```{index} single: FFI::CheckLib ``` # FFI::CheckLib Check that a library is available for FFI ## VERSION version 0.31 ## SYNOPSIS ```perl use FFI::CheckLib; check_lib_or_exit( lib => 'jpeg', symbol => 'jinit_memory_mgr' ); check_lib_or_exit( lib => [ 'iconv', 'jpeg' ] ); # or prompt for path to library and then: print "where to find jpeg library: "; my $path = ; check_lib_or_exit( lib => 'jpeg', libpath => $path ); ``` ## DESCRIPTION This module checks whether a particular dynamic library is available for FFI to use. It is modeled heavily on [Devel::CheckLib](https://metacpan.org/pod/Devel::CheckLib), but will find dynamic libraries even when development packages are not installed. It also provides a [find\_lib](CheckLib.md) function that will return the full path to the found dynamic library, which can be feed directly into [FFI::Platypus](Platypus.md) or another FFI system. Although intended mainly for FFI modules via [FFI::Platypus](Platypus.md) and similar, this module does not actually use any FFI to do its detection and probing. This module does not have any non-core runtime dependencies. The test suite does depend on [Test2::Suite](../Test2/Suite.md). ## FUNCTIONS All of these take the same named parameters and are exported by default. ### find\_lib ```perl my(@libs) = find_lib(%args); ``` This will return a list of dynamic libraries, or empty list if none were found. \[version 0.05\] If called in scalar context it will return the first library found. Arguments are key value pairs with these keys: - lib Must be either a string with the name of a single library or a reference to an array of strings of library names. Depending on your platform, `CheckLib` will prepend `lib` or append `.dll` or `.so` when searching. \[version 0.11\] As a special case, if `*` is specified then any libs found will match. - libpath A string or array of additional paths to search for libraries. - systempath \[version 0.11\] A string or array of system paths to search for instead of letting [FFI::CheckLib](CheckLib.md) determine the system path. You can set this to `[]` in order to not search _any_ system paths. - symbol A string or a list of symbol names that must be found. - verify A code reference used to verify a library really is the one that you want. It should take two arguments, which is the name of the library and the full path to the library pathname. It should return true if it is acceptable, and false otherwise. You can use this in conjunction with [FFI::Platypus](Platypus.md) to determine if it is going to meet your needs. Example: ```perl use FFI::CheckLib; use FFI::Platypus; my($lib) = find_lib( lib => 'foo', verify => sub { my($name, $libpath) = @_; my $ffi = FFI::Platypus->new; $ffi->lib($libpath); my $f = $ffi->function('foo_version', [] => 'int'); return $f->call() >= 500; # we accept version 500 or better }, ); ``` - recursive \[version 0.11\] Recursively search for libraries in any non-system paths (those provided via `libpath` above). - try\_linker\_script \[version 0.24\] Some vendors provide `.so` files that are linker scripts that point to the real binary shared library. These linker scripts can be used by gcc or clang, but are not directly usable by [FFI::Platypus](Platypus.md) and friends. On select platforms, this options will use the linker command (`ld`) to attempt to resolve the real `.so` for non-binary files. Since there is extra overhead this is off by default. An example is libyaml on Red Hat based Linux distributions. On Debian these are handled with symlinks and no trickery is required. - alien \[version 0.25\] If no libraries can be found, try the given aliens instead. The Alien classes specified must provide the [Alien::Base](https://metacpan.org/pod/Alien::Base) interface for dynamic libraries, which is to say they should provide a method called `dynamic_libs` that returns a list of dynamic libraries. \[version 0.28\] In 0.28 and later, if the [Alien](https://metacpan.org/pod/Alien) is not installed then it will be ignored and this module will search in system or specified directories only. This module _will_ still throw an exception, if the [Alien](https://metacpan.org/pod/Alien) doesn't look like a module name or if it does not provide a `dynamic_libs` method (which is implemented by all [Alien::Base](https://metacpan.org/pod/Alien::Base) subclasses). \[version 0.30\] \[breaking change\] Starting with version 0.30, libraries provided by [Alien](https://metacpan.org/pod/Alien)s is preferred over the system libraries. The original thinking was that you want to prefer the system libraries because they are more likely to get patched with regular system updates. Unfortunately, the reason a module needs to install an Alien is likely because the system library is not new enough, so we now prefer the [Alien](https://metacpan.org/pod/Alien)s instead. ### assert\_lib ```perl assert_lib(%args); ``` This behaves exactly the same as [find\_lib](CheckLib.md), except that instead of returning empty list of failure it throws an exception. ### check\_lib\_or\_exit ```perl check_lib_or_exit(%args); ``` This behaves exactly the same as [assert\_lib](CheckLib.md), except that instead of dying, it warns (with exactly the same error message) and exists. This is intended for use in `Makefile.PL` or `Build.PL` ### find\_lib\_or\_exit \[version 0.05\] ```perl my(@libs) = find_lib_or_exit(%args); ``` This behaves exactly the same as [find\_lib](CheckLib.md), except that if the library is not found, it will call exit with an appropriate diagnostic. ### find\_lib\_or\_die \[version 0.06\] ```perl my(@libs) = find_lib_or_die(%args); ``` This behaves exactly