Design of the design of phpni, a native interface for PHP, designed to replace the Zend API.
The need for such a native interface is described separately in remove_zend_api.
This describes the design of phpni, the PHP Native Interface. This design is in early stages.
Take the use case of wrapping a C library to expose its functionality in user space. The major idea is to “automatically” import C functions into a special namespace. The PHP library functions would then be comprised of PHP user space code which calls those C functions directly. That way it is possible to craft an API that is separate from the C implementation.
Lets take a simple example. Assume we have a C library XXX, with 3 functions, x, y and z. We'd like to expose this in user space as a class called MyXXX, with methods a and b. We create a file with the signatures of x, y and z:
extensions/xxx/sigs.h
int x (int, int); void y (char*, int); void z (char*, int);
We then write our user space code:
extensions/xxx/MyXXX.php
class MyXXX
{
function __construct ($username)
{
$this->username = $username;
}
function a ($w1, $w2)
{
$foo = \internals\XXX\x ($w1, $w2);
\internals\XXX\y ($this->username, $foo);
}
function b ($m1, $m2)
{
$foo = \internals\XXX\x ($m1, $m2);
\internals\XXX\z ($this->username, $foo);
return $foo;
}
}
In order to interface between the PHP code and the C functions, a tool will be required to generate code. This tool will obviously be implementation specific. SWIG could be used to create this.
Since the libraries would no longer use the Zend API, the tight coupling would be broken. It would now be possible to change major parts of the Zend engine without affecting the operation of any other part of PHP.
It would no longer be necessary to know the Zend API to write extensions. Instead, only the API of the C library is necessary, and the interface can be created in PHP user code.
The same interface used for libraries can be used to handle many of the use cases of the C API. However, we do need to specify a means to call PHP user code from C/C++ code.
Since PHP extensions are no longer written in the Zend API, other PHP implementations, such as Roadsend, Project Zero, Phalanger and Quercus should be reuse the libraries without difficulty. In addition, if the coupling is between the interpreter and its components is simple enough, it may be possible for other implementations to be slotted in directly. However, though this would be a nice side-effect, it should probably not be considered a priority.
Note that the design described requires the Zend engine to generate interfacing code from the phpni specification. Other implementations would be required to generate their own code for this interface.
Input from other PHP implementations:
As the design progresses, problems will be identified, which must be solved. This section will keep track of them:
phpni differs from many of these in that it is designed not to add new features, but instead to replace an existing facility - the ability to call C libraries. As such, dynamic linking is not part of the spec.
There is no reason we shouldn't reuse these, if they fit the bill.
This is a simple design. In reality, it would need to be prototyped to determine whether this makes sense for every use case, and that there would be little sacrificed to make it work. The work on it should probably progress in roughly the following order: