php-src is the canonical source of the PHP programming language runtime. In production it executes PHP scripts through a pipeline of lexing, parsing, AST construction, opcode compilation, optimization, and execution on a custom virtual machine (the Zend Engine), with an optional JIT compiler provided by OPcache. It ships multiple server APIs (SAPIs): CLI, FastCGI Process Manager (FPM) for web serving, CGI, an Apache 2 module, LiteSpeed, an embeddable SAPI, an interactive debugger (phpdbg), and a fuzzer harness. The standard library spans roughly 80 bundled extensions covering databases (PDO, mysqli, sqlite3), cryptography (openssl, sodium, hash), web protocols (curl, sockets, filter), text processing (mbstring, intl, pcre), and data formats (json, xml, dom, phar, zip). The architecture is a modular C codebase. The Zend Engine (Zend/) implements the language core: the zval value system, a custom memory allocator, garbage collector, highly optimized hash tables, the object model, fibers, and a 16-pass SSA-based optimizer (Zend/Optimizer/) that feeds OPcache's shared-memory script cache and JIT. Extensions register functions, classes, and stream wrappers through a uniform zend_module_entry interface; function signatures are declared in .stub.php files and compiled into generated arginfo headers. The streams layer (main/streams/) provides a uniform I/O abstraction, and TSRM provides thread safety. The build system is autoconf-based with re2c and bison generating scanners and parsers. Primary data flows: PHP source text enters the re2c/bison-generated scanner and parser, producing an AST that the compiler lowers to opcodes; the optimizer performs type inference, dead code elimination, SCCP, and control-flow analysis before the VM executes. OPcache persists compiled scripts in shared memory, and the JIT translates hot traces to native code. Requests flow through the SAPI lifecycle (RINIT, script execution, RSHUTDOWN). Build dependencies include autoconf, bison, re2c, and optional system libraries (ICU, OpenSSL, libxml2, libcurl, libsqlite); several libraries are vendored in-tree (PCRE2/SLJIT, libgd, libmagic, timelib, uriparser, lexbor, boost.context, Keccak). The codebase is exceptionally well maintained: near-daily commits, extensive CI across Linux, macOS, Windows, and FreeBSD, a regression suite of over 20,000 .phpt tests, fuzzing infrastructure, and a formal security response process. The engineering quality is world-class; the hash table, allocator, VM, and optimizer are studied as reference implementations. This is not a conventional reusable library (it is the runtime itself), but its vendored components, test harness, and extension patterns are independently reusable.

PIE (PHP Installer for Extensions) is a CLI tool designed to replace PECL for installing PHP extensions. It downloads, builds (or downloads precompiled binaries), installs, and manages PHP extensions across Unix, macOS, and Windows platforms. The tool is distributed as a PHAR and integrates deeply with Composer for dependency resolution, package metadata, and installation workflows. Its architecture is modular, using Symfony Console for command handling, a custom DI container (Illuminate Container), and a variety of strategy patterns for platform-specific operations (e.g., INI configuration methods like phpenmod, docker-php-ext-enable, standard ini). It also includes self-update functionality with cryptographic attestation verification via GitHub CLI or OpenSSL, and supports system dependency auto-installation through package managers (apt, dnf, apk, brew). The codebase exhibits strong engineering practices: extensive unit and integration tests, Behat behavior specifications, static analysis, mutation testing, and Docker-based e2e tests across multiple Linux distributions. While many internal classes are marked @internal, the interfaces and value objects are clean and well-separated, demonstrating a high degree of craftsmanship. The project is actively maintained and appears to be the official future of PHP extension installation.