655 lines
20 KiB
Markdown
655 lines
20 KiB
Markdown
---
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title: Portable Foreign Function Interface for R7RS Documentation
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version: 0.6.0
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---
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# Portable Foreign Function Interface for R7RS
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Portable foreign function interface for R7RS. It is portable in the sense that
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it supports multiple implementations, as opposed to being portable by
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conforming to some specification.
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[Project](https://todo.sr.ht/~retropikzel/r7rs-pffi)
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[Issue trackers](https://sr.ht/~retropikzel/r7rs-pffi/trackers)
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[Maling lists](https://sr.ht/~retropikzel/r7rs-pffi/lists)
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[Jenkins](https://jenkins.scheme.org/job/r7rs_pffi/job/r7rs-pffi/)
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## Table of contents
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<nav>
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- [Goals](#goals)
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- [Non Goals](#non-goals)
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- [Status](#status)
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- [Current caveats](#current-caveats)
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- [Roadmap](#roadmap)
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- [Feature implementation table](#feature-implementation-table)
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- [Primitives](#feature-implementation-table-primitives)
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- [Built upon](#feature-implementation-table-built-upon)
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- [Documentation](#documentation)
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- [Dependencies](#dependencies)
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- [Chibi](#dependencies-chibi)
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- [Chicken](#dependencies-chicken)
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- [Gauche](#dependencies-gauche)
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- [Racket](#dependencies-racket)
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- [Kawa](#dependencies-kawa)
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- [Installation](#installation)
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- [Project local](#installation-project-local)
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- [Linux](#installation-project-local-linux)
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- [Windows](#installation-project-local-windows)
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- [System global](#installation-system-global)
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- [Reference](#reference)
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- [Types](#types)
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- [Environment variables](#environment-variables)
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- [PFFI\_LOAD\_PATH](#environment-variables-pffi-load-path)
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- [Procedures and macros](#procedures-and-macros)
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- [pffi-init](#pffi-init)
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- [c-size-of](#c-size-of)
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- [pffi-align-of](#pffi-align-of)
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- [define-c-library](#define-c-library)
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- [make-c-null](#make-c-null)
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- [c-null?](#is-c-null)
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- [make-c-bytevector ](#make-c-bytevector )
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- [pffi-pointer-address](#pffi-pointer-address)
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- [c-bytevector?](#is-c-bytevector)
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- [c-free](#c-free)
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- [pffi-pointer-set!](#pffi-pointer-set!)
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- [pffi-pointer-get](#pffi-pointer-get)
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- [utf8->c-bytevector](#utf8-into-c-bytevector)
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- [c-bytevector->sring](#c-bytevector-into-string)
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- [pffi-struct-make](#pffi-struct-make)
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- [pffi-struct-pointer](#pffi-struct-pointer)
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- [pffi-struct-offset-get](#pffi-struct-offset-get)
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- [pffi-struct-get](#pffi-struct-get)
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- [pffi-struct-set!](#pffi-struct-set!)
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- [pffi-array-allocate](#pffi-array-allocate)
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- [pffi-array-pointer](#pffi-array-pointer)
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- [pffi-array?](#pffi-array)
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- [pffi-pointer->array](#pffi-pointer->array)
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- [pffi-array-get](#pffi-array-get)
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- [pffi-array-set!](#pffi-array-set!)
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- [pffi-list->array](#pffi-list->array)
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- [pffi-array->list](#pffi-array->list)
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- [define-c-procedure](#define-c-procedure)
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- [pffi-define-callback](#pffi-define-callback)
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</nav>
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<main>
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## Goals
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<a name="goals"></a>
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- Support only R7RS implementations
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- Same interface on all implementations
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- Some things that are procedures on one implementation are macros on other,
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but they must behave the same
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- Stability and being boring after 1.0.0 is reached
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## Non goals
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<a name="non-goals"></a>
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- Compiling of used library C code at any point
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- That is no stubs, no C code generated by the library and so on
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- The pffi library itself may require compilation on installation
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## Status
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<a name="status"></a>
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In alpha.
