Data serialization of objects, want to iterate 'sealed' properties then dynamic ones View as Markdown

Thank you, Sean. Still looking for a couple of answers...

1. 'Default Properties' or properties stored on the class (not object)
   can be found on the zend_class_entry[0], they are just accessed by offset
   [1]
   This isn't a stable/public API, but good for a cool hack!

I'm afraid I don't follow. Could you elaborate? I've seen one way to get
'default properties' from a zend_class_entry object:
zendClassEntry->default_properties;
This gets us a list of default properties. I've also seen
zendClassEntry->properties_info;
Which, if I'm not mistaken, involves more elaborate parsing logic but also
tells you whether properties are accessible.

Seems like numerous ways to skin a cat. What is the orthodox approach here?
Also, what do you suggest to distinguish 'sealed' (i.e., default)
properties from dynamic ones? Is there some counterpart to
default_properties that returns non_default_properties -- i.e., just the
dynamic ones? Or should I just get all of the object's properties and check
each key to see if it's one of the default_properties by searching a
HashTable of these default properties?

3. Never used this, but it seems to be to confirm that a mangled prop
   name matches a zend_property_info *

Not sure I follow. We create a separate zobj of type zend_object using the
function:
zobj = zend_objects_get_address(obj TSRMLS_CC);
And then use zobj to check access:
if (zend_check_property_access(zobj, key, key_len-1 TSRMLS_CC) ==
SUCCESS) {

I find it odd that our native zval type would not encompass member
accessibility. I'm wondering if zend_object might be some kind of
historical add-on concept to expand very old PHP functionality or if
there's some reason for this distinct object type.

I'm working on a data serialization routine wherein I must iterate
through
an object's properties while distinguishing between "sealed" properties
(i.e., those specified by class definitions) and "dynamic" properties"
(i.e., those assigned ad-hoc to some object that are not party of any
class
definition).

I found the source of the php function get_object_vars():
http://lxr.php.net/xref/PHP_5_6/Zend/zend_builtin_functions.c#985
However, I am still pretty confused. PHP source is full of macros and
has
basically no comments. Hoping for some tips to keep me on the right
track.
I'm pretty sure I can get something kludgy working, but I want my code to
be orthodox and work well.

QUESTIONS

1. Sadly, this approach is unable to distinguish "sealed" properties from
   dynamic ones. If anyone can refer me to some source (or outline a general
   approach) which can first iterate sealed properties and then iterate only
   dynamic ones, that would be extremely helpful.

2. What does zend_objects_get_address do? This reference looks very
   different than the usual macro, e.g. Z_OBJ_HT_P

3. Am I correct in understanding that zend_check_property_access simply
   checks if the property in question is availabe in the scope in which this
   function call gets executed? Is this the canonical/orthodox way to make
   this check?

4. What does zend_unmangle_property_name do? Why is this function changed
   to zend_unmangle_property_name_ex in 5.5 and later?

5. Why do we call Z_ADDREF_PP(value) here? Is this reference counting to
   prevent garbage collection?

6. An IS_INTERNED check is added in php 5.6 and yet the macro for
   IS_INTERNED is zero. What's that all about?

7. The code looks quite different between the different versions:
   5.3 - http://lxr.php.net/xref/PHP_5_3/Zend/zend_builtin_functions.c#950
   5.5 - http://lxr.php.net/xref/PHP_5_5/Zend/zend_builtin_functions.c#982
   5.6 - http://lxr.php.net/xref/PHP_5_6/Zend/zend_builtin_functions.c#985
   From what I can tell there is at least one difference between 5.3 and 5.6
   -- zend_unmangle_property_name_ex does not exist before 5.5. Can anyone
   recommend how to make code that'll work in 5.3-5.6? Also, with 7 coming
   out
   I'd like it work there too.

Any answers or assistance would be greatly appreciated.
Hey,

1. 'Default Properties' or properties stored on the class (not object)
   can be found on the zend_class_entry[0], they are just accessed by offset
   [1]

This isn't a stable/public API, but good for a cool hack!

3. Never used this, but it seems to be to confirm that a mangled prop name
   matches a
   zend_property_info *

4. [2] Is some good reading on property name mangling

5. [3] Pretty much! Refcount is just to keep track of when a zval can be
   destroyed

Hopefully the more educated members of the list can follow up and fix my
errors, but for now that
will at least get you going/able to dive deeper.

[0] http://lxr.php.net/xref/PHP_5_6/Zend/zend.h#488
[1] http://lxr.php.net/xref/PHP_5_6/ext/reflection/php_reflection.c#3410
[2]
http://www.phpinternalsbook.com/classes_objects/internal_structures_and_implementation.html
[3] http://www.phpinternalsbook.com/zvals/memory_management.html

Welcome to the jungle

Thank you, Francois. Malheuresement, plus de questions...

