\input texinfo   @c -*-texinfo-*-
@c %**start of header
@setfilename cffi-sys.info
@settitle CFFI-SYS Interface Specification

@c Show types in the same index as the functions.
@synindex tp fn

@copying
Copyright @copyright{} 2005-2006, James Bielman  <jamesjb at jamesjb.com>

@quotation
Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documentation
files (the ``Software''), to deal in the Software without
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of the Software, and to permit persons to whom the Software is
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The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

@sc{The software is provided ``as is'', without warranty of any kind,
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holders be liable for any claim, damages or other liability,
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@end quotation
@end copying

@macro impnote {text}
@emph{Implementor's note: \text\}
@end macro
@c %**end of header

@dircategory Software development
@direntry
* CFFI Sys spec: (cffi-sys-spec).       CFFI Sys spec.
@end direntry

@titlepage
@title CFFI-SYS Interface Specification
@c @subtitle Version X.X
@c @author James Bielman

@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@contents

@ifnottex
@node Top
@top cffi-sys
@insertcopying
@end ifnottex

@menu
* Introduction::                
* Built-In Foreign Types::      
* Operations on Foreign Types::  
* Basic Pointer Operations::    
* Foreign Memory Allocation::   
* Memory Access::               
* Foreign Function Calling::    
* Loading Foreign Libraries::   
* Foreign Globals::             
* Symbol Index::                
@end menu

@node Introduction
@chapter Introduction

@acronym{CFFI}, the Common Foreign Function Interface, purports to be
a portable foreign function interface for Common Lisp.

This specification defines a set of low-level primitives that must be
defined for each Lisp implementation supported by @acronym{CFFI}.
These operators are defined in the @code{CFFI-SYS} package.

The @code{CFFI} package uses the @code{CFFI-SYS} interface
to implement an extensible foreign type system with support for
typedefs, structures, and unions, a declarative interface for
defining foreign function calls, and automatic conversion of
foreign function arguments to/from Lisp types.

Please note the following conventions that apply to everything in
@code{CFFI-SYS}:

@itemize @bullet
@item
Functions in @code{CFFI-SYS} that are low-level versions of functions
exported from the @code{CFFI} package begin with a leading
percent-sign (eg. @code{%mem-ref}).

@item
Where ``foreign type'' is mentioned as the kind of an argument, the
meaning is restricted to that subset of all foreign types defined in
@ref{Built-In Foreign Types}.  Support for higher-level types is
always defined in terms of those lower-level types in @code{CFFI}
proper.
@end itemize


@node Built-In Foreign Types
@chapter Built-In Foreign Types

@deftp {Foreign Type} :char
@deftpx {Foreign Type} :unsigned-char
@deftpx {Foreign Type} :short
@deftpx {Foreign Type} :unsigned-short
@deftpx {Foreign Type} :int
@deftpx {Foreign Type} :unsigned-int
@deftpx {Foreign Type} :long
@deftpx {Foreign Type} :unsigned-long
@deftpx {Foreign Type} :long-long
@deftpx {Foreign Type} :unsigned-long-long
These types correspond to the native C integer types according to the
ABI of the system the Lisp implementation is compiled against.
@end deftp

@deftp {Foreign Type} :int8
@deftpx {Foreign Type} :uint8
@deftpx {Foreign Type} :int16
@deftpx {Foreign Type} :uint16
@deftpx {Foreign Type} :int32
@deftpx {Foreign Type} :uint32
@deftpx {Foreign Type} :int64
@deftpx {Foreign Type} :uint64
Foreign integer types of specific sizes, corresponding to the C types
defined in @code{stdint.h}.
@end deftp

@deftp {Foreign Type} :size
@deftpx {Foreign Type} :ssize
@deftpx {Foreign Type} :ptrdiff
@deftpx {Foreign Type} :time
Foreign integer types corresponding to the standard C types (without
the @code{_t} suffix).
@end deftp

@impnote{I'm sure there are more of these that could be useful, let's
add any types that can't be defined portably to this list as
necessary.}

@deftp {Foreign Type} :float
@deftpx {Foreign Type} :double
The @code{:float} type represents a C @code{float} and a Lisp
@code{single-float}. @code{:double} represents a C @code{double} and a
Lisp @code{double-float}.
@end deftp

@deftp {Foreign Type} :pointer
A foreign pointer to an object of any type, corresponding to
@code{void *}.
@end deftp

@deftp {Foreign Type} :void
No type at all. Only valid as the return type of a function.
@end deftp


@node Operations on Foreign Types
@chapter Operations on Built-in Foreign Types

@defun %foreign-type-size type @result{} size
Return the @var{size}, in bytes, of objects having foreign type
@var{type}. An error is signalled if @var{type} is not a known
built-in foreign type.
@end defun

@defun %foreign-type-alignment type @result{} alignment
Return the default alignment in bytes for structure members of foreign
type @var{type}. An error is signalled if @var{type} is not a known
built-in foreign type.