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### Current caveats
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<a name="current-caveats"></a>
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- No way to pass structs by value
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- Most implementations are missing callback support
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- Always pass arguments to pffi functions/macros as '(1 2 3) and not (list 1 2 3)
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- Always pass pffi-define-callback procedure as lambda in place
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- No support for variadic function arguments
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- Can be partially worked around by defining multiple versions of same
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function with different number of arguments
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## Roadmap
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For roadmap to 1.0.0 see [issues](https://todo.sr.ht/~retropikzel/r7rs-pffi?search=status%3Aopen%20label%3A%221.0.0%22)
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## Feature mplementation table
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<a name="feature-implementation-table"></a>
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## Primitives
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<a name="feature-implementation-table-primitives"></a>
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| | c-size-of | define-c-library | c-bytevector? | pffi-pointer-set! | pffi-pointer-get | define-c-procedure | pffi-define-callback |
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|--------------|:------------:|:-------------------:|:-------------:|:-----------------:|:----------------:|:-------------------:|:--------------------:|
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| Chibi | X | X | X | X | X | X | |
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| Chicken | X | X | X | X | X | X | X |
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| Cyclone | X | X | X | X | X | X | |
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| Gambit | X | | | | | | |
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| Gauche | X | X | X | X | X | X | |
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| Gerbil | | | | | | | |
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| Guile | X | X | X | X | X | X | X |
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| Kawa | X | X | X | X | X | X | X |
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| Larceny | | | | | | | |
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| Mosh | X | X | X | X | X | X | X |
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| Racket | X | X | X | X | X | X | X |
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| Saggittarius | X | X | X | X | X | X | X |
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| Skint | | | | | | | |
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| Stklos | X | X | X | | | | |
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| tr7 | | | | | | | |
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| Ypsilon | X | X | X | X | X | X | X |
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## Built upon
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<a name="feature-implementation-table-built-upon"></a>
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These features are built upon the primitives and if primitives are implemented
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and work, they should work too.
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- make-c-bytevector
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- make-c-null
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- c-null?
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- pffi-pointer-address
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- c-free
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- pffi-pointer-\>string
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- pffi-string-\>pointer
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- pffi-struct-make
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- pffi-struct-pointer
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- pffi-struct-offset-get
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- pffi-struct-get
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- pffi-struct-set!
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- pffi-array-allocate
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- pffi-array?
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- pffi-pointer-\>array
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- pffi-array-get
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- pffi-array-set!
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- pffi-list-\>array
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- pffi-array-\>list
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### Not started
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<a name="not-started"></a>
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- [LIPS](https://lips.js.org/)
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- Will work on nodejs by using some C FFI library from npm
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- Javascript side needs design
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- [Biwascheme](https://www.biwascheme.org/)
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- Will work on nodejs by using some C FFI library from npm
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- Javascript side needs design
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- [MIT-Scheme](https://www.gnu.org/software/mit-scheme/)
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- Need to study the implementation more
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- [Airship](https://gitlab.com/mbabich/airship-scheme)
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- Need to study the implementation more
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- [Other gambit targets](https://gambitscheme.org/)
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- Gambit compiles to different targets other than C too, for example Javascript. It would be cool
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and interesting to see if this FFI could also support some of those
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- When LIPS and Biwascheme Javascript side is done then Gambit should be done too
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- [s48-r7rs](https://codeberg.org/prescheme/s48-r7rs)
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- Need to study the implementation more
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- [prescheme](https://codeberg.org/prescheme/prescheme)
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- Need to study the implementation more
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### Other
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<a name="other"></a>
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- [s7](https://scheme.fail://ccrma.stanford.edu/software/snd/snd/s7.html)
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- Propably does not need FFI as it is embeddable only
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- [Loko](https://scheme.fail/)
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- Desires no C interop, I can respect that
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## Documentation
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<a name="documentation"></a>
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### Dependencies
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<a name="dependencies"></a>
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Some implementations have extra dependencies/requirements beyond just the
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library.
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#### Chibi
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<a name="dependencies-chibi"></a>
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Building depends on libffi.
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Debian/Ubuntu/Mint install with:
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apt install libffi-dev
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#### Chicken
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<a name="dependencies-chicken"></a>
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Chicken needs r7rs egg installed. Install it with:
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chicken-install r7rs
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#### Gauche
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<a name="dependencies-gauche"></a>
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Building depends on libffi.
