How to Use PHP FFI in Programming

For PHP, the first thing we did was to uncomment the extension ffi in php.ini (/etc/php/php.ini in ArchLinux).

Next, we needed to declare our conditional interface. There are some restrictions that are currently present in PHP FFI, in particular, the inability to use a C-preprocessor (#include, #define, etc.), except for some special ones. In PHP type:

$ffi = FFI::cdef(
     "int Fib(int n);",
    "/PATH/TO/SO/lib.so");

1. FFI::cdef – with this operation we define the interaction interface.
2. int Fib (int n) – IT’s the name of the exported method of the compiled language. We will talk about how to do it right a little bit later.
3. /PATH/TO/SO/lib.so – the path to the dynamic library where the function above is located.

The full PHP script we used:

PHP FFI

function fib($n)
{
    if ($n === 1 || $n === 2) {
        return 1;
    }
    return fib($n - 1) + fib($n - 2);
}

$start = microtime(true);
$p = 0;
for ($i = 0; $i < 1000000; $i++) {
    $p = fib(12);
}

echo '[PHP] execution time: '.(microtime(true) - $start).' Result: '.$p.PHP_EOL;

RUST FFI

$rust_ffi = FFI::cdef(
    "int Fib(int n);",
    "lib/libphp_rust_ffi.so");

$start = microtime(true);
$r = 0;
for ($i=0; $i < 1000000; $i++) { $r = $rust_ffi->Fib(12);
}

echo '[RUST] execution time: '.(microtime(true) - $start).' Result: '.$r.PHP_EOL;

CPP FFI

$cpp_ffi = FFI::cdef(
    "int Fib(int n);",
    "lib/libphp_cpp_ffi.so");

$start = microtime(true);
$c = 0;
for ($i=0; $i < 1000000; $i++) { $c = $cpp_ffi->Fib(12);
}

echo '[CPP] execution time: '.(microtime(true) - $start).' Result: '.$c.PHP_EOL;

GOLANG FFI

$golang_ffi = FFI::cdef(
    "int Fib(int n);",
    "lib/libphp_go_ffi.so");

$start = microtime(true);

for ($i=0; $i < 1000000; $i++) { $golang_ffi->Fib(12);
}

echo '[GOLANG] execution time: '.(microtime(true) - $start).' Result: '.$c.PHP_EOL;

The first step was to make a dynamic library in the Rust language.

This required some preparation:

1. On any platform, for the installation we needed only one instruction from here.

2. After that, we could create a project anywhere with the command cargo new rust_php_ffi. And that was it!

Here is the function we used:

RUST:

//src/lib.rs

#[no_mangle]
extern "C" fn Fib(n: i32) -> i32 {
    if (n == 0) || (n == 1) {
        return 1;
    }

    Fib(n - 1) + Fib(n - 2)
}

NOTE: It is critical to add the attribute # [no_mangle] to the required function, because otherwise the compiler will replace the name of your function with something like: _аgs @ fs34. And when exporting it to PHP, libffi simply won’t be able to find a function named Fib in the dynamic library. You can read more about this issue here.

In Cargo.toml, we added the attribute:

[lib]
crate-type = ["cdylib"]

I would like to draw your attention to the fact that there are three options for a dynamic library through an attribute in Cargo.toml:

1. dylib – Rust shares this library with an unstable ABI, which can change from version to version (as in Go internal ABI).

2. cdylib is a dynamic library for using in C/C++. This is our top choice.

3. rlib – Rust static library with rlib extestion (.rlib). It also contains metadata used to link various rlibs written respectively in Rust

Then, we compiled it using cargo build --release. And in the folder target/release we saw the .so file. This would be our dynamic library.
C++

Next in line is C++. Here everything is quite simple, too:

CPP:

// in php_cpp_ffi.cpp

int main() {
    
}

extern "C" int Fib(int n) {
    if ((n==1) || (n==2)) {
        return 1;
    }

    return Fib(n-1) + Fib(n-2);
}

We needed to declare the extern function so that it could be imported from php.

We compiled:

g++ -fPIC -O3 -shared src/php_cpp_ffi.cpp -o ../lib/ libphp_cpp_ffi.so

A few comments on the compilation:

1. -fPIC position-independence code. For a dynamic library, it is important to be independent of the address at which it is loaded in memory.

2. -O3 – maximum optimization