Rust FFI

2020-02-06

Roland Brand

About Rust Basel

• Meetup group since April 2019
• This is the 4th Meetup
• Talks from Stefan Braun, Reto Kaiser, Roland Brand
• Thanks to my employer greenmatch for hosting
  • We are moving soon

next meetup will be

here

The next talk

• about your first steps with Rust?
• About similar languages?
  • C/C++
  • Go
  • Crystal
  • Nim
  • ...
• About things important to the Rust ecosystem
  • Command Line
  • Web assembly
  • Networking
  • Embedded

TOC

• Why FFI?
• FFI in general
• Rust C FFI
• Other Rust FFI
• PHP Example: expression-language

Why

FFI

use shared libs

• use (or provide) system libraries such as databases, git, directly
  • efficient, low waste
• long term backwards compatibility (C ABI)

interface to other high level langs

C FFI as common denominator allows for almost any combination without direct support

But really, why?

• You (usually) shouldn't build complex programs with systems languages such as C.
  • Faster and safer development with expressive high-level OOP or FP languages
• But performance and memory efficiency are a trade off
• C/C++/Rust implementation of critical spots

FFI

in general

Typical

• heavily algorithmic libraries
• "workhorses" for platforms or libraries
  • Numpy

• bottlenecks
  • built-in XML or JSON parsers in almost any language

API vs ABI

Direct Interface vs. FFI

• FFI ist typically interfacing to C and relying on the stable C ABI
• Direct interfaces exist as well (e.g Haskell and the JVM) without FFI

Examples

See Wikipedia "FFI" article

Bindgen

Rust

C FFI

Types

• common data representation
• std::os::raw module types are guaranteed to have the same representation as certain C types

#[no_mangle]

• name mangling not compatible with C
  • -> anyone jump in and explain name mangling?
• necessary if you want to build a "C" library with rust to be called from outside, e.g. a PostgreSQL extension

pub extern "C"

cdylib

• Dynamic Library
  • DLL, .so

Other

Rust
bindings

neon (node.js)

• nodejs to rust interface
• easy to use

Python

Rust bindings for the python interpreter

Classical FFI

• CFFI
• ctypes

PHP Example

expression-language

general idea

• symfony expression language
• widely used to express business rules and other customization definitions.
• provides parser, but PHP is not the best option for performance

PHP FFI

• experimental feature since PHP 7.4
• before, you needed to install extensions (e.g php-mbstring)

Speed?

• We'll see....

Pest (PEG Parser)

• Pest (expressive) vs nom (faster)
• comparable to Regex, Pattern matching

State

• initial development
• Can evaluate arithmetic expressions (like a calculator)
• Is ~3x faster than php
• https://github.com/bar9/expression-language
• contributors welcome :)

In summary,

• Rust beats PHP's ass
  • even with an experimental, slow FFI
  • even with the slower parser option
  • even on short inputs
• ...let's get on with it!