PHP uses an object store.
Am I correct in understanding that the object store is a global data
structure? Wouldn't this tend to discourage any attempts at
multithreading/multiprocessing within one's PHP script--unless the object
store is protected by a lock...

It would appear that for some zend_object ,zobj, that if the object has any
dynamic properties at all then zobj->properties will be defined a HashTable
that contains not just the dynamic properties, but all the default object
properties (i.e., those defined explicitly by the class) as well. At least
that appears to be the case from my code below.

Is there not any way to first iterate through the default properties and
then iterate through only the dynamic properties ? If so, please
advise? If not, it sounds like I must iterate through all properties and
check each property's key to see if it's included among the default
properties.

Also -- and this is very important:

1. Will this code ALWAYS return the properties in the same sequence? E.g.,
   if I am iterating through N objects of type MyClass, will each instance
   iterate the properties in the same order?

2. Will this code ALWAYS iterate over default properties (i.e., "sealed"
   properties, those explicitly defined by class definitinos) FIRST and then
   iterate any dynamically assigned properties?
   These questions are very important for my serialization algorithm.

        zobj = zend_objects_get_address(*val TSRMLS_CC);
   
        if (!zobj->properties) {
            php_printf("***No dynamic properties!\n");
        } else {
            php_printf("***we got dynamic properties...sadly, this will
   

also iterate through default properties too\n");
zend_hash_internal_pointer_reset_ex(zobj->properties, &pos);
while (zend_hash_get_current_data_ex(zobj->properties,
(void **) &value, &pos) == SUCCESS) {
if (zend_hash_get_current_key_ex(zobj->properties,
&key, &key_len, &num_index, 0, &pos) == HASH_KEY_IS_STRING) {
if (zend_check_property_access(zobj, key, key_len-1
TSRMLS_CC) == SUCCESS) {

                        zend_unmangle_property_name(key, key_len - 1,

&class_name, &prop_name);

                        php_printf("dynamic property is %s, key_len is

%d\n", prop_name, key_len);
}
}
zend_hash_move_forward_ex(zobj->properties, &pos);
}
}

On Tue, Sep 22, 2015 at 5:42 PM, François Laupretre francois@php.net
wrote:

Hi,

Hope this can help.

Le 22/09/2015 20:16, j adams a écrit :

I'm working on a data serialization routine wherein I must iterate through
an object's properties while distinguishing between "sealed" properties
(i.e., those specified by class definitions) and "dynamic" properties"
(i.e., those assigned ad-hoc to some object that are not party of any
class
definition).

I found the source of the php function get_object_vars():
http://lxr.php.net/xref/PHP_5_6/Zend/zend_builtin_functions.c#985
However, I am still pretty confused. PHP source is full of macros and
has
basically no comments.

Welcome to the jungle

2. What does zend_objects_get_address do? This reference looks very

different than the usual macro, e.g. Z_OBJ_HT_P

PHP uses an object store. This allows handling objects by reference. Every
object instance is defined by a numeric handle (an offset in the object
store). Object zvals contain the object handle. The object address is
obtained through the object store. Look
http://lxr.php.net/xref/PHP_5_6/Zend/zend_objects_API.c#274

Z_OBJ_HT() is used to call an object's handlers. This information is also
present in the zend_object but, for a better performance AFAIK, also made
available in the zval struct.

3. Am I correct in understanding that zend_check_property_access simply

checks if the property in question is availabe in the scope in which this
function call gets executed?

Yes

4. What does zend_unmangle_property_name do? Why is this function changed
   to zend_unmangle_property_name_ex in 5.5 and later?

Properties are stored using 'mangled' names. The format of a mangled name
is '<NULL><class name><NULL><property name><NULL>', where <NULL> is a null
byte. Class name and property name are 'decoded' by
zend_unmangle_property_name(). Look
http://lxr.php.net/xref/PHP_5_6/Zend/zend_compile.c#5373

5. Why do we call Z_ADDREF_PP(value) here? Is this reference counting to

prevent garbage collection?

This is reference counting. Incremented because a reference to the 'value'
zval is added to the result array.

7. The code looks quite different between the different versions:

5.3 - http://lxr.php.net/xref/PHP_5_3/Zend/zend_builtin_functions.c#950
5.5 - http://lxr.php.net/xref/PHP_5_5/Zend/zend_builtin_functions.c#982
5.6 - http://lxr.php.net/xref/PHP_5_6/Zend/zend_builtin_functions.c#985
From what I can tell there is at least one difference between 5.3 and 5.6
-- zend_unmangle_property_name_ex does not exist before 5.5. Can anyone
recommend how to make code that'll work in 5.3-5.6? Also, with 7 coming
out
I'd like it work there too.

Making code working with 5.3-5.6 is quite easy with a pair of ifdef.
Unfortunately, writing code to compile on PHP 5 & 7 is complex. It seems
most people porting extensions to PHP 7 finally duplicated most, if not all
of their code.

Regards

François