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Debian/Ubuntu/Mint install with:
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apt install libffi-dev
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#### Racket
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<a name="dependencies-racket"></a>
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Needs [racket-r7rs](https://github.com/lexi-lambda/racket-r7rs), install with:
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raco pkg install --auto r7rs
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#### Kawa
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<a name="dependencies-kawa"></a>
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Kawa Needs at least Java version 22 these flags before any other arguments:
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- \-J--add-exports=java.base/jdk.internal.foreign.abi=ALL-UNNAMED
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- \-J--add-exports=java.base/jdk.internal.foreign.layout=ALL-UNNAMED
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- \-J--add-exports=java.base/jdk.internal.foreign=ALL-UNNAMED
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- \-J--enable-native-access=ALL-UNNAMED
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If you are running kawa.jar with plain java then give same arguments to java
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without the -J prefix.
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### Installation
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<a name="installation"></a>
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Since the project is under active development is best to clone it from git,
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### Project local
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<a name="installation-project-local"></a>
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#### Linux
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<a name="installation-project-local-linux"></a>
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Assuming you have a project and your libraries live in directory called snow
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in it:
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git clone https://git.sr.ht/~retropikzel/r7rs-pffi
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mkdir -p snow
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cp -r r7rs-pffi/retropikzel snow/
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cd snow/retropikzel/pffi
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make <SCHEME>
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#### Windows
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<a name="installation-project-local-windows"></a>
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There is no build scripts yet for Windows, that said many implementations work
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without compiling anything. If you run this and it says "There is notching to
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build for SCHEME" then you should be good to go.
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### System global
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<a name="installation-system-global"></a>
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Still work in progress.
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## Reference
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<a name="reference"></a>
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### Types
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<a name="types"></a>
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Types are given as symbols, for example 'int8 or 'pointer.
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- int8
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- uint8
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- int16
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- uint16
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- int32
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- uint32
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- int64
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- uint64
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- char
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- unsigned-char
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- short
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- unsigned-short
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- int
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- unsigned-int
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- long
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- unsigned-long
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- float
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- double
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- pointer
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- callback
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- Callback function
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### Types
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<a name="types"></a>
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### Environment variables
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<a name="environment-variables"></a>
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Setting environment variables like this on Windows works for this library:
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set "PFFI_LOAD_PATH=C:\Program Files (x86)/foo/bar"
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#### PFFI\_LOAD\_PATH
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<a name="environment-variables-pffi-load-path"></a>
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To add more paths to where pffi looks for libraries set PFFI\_LOAD\_PATH to
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paths separated by ; on windows, and : on other operating systems.
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### Procedures and macros
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<a name="procedures-and-macros"></a>
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Some of these are procedures and some macros, it might also change implementation to implementation.
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#### pffi-init
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<a name="pffi-init"></a>
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**pffi-init**
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Always call this first, on most implementation it does nothing but some implementations might need
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initialisation run.
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#### c-size-of
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<a name="c-size-of"></a>
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**c-size-of** object -> number
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Returns the size of the pffi-struct, pffi-enum or pffi-type.
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#### pffi-align-of
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<a name="pffi-align-of"></a>
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**pffi-align-of** type -> number
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Returns the align of the type.
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#### define-c-library
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<a name="define-c-library"></a>
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**define-c-library** headers shared-object-name [options] -> object
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Load given shared object automatically searching many predefined paths.
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Takes as argument a list of C headers, these are for the compiler ones. And an shared-object name,
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used by the dynamic FFI's. The name of the shared object should not contain suffix like .so or
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.dll. Nor should it contain any prefix like "lib".
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Additional options argument can be provided, theys should be a pair with a
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keyword. The options are:
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- additional-versions
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- Search for additional versions of shared object, given shared object "c" and additional
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versions "6" "7" on linux the files "libc", "libc.6", "libc.7" are searched for.
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- Can be either numbers or strings
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- additional-paths
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- Give additional paths to search shared objects for
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Example:
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(cond-expand
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(windows (define-c-library libc-stdlib
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'("stdlib.h")
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"ucrtbase"
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'((additional-versions ("0" "6"))
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(additiona-paths (".")))))
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(else (define-c-library libc-stdlib
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(list "stdlib.h")
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"c"
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'((additional-versions ("0" "6"))
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(additiona-paths ("."))))))
