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><A
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>stream_register_filter</H1
><DIV
CLASS="refnamediv"
><A
NAME="AEN73725"
></A
><P
> (PHP 5 CVS only)</P
>stream_register_filter -- Register a stream filter implemented as a PHP class derived from <TT
CLASS="literal"
>php_user_filter</TT
></DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN73729"
></A
><H2
>Description</H2
>boolean <B
CLASS="methodname"
>stream_register_filter</B
> ( string filtername, string classname)<BR
></BR
><P
> <B
CLASS="function"
>stream_register_filter()</B
> allows you to implement
your own filter on any registered stream used with all the other
filesystem functions (such as <A
HREF="function.fopen.html"
><B
CLASS="function"
>fopen()</B
></A
>,
<A
HREF="function.fread.html"
><B
CLASS="function"
>fread()</B
></A
> etc.).
</P
><P
> To implement a filter, you need to define a class as an extension of
<TT
CLASS="literal"
>php_user_fitler</TT
> with a number of member functions
as defined below. When performing read/write opperations on the stream
to which your filter is attached, PHP will pass the data through your
filter (and any other filters attached to that stream) so that the
data may be modified as desired. You must implement the methods
exactly as described below - doing otherwise will lead to undefined
behaviour.
</P
><P
> <B
CLASS="function"
>stream_register_filter()</B
> will return <TT
CLASS="constant"
><B
>FALSE</B
></TT
> if the
<TT
CLASS="parameter"
><I
>filtername</I
></TT
> is already defined.
</P
>int <B
CLASS="methodname"
>write</B
> ( string data)<BR
></BR
><P
> This method is called whenever data is written to the attached
stream (such as with <A
HREF="function.fwrite.html"
><B
CLASS="function"
>fwrite()</B
></A
>). After
modifying <TT
CLASS="parameter"
><I
>data</I
></TT
> as needed your
filter should issue: <TT
CLASS="literal"
>return parent::write($data);</TT
>
so that the next filter in the chain can perform its filter.
When no filters remain, the stream will write <TT
CLASS="parameter"
><I
>data</I
></TT
>
in its final form.
<DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Nota: </B
>
If your filter alters the length of <TT
CLASS="parameter"
><I
>data</I
></TT
>, for
example by removing the first character, before passing onto
<TT
CLASS="literal"
>parent::write($data);</TT
> it must be certain to include
that stolen character in the return count.
</P
></BLOCKQUOTE
></DIV
>
<DIV
CLASS="informalexample"
><A
NAME="AEN73765"
></A
><P
></P
><TABLE
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><TR
><TD
><PRE
CLASS="php"
>class myfilter extends php_user_filter {
function write($data) {
$data = substr($data,1);
$written_by_parent = parent::write($data);
return ($written_by_parent + 1);
}
}</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
</P
>string <B
CLASS="methodname"
>read</B
> ( int maxlength)<BR
></BR
><P
> This method is called whenever data is read from the attached
stream (such as with <A
HREF="function.fread.html"
><B
CLASS="function"
>fread()</B
></A
>). A filter
should first call <TT
CLASS="literal"
>parent::read($maxlength);</TT
> to
retrieve the data from the previous filter who, ultimately,
retrieved it from the stream. Your filter may then modify the
data as needed and <TT
CLASS="literal"
>return</TT
> it.
Your filter should never return more than <TT
CLASS="parameter"
><I
>maxlength</I
></TT
>
bytes. Since <TT
CLASS="literal"
>parent::read($maxlength);</TT
> will also
not return more than <TT
CLASS="parameter"
><I
>maxlength</I
></TT
> bytes this
will ordinarily be a non-issue. However, if your filter
increases the size of the data being returned, you should either
call <TT
CLASS="literal"
>parent::read($maxlength-$x);</TT
> where
<TT
CLASS="parameter"
><I
>x</I
></TT
> is the most your filter will grow
the size of the data read. Alternatively, you can build a
read-buffer into your class.
