php get string from binary file

Question

I have JPG image with XMP meta data inside.
I'd like to read this data, but how?

$content = file_get_contents($fileName);
var_dump($content);

displays real number of bytes 553700 but

$len = strlen($content);
var_dump($len);

displays 373821

So, I can't simple do

$xmpStart = strpos($content, '<x:xmpmeta');

because I get wrong offset. So, the question is, how to find and read string from binary file in PHP? (I have mb_string option ON in php.ini)

UPD1:

I have some binary file. How can I check in PHP, this file contains several strings or not?

Ah, it's clearer now. Essentially, it shouldn't matter what kind of data is being used. Can you try whether strlen($content, "iso-8859-1") gives the correct value? — Pekka
– Pekka, Commented Sep 30, 2011 at 12:25
$pos = strpos($content, '<x:xmpmeta', 0, 'iso-8859-1'); now it pointers to right offset. Thanks. But how can I know about last encoding parameter? :) There is no information about this in php.net/manual/en/function.strpos.php huh... — Lari13
– Lari13, Commented Sep 30, 2011 at 19:28

Pekka · Accepted Answer · 2011-09-30 19:31:47Z

1

Essentially, it doesn't matter what kind of data you are reading - strlen() et al. should always work.

What I think is happening here is that on your server, strlen() is internally overridden by mb_strlen() and the internal character encoding is set to UTF-8.

UTF-8 is a multi-byte encoding, so some of the characters in your (wildly arbitrary) byte stream get interpreated as multi-byte characters - resulting in a shortened length of 373821 instead of 553700.

I can't think of a better workaround than always explicitly specifying a single-byte encoding like iso-8859-1:

 $pos = strpos($content, '<x:xmpmeta', 0, 'iso-8859-1');

this forces strpos() (or rather, mb_strpos()) to count every single byte in the data.

This will always work; I do not know whether there is a more elegant way to force the use of a single-byte encoding.

answered Sep 30, 2011 at 19:31

Pekka

451k150 gold badges989 silver badges1.1k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Pekka · Accepted Answer · 2011-09-30 08:03:51Z

1

Getid3 is a PHP package that claims to be able to read XMP Metadata.

answered Sep 30, 2011 at 8:03

Pekka

451k150 gold badges989 silver badges1.1k bronze badges

3 Comments

Lari13 Over a year ago

Ok, thanks. It can help, but if I have to read own strings from binary files? How can it be done?

Pekka Over a year ago

@Lari you'd have to build your own JPG parser. While surely very interesting, it's likely to be a huge task.

Lari13 Over a year ago

Let's forget JPG. :) I have some binary file. How can I check in PHP, this file contains several strings or not?

Sheitan · Accepted Answer · 2011-09-30 08:10:22Z

0

The exif_read_data() PHP function could help the XMP meta data

More info here: http://php.net/manual/en/function.exif-read-data.php

answered Sep 30, 2011 at 8:10

Sheitan

1411 silver badge7 bronze badges

Collectives™ on Stack Overflow

php get string from binary file

3 Answers 3

Comments

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related