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#### Notes
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- Do not cond-expand inside the arguments, that might lead to problems on some
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implementations.
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- Do not store options in variables, that might lead to problems on some
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implementations.
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- Do pass the headers using quote
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- As '(... and not (list...
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- Do pass the options using quote
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- As '(... and not (list...
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#### make-c-null
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<a name="make-c-null"></a>
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**make-c-null** -> pointer
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Returns a new NULL pointer.
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#### c-null?
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<a name="is-c-null"></a>
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**c-null?** pointer -> boolean
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Returns #t if given pointer is null pointer, #f otherwise.
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#### make-c-bytevector
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<a name="make-c-bytevector "></a>
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(make-c-bytevector *k*)
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(make-c-bytevector *k* *fill*)
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Returns a newly allocated C bytevector(pointer) of length k. If byte is given,
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then all elements of the C bytevector are initialized to byte, otherwise the
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contents of each element are unspecified.
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#### pffi-pointer-address
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<a name="pffi-pointer-address"></a>
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**pffi-pointer-address** pointer -> pointer
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Returns the address of given pointer inside a pointer. This is used when
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passing pointers to pointers to foreign procedures. This is similar to the
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c's &. One **important difference** is that after you have passed a pointer to
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the procedure you must get value from it back to the pointer which address you
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are passing. Example:
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(define input-pointer (make-c-bytevector <needed size>))
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(define input-pointer-address (pffi-pointer-address input-pointer))
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(<foreign-procedure-that takes &pointer as argument> input-pointer-address)
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(set! input-pointer (pffi-pointer-get input-pointer-address 'pointer 0))
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#### c-bytevector?
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<a name="pffi-pointer"></a>
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**c-bytevector?** object -> boolean
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Returns #t if given object is pointer, #f otherwise.
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#### c-free
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<a name="c-free"></a>
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**c-free** pointer
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Frees given pointer.
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#### pffi-pointer-set!
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<a name="pffi-pointer-set!"></a>
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**pffi-pointer-set!** pointer type offset value
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Sets the value on a pointer on given offset. For example:
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(define p (make-c-bytevector 128))
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(pffi-pointer-set! p 'int 64 100)
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Would set the offset of 64, on pointer p to value 100.
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#### pffi-pointer-get
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<a name="pffi-pointer-get"></a>
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**pffi-pointer-get** pointer type offset -> object
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Gets the value from a pointer on given offset. For example:
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(define p (make-c-bytevector 128))
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(pffi-pointer-set! p 'int 64 100)
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(pffi-pointer-get p 'int 64)
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> 100
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#### utf8->c-bytevector
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<a name="utf8-into-c-bytevector"></a>
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**utf8->c-bytevector** string -> pointer
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Makes pointer out of a given string.
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#### c-bytevector->string
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<a name="c-bytevector-into-string"></a>
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**c-bytevector->sring** pointer -> string
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Makes string out of a given pointer.
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#### pffi-struct-make
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<a name="pffi-struct-make"></a>
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**pffi-struct-make** c-type members . pointer -> pffi-struct
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Creates a new pffi-struct and allocates pointer for it. The members argument is a list of member
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names and types. For example:
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(define color (pffi-struct-make 'color '((int8 . r) (int8 . g) (int8 . b) (int8 .a ))))
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(define test (pffi-struct-make "struct test" '((int8 . r) (int8 . g) (int8 . b) (int8 .a ))))
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C-type argument can be symbol or a string.
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#### pffi-struct-pointer
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<a name="pffi-struct-pointer"></a>
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**pffi-struct-pointer** pffi-struct -> pointer
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Returns the pointer that holds the struct content. You need to use this when passing a struct as
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a pointer to foreign functions.
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(define s (pffi-struct-make 'test '((int . r) (int . g) (int . b))))
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(pffi-struct-pointer s)
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#### pffi-struct-offset-get
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<a name="pffi-struct-offset-get"></a>
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**pffi-struct-offset-get** member-name -> number
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Returns the offset of a struct member with given name.
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#### pffi-struct-get
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<a name="pffi-struct-get"></a>
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**pffi-struct-get** pffi-struct member-name -> object
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Returns the value of the givens struct member.
