kamailio server... May 25 14:30:06 myserver systemd[1]: Started Kamailio server.

- The output of commands like `systemctl status kamailio.service` only shows informational messages of success.

### Actual observed behavior

- The operating system log files, like `/var/log/syslog`, also adds error messages like the following one after restarting Kamailio:

May 25 14:30:06 myserver /sbin/kamailio[1827476]: ERROR: app_perl [kamailioxs.xs:1041]: XS_Kamailio__Message_log(): perl error: Can't locate Cpanel/JSON/XS.pm in @INC (you may need to install the Cpanel::JSON::XS module) (@INC contains: /opt/myprogram/perllib /etc/perl /usr/local/lib/x86_64-linux-gnu/perl/5.30.0 /usr/local/share/perl/5.30.0 /usr/lib/x86_64-linux-gnu/perl5/5.30 /usr/share/perl5 /usr/lib/x86_64-linux-gnu/perl/5.30 /usr/share/perl/5.30 /usr/local/lib/site_perl) at /usr/local/lib/x86_64-linux-gnu/perl/5.30.0/CryptX.pm line 14.

- The output of commands like `systemctl status kamailio.service` adds that same error message at its end.

### What could be changed in Kamailio?

The `kamailio/src/modules/app_perl/lib/perl/Kamailio.pm` file could ignore, or bypass, the `__DIE__` signals coming from `eval` blocks, like this changed code fragment shows:

```perl $SIG{'__DIE__'} = sub { die @_ if( $^S or not defined $^S ); Kamailio::Message::log(undef, L_ERR, "perl error: $_[0]\n"); }; ```

That changed is based on the following references:

- The [Override die with END or CORE::GLOBAL::die](https://www.effectiveperlprogramming.com/2011/05/override-die-with-end-or-co...) article, which says:

There’s a Perl special variable that can help. The documentation for die recommends that you start your `__DIE__` handler by checking `$^S` before you continue. Inside the handler, the special handler is turned off so `die` inside `$SIG{__DIE__}` is the real `die`. The value of `$^S` will be true if it came from within an `eval`, so this just re-throws the exception without handling it.

- The [Perl documentation for the `$^S` variable](https://perldoc.perl.org/perlvar#%24%5ES), which says:

Current state of the interpreter.

$^S State --------- ------------------------------------- undef Parsing module, eval, or main program true (1) Executing an eval false (0) Otherwise

The first state may happen in `$SIG{__DIE__}` and `$SIG{__WARN__}` handlers.

- The [Perl documentation for the `die` function](https://perldoc.perl.org/functions/die), which says:

You can arrange for a callback to be run just before the `die` does its deed, by setting the `$SIG{__DIE__}` hook. The associated handler is called with the exception as an argument, and can change the exception, if it sees fit, by calling `die` again. See `"%SIG"` in perlvar for details on setting `%SIG` entries, and `eval` for some examples. Although this feature was to be run only right before your program was to exit, this is not currently so: the `$SIG{__DIE__}` hook is currently called even inside `eval`ed blocks/strings! If one wants the hook to do nothing in such situations, put

```perl die @_ if $^S; ```

as the first line of the handler (see "`$^S`" in perlvar). Because this promotes strange action at a distance, this counterintuitive behavior may be fixed in a future release.

### Additional Information

* **Kamailio Version** - output of `kamailio -v`

```bash root@myserver:~# kamailio -V version: kamailio 5.4.3 (x86_64/linux) e19ae3 flags: USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MMAP, PKG_MALLOC, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLACKLIST, HAVE_RESOLV_RES, TLS_PTHREAD_MUTEX_SHARED ADAPTIVE_WAIT_LOOPS 1024, MAX_RECV_BUFFER_SIZE 262144, MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB poll method support: poll, epoll_lt, epoll_et, sigio_rt, select. id: e19ae3 compiled on 17:51:35 Feb 14 2021 with gcc 9.3.0 ```

* **Operating System**:

