NAME
FFI::Platypus::Lang::Rust - Documentation and tools for using Platypus
with the Rust programming language
VERSION
version 0.15
SYNOPSIS
Rust:
#![crate_type = "cdylib"]
#[no_mangle]
pub extern "C" fn add(a: i32, b: i32) -> i32 {
a + b
}
Perl:
use FFI::Platypus 2.00;
use FFI::CheckLib qw( find_lib_or_die );
use File::Basename qw( dirname );
my $ffi = FFI::Platypus->new( api => 2, lang => 'Rust' );
$ffi->lib(
find_lib_or_die(
lib => 'add',
libpath => [dirname __FILE__],
systempath => [],
)
);
$ffi->attach( add => ['i32', 'i32'] => 'i32' );
print add(1,2), "\n"; # prints 3
DESCRIPTION
This module provides native Rust types for FFI::Platypus in order to
reduce cognitive load and concentrate on Rust and forget about C types.
This document also documents issues and caveats that I have discovered
in my attempts to work with Rust and FFI.
Note that in addition to using pre-compiled Rust libraries, you can
bundle Rust code with your Perl distribution using FFI::Build and
FFI::Build::File::Cargo.
EXAMPLES
The examples in this discussion are bundled with this distribution and
can be found in the examples directory.
Passing and Returning Integers
Rust Source
#![crate_type = "cdylib"]
#[no_mangle]
pub extern "C" fn add(a: i32, b: i32) -> i32 {
a + b
}
Perl Source
use FFI::Platypus 2.00;
use FFI::CheckLib qw( find_lib_or_die );
use File::Basename qw( dirname );
my $ffi = FFI::Platypus->new( api => 2, lang => 'Rust' );
$ffi->lib(
find_lib_or_die(
lib => 'add',
libpath => [dirname __FILE__],
systempath => [],
)
);
$ffi->attach( add => ['i32', 'i32'] => 'i32' );
print add(1,2), "\n"; # prints 3
Execute
$ rustc add.rs
$ perl add.pl
3
Notes
Basic types like integers and floating points are the easiest to pass
across the FFI boundary. The Platypus Rust language plugin (this
module) provides the basic types used by Rust (for example: bool, i32,
u64, f64, isize and others) will all work as a Rust programmer would
expect. This is nice because you don't have to think about what the
equivalent types would be in C when you are writing your Perl extension
in Rust.
Rust symbols are "mangled" by default, which means that you cannot use
the name of the function from the source code without knowing what the
mangled name is. Rust provides a function attribute #[no_mangle] which
will tell the compiler not to mangle the name, making lookup of the
symbol possible from other programming languages like Perl.
Rust functions do not use the same ABI as C by default, so if you want
to be able to call Rust functions from Perl they need to be declared as
extern "C" as in this example.
We also set the "crate type" to cdylib in the first line to tell the
Rust compiler to generate a dynamic library that will be consumed by a
non-Rust language like Perl.
String Arguments
Rust Source
#![crate_type = "cdylib"]
use std::ffi::CStr;
#[no_mangle]
pub extern "C" fn how_many_characters(s: *const i8) -> isize {
if s.is_null() {
return -1;
}
let s = unsafe { CStr::from_ptr(s) };
match s.to_str() {
Ok(s) => s.chars().count() as isize,
Err(_) => -2,
}
}
Perl Source
use FFI::Platypus 2.00;
use FFI::CheckLib qw( find_lib_or_die );
use File::Basename qw( dirname );
my $ffi = FFI::Platypus->new( api => 2, lang => 'Rust' );
$ffi->lib(
find_lib_or_die(
lib => 'argument',
libpath => [dirname __FILE__],
systempath => [],
)
);
$ffi->attach( how_many_characters => ['string'] => 'isize' );
print how_many_characters(undef), "\n"; # prints -1
print how_many_characters("frooble bits"), "\n"; # prints 12
Execute
$ rustc argument.rs
$ perl argument.pl
-1
12
Notes
Strings are considerably more complicated for a number of reasons, but
for passing them into Rust code the main challenge is that the
representation is different from what C uses. C Uses NULL terminated
strings and Rust uses a pointer and size combination that allows NULLs
inside strings. Perls internal representation of strings is actually
closer to what Rust uses, but when Perl talks to other languages it
typically uses C Strings.