the same as [find\_lib](CheckLib.md), except that if the library is not found, it will die with an appropriate diagnostic. ### check\_lib ```perl my $bool = check_lib(%args); ``` This behaves exactly the same as [find\_lib](CheckLib.md), except that it returns true (1) on finding the appropriate libraries or false (0) otherwise. ### which \[version 0.17\] ```perl my $path = which($name); ``` Return the path to the first library that matches the given name. Not exported by default. ### where \[version 0.17\] ```perl my @paths = where($name); ``` Return the paths to all the libraries that match the given name. Not exported by default. ### has\_symbols \[version 0.17\] ```perl my $bool = has_symbols($path, @symbol_names); ``` Returns true if _all_ of the symbols can be found in the dynamic library located at the given path. Can be useful in conjunction with `verify` with `find_lib` above. Not exported by default. ### system\_path \[version 0.20\] ```perl my $path = FFI::CheckLib::system_path; ``` Returns the system path as a list reference. On some systems, this is `PATH` on others it might be `LD_LIBRARY_PATH` on still others it could be something completely different. So although you _may_ add items to this list, you should probably do some careful consideration before you do so. This function is not exportable, even on request. ## ENVIRONMENT [FFI::CheckLib](CheckLib.md) responds to these environment variables: - FFI\_CHECKLIB\_PACKAGE On macOS platforms with [Homebrew](http://brew.sh) and/or [MacPorts](https://www.macports.org) installed, their corresponding lib paths will be automatically appended to `$system_path`. In case of having both managers installed, Homebrew will appear before. This behaviour can be overridden using the environment variable `FFI_CHECKLIB_PACKAGE`. Allowed values are: \- `none`: Won't use either Homebrew's path nor MacPorts \- `homebrew`: Will append `$(brew --prefix)/lib` to the system paths \- `macports`: Will append `port`'s default lib path A comma separated list is also valid: ```text export FFI_CHECKLIB_PACKAGE=macports,homebrew ``` Order matters. So in this example, MacPorts' lib path appears before Homebrew's path. - FFI\_CHECKLIB\_PATH List of directories that will be considered by [FFI::CheckLib](CheckLib.md) as additional "system directories". They will be searched before other system directories but after `libpath`. The variable is colon separated on Unix and semicolon separated on Windows. If you use this variable, `FFI_CHECKLIB_PACKAGE` will be ignored. - PATH On Windows the `PATH` environment variable will be used as a search path for libraries. On some operating systems `LD_LIBRARY_PATH`, `DYLD_LIBRARY_PATH`, `DYLD_FALLBACK_LIBRARY_PATH` or others _may_ be used as part of the search for dynamic libraries and _may_ be used (indirectly) by [FFI::CheckLib](CheckLib.md) as well. ## FAQ - Why not just use `dlopen`? Calling `dlopen` on a library name and then `dlclose` immediately can tell you if you have the exact name of a library available on a system. It does have a number of drawbacks as well. - No absolute or relative path It only tells you that the library is _somewhere_ on the system, not having the absolute or relative path makes it harder to generate useful diagnostics. - POSIX only This doesn't work on non-POSIX systems like Microsoft Windows. If you are using a POSIX emulation layer on Windows that provides `dlopen`, like Cygwin, there are a number of gotchas there as well. Having a layer written in Perl handles this means that developers on Unix can develop FFI that will more likely work on these platforms without special casing them. - inconsistent implementations Even on POSIX systems you have inconsistent implementations. OpenBSD for example don't usually include symlinks for `.so` files meaning you need to know the exact `.so` version. - non-system directories By default `dlopen` only works for libraries in the system paths. Most platforms have a way of configuring the search for different non-system paths, but none of them are portable, and are usually discouraged anyway. [Alien](https://metacpan.org/pod/Alien) and friends need to do searches for dynamic libraries in non-system directories for `share` installs. - My 64-bit Perl is misconfigured and has 32-bit libraries in its search path. Is that a bug in [FFI::CheckLib](CheckLib.md)? Nope. - The way [FFI::CheckLib](CheckLib.md) is implemented it won't work on AIX, HP-UX, OpenVMS or Plan 9. I know for a fact that it doesn't work on AIX _as currently implemented_ because I used to develop on AIX in the early 2000s, and I am aware of some of the technical challenges. There are probably other systems that it won't work on. I would love to add support for these platforms. Realistically these platforms have a tiny market share, and absent patches from users or the companies that own these operating systems (patches welcome), or hardware / CPU time donations, these platforms are unsupportable anyway. ## SEE ALSO - [FFI::Platypus](Platypus.md) Call library functions dynamically without a compiler. - [Dist::Zilla::Plugin::FFI::CheckLib](https://metacpan.org/pod/Dist::Zilla::Plugin::FFI::CheckLib) [Dist::Zilla](https://metacpan.org/pod/Dist::Zilla) plugin for this module. ## AUTHOR Author: Graham Ollis Contributors: Bakkiaraj Murugesan (bakkiaraj) Dan Book (grinnz, DBOOK) Ilya Pavlov (Ilya, ILUX) Shawn Laffan (SLAFFAN) Petr Písař (ppisar) Michael R. Davis (MRDVT) Shawn Laffan (SLAFFAN) Carlos D. Álvaro (cdalvaro) ## COPYRIGHT AND LICENSE This software is copyright (c) 2014-2022 by Graham Ollis. This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.