```bash root@myserver:~# uname -a Linux myserver 5.4.0-54-generic #60-Ubuntu SMP Fri Nov 6 10:37:59 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux ```

```bash root@myserver:~# cat /etc/os-release NAME="Ubuntu" VERSION="20.04.1 LTS (Focal Fossa)" ID=ubuntu ID_LIKE=debian PRETTY_NAME="Ubuntu 20.04.1 LTS" VERSION_ID="20.04" HOME_URL="https://www.ubuntu.com/" SUPPORT_URL="https://help.ubuntu.com/" BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/" PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy" VERSION_CODENAME=focal UBUNTU_CODENAME=focal ```

* **Perl version**:

```bash root@myserver:~# perl -V Summary of my perl5 (revision 5 version 30 subversion 0) configuration:

Platform: osname=linux osvers=4.19.0 archname=x86_64-linux-gnu-thread-multi uname='linux localhost 4.19.0 #1 smp debian 4.19.0 x86_64 gnulinux ' config_args='-Dmksymlinks -Dusethreads -Duselargefiles -Dcc=x86_64-linux-gnu-gcc -Dcpp=x86_64-linux-gnu-cpp -Dld=x86_64-linux-gnu-gcc -Dccflags=-DDEBIAN -Wdate-time -D_FORTIFY_SOURCE=2 -g -O2 -fdebug-prefix-map=/build/perl-Wfb2Cd/perl-5.30.0=. -fstack-protector-strong -Wformat -Werror=format-security -Dldflags= -Wl,-Bsymbolic-functions -Wl,-z,relro -Dlddlflags=-shared -Wl,-Bsymbolic-functions -Wl,-z,relro -Dcccdlflags=-fPIC -Darchname=x86_64-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.30 -Darchlib=/usr/lib/x86_64-linux-gnu/perl/5.30 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/x86_64-linux-gnu/perl5/5.30 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.30.0 -Dsitearch=/usr/local/lib/x86_64-linux-gnu/perl/5.30.0 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 -Duse64bitint -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Ud_ualarm -Uusesfio -Uusenm -Ui_libutil -Ui_xlocale -Uversiononly -DDEBUGGING=-g -Doptimize=-O2 -dEs -Duseshrplib -Dlibperl=libperl.so.5.30.0' hint=recommended useposix=true d_sigaction=define useithreads=define usemultiplicity=define use64bitint=define use64bitall=define uselongdouble=undef usemymalloc=n default_inc_excludes_dot=define bincompat5005=undef Compiler: cc='x86_64-linux-gnu-gcc' ccflags ='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fwrapv -fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64' optimize='-O2 -g' cppflags='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fwrapv -fno-strict-aliasing -pipe -I/usr/local/include' ccversion='' gccversion='9.3.0' gccosandvers='' intsize=4 longsize=8 ptrsize=8 doublesize=8 byteorder=12345678 doublekind=3 d_longlong=define longlongsize=8 d_longdbl=define longdblsize=16 longdblkind=3 ivtype='long' ivsize=8 nvtype='double' nvsize=8 Off_t='off_t' lseeksize=8 alignbytes=8 prototype=define Linker and Libraries: ld='x86_64-linux-gnu-gcc' ldflags =' -fstack-protector-strong -L/usr/local/lib' libpth=/usr/local/lib /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt perllibs=-ldl -lm -lpthread -lc -lcrypt libc=libc-2.31.so so=so useshrplib=true libperl=libperl.so.5.30 gnulibc_version='2.31' Dynamic Linking: dlsrc=dl_dlopen.xs dlext=so d_dlsymun=undef ccdlflags='-Wl,-E' cccdlflags='-fPIC' lddlflags='-shared -L/usr/local/lib -fstack-protector-strong'

