php:// — Accessing various I/O streams
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.
php://stdin, php://stdout and
php://stderr 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 php://stdin
and later close it, you close only your copy of the descriptor-the actual
stream referenced by STDIN 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 STDIN,
STDOUT and STDERR instead of
manually opening streams using these wrappers.
php://stdin is read-only, whereas php://stdout and php://stderr are write-only.
php://input 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 php://input instead of $HTTP_RAW_POST_DATA as it does not depend on special php.ini directives. Moreover, for those cases where $HTTP_RAW_POST_DATA is not populated by default, it is a potentially less memory intensive alternative to activating always_populate_raw_post_data. php://input is not available with enctype="multipart/form-data".
Note: A stream opened with php://input can only be read once; the stream does not support seek operations. However, depending on the SAPI implementation, it may be possible to open another php://input stream and restart reading. This is only possible if the request body data has been saved. Typically, this is the case for POST requests, but not other request methods, such as PUT or PROPFIND.
php://output is a write-only stream that allows you to write to the output buffer mechanism in the same way as print and echo.
php://fd allows direct access to the given file descriptor. For example, php://fd/3 refers to file descriptor 3.
php://memory and php://temp are read-write streams that allow temporary data to be stored in a file-like wrapper. The only difference between the two is that php://memory will always store its data in memory, whereas php://temp 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 sys_get_temp_dir() function.
The memory limit of php://temp can be controlled by appending /maxmemory:NN, where NN is the maximum amount of data to keep in memory before using a temporary file, in bytes.
php://filter is a kind of meta-wrapper designed to permit the application of filters to a stream at the time of opening. This is useful with all-in-one file functions such as readfile(), file(), and file_get_contents() where there is otherwise no opportunity to apply a filter to the stream prior the contents being read.
The php://filter target takes the following parameters as part of its path. Please refer to the examples for specifics on using these parameters.
| Name | Description |
|---|---|
| resource=<stream to be filtered> | This parameter is required. It specifies the stream that you would like to filter. |
| read=<filter list to apply to read chain> | This parameter is optional. One or more filter names can be provided here, separated by the pipe character (|). |
| write=<filter list to apply to write chain> | This parameter is optional. One or more filter names can be provided here, separated by the pipe character (|). |
| <filter list to apply to both chains> | Any filter lists which are not prefixed by read= or write= will be applied to both the read and write chains as appropriate. |
| Version | Description |
|---|---|
| 5.3.6 | php://fd was added. |
| 5.1.0 | php://memory and php://temp were added. |
| 5.0.0 | php://filter was added. |
Example #1 php://temp/maxmemory
This optional parameter allows setting the memory limit before php://temp starts using a temporary file.
<?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);
?>
Example #2 php://filter/resource=<stream to be filtered>
This parameter must be located at the end of your php://filter specification and should point to the stream which you want filtered.
<?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");
?>
Example #3 php://filter/read=<filter list to apply to read chain>
This parameter takes one or more filternames separated by the pipe character |.
<?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");
?>
Example #4 php://filter/write=<filter list to apply to write chain>
This parameter takes one or more filternames separated by the pipe character |.
<?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");
?>