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Streaming CSV (Comma-Separated Values or Character-Separated Values) parser and encoder for ReactPHP.

CSV (Comma-Separated Values or less commonly Character-Separated Values) can be used to store a large number of (uniform) records in simple text-based files, such as a list of user records or log entries. CSV is not exactly a new format and has been used in a large number of systems for decades. In particular, CSV is often used for historical reasons and despite its shortcomings, it is still a very common export format for a large number of tools to interface with spreadsheet processors (such as Excel, Calc etc.). This library provides a simple streaming API to process very large CSV files with thousands or even millions of rows efficiently without having to load the whole file into memory at once.

Table of contents

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CSV format

CSV (Comma-Separated Values or less commonly Character-Separated Values) is a very simple text-based format for storing a large number of (uniform) records, such as a list of user records or log entries.

Alice,30
Bob,50
Carol,40
Dave,30

While this may look somewhat trivial, this simplicity comes at a price. CSV is limited to untyped, two-dimensional data, so there's no standard way of storing any nested structures or to differentiate a boolean value from a string or integer.

CSV allows for optional field names. Whether field names are used is application-dependant, so this library makes no attempt at guessing whether the first line contains field names or field values. For many common use cases it's a good idea to include them like this:

name,age
Alice,30
Bob,50
Carol,40
Dave,30

CSV allows handling field values that contain spaces, the delimiting comma or even newline characters (think of URLs or user-provided descriptions) by enclosing them with quotes like this:

name,comment
Alice,"Yes, I like cheese"
Bob,"Hello
World!"

Note that these more advanced parsing rules are often handled inconsistently by other applications. Nowadays, these parsing rules are defined as part of RFC 4180, however many applications started using some CSV-variant long before this standard was defined.

Some applications refer to CSV as Character-Separated Values, simply because using another delimiter (such as a semicolon or tab) is a rather common approach to avoid the need to enclose common values in quotes. This is particularly common for systems in Europe (and elsewhere) that use a comma as a decimal separator.

name;comment
Alice;Yes, I like cheese
Bob;Turn 22,5 degree clockwise

CSV files are often limited to only ASCII characters for best interoperability. However, many legacy CSV files often use ISO 8859-1 encoding or some other variant. Newer CSV files are usually best saved as UTF-8 and may thus also contain special characters from the Unicode range. The text-encoding is usually application-dependant, so your best bet would be to convert to (or assume) UTF-8 consistently.

Despite its shortcomings, CSV is widely used and this is unlikely to change any time soon. In particular, CSV is a very common export format for a lot of tools to interface with spreadsheet processors (such as Excel, Calc etc.). This means that CSV is often used for historical reasons and using CSV to store structured application data is usually not a good idea nowadays – but exporting to CSV for known applications continues to be a very reasonable approach.

As an alternative, if you want to process structured data in a more modern JSON-based format, you may want to use clue/reactphp-ndjson to process newline-delimited JSON (NDJSON) files (.ndjson file extension).

{"name":"Alice","age":30,"comment":"Yes, I like cheese"}
{"name":"Bob","age":50,"comment":"Hello\nWorld!"}

As another alternative, if you want to use a CSV-variant that avoids some of its shortcomings (and is somewhat faster!), you may want to use clue/reactphp-tsv to process Tab-Separated-Values (TSV) files (.tsv file extension).

name	age	comment
Alice	30	Yes, I like cheese
Bob	50	Hello world!

Usage

Decoder

The Decoder (parser) class can be used to make sure you only get back complete, valid CSV elements when reading from a stream. It wraps a given ReadableStreamInterface and exposes its data through the same interface, but emits the CSV elements as parsed values instead of just chunks of strings:

test,1,24
"hello world",2,48

$stdin = new React\Stream\ReadableResourceStream(STDIN);

$csv = new Clue\React\Csv\Decoder($stdin);

$csv->on('data', function (array $data) {
    // $data is a parsed element from the CSV stream
    // line 1: $data = array('test', '1', '24');
    // line 2: $data = array('hello world', '2', '48');
    var_dump($data);
});

ReactPHP's streams emit chunks of data strings and make no assumption about their lengths. These chunks do not necessarily represent complete CSV elements, as an element may be broken up into multiple chunks. This class reassembles these elements by buffering incomplete ones.

The Decoder supports the same optional parameters as the underlying str_getcsv() function. This means that, by default, CSV fields will be delimited by a comma (,), will use a quote enclosure character (") and a backslash escape character (\). This behavior can be controlled through the optional constructor parameters:

$csv = new Clue\React\Csv\Decoder($stdin, ';');

$csv->on('data', function (array $data) {
    // CSV fields will now be delimited by semicolon
});

Additionally, the Decoder limits the maximum buffer size (maximum line length) to avoid buffer overflows due to malformed user input. Usually, there should be no need to change this value, unless you know you're dealing with some unreasonably long lines. It accepts an additional argument if you want to change this from the default of 64 KiB:

$csv = new Clue\React\Csv\Decoder($stdin, ',', '"', '\\', 64 * 1024);