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#### pffi-struct-set!
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<a name="pffi-struct-set!"></a>
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**pffi-struct-set!** pffi-struct member-name value
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Sets the value of the givens struct member. It is up to you to make sure that the type of value is
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correct.
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#### pffi-array-allocate
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<a name="pffi-array-allocate"></a>
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**pffi-array-allocate** type size
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Allocates pointer array of given type and size.
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#### pffi-array-pointer
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<a name="pffi-array-pointer"></a>
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**pffi-array-pointer** array
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|
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Returns the pointer of the array.
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#### pffi-array?
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|
<a name="pffi-array"></a>
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|
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**pffi-array?** object
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|
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Returns #t of given object is array, #f otherwise.
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|
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#### pffi-pointer->array
|
|
<a name="pffi-pointer->array"></a>
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|
|
**pffi-pointer->array** pointer type size
|
|
|
|
Converts given pointer to an array of giben type and size.
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|
|
#### pffi-array-get
|
|
<a name="pffi-array-get"></a>
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|
|
**pffi-array-get** array index
|
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|
|
Returns the value of given index from given array.
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|
|
#### pffi-array-set!
|
|
<a name="pffi-array-set!"></a>
|
|
|
|
**pffi-array-set!** array index value
|
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|
|
Sets the given value of given index in given array.
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|
|
#### pffi-list->array
|
|
<a name="pffi-list->array"></a>
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|
|
**pffi-list->array** type list
|
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|
|
Converts given list into C array of given type.
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|
|
#### pffi-array->list
|
|
<a name="pffi-array->list"></a>
|
|
|
|
**pffi-array->list** type list length
|
|
|
|
Converts given C array into list of given type and length.
|
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|
|
#### define-c-procedure
|
|
<a name="define-c-procedure"></a>
|
|
|
|
**define-c-procedure** scheme-name shared-object c-name return-type argument-types
|
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|
|
Defines a new foreign function to be used from Scheme code. For example:
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|
|
(cond-expand
|
|
(windows (define-c-library libc-stdlib '("stdlib.h") "ucrtbase" '("")))
|
|
(else (define-c-library libc-stdlib '("stdlib.h") "c" '("" "6"))))
|
|
(define-c-procedure c-puts libc-stdlib 'puts 'int '(pointer))
|
|
(c-puts "Message brought to you by FFI!")
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|
|
#### pffi-define-callback
|
|
<a name="pffi-define-callback"></a>
|
|
|
|
**pffi-define-callback** scheme-name return-type argument-types procedure
|
|
|
|
Defines a new Sceme function to be used as callback to C code. For example:
|
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|
|
; Load the shared library
|
|
(cond-expand
|
|
(windows (define-c-library libc-stdlib '("stdlib.h") "ucrtbase" '()))
|
|
(else (define-c-library '("stdlib.h") "c" '("" "6"))))
|
|
|
|
; Define C function that takes a callback
|
|
(define-c-procedure qsort libc-stdlib 'qsort 'void '(pointer int int callback))
|
|
|
|
; Define our callback
|
|
(pffi-define-callback compare
|
|
'int
|
|
'(pointer pointer)
|
|
(lambda (pointer-a pointer-b)
|
|
(let ((a (pffi-pointer-get pointer-a 'int 0))
|
|
(b (pffi-pointer-get pointer-b 'int 0)))
|
|
(cond ((> a b) 1)
|
|
((= a b) 0)
|
|
((< a b) -1)))))
|
|
|
|
; Create new array of ints to be sorted
|
|
(define array (make-c-bytevector (* (c-size-of 'int) 3)))
|
|
(pffi-pointer-set! array 'int (* (c-size-of 'int) 0) 3)
|
|
(pffi-pointer-set! array 'int (* (c-size-of 'int) 1) 2)
|
|
(pffi-pointer-set! array 'int (* (c-size-of 'int) 2) 1)
|
|
|
|
(display array)
|
|
(newline)
|
|
;> (3 2 1)
|
|
|
|
; Sort the array
|
|
(qsort array 3 (c-size-of 'int) compare)
|
|
|
|
(display array)
|
|
(newline)
|
|
;> (1 2 3)
|
|
|
|
</main>
|