Getting a Rust string slice &str requires a few stems
We have to ensure the C pointer is not NULL
We return -1 to indicate an error here. As we can see from the
calling Perl code passing an undef from Perl is equivalent to passing
in NULL from C.
Wrap using Cstr
We then wrap the pointer using an unsafe block. Even though we know
at this point that the pointer cannot be NULL it could technically be
pointing to uninitialized or unaddressable memory. This unsafe block
is unfortunately necessary, though it is relatively isolated so it is
easy to reason about and review.
Convert to UTF-8
If the string that we passed in is valid UTF-8 we can convert it to a
&str using to_str and compute the length of the string. Otherwise, we
return -2 error.
(This example is based on one provided in the Rust FFI Omnibus
<http://jakegoulding.com/rust-ffi-omnibus/string_arguments/>)
Returning allocated strings
Rust Source
#![crate_type = "cdylib"]
use std::ffi::CString;
use std::iter;
#[no_mangle]
pub extern "C" fn theme_song_generate(length: u8) -> *mut i8 {
let mut song = String::from("💣 ");
song.extend(iter::repeat("na ").take(length as usize));
song.push_str("Batman! 💣");
let c_str_song = CString::new(song).unwrap();
c_str_song.into_raw()
}
#[no_mangle]
pub extern "C" fn theme_song_free(s: *mut i8) {
if s.is_null() {
return;
}
unsafe { CString::from_raw(s) };
}
Perl Source
use FFI::Platypus 2.00;
use FFI::CheckLib qw( find_lib_or_die );
use File::Basename qw( dirname );
my $ffi = FFI::Platypus->new( api => 2, lang => 'Rust' );
$ffi->lib(
find_lib_or_die(
lib => 'return',
libpath => [dirname __FILE__],
systempath => [],
)
);
$ffi->attach( theme_song_free => ['opaque'] => 'void' );
$ffi->attach( theme_song_generate => ['u8'] => 'opaque' => sub {
my($xsub, $length) = @_;
my $ptr = $xsub->($length);
my $str = $ffi->cast( 'opaque' => 'string', $ptr );
theme_song_free($ptr);
$str;
});
print theme_song_generate(42), "\n";
Execute
$ rustc return.rs
$ perl return.pl
💣 na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na Batman! 💣
Notes
The big challenge of returning strings from Rust into Perl is handling
the ownership. In this example we have a C API implemented in Rust that
returns a C NULL terminated string, but we have to pass it back into
Rust in order to deallocate it when we are done.
Unfortunately Platypus' string type assumes that the callee retains
ownership of the returned string, so we have to get the pointer instead
as an opaque so that we can later free it. Before freeing it though we
cast it into a Perl string.
In order to hide the complexities from caller of our
theme_song_generate function, we use a function wrapper to do all of
that for us.
