Stream Filters

To ease performing operations on the CSV document as it is being read from or written to, you can add PHP stream filters to the Reader and Writer objects.

Detecting stream filter support

public AbstractCsv::supportsStreamFilter(void): bool
public AbstractCsv::getStreamFilterMode(void): int

The supportsStreamFilter tells whether the stream filter API is supported by the current object whereas the getStreamFilterMode returns the filter mode used to add new stream filters to the CSV object.
The filter mode value is one of the following PHP’s constant:

Regardless of stream filter API support by a specific CSV object, getStreamFilterMode will always return a value.

use League\Csv\Reader;
use League\Csv\Writer;

$reader = Reader::createFromPath('/path/to/my/file.csv', 'r');
$reader->supportsStreamFilter(); //return true
$reader->getStreamFilterMode(); //return STREAM_FILTER_READ

$writer = Writer::createFromFileObject(new SplTempFileObject());
$writer->supportsStreamFilter(); //return false the API can not be use
$writer->getStreamFilterMode(); //return STREAM_FILTER_WRITE

A League\Csv\Exception exception will be thrown if you use the API on a object where supportsStreamFilter returns false.

Cheat sheet

Here’s a table to quickly determine if PHP stream filters works depending on how the CSV object was instantiated.

Named constructor supports stream
createFromString true
createFromPath true
createFromStream true
createFromFileObject false

Adding a stream filter

public AbstractCsv::addStreamFilter(string $filtername, mixed $params = null): self
public AbstractCsv::hasStreamFilter(string $filtername): bool

The AbstractCsv::addStreamFilter method adds a stream filter to the connection.

Each time your call addStreamFilter with the same argument the corresponding filter is registered again.

The AbstractCsv::hasStreamFilter method tells whether a specific stream filter is already attached to the connection.

use League\Csv\Reader;
use MyLib\Transcode;

stream_filter_register('convert.utf8decode', Transcode::class);
// 'MyLib\Transcode' is a class that extends PHP's php_user_filter class

$reader = Reader::createFromPath('/path/to/my/chinese.csv', 'r');
if ($reader->supportsStreamFilter()) {

$reader->hasStreamFilter('string.toupper'); //returns true
$reader->hasStreamFilter('string.tolower'); //returns false

foreach ($reader as $row) {
	// each row cell now contains strings that have been:
	// first UTF8 decoded and then uppercased

Stream filters removal

Stream filters attached with addStreamFilter are:

Conversely, stream filters added without addStreamFilter are:

use League\Csv\Reader;
use MyLib\Transcode;

stream_filter_register('convert.utf8decode', Transcode::class);
$fp = fopen('/path/to/my/chines.csv', 'r');
stream_filter_append($fp, 'string.rot13'); //stream filter attached outside of League\Csv
$reader = Reader::createFromStream($fp);
$reader->hasStreamFilter('string.rot13'); //returns false
$reader = null;
// 'string.rot13' is still attached to `$fp`
// filters added using `addStreamFilter` are removed

Bundled stream filters

The library comes bundle with two (2) stream filters: