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Making stream functions accepting SplFileObject as valid parameter

php.internals

nyamsprod the funky webmaster

8 years ago

Hi internals,

I've been following the resolution of this bug:

https://bugs.php.net/bug.php?id=44392

and it seems that there is no safe way to expose the internal
`SplFileObject` filepointer.

So I was wondering if we could not do things differently and instead of
trying to expose the internal file pointer make any `stream_*` function
which accept a resource stream as parameter accept a `SplFileObject`. By
doing so we could resolve a couple of issues I encountered while using this
SPL object without adding any new method to the class we could:

- get informations about the object seekable and open mode status using
`stream_get_meta_data`.
- append/prepend stream filters without using the `php://filter/` hack
which has its own limitations.

What do you think ?

Dan Ackroyd

8 years ago

On 29 September 2017 at 07:46, nyamsprod the funky webmaster
<nyamsprod@gmail.com> wrote:

> Hi internals,
>
> I've been following the resolution of this bug:
>
> https://bugs.php.net/bug.php?id=44392
>
> and it seems that there is no safe way to expose the internal
> `SplFileObject` filepointer.

Hi nyamsprod the funky webmaster,

It seems that people are scared to comment on a streams related question...

I'm not sure that making stream_* functions accept SplFileObject's
would be an appropriate way to solve this problem; it's just too much
of a hack.

However, although it's not safe to expose the underlying file handle
used by SplFileObject, I think it _might_ be safe to allow the
SplFileObject to return a stream that represents the file, but with
the necessary php_stream_ops that aren't safe to use replaced with NOP
operations, similar to how it is done in the pgsql extension:
https://github.com/php/php-src/blob/879126a2cedef5b6e1c1f701ade17ca3da9a39ec/ext/pgsql/pgsql.c#L5406-L5409

static int php_pgsql_fd_close(php_stream *stream, int close_handle) /* {{{ */
{
return EOF;
}

To expose the internal stream to userland.

I'd really like to hear from anyone who knows about streams internals
to know if that's a viable approach.

cheers
Dan
Ack

Sara Golemon

8 years ago

On Tue, Oct 3, 2017 at 9:44 AM, Dan Ackroyd <danack@basereality.com> wrote:

> On 29 September 2017 at 07:46, nyamsprod the funky webmaster
> <nyamsprod@gmail.com> wrote:
>>
>> I've been following the resolution of this bug:
>>
>> https://bugs.php.net/bug.php?id=44392
>>
>> and it seems that there is no safe way to expose the internal
>> `SplFileObject` filepointer.
>
>
> It seems that people are scared to comment on a streams related question...
>

Nah, just distr... OOH SHINY!

> I'm not sure that making stream_* functions accept SplFileObject's
> would be an appropriate way to solve this problem; it's just too much
> of a hack.
>

Implementation wise, about as difficult as you'd imagine.  We have
php_stream_from_zval() which is a central place which could be made
smarter, though most (all?) stream related functions have IS_RESOURCE
checks that'd have to be dealt with, so it still means touching the
world.

> However, although it's not safe to expose the underlying file handle
> used by SplFileObject, I think it _might_ be safe to allow the
> SplFileObject to return a stream that represents the file, but with
> the necessary php_stream_ops that aren't safe to use replaced with NOP
> operations, similar to how it is done in the pgsql extension:
> https://github.com/php/php-src/blob/879126a2cedef5b6e1c1f701ade17ca3da9a39ec/ext/pgsql/pgsql.c#L5406-L5409
>

I like this approach in the abstract (though I haven't paged in the
entire problem space yet).  A proxy wrapper provides (possibily
implemeted on the SplFileObject itself) keeps the scope of the change
localized to SPL and has little residual hack smell.

-Sara

nyamsprod the funky webmaster

8 years ago

Does adding new methods to SplFileObject easier ? It would mean adding a
getMetaData() (to return stream_get_meta_data infos) method and
(append/prepend/remove)Filter methods to add stream filters API.

On Tue, Oct 3, 2017 at 5:21 PM, Sara Golemon <pollita@php.net> wrote:

Sara Golemon

8 years ago

On Thu, Oct 5, 2017 at 6:42 AM, ignace nyamagana butera
<nyamsprod@gmail.com> wrote:

> Does adding new methods to SplFileObject easier ? It would mean adding a
> getMetaData() (to return stream_get_meta_data infos) method and
> (append/prepend/remove)Filter methods to add stream filters API.
>

That's still a hack, and a piecemeal one at that.  Danack's approach
of creating a proxy stream really is more comprehensive and correct.

-Sara