php-doc-en/language/wrappers/php.xml

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<refentry xml:id="wrappers.php" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" role="noversion">
 <refnamediv>
  <refname>php://</refname>
  <refpurpose>Accessing various I/O streams</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <para>
   PHP provides a number of miscellaneous I/O streams that allow access to
   PHP's own input and output streams, the standard input, output and error
   file descriptors, in-memory and disk-backed temporary file streams, and
   filters that can manipulate other file resources as they are read from and
   written to.
  </para>

  <refsect2 xml:id="wrappers.php.std">
   <title>php://stdin, php://stdout and php://stderr</title>
   <simpara>
    <filename>php://stdin</filename>, <filename>php://stdout</filename> and
    <filename>php://stderr</filename> allow direct access to the corresponding
    input or output stream of the PHP process.  The stream references a
    duplicate file descriptor, so if you open <filename>php://stdin</filename>
    and later close it, you close only your copy of the descriptor-the actual
    stream referenced by <constant>STDIN</constant> is unaffected.  Note that
    PHP exhibited buggy behavior in this regard until PHP 5.2.1.  It is
    recommended that you simply use the constants <constant>STDIN</constant>,
    <constant>STDOUT</constant> and <constant>STDERR</constant> instead of
    manually opening streams using these wrappers.
   </simpara>
   <simpara>
    <filename>php://stdin</filename> is read-only, whereas
    <filename>php://stdout</filename> and <filename>php://stderr</filename> are
    write-only.
   </simpara>
  </refsect2>

  <refsect2 xml:id="wrappers.php.input">
   <title>php://input</title>
   <simpara>
    <filename>php://input</filename> is a read-only stream that allows you to
    read raw data from the request body. In the case of POST requests, it is
    preferable to use <filename>php://input</filename> instead of <varname>$HTTP_RAW_POST_DATA</varname> as it does not depend
    on special &php.ini; directives. Moreover, for those cases where
    <varname>$HTTP_RAW_POST_DATA</varname> is not populated by default, it is a
    potentially less memory intensive alternative to activating
    <literal>always_populate_raw_post_data</literal>.
    <filename>php://input</filename> is not available with
    <literal>enctype="multipart/form-data"</literal>.
   </simpara>
  </refsect2>

  <refsect2 xml:id="wrappers.php.output">
   <title>php://output</title>
   <para>
    <filename>php://output</filename> is a write-only stream that allows you to
    write to the output buffer mechanism in the same way as
    <function>print</function> and <function>echo</function>.
   </para>
  </refsect2>

  <refsect2 xml:id="wrappers.php.fd">
   <title>php://fd</title>
   <simpara>
    <filename>php://fd</filename> allows direct access to the given file
    descriptor. For example, <filename>php://fd/3</filename> refers to file
    descriptor 3.
   </simpara>
  </refsect2>

  <refsect2 xml:id="wrappers.php.memory">
   <title>php://memory and php://temp</title>
   <simpara>
    <filename>php://memory</filename> and <filename>php://temp</filename> are
    read-write streams that allow temporary data to be stored in a file-like
    wrapper. The only difference between the two is that
    <filename>php://memory</filename> will always store its data in memory,
    whereas <filename>php://temp</filename> will use a temporary file once the
    amount of data stored hits a predefined limit (the default is 2 MB). The
    location of this temporary file is determined in the same way as the
    <function>sys_get_temp_dir</function> function.
   </simpara>
   <simpara>
    The memory limit of <filename>php://temp</filename> can be controlled by
    appending <literal>/maxmemory:NN</literal>, where <literal>NN</literal> is
    the maximum amount of data to keep in memory before using a temporary
    file, in bytes.
   </simpara>
  </refsect2>

