README

Hook0 PHP SDK

Send and verify webhooks with the extensions every distribution already ships

What is this?

The PHP SDK for Hook0, the open source Webhooks-as-a-Service platform for SaaS applications. It sends events, declares the event types your application uses, verifies the signature of a webhook you receive, and calls every operation the API declares through generated, documented types.

It reaches the network with ext-curl, verifies signatures with ext-hash, decodes documents with ext-json and mints identifiers with random_bytes, all of them shipped by every distribution of the language. Installing it never drags a package into an application that only wanted to send an event.

Features

Send events - under an ID the client mints, so a retry cannot duplicate one
Declare event types - upsert the ones your application emits, in one call
Verify signatures - HMAC-SHA256 over a bilateral clock window
The whole API, typed - one class per schema, one backed enum per closed list, one exception per problem
Bounded everywhere - attempts, backoff, timeouts, payload and answer, all yours to set
Zero dependencies - the language and its bundled extensions, nothing more

Quick Start

1. Install

composer require hook0/client

PHP 8.2 or later.

2. Send an event

<?php

use Hook0\Client;
use Hook0\Event;

$client = new Client(
    'https://app.hook0.com/api/v1',
    $applicationId,
    $token,
);

$eventId = $client->sendEvent(new Event(
    eventType: 'billing.invoice.paid',
    payload: '{"invoice": "in_123"}',
    payloadContentType: 'application/json',
    labels: ['environment' => 'production'],
));

3. Verify a webhook you receive

use Hook0\ClientError;
use Hook0\Signature;

try {
    Signature::verify(
        $request->header('X-Hook0-Signature'),
        $request->body(),
        $request->headers(),
        $subscriptionSecret,
        300.0,
    );
} catch (ClientError) {
    // answer 400, and do not act on the delivery
}

The clock window is bilateral, so a delivery dated too far ahead is refused exactly like one dated too far behind, because a window that only looked backwards is one a sender widens by dating its own delivery in the future. A header the signature covers but the request did not carry is refused before any code is computed.

Configuration

Every bound one send is held to is yours to set, and every one has a default.

Bound	Default	What it holds back
`maxAttempts`	4	requests one send issues, capped at 16 whatever a policy says
`initialBackoff`	100 ms	the ceiling of the wait before the first retry
`maxBackoff`	2 s	the ceiling no single wait between attempts crosses
`maxTotalDelay`	5 s	the budget every wait of one send shares
`requestTimeout`	10 s	how long one attempt is given
`maxPayloadBytes`	1 MiB	the payload, refused before a socket is opened
`maxResponseBytes`	8 MiB	the body read off a socket
`maxHeadBytes`	16 KiB	the head of an answer, every line taken together
`maxResponseHeaders`	64	header lines one answer may carry
`maxHeaderBytes`	64 KiB	one header line

Every default comes from clients/conformance/bounds.json, the corpus every Hook0 SDK reads. A number changed there fails every SDK still carrying the old one, so no two of them can bound different things.

The last three bound what the other end may cost you. A server that is broken or hostile can otherwise stream a head, a header or a body of any length into your process.

use Hook0\Client;
use Hook0\Options;
use Hook0\RetryPolicy;

$client = new Client(
    'https://app.hook0.com/api/v1',
    $applicationId,
    $token,
    new Options(
        retryPolicy: new RetryPolicy(
            maxAttempts: 4,
            initialBackoff: 0.1,
            maxBackoff: 2.0,
            maxTotalDelay: 5.0,
        ),
        requestTimeout: 10.0,
        maxPayloadBytes: 1024 * 1024,
        maxResponseBytes: 8 * 1024 * 1024,
    ),
);

Usage

Sending is idempotent, and retried

sendEvent sends every event under an ID it knows, either the one set on the event or a UUIDv7 it mints when the event carries none. Passing no ID does not mean the ID comes from Hook0. The value comes from the client, travels with the request, and is what sendEvent answers.

That is what makes a retry safe. Hook0 keys events on their ID, so a request repeated after a network failure or a server error ingests the event once rather than twice. Without a client-chosen ID, the repeated request would create a second event and deliver it to every subscriber.

Retrying is limited to what could end differently. A request that got no answer, a server error and an instance saying it is being reached faster than it accepts are all retried. A 429 naming a spent quota is not, because a quota clears when a plan changes or a day turns, and no send can wait for that. A Retry-After the answer carries is honoured, clamped to what is left of the delay budget. A retried request Hook0 answers with EventAlreadyIngested reports success, since an earlier attempt of that same send reached the API. The same answer to a first attempt is a genuine conflict, and is reported as an error.

Declaring the event types you use

$created = $client->upsertEventTypes([
    'billing.invoice.paid',
    'billing.invoice.voided',
]);

Only the ones your application does not declare yet are created, and those are what comes back.

Calling the rest of the API

Every operation the API declares is a method of a generated group, one group per entity.

use Hook0\Generated\ApplicationsApi;
use Hook0\Generated\NotFoundError;
use Hook0\Transport;

$applications = new ApplicationsApi(new Transport('https://app.hook0.com', $token));

try {
    $application = $applications->get($applicationId);
} catch (NotFoundError $reported) {
    // every problem the API names is its own exception, all of them `ProblemError`
}

Names travel as the API spells them

A closed list of values is a backed enum, so a value the API does not declare cannot be built at all. PHP reads what follows ->, :: and $ as a name rather than as a keyword, so a member called method, until or type is called exactly that on both sides.

Development

clients/php/src/Generated/ is written by hook0-sdkgen from the OpenAPI snapshot the API commits, and is rewritten whole on every regeneration. A hand edit there is reverted the next time anyone regenerates, and the drift guard says so before that. Change the generator, then run:

UPDATE_SDK=php cargo test -p hook0-sdkgen sdk_targets

Everything else under src/ is hand-written and never regenerated, and so is tests/.

What a send retries, the bounds it is held to and how a signature is verified are dictated by the shared corpus at clients/conformance, which every SDK's suite reads, so a verdict changed there fails this client until it agrees again.

Every case runs against a real Hook0 over a loopback socket. Nothing here stands in for a part of the client.

phpcs
phpunit --no-coverage

License

The Hook0 PHP SDK is free and open source, released under the MIT License. Use it, change it, ship it, in open source and in commercial work alike, as long as the copyright notice travels with it.

Hook0 itself is open source too. Read what Hook0 is, visit hook0.com, join the community, or write to support@hook0.com.

Maintained by David Sferruzza and François-Guillaume Ribreau.

hook0 / client

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