(This example is based on one provided in the Rust FFI Omnibus
<http://jakegoulding.com/rust-ffi-omnibus/string_return/>)
Returning allocated strings, but keeping ownership
Rust Source
#![crate_type = "cdylib"]
use std::cell::RefCell;
use std::ffi::CString;
use std::iter;
#[no_mangle]
pub extern "C" fn theme_song_generate(length: u8) -> *const i8 {
thread_local! {
static KEEP: RefCell<Option<CString>> = RefCell::new(None);
}
let mut song = String::from("💣 ");
song.extend(iter::repeat("na ").take(length as usize));
song.push_str("Batman! 💣");
let c_str_song = CString::new(song).unwrap();
let ptr = c_str_song.as_ptr();
KEEP.with(|k| {
*k.borrow_mut() = Some(c_str_song);
});
ptr
}
Perl Source
use FFI::Platypus 2.00;
use FFI::CheckLib qw( find_lib_or_die );
use File::Basename qw( dirname );
my $ffi = FFI::Platypus->new( api => 2, lang => 'Rust' );
$ffi->lib(
find_lib_or_die(
lib => 'keep',
libpath => [dirname __FILE__],
systempath => [],
)
);
$ffi->attach( theme_song_generate => ['u8'] => 'string' );
print theme_song_generate($_), "\n" for 1..10;
Execute
$ rustc keep.rs
$ perl keep.pl
💣 na Batman! 💣
💣 na na Batman! 💣
💣 na na na Batman! 💣
💣 na na na na Batman! 💣
💣 na na na na na Batman! 💣
💣 na na na na na na Batman! 💣
💣 na na na na na na na Batman! 💣
💣 na na na na na na na na Batman! 💣
💣 na na na na na na na na na Batman! 💣
💣 na na na na na na na na na na Batman! 💣
Notes
For frequently called functions with smaller strings it may make more
sense to keep ownership of the string and just return a pointer. Perl
makes its own copy on return anyway when you use the string type.
In this example we use thread local storage to keep the CString until
the next call when it will be freed. Since we are using thread local
storage, it should even be safe to use this interface from a threaded
Perl program (although you should probably not be using threaded Perl).
(This example is based on one provided in the Rust FFI Omnibus
<http://jakegoulding.com/rust-ffi-omnibus/string_arguments/>)
Return static strings
Rust Source
#![crate_type = "cdylib"]
#[no_mangle]
pub extern "C" fn hello_rust() -> *const u8 {
"Hello, world!\0".as_ptr()
}
Perl Source
#![crate_type = "cdylib"]
#[no_mangle]
pub extern "C" fn hello_rust() -> *const u8 {
"Hello, world!\0".as_ptr()
}
Execute
$ rustc static.rs
$ perl static.pl
Hello, world!
Notes
Sometimes you just want to return a static NULL terminated string from
Rust to Perl. This can sometimes be useful for returning error
messages.
Callbacks
Rust Source
#![crate_type = "cdylib"]
use std::ffi::CString;
type PerlLog = extern "C" fn(line: *const i8);
#[no_mangle]
pub extern "C" fn rust_log(logf: PerlLog) {
let lines: [&str; 3] = ["Hello from rust!", "Something else.", "The last log line"];
for line in lines.iter() {
// convert string slice to a C style NULL terminated string
let line = CString::new(*line).unwrap();
logf(line.as_ptr());
}
}
Perl Source
use FFI::Platypus 2.00;
use FFI::CheckLib qw( find_lib_or_die );
use File::Basename qw( dirname );
my $ffi = FFI::Platypus->new( api => 2, lang => 'Rust' );
$ffi->lib(
find_lib_or_die(
lib => 'callback',
libpath => [dirname __FILE__],
systempath => [],
)
);
$ffi->type( '(string)->void' => 'PerlLog' );
$ffi->attach( rust_log => ['PerlLog'] );
my $perl_log = $ffi->closure(sub {
my $message = shift;
print "log> $message\n";
});
rust_log($perl_log);
Execute
$ rustc callback.rs
$ perl callback.pl
log> Hello from rust!
log> Something else.
log> The last log line
Notes
Calling back into Perl from Rust is easy, so long as you have the
correct types defined. The above Rust function takes a C function
pointer. We can crate a Platypus closure object from Perl from a plain
Perl sub and pass the closure into Rust.
