FD

PHP-controllable UNIX file descriptor extension built with Zephir.

The FD extension allows PHP to open raw UNIX file descriptors, enabling control beyond simple stream-based I/O. The integer descriptor can be passed into other extensions or used directly for system-level interfaces such as GPIO, I2C, SPI, and UART.

Requirements

• PHP 8.x
• A UNIX-like operating system (Linux, macOS)
• Standard C build tools (gcc, make, PHP development headers)

Installation

Via PHP PIE (recommended)

PHP PIE is the official PHP extension installer. It handles the full build and activation pipeline automatically.

Install PIE if you haven't already:

curl -Lo pie.phar https://github.com/php/pie/releases/latest/download/pie.phar
chmod +x pie.phar
sudo mv pie.phar /usr/local/bin/pie

Then install the extension:

pie install php-io-extensions/fd

PIE will build the extension from source, copy the .so into PHP's extension directory, and write the ini activation file. No Zephir required — the C source is pre-generated in the package.

Manual installation

Clone the repository and run the bundled installer script. PHP dev headers and gcc must be present; Zephir is not required.

git clone https://github.com/php-io-extensions/fd
cd fd
bash install.sh

The script builds from the pre-generated C source in ext/, installs the .so, and enables the extension across all detected SAPIs (CLI, FPM, Apache).

Verifying installation

php -m | grep fd
php --ri fd

Usage

All methods are static on the Fd\FD class.

Flags

$flags parameters accept plain integers. They map directly to the POSIX constants from fcntl.h — PHP does not define these, so pass the values directly or define your own:

Constant	Linux	macOS
O_RDONLY	0	0
O_WRONLY	1	1
O_RDWR	2	2
O_NONBLOCK	2048	4

Combine multiple flags with the bitwise OR operator (|):

// O_WRONLY | O_NONBLOCK on Linux
$fd = Fd\FD::open('/dev/ttyUSB0', 1 | 2048);

---

FD::open

Opens a file or device and returns a file descriptor integer.

$fd = Fd\FD::open(string $device_path, int $flags): int

Returns the file descriptor on success, or a negative value on failure.

// Open an I2C device for reading and writing (O_RDWR = 2)
$fd = Fd\FD::open('/dev/i2c-1', 2);

if ($fd < 0) {
    throw new RuntimeException("Failed to open device");
}

---

FD::close

Closes an open file descriptor.

$result = Fd\FD::close(int $fd): int

Returns 0 on success, -1 on failure.

Fd\FD::close($fd);

---

FD::addFlags

Adds file status flags to an open file descriptor using fcntl. Existing flags are preserved; the provided flags are OR'd in.

$result = Fd\FD::addFlags(int $fd, int $flags): int

Returns 0 on success, -1 on failure. Useful for setting a descriptor non-blocking after it has already been opened.

// Set O_NONBLOCK on an open descriptor (Linux: 2048, macOS: 4)
Fd\FD::addFlags($fd, 2048);

// Combine flags: O_NONBLOCK | O_APPEND on Linux
Fd\FD::addFlags($fd, 2048 | 1024);

---

FD::read

Reads up to $bytes_to_read bytes from a file descriptor and returns them as a string.

$data = Fd\FD::read(int $fd, int $bytes_to_read): string

Returns the bytes read as a binary string. Returns an empty string on error. A zero-length read (e.g. EOF) also returns an empty string, so callers that need to distinguish the two cases should check the descriptor state beforehand.

// Read 2 bytes from a UART device
$bytes = Fd\FD::read($fd, 2);

---

FD::write

Writes bytes to a file descriptor.

$written = Fd\FD::write(int $fd, string $data, int $bytes_to_write): int

Returns the number of bytes written on success, or -1 on failure.

// Send a command byte over SPI
Fd\FD::write($fd, "\x3A", 1);

---

Example: I2C Read/Write

// O_RDWR = 2
$fd = Fd\FD::open('/dev/i2c-1', 2);

if ($fd < 0) {
    throw new RuntimeException('Could not open I2C device');
}

// Write a register address
Fd\FD::write($fd, "\x00", 1);

// Read 2 bytes back
$data = Fd\FD::read($fd, 2);

Fd\FD::close($fd);

License

Project Saturn Studios, LLC.