@impnote{Maybe this should take an optional keyword argument specifying an
alternate alignment system, eg. :mac68k for 68000-compatible alignment
on Darwin.}
@end defun


@node Basic Pointer Operations
@chapter Basic Pointer Operations

@defun pointerp ptr @result{} boolean
Return true if @var{ptr} is a foreign pointer.
@end defun

@defun null-pointer @result{} pointer
Return a null foreign pointer.
@end defun

@defun null-pointer-p ptr @result{} boolean
Return true if @var{ptr} is a null foreign pointer.
@end defun

@defun make-pointer address @result{} pointer
Return a pointer corresponding to the numeric integer @var{address}.
@end defun

@defun inc-pointer ptr offset @result{} pointer
Return the result of numerically incrementing @var{ptr} by @var{offset}.
@end defun


@node Foreign Memory Allocation
@chapter Foreign Memory Allocation

@defun foreign-alloc size @result{} pointer
Allocate @var{size} bytes of foreign-addressable memory and return
a @var{pointer} to the allocated block. An implementation-specific
error is signalled if the memory cannot be allocated.
@end defun

@defun foreign-free ptr @result{} unspecified
Free a pointer @var{ptr} allocated by @code{foreign-alloc}. The
results are undefined if @var{ptr} is used after being freed.
@end defun

@defmac with-foreign-pointer (var size &optional size-var) &body body
Bind @var{var} to a pointer to @var{size} bytes of
foreign-accessible memory during @var{body}.  Both @var{ptr} and the
memory block it points to have dynamic extent and may be stack
allocated if supported by the implementation. If @var{size-var} is
supplied, it will be bound to @var{size} during @var{body}.
@end defmac


@node Memory Access
@chapter Memory Access

@deffn {Accessor} %mem-ref ptr type &optional offset
Dereference a pointer @var{offset} bytes from @var{ptr} to an object
for reading (or writing when used with @code{setf}) of built-in type
@var{type}.
@end deffn

@heading Example

@lisp
;; An impractical example, since time returns the time as well,
;; but it demonstrates %MEM-REF. Better (simple) examples wanted!
(with-foreign-pointer (p (foreign-type-size :time))
  (foreign-funcall "time" :pointer p :time)
  (%mem-ref p :time))
@end lisp


@node Foreign Function Calling
@chapter Foreign Function Calling

@defmac %foreign-funcall name @{arg-type arg@}* &optional result-type @result{} object
@defmacx %foreign-funcall-pointer ptr @{arg-type arg@}* &optional result-type @result{} object
Invoke a foreign function called @var{name} in the foreign source code.

Each @var{arg-type} is a foreign type specifier, followed by
@var{arg}, Lisp data to be converted to foreign data of type
@var{arg-type}.  @var{result-type} is the foreign type of the
function's return value, and is assumed to be @code{:void} if not
supplied.

@code{%foreign-funcall-pointer} takes a pointer @var{ptr} to the
function, as returned by @code{foreign-symbol-pointer}, rather than a
string @var{name}.
@end defmac

@defmac %foreign-funcall-varargs name (@{fixed-type arg@}*) @{vararg-type arg@}* &optional result-type @result{} object
@defmacx %foreign-funcall-varargs-pointer ptr (@{fixed-type arg@}*) @{vararg-type arg@}* &optional result-type @result{} object
Invoke a foreign variadic function called @var{name} in the foreign
source code.

Each @var{fixed-type} and @var{vararg-type} is a foreign type
specifier, followed by @var{arg}, Lisp data to be converted to foreign
data of type @var{arg-type}.  @var{result-type} is the foreign type of
the function's return value, and is assumed to be @code{:void} if not
supplied.

@code{%foreign-funcall-pointer-varargs} takes a pointer @var{ptr} to
the variadic function, as returned by @code{foreign-symbol-pointer},
rather than a string @var{name}.

Both functions have default implementation which call
@code{%foreign-funcall} and @code{%foreign-funcall-pointer}
approprietly.
@end defmac

@heading Examples

@lisp
;; Calling a standard C library function:
(%foreign-funcall "sqrtf" :float 16.0 :float) @result{} 4.0
@end lisp

@lisp
;; Dynamic allocation of a buffer and passing to a function:
(with-foreign-ptr (buf 255 buf-size)
  (%foreign-funcall "gethostname" :pointer buf :size buf-size :int)
  ;; Convert buf to a Lisp string using MAKE-STRING and %MEM-REF or
  ;; a portable CFFI function such as CFFI:FOREIGN-STRING-TO-LISP.
  )
@end lisp


@node Loading Foreign Libraries
@chapter Loading Foreign Libraries

@defun %load-foreign-library name @result{} unspecified
Load the foreign shared library @var{name}.

@impnote{There is a lot of behavior to decide here.  Currently I lean
toward not requiring NAME to be a full path to the library so
we can search the system library directories (maybe even get
LD_LIBRARY_PATH from the environment) as necessary.}
@end defun


@node Foreign Globals
@chapter Foreign Globals

@defun foreign-symbol-pointer name @result{} pointer
Return a pointer to a foreign symbol @var{name}.
@end defun

@node Symbol Index
@unnumbered Symbol Index
@printindex fn

@bye
