README

PHP library for the OpenTracing's API.

Required Reading

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

Installation

OpenTracing-PHP can be installed via Composer:

composer require opentracing/opentracing

Usage

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

Singleton initialization

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

    use OpenTracing\GlobalTracer;
    use AnOpenTracingImplementation\MyTracer;
    
    GlobalTracer::set(new MyTracer());

Creating a Span given an existing Request

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

    use OpenTracing\Formats;
    use OpenTracing\GlobalTracer;

    ...

    $spanContext = GlobalTracer::get()->extract(
        Formats\HTTP_HEADERS,
        $request->getHeaders()
    );
    
    function doSomething(SpanContext $spanContext, ...) {
        ...
        
        $span = GlobalTracer::get()->startSpan('my_span', [
        	'child_of' => $spanContext,
        ]);
        
        ...
        
        $span->log([
            'event' => 'soft error',
            'type' => 'cache timeout',
            'waiter.millis' => 1500,
        ])
        
        $span->finish();
    }

Starting an empty trace by creating a "root span"

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

    $span = $tracer->startSpan('my_span');
    ...
    $span->finish();

Creating a (child) Span given an existing (parent) Span

    function xyz(Span $parentSpan, ...) {
        ...
        $span = GlobalTracer::get()->startSpan(
        	'my_span',
        	[
        		'child_of' => $parentSpan,
        	]
        );
        
        $span->finish();
        ...
    }

Serializing to the wire

    use OpenTracing\GlobalTracer;
    use OpenTracing\Formats;
    
    ...
    
    $tracer = GlobalTracer::get(); 
    
    $spanContext = $tracer->extract(
        Formats\HTTP_HEADERS,
        $request->getHeaders()
    );
    
    try {
        $span = $tracer->startSpan('my_span', ['child_of' => $spanContext]);

        $client = new GuzzleHttp\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) {
        ...
    }
    ...        

Deserializing from the wire

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

    use OpenTracing\GlobalTracer;
    use OpenTracing\Formats;
    
    $request = Request::createFromGlobals();
    $tracer = GlobalTracer::get();
    $spanContext = $tracer->extract(Formats\HTTP_HEADERS, $request->getHeaders());
    $tracer->startSpan('my_span', [
        'child_of' => $spanContext,
    ]); 

Flushing Spans

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;

// Do application work, buffer spans in memory
$application->run();

fastcgi_finish_request();

$tracer = GlobalTracer::get();
$tracer->flush(); // release buffer to backend

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.

Using Span Options

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

Propagation Formats

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.

Coding Style

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