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Restore output buffer in case of exceptions

php.internals

Mehmet Yavuz Selim Soyturk

18 years ago

Hello,

I'm sorry if that's the wrong list.

I am neither a PHP nor a webscripting guy so I'm sorry if this does
not make sense. I just thought that it could be useful.

PHP 5 supports exception handling. When an exception occurs, PHP does
stack unwinding so that it restores the state of the script. But an
important state of the script does not get restored: the output. Would
it not be a good idea if PHP also did some sort of output buffer
unwinding?

That is the idea:

<?php

exceptional_ob_start();

echo "Begin\n";
try {
echo "Exception\n";
throw new Exception();
} catch (Exception $e) {}
echo "End\n";

exceptional_ob_end_flush();

?>

And that would be the only output:

Begin
End

Antony Dovgal

18 years ago

On 18.11.2007 01:36, Mehmet Yavuz Selim Soyturk wrote:

> That is the idea:
>
> <?php
>
> exceptional_ob_start();
>
> echo "Begin\n";
> try {
>    echo "Exception\n";
>    throw new Exception();
> } catch (Exception $e) {}
> echo "End\n";
>
> exceptional_ob_end_flush();
>
> ?>
>
> And that would be the only output:
>
> Begin
> End
>

Following this logic, we would also need to "unwind" all file descriptors,
database transactions, network connections etc. etc.
This makes no sense.

--
Wbr,
Antony Dovgal

Alexey Zakhlestin

18 years ago

On 11/18/07, Antony Dovgal <tony@daylessday.org> wrote:

> On 18.11.2007 01:36, Mehmet Yavuz Selim Soyturk wrote:
> > That is the idea:
> >
> > <?php
> >
> > exceptional_ob_start();
> >
> > echo "Begin\n";
> > try {
> >    echo "Exception\n";
> >    throw new Exception();
> > } catch (Exception $e) {}
> > echo "End\n";
> >
> > exceptional_ob_end_flush();
> >
> > ?>
> >
> > And that would be the only output:
> >
> > Begin
> > End
> >
>
> Following this logic, we would also need to "unwind" all file descriptors,
> database transactions, network connections etc. etc.
> This makes no sense.

This makes sense, but it's almost impossible to implement it this way :)

On the other hand, implementing output-buffer the way it is proposed
can actually be possible and it can be really useful

edge-cases are not obvious, though

--
Alexey Zakhlestin
http://blog.milkfarmsoft.com/

Evert | Rooftop

18 years ago

Mehmet Yavuz Selim Soyturk wrote:

> Hello,
>
> I'm sorry if that's the wrong list.
>
> I am neither a PHP nor a webscripting guy so I'm sorry if this does
> not make sense. I just thought that it could be useful.
>
> PHP 5 supports exception handling. When an exception occurs, PHP does
> stack unwinding so that it restores the state of the script. But an
> important state of the script does not get restored: the output. Would
> it not be a good idea if PHP also did some sort of output buffer
> unwinding?
>

Generally I make sure that the parts of my code that start an output
buffer are also responsible for closing the output buffer.. so something
like this wouldn't be uncommon in my code..


ob_start();
try {
do_something();
} catch (Exception $e) {
ob_end_clean();
throw $e;
}

$data = ob_get_clean();

Edward Z. Yang

18 years ago

Evert | Rooftop wrote:

> Generally I make sure that the parts of my code that start an output
> buffer are also responsible for closing the output buffer.. so something
> like this wouldn't be uncommon in my code..

Agreed. If you'd like to implement transaction support using PHP's
exceptions, you'll need to implement rollback functionality yourself in
the catch block.

--
Edward Z. Yang                        GnuPG: 0x869C48DA
HTML Purifier <http://htmlpurifier.org> Anti-XSS Filter
[[ 3FA8 E9A9 7385 B691 A6FC B3CB A933 BE7D 869C 48DA ]]

Mehmet Yavuz Selim Soyturk

18 years ago

On Nov 18, 2007 1:38 AM, Evert | Rooftop <evert@rooftopsolutions.nl> wrote:

> Generally I make sure that the parts of my code that start an output
> buffer are also responsible for closing the output buffer.. so something
> like this wouldn't be uncommon in my code..
>
>
> ob_start();
> try {
>   do_something();
> } catch (Exception $e) {
>    ob_end_clean();
>    throw $e;
> }
>
> $data = ob_get_clean();
>

Thanks for the answers. I wasn't aware of the fact that ob's could
nest. So one can manually translate the first try-catch to the second:

try {
// ... code
} catch (Exception $e) {
// ... code
}


ob_start();
try {
// ... code
ob_end_flush();
} catch (Exception $e) {
ob_end_clean();
// ... code
}

More verbose, but works.

--
Mehmet

Stanislav Malyshev

18 years ago

> That is the idea:
>
> <?php
>
> exceptional_ob_start();
>
> echo "Begin\n";
> try {
>    echo "Exception\n";
>    throw new Exception();
> } catch (Exception $e) {}
> echo "End\n";
>
> exceptional_ob_end_flush();

You can do it, I think - just another bufferign inside try() and clean
it on exception, then output it after try block ends. Buffers are
stackable in PHP.

--
Stanislav Malyshev, Zend Software Architect
stas@zend.com   http://www.zend.com/
(408)253-8829   MSN: stas@zend.com