[expert advice required][Is getImageSize really smart ?]

[jfsebastian]

Hi,

I am wondering if getImageSize does fetch images
*before* extracting the size infos (like perl
modules...) or if the function only fetch the
few bytes in the file headers which contains
the size information ?

I am trying to code a similar function in perl,
and i think it is very stupid to have to fetch
a 2Mo image to just retrieve its size...

Need your help gurus...!

Thanxs

[Andy Hassall]

Re: [expert advice required][Is getImageSize really smart ?]

On 29 Mar 2004 23:55:36 -0800, jfsebastian@net courrier.com (jfsebastian) wrote:
[color=blue]
>I am wondering if getImageSize does fetch images
>*before* extracting the size infos (like perl
>modules...) or if the function only fetch the
>few bytes in the file headers which contains
>the size information ?
>
>I am trying to code a similar function in perl,
>and i think it is very stupid to have to fetch
>a 2Mo image to just retrieve its size...[/color]

From a quick glance at the source code, it looks like it should be bailing out
once it's got all the header, and shouldn't have to fetch the whole image.

But:

<pre>
<?php
$x = getimagesize('h ttp://localhost/~andyh/j5_360.jpg');
var_dump($x);
?>
</pre>

Output:

array(7) {
[0]=>
int(6894)
[1]=>
int(963)
[2]=>
int(2)
[3]=>
string(25) "width="689 4" height="963""
["bits"]=>
int(8)
["channels"]=>
int(3)
["mime"]=>
string(10) "image/jpeg"
}

(i.e. it's a pretty big image)

Apache log shows:

127.0.0.1 - - [30/Mar/2004:23:13:53 +0100] "GET /~andyh/j5_360.jpg HTTP/1.0"
200 2833418 "-" "-"

Which seems to say it's fetched all 2.8M of it :-(
Apache's server-info page agrees, from the increase in Total Traffic.

--
Andy Hassall <andy@andyh.co. uk> / Space: disk usage analysis tool
http://www.andyh.co.uk / http://www.andyhsoftware.co.uk/space

[jfsebastian]

Re: [expert advice required][Is getImageSize really smart ?]

Andy Hassall <andy@andyh.co. uk> wrote in message news:<d5sj605e0 dtrk0t5krq7o3u4 rtd9i0hhkt@4ax. com>...[color=blue]
> On 29 Mar 2004 23:55:36 -0800, jfsebastian@net courrier.com (jfsebastian) wrote:
>
> From a quick glance at the source code, it looks like it should be bailing out
> once it's got all the header, and shouldn't have to fetch the whole image.
>
> But:
>
> ...
>
> (i.e. it's a pretty big image)
>
> Apache log shows:
>
> 127.0.0.1 - - [30/Mar/2004:23:13:53 +0100] "GET /~andyh/j5_360.jpg HTTP/1.0"
> 200 2833418 "-" "-"
>
> Which seems to say it's fetched all 2.8M of it :-(
> Apache's server-info page agrees, from the increase in Total Traffic.[/color]

Tanks Andy for this test: very instructive, indeed.
It is unbelievable that you have to fecth 2Mo to just read a few bytes...
Even more surprising is that nobody thought about fopen(blabla)
read the headers blabla and fclose and finished !

Do you think that opening an image on a remote host may change
the results ?
:-/

[Andy Hassall]

Re: [expert advice required][Is getImageSize really smart ?]

On 31 Mar 2004 04:33:19 -0800, jfsebastian@net courrier.com (jfsebastian) wrote:
[color=blue]
>Andy Hassall <andy@andyh.co. uk> wrote in message news:<d5sj605e0 dtrk0t5krq7o3u4 rtd9i0hhkt@4ax. com>...[color=green]
>> On 29 Mar 2004 23:55:36 -0800, jfsebastian@net courrier.com (jfsebastian) wrote:
>>
>> From a quick glance at the source code, it looks like it should be bailing out
>> once it's got all the header, and shouldn't have to fetch the whole image.
>>
>> But:
>>
>> ...
>>
>> (i.e. it's a pretty big image)
>>
>> Apache log shows:
>>
>> 127.0.0.1 - - [30/Mar/2004:23:13:53 +0100] "GET /~andyh/j5_360.jpg HTTP/1.0"
>> 200 2833418 "-" "-"
>>
>> Which seems to say it's fetched all 2.8M of it :-(
>> Apache's server-info page agrees, from the increase in Total Traffic.[/color]
>
>Tanks Andy for this test: very instructive, indeed.
>It is unbelievable that you have to fecth 2Mo to just read a few bytes...
>Even more surprising is that nobody thought about fopen(blabla)
>read the headers blabla and fclose and finished ![/color]

What's somewhat confusing is that this appears to be exactly what they tried
to do in the source code.

See ext/standard/image.c, php_handle_jpeg function. It's got a big switch
statement for each token it goes through, with this near the end:

case M_SOS:
case M_EOI:
return result; /* we're about to hit image data, or are at
EOF. stop processing. */

It then returns back to getimagesize, and closes the stream.
Perhaps it's not hitting these cases? Probably needs some more testing and
tracing to work out what's really going on.
[color=blue]
>Do you think that opening an image on a remote host may change
>the results ?[/color]

No, I don't - a URL is a URL, it doesn't know whether it's local or remote.

--
Andy Hassall <andy@andyh.co. uk> / Space: disk usage analysis tool
http://www.andyh.co.uk / http://www.andyhsoftware.co.uk/space