Slice arguments
Rust Source
#![crate_type = "cdylib"]
use std::slice;
#[no_mangle]
pub extern "C" fn sum_of_even(numbers: *const u32, len: usize) -> i64 {
if numbers.is_null() {
return -1;
}
let numbers = unsafe { slice::from_raw_parts(numbers, len) };
let sum: u32 = numbers.iter().filter(|&v| v % 2 == 0).sum();
sum as i64
}
Perl Source
#![crate_type = "cdylib"]
use std::slice;
#[no_mangle]
pub extern "C" fn sum_of_even(numbers: *const u32, len: usize) -> i64 {
if numbers.is_null() {
return -1;
}
let numbers = unsafe { slice::from_raw_parts(numbers, len) };
let sum: u32 = numbers.iter().filter(|&v| v % 2 == 0).sum();
sum as i64
}
Execute
$ rustc slice.rs
$ perl slice.pl
-1
12
Notes
A Rust slice is a pointer to a chunk of homogeneous data, and the
number of elements in the slice. We can pass these two pieces in from
Perl and combine them into a slice in Rust.
This example sums the even numbers from a slice and returns the result.
(This example is based on one provided in the Rust FFI Omnibus
<http://jakegoulding.com/rust-ffi-omnibus/slice_arguments/>)
Tuples
Rust Source
#![crate_type = "cdylib"]
use std::convert::From;
// A Rust function that accepts a tuple
fn flip_things_around_rust(tup: (u32, u32)) -> (u32, u32) {
let (a, b) = tup;
(b + 1, a - 1)
}
// A struct that can be passed between C and Rust
#[repr(C)]
pub struct Tuple {
x: u32,
y: u32,
}
// Conversion functions
impl From<(u32, u32)> for Tuple {
fn from(tup: (u32, u32)) -> Tuple {
Tuple { x: tup.0, y: tup.1 }
}
}
impl From<Tuple> for (u32, u32) {
fn from(tup: Tuple) -> (u32, u32) {
(tup.x, tup.y)
}
}
// The exported C method
#[no_mangle]
pub extern "C" fn flip_things_around(tup: Tuple) -> Tuple {
flip_things_around_rust(tup.into()).into()
}
Perl Source
use FFI::Platypus 2.00;
use FFI::CheckLib qw( find_lib_or_die );
use File::Basename qw( dirname );
my $ffi = FFI::Platypus->new( api => 2, lang => 'Rust' );
$ffi->lib(
find_lib_or_die(
lib => 'tuple',
libpath => [dirname __FILE__],
systempath => [],
)
);
package Tuple;
use FFI::Platypus::Record;
use overload
'""' => sub { shift->as_string },
bool => sub { 1 }, fallback => 1;
record_layout_1($ffi, qw(
u32 x
u32 y
));
sub as_string {
my $self = shift;
sprintf "[%d,%d]", $self->x, $self->y;
}
package main;
$ffi->type('record(Tuple)' => 'tuple_t');
$ffi->attach( flip_things_around => ['tuple_t'] => 'tuple_t' );
print flip_things_around(Tuple->new(x => 10, y => 20)), "\n";
Execute
$ rustc tuple.rs
$ perl tuple.pl
[21,9]
Notes
Rust's tuples do not have a standard representation that can be used
directly from Perl, but if your tuple contains only simple types you
can use the Platypus Record class and translate in Rust between the
tuple and the struct.
Because we are passing in and out the entire struct, not pointers to a
struct we don't have to worry about freeing them from Perl. They just
get allocated and freed on the stack.