</P
>int <B
CLASS="methodname"
>flush</B
> ( bool closing)<BR
></BR
><P
> This method is called in response to a request to flush the
attached stream (such as with <A
HREF="function.fflush.html"
><B
CLASS="function"
>fflush()</B
></A
> or
<A
HREF="function.fclose.html"
><B
CLASS="function"
>fclose()</B
></A
>). The <TT
CLASS="parameter"
><I
>closing</I
></TT
>
parameter tells you whether the stream is, in fact, in the
process of closing. The default action is to simply call:
<TT
CLASS="literal"
>return parent::flush($closing);</TT
> , your
filter may wish to perform additional writes and/or cleanup
calls prior to or directly after a successful flush.
</P
>void <B
CLASS="methodname"
>oncreate</B
> ( void)<BR
></BR
><P
> This method is called during instantiation of the filter class
object. If your filter allocates or initializes any other resources
(such as a buffer), this is the place to do it.
</P
>void <B
CLASS="methodname"
>onclose</B
> ( void)<BR
></BR
><P
> This method is called upon filter shutdown (typically, this is also
during stream shutdown), and is executed <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>after</I
></SPAN
>
the <TT
CLASS="literal"
>flush</TT
> method is called. If any resources
were allocated or initialzed during <TT
CLASS="literal"
>oncreate</TT
>
this would be the time to destroy or dispose of them.
</P
><P
> The example below implements a filter named <TT
CLASS="literal"
>rot13</TT
>
on the <TT
CLASS="literal"
>foo-bar.txt</TT
> stream which will perform
ROT-13 encryption on all letter characters written to/read from
that stream.
<TABLE
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><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN73809"
></A
><P
><B
>Ejemplo 1. Filter for ROT13 encoding data on foo-bar.txt stream</B
></P
><TABLE
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><PRE
CLASS="php"
><?php
/* Define our filter class */
class rot13_filter extends php_user_filter {
function read($length) {
$tempstr = parent::read($length);
for($i = 0; $i < strlen($tempstr); $i++)
if (($tempstr[$i] >= 'A' AND $tempstr[$i] <= 'M') OR
($tempstr[$i] >= 'a' AND $tempstr[$i] <= 'm')) $tempstr[$i] = chr(ord($tempstr[$i]) + 13);
else if (($tempstr[$i] >= 'N' AND $tempstr[$i] <= 'Z') OR
($tempstr[$i] >= 'n' AND $tempstr[$i] <= 'z')) $tempstr[$i] = chr(ord($tempstr[$i]) - 13);
return $tempstr;
}
function write($data) {
for($i = 0; $i < strlen($data); $i++)
if (($data[$i] >= 'A' AND $data[$i] <= 'M') OR
($data[$i] >= 'a' AND $data[$i] <= 'm')) $data[$i] = chr(ord($data[$i]) + 13);
else if (($data[$i] >= 'N' AND $data[$i] <= 'Z') OR
($data[$i] >= 'n' AND $data[$i] <= 'z')) $data[$i] = chr(ord($data[$i]) - 13);
return parent::write($data);
}
}
/* Register our filter with PHP */
stream_register_filter("rot13", "rot13_filter")
or die("Failed to register filter");
$fp = fopen("foo-bar.txt", "w");
/* Attach the registered filter to the stream just opened */
stream_filter_append($fp, "rot13");
fwrite($fp, "Line1\n");
fwrite($fp, "Word - 2\n");
fwrite($fp, "Easy As 123\n");
fclose($fp);
/* The filter only applies to the $fp stream
* so this readfile will read -without- applying
* a second pass of rot13 encoding
*/
readfile("foo-bar.txt");
/* Output
* ------
Yvar1
Jbeq - 2
Rnfl Nf 123
*/
?></PRE
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>
</P
><P
> See Also:
<A
HREF="function.stream-register-wrapper.html"
><B
CLASS="function"
>stream_register_wrapper()</B
></A
>,
<A
HREF="function.stream-filter-prepend.html"
><B
CLASS="function"
>stream_filter_prepend()</B
></A
>, and
<A
HREF="function.stream-filter-append.html"
><B
CLASS="function"
>stream_filter_append()</B
></A
>
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