If the underlying stream emits an error event or the plain stream contains any data that does not represent a valid CSV stream, it will emit an error event and then close the input stream:

$csv->on('error', function (Exception $error) {
    // an error occurred, stream will close next
});

If the underlying stream emits an end event, it will flush any incomplete data from the buffer, thus either possibly emitting a final data event followed by an end event on success or an error event for incomplete/invalid CSV data as above:

$csv->on('end', function () {
    // stream successfully ended, stream will close next
});

If either the underlying stream or the Decoder is closed, it will forward the close event:

$csv->on('close', function () {
    // stream closed
    // possibly after an "end" event or due to an "error" event
});

The close(): void method can be used to explicitly close the Decoder and its underlying stream:

$csv->close();

The pipe(WritableStreamInterface $dest, array $options = array(): WritableStreamInterface method can be used to forward all data to the given destination stream. Please note that the Decoder emits decoded/parsed data events, while many (most?) writable streams expect only data chunks:

$csv->pipe($logger);

For more details, see ReactPHP's ReadableStreamInterface.

AssocDecoder

The AssocDecoder (parser) class can be used to make sure you only get back complete, valid CSV elements when reading from a stream. It wraps a given ReadableStreamInterface and exposes its data through the same interface, but emits the CSV elements as parsed assoc arrays instead of just chunks of strings:

name,id
test,1
"hello world",2

$stdin = new React\Stream\ReadableResourceStream(STDIN);

$csv = new Clue\React\Csv\AssocDecoder($stdin);

$csv->on('data', function (array $data) {
    // $data is a parsed element from the CSV stream
    // line 1: $data = array('name' => 'test', 'id' => '1');
    // line 2: $data = array('name' => 'hello world', 'id' => '2');
    var_dump($data);
});

Whether field names are used is application-dependant, so this library makes no attempt at guessing whether the first line contains field names or field values. For many common use cases it's a good idea to include them and explicitly use this class instead of the underlying Decoder.

In fact, it uses the Decoder class internally. The only difference is that this class requires the first line to include the name of headers and will use this as keys for all following row data which will be emitted as assoc arrays. After receiving the name of headers, this class will always emit a headers event with a list of header names.

$csv->on('headers', function (array $headers) {
    // header line: $headers = array('name', 'id');
    var_dump($headers);
});

This implies that the input stream MUST start with one row of header names and MUST use the same number of columns for all records. If the input stream does not emit any data, if any row does not contain the same number of columns, if the input stream does not represent a valid CSV stream or if the input stream emits an error event, this decoder will emit an appropriate error event and close the input stream.

This class otherwise accepts the same arguments and follows the exact same behavior of the underlying Decoder class. For more details, see the Decoder class.

Encoder

The Encoder (serializer) class can be used to make sure anything you write to a stream ends up as valid CSV elements in the resulting CSV stream. It wraps a given WritableStreamInterface and accepts its data through the same interface, but handles any data as complete CSV elements instead of just chunks of strings:

$stdout = new React\Stream\WritableResourceStream(STDOUT);

$csv = new Clue\React\Csv\Encoder($stdout);

$csv->write(array('test', true, 24));
$csv->write(array('hello world', 2, 48));

test,1,24
"hello world",2,48

The Encoder supports the same optional parameters as the underlying fputcsv() function. This means that, by default, CSV fields will be delimited by a comma (,), will use a quote enclosure character ("), a backslash escape character (\), and a Unix-style EOL (\n or LF). This behavior can be controlled through the optional constructor parameters:

$csv = new Clue\React\Csv\Encoder($stdout, ';');

$csv->write(array('hello', 'world'));

hello;world

If the underlying stream emits an error event or the given data contains any data that can not be represented as a valid CSV stream, it will emit an error event and then close the input stream:

$csv->on('error', function (Exception $error) {
    // an error occurred, stream will close next
});

If either the underlying stream or the Encoder is closed, it will forward the close event:

$csv->on('close', function () {
    // stream closed
    // possibly after an "end" event or due to an "error" event
});

The end(mixed $data = null): void method can be used to optionally emit any final data and then soft-close the Encoder and its underlying stream:

$csv->end();

The close(): void method can be used to explicitly close the Encoder and its underlying stream:

$csv->close();

For more details, see ReactPHP's WritableStreamInterface.

Install

The recommended way to install this library is through Composer. New to Composer?

This project follows SemVer. This will install the latest supported version:

composer require clue/reactphp-csv:^1.2

See also the CHANGELOG for details about version upgrades.

This project aims to run on any platform and thus does not require any PHP extensions and supports running on legacy PHP 5.3 through current PHP 8+ and HHVM. It's highly recommended to use the latest supported PHP version for this project.

Tests

To run the test suite, you first need to clone this repo and then install all dependencies through Composer:

composer install

To run the test suite, go to the project root and run:

vendor/bin/phpunit

License

This project is released under the permissive MIT license.

Did you know that I offer custom development services and issuing invoices for sponsorships of releases and for contributions? Contact me (@clue) for details.

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