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https://github.com/cffi/cffi

The Common Foreign Function Interface
https://github.com/cffi/cffi

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The Common Foreign Function Interface

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README 

        
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# What



CFFI, the Common Foreign Function Interface, purports

to be a portable FFI for Common Lisp. It abstracts away the

differences between the API of the native FFI's of the various Common

Lisp implementations.



# How



The CFFI library is composed of a Lisp-implementation-specific backend

in the CFFI-SYS package, and a portable frontend in the CFFI package.



The CFFI-SYS backend package defines a low-level interface to the

native FFI support in the Lisp implementation. It offers operators for

allocating and dereferencing foreign memory, calling foreign

functions, and loading shared libraries.



The CFFI frontend provides a more comfortable, declarative interface

for defining foreign functions, structures, typedefs, enumerated

types, etc. It is implemented in portable ANSI CL making use of the

low-level operators exported by CFFI-SYS.



The CFFI-LIBFFI subsystem loads support for passing structs by

value. It requires [libffi](https://sourceware.org/libffi/) for that.



Please consult [the

manual](http://common-lisp.net/project/cffi/manual/html_node/) for

further details, including installation instructions.



# Where



Please visit [Github](https://github.com/cffi/cffi/issues) for bug

reports, feature suggestions, the latest version, and to send your

contributions. CFFI also has a [mailing

list](https://mailman.common-lisp.net/listinfo/cffi-devel), and a

project page at [cffi.common-lisp.dev](https://cffi.common-lisp.dev/).



# Notes



### CFFI/C2FFI



CFFI/C2FFI is an ASDF-integrated mechanism to automatically generate a

complete CFFI binding from C header files.



Its input is one `.h` file (with possible `#include`s of course), and

its final output is a lisp file with the relevant CFFI binding forms.



It requires a CLI tool called [c2ffi](https://github.com/rpav/c2ffi),

but only for the developers of the C binding libraries, not their

users. `c2ffi` is written in C++, and it uses Clang as a library to

parse the C code, and emit the result as JSON. To skip this step,

these host-specific JSON files can be checked into the repos of the

binding libraries. This breaks the dependence on a working c2ffi

binary and the C header files, which can be a hurdle.



These JSON files are then used to automatically generate a CL file

with the corresponding CFFI forms. The generated bindings mirror the C

namespace into an empty CL package as closely as possible. This means

that the upper/lower case of the C names are retained. It helps with

reading the original docs and with rewriting C examples into

lisp. `#define`s are also mirrored as CL `defconstant`s.



Binding library developers are advised to introduce another package on

top of this raw layer to add more lispy constructs where appropriate

(e.g. `with-` macros that manage resources, etc).



Until CFFI/C2FFI is properly documented, you may check out these

projects as examples:

[hu.dwim.zlib](https://github.com/hu-dwim/hu.dwim.zlib),

[hu.dwim.sdl](https://github.com/hu-dwim/hu.dwim.sdl),

[hu.dwim.bluez](https://github.com/hu-dwim/hu.dwim.bluez), and

[hu.dwim.mosquitto](https://github.com/attila-lendvai/hu.dwim.mosquitto).



### Related projects



- [cl-autowrap](https://github.com/rpav/cl-autowrap) is another

  project that uses `c2ffi` to generate CFFI bindings.