Characteristics of this binary (from libperl): Compile-time options: HAS_TIMES MULTIPLICITY PERLIO_LAYERS PERL_COPY_ON_WRITE PERL_DONT_CREATE_GVSV PERL_IMPLICIT_CONTEXT PERL_MALLOC_WRAP PERL_OP_PARENT PERL_PRESERVE_IVUV USE_64_BIT_ALL USE_64_BIT_INT USE_ITHREADS USE_LARGE_FILES USE_LOCALE USE_LOCALE_COLLATE USE_LOCALE_CTYPE USE_LOCALE_NUMERIC USE_LOCALE_TIME USE_PERLIO USE_PERL_ATOF USE_REENTRANT_API USE_THREAD_SAFE_LOCALE Locally applied patches: DEBPKG:debian/cpan_definstalldirs - Provide a sensible INSTALLDIRS default for modules installed from CPAN. DEBPKG:debian/db_file_ver - https://bugs.debian.org/340047 Remove overly restrictive DB_File version check. DEBPKG:debian/doc_info - Replace generic man(1) instructions with Debian-specific information. DEBPKG:debian/enc2xs_inc - https://bugs.debian.org/290336 Tweak enc2xs to follow symlinks and ignore missing @INC directories. DEBPKG:debian/errno_ver - https://bugs.debian.org/343351 Remove Errno version check due to upgrade problems with long-running processes. DEBPKG:debian/libperl_embed_doc - https://bugs.debian.org/186778 Note that libperl-dev package is required for embedded linking DEBPKG:fixes/respect_umask - Respect umask during installation DEBPKG:debian/writable_site_dirs - Set umask approproately for site install directories DEBPKG:debian/extutils_set_libperl_path - EU:MM: set location of libperl.a under /usr/lib DEBPKG:debian/no_packlist_perllocal - Don't install .packlist or perllocal.pod for perl or vendor DEBPKG:debian/fakeroot - Postpone LD_LIBRARY_PATH evaluation to the binary targets. DEBPKG:debian/instmodsh_doc - Debian policy doesn't install .packlist files for core or vendor. DEBPKG:debian/ld_run_path - Remove standard libs from LD_RUN_PATH as per Debian policy. DEBPKG:debian/libnet_config_path - Set location of libnet.cfg to /etc/perl/Net as /usr may not be writable. DEBPKG:debian/perlivp - https://bugs.debian.org/510895 Make perlivp skip include directories in /usr/local DEBPKG:debian/squelch-locale-warnings - https://bugs.debian.org/508764 Squelch locale warnings in Debian package maintainer scripts DEBPKG:debian/patchlevel - https://bugs.debian.org/567489 List packaged patches for 5.30.0-9ubuntu0.2 in patchlevel.h DEBPKG:fixes/document_makemaker_ccflags - https://bugs.debian.org/628522 [rt.cpan.org #68613] Document that CCFLAGS should include $Config{ccflags} DEBPKG:debian/find_html2text - https://bugs.debian.org/640479 Configure CPAN::Distribution with correct name of html2text DEBPKG:debian/perl5db-x-terminal-emulator.patch - https://bugs.debian.org/668490 Invoke x-terminal-emulator rather than xterm in perl5db.pl DEBPKG:debian/cpan-missing-site-dirs - https://bugs.debian.org/688842 Fix CPAN::FirstTime defaults with nonexisting site dirs if a parent is writable DEBPKG:fixes/memoize_storable_nstore - [rt.cpan.org #77790] https://bugs.debian.org/587650 Memoize::Storable: respect 'nstore' option not respected DEBPKG:debian/makemaker-pasthru - https://bugs.debian.org/758471 Pass LD settings through to subdirectories DEBPKG:debian/makemaker-manext - https://bugs.debian.org/247370 Make EU::MakeMaker honour MANnEXT settings in generated manpage headers DEBPKG:debian/kfreebsd-softupdates - https://bugs.debian.org/796798 Work around Debian Bug#796798 DEBPKG:fixes/autodie-scope - https://bugs.debian.org/798096 