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Compiling PHP

The build pipeline lives in a Dockerfile. It was originally forked from seanmorris/php-wasm

In broad strokes, that Dockerfile:

  • Installs all the necessary linux packages (like build-essential)
  • Downloads PHP and the required libraries, e.g. sqlite3.
  • Applies a few patches.
  • Compiles everything using Emscripten, a drop-in replacement for the C compiler.
  • Compiles php_wasm.c – a convenient API for JavaScript.
  • Outputs a php.wasm file and one or more JavaScript loaders, depending on the configuration.
  • Transforms the Emscripten's default php.js output into an ESM module with additional features.

To find out more about each step, refer directly to the Dockerfile.


To build all PHP versions, run nx recompile-php:all php-wasm-web (or php-wasm-node) in the repository root. You'll find the output files in packages/php-wasm/php-web/public. To build a specific version, run nx recompile-php:all php-wasm-node --PHP_VERSION=8.0.

PHP extensions

PHP is built with several extensions listed in the Dockerfile.

Some extensions, like zip, can be turned on or off during the build. Others, like sqlite3, are hardcoded.

If you need to turn off one of the hardcoded extensions, feel free to open an issue in this repo. Better yet, this project needs contributors. You are more than welcome to open a PR and author the change you need.

C API exposed to JavaScript

The C API exposed to JavaScript lives in the php_wasm.c file. The most important functions are:

  • void phpwasm_init() – It creates a new PHP context and must be called before running any PHP code.
  • int phpwasm_run(char *code) – Runs a PHP script and writes the output to /tmp/stdout and /tmp/stderr. Returns the exit code.
  • void phpwasm_refresh() – Destroy the current PHP context and starts a new one. Call it after running one PHP script and before running another.

Refer to the inline documentation in php_wasm.c to learn more.

Build configuration

The build is configurable via the Docker --build-arg feature. You can set them up through the build.js script, just run this command to get the usage message:

nx recompile-php php-wasm-web

Supported build options:

  • PHP_VERSION – The PHP version to build, default: 8.0.24. This value must point to an existing branch of the repository when prefixed with PHP-. For example, 7.4.0 is valid because the branch PHP-7.4.0 exists, but just 7 is invalid because there's no branch PHP-7. The PHP versions that are known to work are 7.4.* and 8.0.*. Others likely work as well but they haven't been tried.
  • EMSCRIPTEN_ENVIRONMENTweb or node, default: web. The platform to build for. When building for web, two JavaScript loaders will be created: php-web.js and php-webworker.js. When building for Node.js, only one loader called php-node.js will be created.
  • WITH_LIBXMLyes or no, default: no. Whether to build with libxml2 and the dom, xml, and simplexml PHP extensions (DOMDocument, SimpleXML, ..).
  • WITH_LIBZIPyes or no, default: yes. Whether to build with zlib, libzip, and the zip PHP extension (ZipArchive).
  • WITH_NODEFSyes or no, default: no. Whether to include the Emscripten's NODEFS JavaScript library. It's useful for loading files and mounting directories from the local filesystem when running php.wasm from Node.js.