(This example is based on one provided in the Rust FFI Omnibus
<http://jakegoulding.com/rust-ffi-omnibus/tuples/>)
Objects
Rust Source
use std::cell::RefCell;
use std::ffi::c_void;
use std::ffi::CStr;
use std::ffi::CString;
struct Person {
name: String,
lucky_number: i32,
}
impl Person {
fn new(name: &str, lucky_number: i32) -> Person {
Person {
name: String::from(name),
lucky_number: lucky_number,
}
}
fn get_name(&self) -> String {
String::from(&self.name)
}
fn set_name(&mut self, new: &str) {
self.name = new.to_string();
}
fn get_lucky_number(&self) -> i32 {
self.lucky_number
}
}
type CPerson = c_void;
#[no_mangle]
pub extern "C" fn person_new(
_class: *const i8,
name: *const i8,
lucky_number: i32,
) -> *mut CPerson {
let name = unsafe { CStr::from_ptr(name) };
let name = name.to_string_lossy().into_owned();
Box::into_raw(Box::new(Person::new(&name, lucky_number))) as *mut CPerson
}
#[no_mangle]
pub extern "C" fn person_name(p: *mut CPerson) -> *const i8 {
thread_local!(
static KEEP: RefCell<Option<CString>> = RefCell::new(None);
);
let p = unsafe { &*(p as *mut Person) };
let name = CString::new(p.get_name()).unwrap();
let ptr = name.as_ptr();
KEEP.with(|k| {
*k.borrow_mut() = Some(name);
});
ptr
}
#[no_mangle]
pub extern "C" fn person_rename(p: *mut CPerson, new: *const i8) {
let new = unsafe { CStr::from_ptr(new) };
let p = unsafe { &mut *(p as *mut Person) };
if let Ok(new) = new.to_str() {
p.set_name(new);
}
}
#[no_mangle]
pub extern "C" fn person_lucky_number(p: *mut CPerson) -> i32 {
let p = unsafe { &*(p as *mut Person) };
p.get_lucky_number()
}
#[allow(non_snake_case)]
#[no_mangle]
pub extern "C" fn person_DESTROY(p: *mut CPerson) {
unsafe { Box::from_raw(p as *mut Person) };
}
#[cfg(test)]
mod test;
Perl Source
Main class:
package Person;
use strict;
use warnings;
use FFI::Platypus 2.00;
our $VERSION = '2.00';
my $ffi = FFI::Platypus->new( api => 2, lang => 'Rust' );
# use the bundled code as a library
$ffi->bundle;
# use the person_ prefix
$ffi->mangler(sub {
my $symbol = shift;
return "person_$symbol";
});
# Create a custom type mapping for the person_t (C) and Person (perl)
# classes.
$ffi->type( 'object(Person)' => 'person_t' );
$ffi->attach( new => [ 'string', 'string', 'i32' ] => 'person_t' );
$ffi->attach( name => [ 'person_t' ] => 'string' );
$ffi->attach( rename => [ 'person_t', 'string' ] );
$ffi->attach( lucky_number => [ 'person_t' ] => 'i32' );
$ffi->attach( DESTROY => [ 'person_t' ] );
1;
Test:
use Test2::V0;
use Person;
my $plicease = Person->new("Graham Ollis", 42);
is $plicease->name, "Graham Ollis";
is $plicease->lucky_number, 42;
$plicease->rename("Graham THE Ollis");
is $plicease->name, "Graham THE Ollis";
done_testing;
Execute
$ prove -lvm t/basic.t
t/basic.t ..
# Seeded srand with seed '20221023' from local date.
ok 1
ok 2
ok 3
1..3
ok
All tests successful.
Files=1, Tests=3, 0 wallclock secs ( 0.02 usr 0.00 sys + 0.19 cusr 0.05 csys = 0.26 CPU)
Result: PASS
Notes
This example includes excerpts from a full Person dist which you can
find in the examples/Person directory of this distribution. You can
install it like a normal Perl distribution using ExtUtils::MakeMaker,
or you can simply run the test file by using App::Prove. That is
because we are using FFI::Build and FFI::Build::File::Cargo to build
the Rust parts for us, which know how to work in either mode. There are
some stuff that we don't show you here for brevity: the Makefile.PL for
example, and also the rust tests in ffi/src/test.rs which test the Rust
crate by calling both its Rust and C interface.
What we have done here is created a Rust struct and then written C
wrappers to create, query and modify the object. We've also created a
destructor to free the object when we are done with it.
In terms of naming conventions, we use person_ prefix to denote that
these are methods for the Person class that we are creating. This is a
common convention in C, where the only namespaces are adding prefixes
like this. We also break the convention of using snake case for the
destructor person_DESTROY because that will make it easier to bind to
from Perl.
