PHP library for the OpenTracing's API.

In order to understand the library, one must first be familiar with the OpenTracing project and specification more specifically.

OpenTracing-PHP can be installed via Composer:

composer require opentracing/opentracing

When consuming this library one really only need to worry about a couple of key abstractions: the Tracer::startActiveSpan and Tracer::startSpan method, the Span interface, and binding a Tracer at bootstrap time. Here are code snippets demonstrating some important use cases:

The simplest starting point is to set the global tracer. As early as possible, do:

use OpenTracing\GlobalTracer;

GlobalTracer::set(new MyTracerImplementation());

To start a new Span, you can use the startActiveSpan method.

use OpenTracing\Formats;
use OpenTracing\GlobalTracer;

...

$spanContext = GlobalTracer::get()->extract(
    Formats\HTTP_HEADERS,
    getallheaders()
);

function doSomething() {
    ...

    $span = GlobalTracer::get()->startActiveSpan('my_span', ['child_of' => $spanContext]);

    ...

    $span->log([
        'event' => 'soft error',
        'type' => 'cache timeout',
        'waiter.millis' => 1500,
    ])

    $span->finish();
}

It's always possible to create a "root" Span with no parent or other causal reference.

$span = $tracer->startActiveSpan('my_first_span');
...
$span->finish();

When using the Tracer::startActiveSpan function the underlying tracer uses an abstraction called scope manager to keep track of the currently active span.

Starting an active span will always use the currently active span as a parent. If no parent is available, then the newly created span is considered to be the root span of the trace.

Unless you are using asynchronuous code that tracks multiple spans at the same time, such as when using cURL Multi Exec or MySQLi Polling you are better of just using Tracer::startActiveSpan everywhere in your application.

The currently active span gets automatically closed and deactivated from the scope when you call $span->finish() as you can see in the previous example.

If you don't want a span to automatically close when Span::finish() is called then you must pass the option 'close_span_on_finish'=> false, to the $options argument of startActiveSpan.

An example of a linear, two level deep span tree using active spans looks like this in PHP code:

$root = $tracer->startActiveSpan('php');

    $controller = $tracer->startActiveSpan('controller');

        $http = $tracer->startActiveSpan('http');
        file_get_contents('http://php.net');
        $http->finish();

    $controller->finish();
$root->finish();

$parent = GlobalTracer::get()->startSpan('parent');

$child = GlobalTracer::get()->startSpan('child', [
    'child_of' => $parent
]);

...

$child->finish();

...

$parent->finish();

Every new span will take the active span as parent and it will take its spot.

$parent = GlobalTracer::get()->startActiveSpan('parent');

...

/*
 * Since the parent span has been created by using startActiveSpan we don't need
 * to pass a reference for this child span
 */
$child = GlobalTracer::get()->startActiveSpan('my_second_span');

...

$child->finish();

...

$parent->finish();

use GuzzleHttp\Client;
use OpenTracing\Formats;

...

$tracer = GlobalTracer::get();

$spanContext = $tracer->extract(
    Formats\HTTP_HEADERS,
    getallheaders()
);

try {
    $span = $tracer->startSpan('my_span', ['child_of' => $spanContext]);

    $client = new Client;

    $headers = [];

    $tracer->inject(
        $span->getContext(),
        Formats\HTTP_HEADERS,
        $headers
    );

    $request = new \GuzzleHttp\Psr7\Request('GET', 'http://myservice', $headers);
    $client->send($request);
    ...

} catch (\Exception $e) {
    ...
}
...

When using http header for context propagation you can use either the Request or the $_SERVER variable:

use OpenTracing\GlobalTracer;
use OpenTracing\Formats;

$tracer = GlobalTracer::get();
$spanContext = $tracer->extract(Formats\HTTP_HEADERS, getallheaders());
$tracer->startSpan('my_span', [
    'child_of' => $spanContext,
]);

PHP as a request scoped language has no simple means to pass the collected spans data to a background process without blocking the main request thread/process. The OpenTracing API makes no assumptions about this, but for PHP that might cause problems for Tracer implementations. This is why the PHP API contains a flush method that allows to trigger a span sending out of process.

use OpenTracing\GlobalTracer;

$application->run();

register_shutdown_function(function() use ($tracer) {
    /* Flush the tracer to the backend */
    $tracer = GlobalTracer::get();
    $tracer->flush();
});

This is optional, tracers can decide to immediately send finished spans to a backend. The flush call can be implemented as a NO-OP for these tracers.

Passing options to the pass can be done using either an array or the SpanOptions wrapper object. The following keys are valid:

• start_time is a float, int or \DateTime representing a timestamp with arbitrary precision.
• child_of is an object of type OpenTracing\SpanContext or OpenTracing\Span.
• references is an array of OpenTracing\Reference.
• tags is an array with string keys and scalar values that represent OpenTracing tags.

$span = $tracer->startActiveSpan('my_span', [
    'child_of' => $spanContext,
    'tags' => ['foo' => 'bar'],
    'start_time' => time(),
]);

The propagation formats should be implemented consistently across all tracers. If you want to implement your own format, then don't reuse the existing constants. Tracers will throw an exception if the requested format is not handled by them.

• Tracer::FORMAT_TEXT_MAP should represents the span context as a key value map. There is no assumption about the semantics where the context is coming from and sent to.

• Tracer::FORMAT_HTTP_HEADERS should represent the span context as HTTP header lines in an array list. For two context details "Span-Id" and "Trace-Id", the result would be ['Span-Id: abc123', 'Trace-Id: def456']. This definition can be passed directly to curl and file_get_contents.

• Tracer::FORMAT_BINARY makes no assumptions about the data format other than it is proprietary and each Tracer can handle it as it wants.

OpenTracing PHP follows the PSR-2 coding standard and the PSR-4 autoloading standard.