Milpa Event Store

A tiny append-only event log for the Milpa PHP framework, with zero package dependencies. Append events, replay a stream, project state from the fold. Two interchangeable stores — file (JSONL) and in-memory — behind one EventStoreInterface. The persistence primitive under Milpa's event-sourced process engine.

milpa/event-store is the smallest possible seam onto an append-only log: an Event is an immutable fact — streamId, type, payload, seq — and a store's only two jobs are "append durably" and "read a stream back in order". No ORM, no serializer, no framework coupling — construct a store with a path (or nothing at all) and call append().

Install

composer require milpa/event-store

Quick example

use Milpa\EventStore\Event;
use Milpa\EventStore\FileEventStore;

$store = new FileEventStore('/var/data/orders.jsonl');

// Append: nextSeq() hands out the store-wide monotonic counter, one call per event.
$store->append(new Event('order-42', 'OrderPlaced', ['total' => 19.99], $store->nextSeq()));
$store->append(new Event('order-42', 'OrderShipped', ['carrier' => 'DHL'], $store->nextSeq()));

// Replay: every event for one stream, in ascending seq order — never other streams' events.
foreach ($store->replay('order-42') as $event) {
    printf("#%d %s %s\n", $event->seq, $event->type, json_encode($event->payload));
}
// #1 OrderPlaced {"total":19.99}
// #2 OrderShipped {"carrier":"DHL"}

$store->streams();  // ["order-42"]
$store->nextSeq();  // 3 — one past the highest seq in the store, across every stream

Project current state by folding the replayed events yourself — the store never stores state, only the facts it was told:

$state = array_reduce(
    $store->replay('order-42'),
    static fn (array $state, Event $event): array => match ($event->type) {
        'OrderPlaced' => [...$state, 'status' => 'placed', 'total' => $event->payload['total']],
        'OrderShipped' => [...$state, 'status' => 'shipped', 'carrier' => $event->payload['carrier']],
        default => $state,
    },
    [],
);
// ['status' => 'shipped', 'total' => 19.99, 'carrier' => 'DHL']

Two stores, one interface

Store	Durability	Use it for
FileEventStore	Appends one JSON line per event to a flat file, under an exclusive flock() so concurrent appenders never interleave partial lines. nextSeq() and replay() both re-derive their answer from the file itself — a fresh instance pointed at the same path, in a different process or a different request, agrees with every other instance about both "what happened" and "what comes next".	Real persistence — the process engine's durable log.
InMemoryEventStore	An in-process array. Nothing is written to disk; nothing survives past the instance's lifetime.	Tests, and zero-file consumers that don't need durability.

Both implement the same four-method EventStoreInterface (append(), replay(), nextSeq(), streams()), verified by one shared contract test suite (EventStoreContractTestCase) so behavior — sequencing, stream isolation, replay order — never drifts between the two.

Requirements

• PHP ≥ 8.3
• Nothing else — milpa/event-store has no package dependencies, Milpa or otherwise

Documentation

Full API reference: getmilpa.github.io/event-store — generated straight from the source DocBlocks and dressed with the Milpa design system.

Contributing

Contributions are welcome — see CONTRIBUTING.md. Please report security issues via SECURITY.md, and note that this project follows a Code of Conduct.

License

Apache-2.0 © TeamX Agency.

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Milpa is designed, built, and maintained by TeamX Agency.