When we creat the object we use Box::new and Box::into_raw to create
the object on the heap, and to return the opaque pointer back to Perl.
For methods we can convert the raw pointers back into a Person struct
using &*(p as *mut Person) inside an unsafe block. In the case of
person_rename we need a mutable version so we use &mut *(p as *mut
Person) instead.
Finally when we are done with the object we can free it by simply
calling Box::from_raw. When it falls out of scope it will be freed.
On the Perl side, we use the mangler method to prepend all symbols with
the person_ prefix, so that we can attach with just the method name.
We also create a Platypus type for object(Person) and give it the alias
person_t. Now we can use it as an argument and return type. This is
really a pointer to an opaque (to perl) struct.
If you look at just the test, then you can't even tell that the
implementation for our Person class is in Rust, which is good because
your users shouldn't have to care!
Panic!
Rust Source
#![crate_type = "cdylib"]
use std::panic::catch_unwind;
fn might_panic(i: u32) -> u32 {
if i % 2 == 1 {
panic!("oops!");
}
i / 2
}
#[no_mangle]
pub extern "C" fn oopsie(i: u32) -> i64 {
let result = catch_unwind(|| might_panic(i));
match result {
Ok(i) => i as i64,
Err(_) => -1,
}
}
Perl Source
use FFI::Platypus 2.00;
use FFI::CheckLib qw( find_lib_or_die );
use File::Basename qw( dirname );
my $ffi = FFI::Platypus->new( api => 2, lang => 'Rust' );
$ffi->lib(
find_lib_or_die(
lib => 'panic',
libpath => [dirname __FILE__],
systempath => [],
)
);
$ffi->attach( oopsie => ['u32'] => 'i64' );
print oopsie(5), "\n"; # -1
print oopsie(10), "\n"; # 5
Execute
$ perl panic.pl
thread '<unnamed>' panicked at 'oops!', panic.rs:7:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-1
5
Notes
Be cautious about code that might panic!. A panic! across the FFI
boundary is undefined behavior and usually results in a crash. You will
want to catch the panic with a catch_unwind and map to an appropriate
error result. In this example, we have a function that returns the
integer passed in divided by 2. It does not like odd numbers though and
will panic. So we catch the panic and return -1 to indicate an error.
As you can see from the run we also get a rather ugly diagnostic, but
at least our program didn't crash!
METHODS
Generally you will not use this class directly, instead interacting
with the FFI::Platypus instance. However, the public methods used by
Platypus are documented here.
native_type_map
my $hashref = FFI::Platypus::Lang::Rust->native_type_map;
This returns a hash reference containing the native aliases for the
Rust programming languages. That is the keys are native Rust types and
the values are libffi native types.
CAVEATS
The bool type
As of this writing, the bool type is in practice always a signed 8
bit integer, but this has not been guaranteed by the Rust
specification. This module assumes that it is a sint8 type, but if
that ever changes this module will need to be updated.
SEE ALSO
FFI::Platypus
The Core Platypus documentation.
FFI::Build::File::Cargo
Bundle Rust code with your FFI / Perl extension.
The Rust FFI Omnibus <http://jakegoulding.com/rust-ffi-omnibus/>
Includes a number of examples of calling Rust from other languages.
The Rustonomicon - Foreign Function Interface
<https://doc.rust-lang.org/nomicon/ffi.html>
Detailed Rust documentation on crossing the FFI barrier.
The Rust Programming Language - Unsafe Rust
<https://doc.rust-lang.org/book/ch19-01-unsafe-rust.html>
Unsafe Rust in the Rust Programming Language book.
AUTHOR
Author: Graham Ollis <plicease@cpan.org>
Contributors:
Andrew Grangaard (SPAZM)
COPYRIGHT AND LICENSE
This software is copyright (c) 2015-2022 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.