Fix a scoping issue with "no autodie" and the "system" sub DEBPKG:fixes/memoize-pod - [rt.cpan.org #89441] Fix POD errors in Memoize DEBPKG:debian/hurd-softupdates - https://bugs.debian.org/822735 Fix t/op/stat.t failures on hurd DEBPKG:fixes/math_complex_doc_great_circle - https://bugs.debian.org/697567 [rt.cpan.org #114104] Math::Trig: clarify definition of great_circle_midpoint DEBPKG:fixes/math_complex_doc_see_also - https://bugs.debian.org/697568 [rt.cpan.org #114105] Math::Trig: add missing SEE ALSO DEBPKG:fixes/math_complex_doc_angle_units - https://bugs.debian.org/731505 [rt.cpan.org #114106] Math::Trig: document angle units DEBPKG:fixes/cpan_web_link - https://bugs.debian.org/367291 CPAN: Add link to main CPAN web site DEBPKG:debian/hppa_op_optimize_workaround - https://bugs.debian.org/838613 Temporarily lower the optimization of op.c on hppa due to gcc-6 problems DEBPKG:debian/installman-utf8 - https://bugs.debian.org/840211 Generate man pages with UTF-8 characters DEBPKG:fixes/getopt-long-4 - https://bugs.debian.org/864544 [rt.cpan.org #122068] Fix issue #122068. DEBPKG:debian/hppa_opmini_optimize_workaround - https://bugs.debian.org/869122 Lower the optimization level of opmini.c on hppa DEBPKG:debian/sh4_op_optimize_workaround - https://bugs.debian.org/869373 Also lower the optimization level of op.c and opmini.c on sh4 DEBPKG:debian/perldoc-pager - https://bugs.debian.org/870340 [rt.cpan.org #120229] Fix perldoc terminal escapes when sensible-pager is less DEBPKG:debian/prune_libs - https://bugs.debian.org/128355 Prune the list of libraries wanted to what we actually need. DEBPKG:debian/mod_paths - Tweak @INC ordering for Debian DEBPKG:debian/configure-regen - https://bugs.debian.org/762638 Regenerate Configure et al. after probe unit changes DEBPKG:debian/deprecate-with-apt - https://bugs.debian.org/747628 Point users to Debian packages of deprecated core modules DEBPKG:debian/disable-stack-check - https://bugs.debian.org/902779 [perl #133327] Disable debugperl stack extension checks for binary compatibility with perl DEBPKG:fixes/eumm-usrmerge - https://bugs.debian.org/913637 Avoid mangling /bin non-perl shebangs on merged-/usr systems DEBPKG:debian/perlbug-editor - https://bugs.debian.org/922609 Use "editor" as the default perlbug editor, as per Debian policy DEBPKG:fixes/gid-parsing - [79e302e] https://bugs.debian.org/941985 [perl #134169] (perl #134169) mg.c reset endptr after use DEBPKG:fixes/CVE-2020-10543.patch - [PATCH v530 1/4] regcomp.c: Prevent integer overflow from nested regex quantifiers. DEBPKG:fixes/CVE-2020-10878-1.patch - [PATCH v530 2/4] study_chunk: extract rck_elide_nothing DEBPKG:fixes/CVE-2020-10878-2.patch - [PATCH v530 3/4] regcomp: use long jumps if there is any possibility of overflow DEBPKG:fixes/CVE-2020-12723.patch - [PATCH v530 4/4] study_chunk: avoid mutating regexp program within GOSUB Built under linux Compiled at Oct 19 2020 10:56:54 @INC: /etc/perl /usr/local/lib/x86_64-linux-gnu/perl/5.30.0 /usr/local/share/perl/5.30.0 /usr/lib/x86_64-linux-gnu/perl5/5.30 /usr/share/perl5 /usr/lib/x86_64-linux-gnu/perl/5.30 /usr/share/perl/5.30 /usr/local/lib/site_perl /usr/lib/x86_64-linux-gnu/perl-base ```

Please evaluate the situation and let me know your feedback and what I could help with.

Thanks in advance for your time and attention.