  <refsect2 xml:id="wrappers.php.filter">
   <title>php://filter</title>
   <simpara>
    <filename>php://filter</filename> is a kind of meta-wrapper designed to
    permit the application of <link linkend="filters">filters</link> to a
    stream at the time of opening.  This is useful with all-in-one file
    functions such as <function>readfile</function>,
    <function>file</function>, and <function>file_get_contents</function>
    where there is otherwise no opportunity to apply a filter to the stream
    prior the contents being read.
   </simpara>
   <para>
    The <filename>php://filter</filename> target takes the following parameters
    as part of its path. Multiple filter chains can be specified on one path.
    Please refer to the examples for specifics on using these parameters.
   </para>
   <para>
    <table>
     <title>php://filter parameters</title>
     <tgroup cols="2">
      <thead>
       <row>
        <entry>Name</entry>
        <entry>Description</entry>
       </row>
      </thead>
      <tbody>
       <row>
        <entry>
         <literal>resource=&lt;stream to be filtered&gt;</literal>
        </entry>
        <entry>
         This parameter is required. It specifies the stream that you would
         like to filter.
        </entry>
       </row>
       <row>
        <entry>
         <literal>read=&lt;filter list to apply to read chain&gt;</literal>
        </entry>
        <entry>
         This parameter is optional. One or more filter names can be provided
         here, separated by the pipe character (<literal>|</literal>).
        </entry>
       </row>
       <row>
        <entry>
         <literal>write=&lt;filter list to apply to write chain&gt;</literal>
        </entry>
        <entry>
         This parameter is optional. One or more filter names can be provided
         here, separated by the pipe character (<literal>|</literal>).
        </entry>
       </row>
       <row>
        <entry>
         <literal>&lt;filter list to apply to both chains&gt;</literal>
        </entry>
        <entry>
         Any filter lists which are not prefixed by <literal>read=</literal>
         or <literal>write=</literal> will be applied to both the read and
         write chains as appropriate.
        </entry>
       </row>
      </tbody>
     </tgroup>
    </table>
   </para>
  </refsect2>
 </refsect1>

 <refsect1 role="options"><!-- {{{ -->
  &reftitle.options;
  <para>
   <table>
    <title>
     Wrapper Summary (for <literal>php://filter</literal>, refer to the
     summary of the wrapper being filtered)
    </title>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>Attribute</entry>
       <entry>Supported</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>Restricted by <link linkend="ini.allow-url-fopen">allow_url_fopen</link></entry>
       <entry>No</entry>
      </row>
      <row>
       <entry>Restricted by <link linkend="ini.allow-url-include">allow_url_include</link></entry>
       <entry>
        <literal>php://input</literal>,
        <literal>php://stdin</literal>,
        <literal>php://memory</literal> and
        <literal>php://temp</literal> only.
       </entry>
      </row>
      <row>
       <entry>Allows Reading</entry>
       <entry>
        <literal>php://stdin</literal>,
        <literal>php://input</literal>,
        <literal>php://fd</literal>,
        <literal>php://memory</literal> and
        <literal>php://temp</literal> only.
       </entry>
      </row>
      <row>
       <entry>Allows Writing</entry>
       <entry>
        <literal>php://stdout</literal>,
        <literal>php://stderr</literal>,
        <literal>php://output</literal>,
        <literal>php://fd</literal>,
        <literal>php://memory</literal> and
        <literal>php://temp</literal> only.
       </entry>
      </row>
      <row>
       <entry>Allows Appending</entry>
       <entry>
        <literal>php://stdout</literal>,
        <literal>php://stderr</literal>,
        <literal>php://output</literal>,
        <literal>php://fd</literal>,
        <literal>php://memory</literal> and
        <literal>php://temp</literal> only. (Equivalent to writing)
       </entry>
      </row>
      <row>
       <entry>Allows Simultaneous Reading and Writing</entry>
       <entry>
        <literal>php://fd</literal>,
        <literal>php://memory</literal> and
        <literal>php://temp</literal> only.
       </entry>
      </row>
      <row>
       <entry>Supports <function>stat</function></entry>
       <entry>
        No.  However, <literal>php://memory</literal> and
        <literal>php://temp</literal> support <function>fstat</function>.
       </entry>
      </row>
      <row>
       <entry>Supports <function>unlink</function></entry>
       <entry>No</entry>
      </row>
      <row>
       <entry>Supports <function>rename</function></entry>
       <entry>No</entry>
      </row>
      <row>
       <entry>Supports <function>mkdir</function></entry>
       <entry>No</entry>
      </row>
      <row>
       <entry>Supports <function>rmdir</function></entry>
       <entry>No</entry>
      </row>
      <row>
       <entry>Supports <function>stream_select</function></entry>
       <entry>
        <literal>php://stdin</literal>,
        <literal>php://stdout</literal>, 
        <literal>php://stderr</literal>,
        <literal>php://fd</literal> and
        <literal>php://temp</literal> only.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </table>
  </para>
 </refsect1> <!-- }}} -->

