README

A PSR-3 / Monolog writer for the PHPdot observability engine.

psr-bridge is a backend for phpdot/logs. It implements the engine's WriterInterface and forwards every record — a log line or a finished span — to an injected PSR-3 logger (Monolog, or any other). It owns no trace identity and writes no files; it is the adapter that lets the engine speak to the entire PSR-3 ecosystem.

It is a peer of phpdot/tracelog (the file backend). An application binds exactly one of them as its WriterInterface; the packages that log never know which. Because it depends only on contracts and psr/log — never on tracelog — a Monolog-only app installs {contracts, logs, psr-bridge} and never pulls the file writer or its OpenSSL/encryption code.

Where it fits

   your packages          the engine               the backend (the app binds one)
   ─────────────          ──────────               ───────────────────────────────
   $tracer->info(...)  →   phpdot/logs          →  ┌─ tracelog    → encrypted files
   $tracer->error(...)     builds a correlated      ├─ Psr3Writer  → any PSR-3 logger ─→ Monolog handlers
   $span->...              record per call          └─ NullWriter  → discarded            (Slack, syslog, files, …)

Install

composer require phpdot/psr-bridge monolog/monolog

(monolog/monolog is a suggestion, not a hard dependency — any PSR-3 logger works.)

Quick start

Bind Psr3Writer as the engine's WriterInterface, pointed at any PSR-3 logger:

use PHPdot\Contracts\Logs\WriterInterface;
use PHPdot\PsrBridge\Psr3Writer;
use Monolog\Logger;
use Monolog\Handler\StreamHandler;

$container->set(WriterInterface::class, static fn () =>
    new Psr3Writer(
        (new Logger('app'))->pushHandler(new StreamHandler('php://stdout')),
    ),
);

Your packages keep logging against TracerInterface — only this binding changes. From here, everything the engine emits flows through your Monolog handler stack (Slack, syslog, Elasticsearch, rotating files, …).

How records map

The engine hands the writer a flat array<string, mixed>. Psr3Writer translates it to a PSR-3 log($level, $message, $context) call:

Log records

Forwarded at their own level, with the trace correlation attached to the PSR-3 context:

$tracer->channel('http')->warning('slow upstream', ['ms' => 820]);

// reaches the PSR-3 logger as:
$logger->log('warning', 'slow upstream', [
    'ms'       => 820,
    'channel'  => 'http',
    'trace_id' => '019f15…',
    'span_id'  => 'c17527…',
]);

The engine's level token is validated against the eight PSR-3 levels; an unknown token falls back to info.

Span records

A finished span becomes one line — span <name> — at info, or error when the span's status is error, with its metadata in the context:

$logger->log('info', 'span db.query', [
    'channel' => 'db', 'trace_id' => '019f15…', 'span_id' => 'a1b2c3…',
    'parent_span_id' => 'c17527…', 'kind' => 'client', 'duration_ms' => 4.2,
    'status' => 'ok', 'status_message' => '', 'attributes' => ['db.rows' => 5], 'events' => [],
]);

So even on a backend that has no concept of spans, the full span tree is preserved as correlated log lines you can group by trace_id.

Trace correlation

channel, trace_id, and span_id are always added to the PSR-3 context, so every line a downstream handler sees carries the trace — group by trace_id in your log aggregator to reassemble a request.

Crash-safety & no sampling

Never throws: write() wraps the forward in a single try/catch. A misbehaving logger (a dead socket, a full disk) is swallowed so logging can never bring down the caller or the coroutine-end span flush. This is the only try/catch — it is crash-safety, never a drop decision.
No sampling: every record received is forwarded. Sampling/retention is left to your Monolog handlers, not decided here.

Any PSR-3 logger

Nothing here is Monolog-specific — Psr3Writer takes a Psr\Log\LoggerInterface. Bind Laminas, Symfony's logger, a test spy, or your own:

new Psr3Writer($anyPsr3Logger);

Package structure

src/
└── Psr3Writer.php   WriterInterface → PSR-3: level mapping, span→line, trace correlation, crash-safety

Development

composer test        # PHPUnit (24 tests)
composer analyse     # PHPStan level 10 + strict rules
composer cs-check    # PHP-CS-Fixer (@PER-CS2.0)
composer check       # all three

Requirements

PHP >= 8.4
psr/log ^3.0
A PSR-3 logger (e.g. monolog/monolog ^3.0)

License

MIT

phpdot / psr-bridge

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