fastjson

Fast JSON encode, decode, and validate for PHP 8.3+. Drop-in alternative to ext/json with a namespaced fastjson_* API and json_last_error-compatible error reporting. Backed by yyjson 0.12.0, one of the fastest portable JSON libraries. Coexists with ext/json; adoption is opt-in per call site.

Status: pre-release. yyjson 0.12.0 is vendored and linked. The full fastjson_encode / fastjson_decode / fastjson_validate trio plus fastjson_last_error / _msg are available. The compat harness against php-src/ext/json/tests/*.phpt passes everything targeting features fastjson aims to mirror; the rest is categorized in tests/upstream-json/.skiplist.

📦 Install

# PIE (PHP Foundation's extension installer; uses the composer.json
# at the repo root with type: "php-ext")
pie install iliaal/fastjson

On a minimal PHP image (e.g. php:8.x-cli from Docker Hub), PIE needs a few build tools installed first:

# Debian/Ubuntu
sudo apt install -y git bison libtool-bin

# macOS
brew install bison libtool

From source

git clone https://github.com/iliaal/fastjson.git
cd fastjson
phpize && ./configure --enable-fastjson
make -j
sudo make install
echo 'extension=fastjson.so' | sudo tee /etc/php/conf.d/fastjson.ini

Windows binaries

Pre-built DLLs for PHP 8.3, 8.4, and 8.5 (TS/NTS, x86/x64) are attached to each GitHub release.

🛠️ Usage

$json = fastjson_encode(['hello' => 'world']);     // string|false
$data = fastjson_decode($json, assoc: true);        // mixed
$ok   = fastjson_validate($json);                   // bool

if ($data === null && fastjson_last_error() !== 0) {
    fwrite(STDERR, fastjson_last_error_msg());
}

Function signatures track ext/json so call sites migrate by search-and-replace from json_* to fastjson_*. PHP 8.4 property hooks and JsonSerializable are honored.

Encode flags: JSON_PRETTY_PRINT, JSON_UNESCAPED_SLASHES, JSON_UNESCAPED_UNICODE, JSON_FORCE_OBJECT, JSON_HEX_TAG, JSON_HEX_AMP, JSON_HEX_APOS, JSON_HEX_QUOT, JSON_NUMERIC_CHECK, JSON_PRESERVE_ZERO_FRACTION, JSON_PARTIAL_OUTPUT_ON_ERROR, JSON_INVALID_UTF8_IGNORE, JSON_INVALID_UTF8_SUBSTITUTE, JSON_THROW_ON_ERROR.

Decode flags: JSON_OBJECT_AS_ARRAY, JSON_BIGINT_AS_STRING, JSON_INVALID_UTF8_IGNORE, JSON_INVALID_UTF8_SUBSTITUTE, JSON_THROW_ON_ERROR.

Validate flags: JSON_INVALID_UTF8_IGNORE (other bits raise ValueError per ext/json's contract).

See CHANGELOG.md for the full feature list and the divergences from ext/json that fastjson does not aim to mirror byte-for-byte.

📊 Performance

Throughput vs ext/json on the full 14.8 MB / 15-file canonical corpus from simdjson_php's jsonexamples. i9-13950HX, release build of both PHP and fastjson (-O2, Debug Build => no):

Operation	fastjson	ext/json	speedup
Decode (stdClass)	602 MB/s	227 MB/s	2.66x
Decode (assoc array)	628 MB/s	237 MB/s	2.65x
Encode	1,092 MB/s	180 MB/s	6.06x
Validate	1,352 MB/s	265 MB/s	5.10x

A visual side-by-side including ext/json + PR-120 (SIMD encode) and simdjson_php on the same PHP 8.6.0-dev build is published at iliaal.github.io/fastjson. Methodology, per-file numbers, small-corpus + per-call latency breakdown, and how to reproduce: bench/README.md and bench/baseline.md.

Memory tradeoff

fastjson trades memory for speed on decode (yyjson's two-stage parser holds the doc alongside the zval tree). Decode peak is ~1.7x ext/json's heap. Encode runs one-stage (direct-write into smart_str using yyjson primitives) so encode memory is at near-parity with ext/json (~1.1x). Validate peaks at ~101x: lower than ext/json's true streaming validator (constant ~80 bytes) but already 2.7x better than yyjson's stock read path thanks to vendor patch P-002. See vendor/yyjson/PATCHES.md. For most callers the speedup is worth the memory headroom; if you're validate-heavy on giant inputs in tight memory_limit settings, it's a real consideration.

✨ What's in the box

• Bundled yyjson 0.12.0 (MIT) with three local patches submitted upstream as ibireme/yyjson #263, #264, #265, #266. Full notes in vendor/yyjson/PATCHES.md.
• yyjson allocator routes every malloc/realloc/free through Zend's emalloc/erealloc/efree. JSON allocations participate in memory_limit accounting and request-scoped cleanup.
• FASTJSON_ERROR_* constants intentionally match JSON_ERROR_* byte-for-byte, so callers can use either set.
• 62-test compat harness rewritten from php-src/ext/json/tests/*.phpt runs alongside the native phpt suite. tests/upstream-json/.skiplist and tests/upstream-json/STATE.md track which upstream tests fastjson does not aim to pass byte-for-byte.
• Depth and stack-overflow guards on encode and decode via zend_call_stack_overflowed. Deeply chained inputs fail cleanly instead of being killed by the OS.

Roadmap

• fastjson_validate success-path depth enforcement (currently argument-validated but the cap is not walked, since yyjson's validate-only mode has no parse-time depth flag and a post-parse walk halves the success-path throughput)
• Streaming / incremental decode and encode

🔗 PHP Performance Toolkit

Companion native PHP extensions for high-throughput PHP workloads:

• php_excel: native Excel I/O. 7-10x faster than PhpSpreadsheet, full XLS/XLSX with formulas, formatting, and styling. Powered by LibXL.
• mdparser: native CommonMark + GFM parser. 15-30x faster than pure-PHP alternatives, 652/652 spec examples pass.
• php_clickhouse: native ClickHouse client speaking the wire protocol directly. Picks up where SeasClick left off.
• fastchart: native chart-rendering extension. 19 chart types behind one fluent OO API; composes with caller-owned \GdImage canvases.

License

• Wrapper code (fastjson*.c, php_fastjson.h) under BSD 3-Clause.
• Bundled yyjson sources under MIT. Upstream LICENSE preserved verbatim and surfaced in Section 2 of the project LICENSE file.

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