 <refsect1 role="examples"><!-- {{{ -->
  &reftitle.examples;
  <example><!-- {{{ -->
   <title>php://temp/maxmemory</title>
   <para>
    This optional parameter allows setting the memory limit before
    <filename>php://temp</filename> starts using a temporary file.
   </para>
   <programlisting role="php">
<![CDATA[
<?php
// Set the limit to 5 MB.
$fiveMBs = 5 * 1024 * 1024;
$fp = fopen("php://temp/maxmemory:$fiveMBs", 'r+');

fputs($fp, "hello\n");

// Read what we have written.
rewind($fp);
echo stream_get_contents($fp);
?>
]]>
   </programlisting>
  </example><!-- }}} -->
  <example><!-- {{{ -->
   <title>php://filter/resource=&lt;stream to be filtered&gt;</title>
   <para>
    This parameter must be located at
    the end of your <filename>php://filter</filename> specification and
    should point to the stream which you want filtered.
   </para>
   <programlisting role="php">
<![CDATA[
<?php
/* This is equivalent to simply:
  readfile("http://www.example.com");
  since no filters are actually specified */

readfile("php://filter/resource=http://www.example.com");
?>
]]>
   </programlisting>
  </example><!-- }}} -->
  <example><!-- {{{ -->
   <title>php://filter/read=&lt;filter list to apply to read chain&gt;</title>
   <para>
    This parameter takes one or more
    filternames separated by the pipe character <literal>|</literal>.
   </para>
   <programlisting role="php">
<![CDATA[
<?php
/* This will output the contents of
  www.example.com entirely in uppercase */
readfile("php://filter/read=string.toupper/resource=http://www.example.com");

/* This will do the same as above
  but will also ROT13 encode it */
readfile("php://filter/read=string.toupper|string.rot13/resource=http://www.example.com");
?>
]]>
   </programlisting>
  </example><!-- }}} -->
  <example><!-- {{{ -->
   <title>php://filter/write=&lt;filter list to apply to write chain&gt;</title>
   <para>
    This parameter takes one or more
    filternames separated by the pipe character <literal>|</literal>.
   </para>
   <programlisting role="php">
<![CDATA[
<?php
/* This will filter the string "Hello World"
  through the rot13 filter, then write to
  example.txt in the current directory */
file_put_contents("php://filter/write=string.rot13/resource=example.txt","Hello World");
?>
]]>
   </programlisting>
  </example><!-- }}} -->
  <example>
   <title>php://memory and php://temp are not reusable</title>
   <para>
    <filename>php://memory</filename> and <filename>php://temp</filename>
    are not reusable, i.e. after the streams have been closed there is no way
    to refer to them again.
   </para>
   <programlisting role="php">
<![CDATA[
file_put_contents('php://memory', 'PHP');
echo file_get_contents('php://memory'); // prints nothing
]]>
   </programlisting>
  </example>
 </refsect1><!-- }}} -->
</refentry>

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