README.md

OpenTracing-Java 0.30 compatibility layer.

The opentracing-v030 artifact provides a 0.30 API compatibility layer which comprises:

1. Exposing all the the 0.30 packages under io.opentracing.v_030 (io.opentracing.v_030.propagation, io.opentracing.v_30.util, etc).
2. A Shim layer to wrap 0.31 Tracer and expose it under the 0.30 API.

Shim Layer

The basic shim layer is exposed through TracerShim, which wraps a io.opentracing.Tracer object and exposes it under the io.opentracing.v_030.Tracer interface:

import io.opentracing.v_030.ActiveSpan;
import io.opentracing.v_030.Tracer;
import io.opentracing.v_030.shim.TracerShim;

io.opentracing.Tracer upstreamTracer = new CustomTracer(..., new CustomScopeManager());
Tracer tracer = new TracerShim(yourUpstreamTracer);

Continuation support.

TracerShim does not support ActiveSpan.capture() nor Continuations. For this usage, AutoFinishTracerShim must be used, along io.opentracing.util.AutoFinishScopeManager as Tracer.scopeManager() (which uses thread-local storage and preserves the reference-count system used in 0.30).

import io.opentracing.v_030.ActiveSpan;
import io.opentracing.v_030.Tracer;
import io.opentracing.v_030.shim.AutoFinishTracerShim;
import io.opentracing.util.AutoFinishScopeManager;

io.opentracing.Tracer upstreamTracer = new CustomTracer(..., new AutoFinishScopeManager());
Tracer tracer = new TracerShim(yourUpstreamTracer);

try (ActiveSpan span = tracer.buildSpan("parent").startActive()) {
    ActiveSpan.Continuation cont = span.capture();
    ...
}

Integration with existing instrumentation code.

To support code being instrumented using the 0.30 API it is required to update the import statements (probably with the help of a refactoring tool) from io.opentracing to io.opentracing.v_030:

import io.opentracing.v_030.Tracer; // Previously io.opentracing.Tracer
import io.opentracing.v_030.Span; // Previously io.opentracing.Span

This is done as io.opentracing refers to the new 0.31 API. It is possible to keep both API versions working side by side with help of the Shim layer, allowing an incremental adoption of the new API:

import io.opentracing.v_030.Tracer;

io.opentracing.Tracer upstreamTracer = ...;
Tracer tracer = new TracerShim(tracer);

class Engine {
    public void getResult(Object input) {
        try (ActiveSpan span = tracer.buildSpan("engine-result").startActive()) {
            Object proxyResult = proxyCall(input);
	    // Do something with proxyResult...

            span.setTag("processed-value", processedValue.toString());
            return processedValue;
        }
    }

    Object proxyCall(Object input) {
        // Will implicitly use the active Span crated in getResult() as the active/parent Span.
        try (Scope scope = upstreamTracer.buildSpan("engine-proxy-call").startActive(true)) {
            Object result = library.invoke(input);
            scope.span().setTag("proxy-value", result.toString());
            return result;
        }
    }
}

Instead of keeping both 0.30 and 0.31 Tracerss around, it's possible to register them using the GlobalTracer classes:

void init() {
    io.opentracing.Tracer upstreamTracer = ...;
    io.opentracing.v_030.Tracer tracer = new TracerShim(upstreamTracer);

    io.opentracing.util.GlobalTracer.register(upstreamTracer);
    io.opentracing.v_030.util.GlobalTracer.register(tracer);
}

Now both GlobalTracer instances will refer to the same Tracer, and can be used anywhere.

Formats

The builtin TEXT_MAP, HTTP_HEADERS and BINARY formats will be automatically translated by the Shim layer. No support exist for custom formats at the moment, however.

Extending the Shim layer

When the Shim layer is required without the reference-count system, it's possible to provide a custom class extending TracerShim, which will need to provide a custom ActiveSpanShim instance upon Span activation:

import io.opentracing.v_030.ActiveSpan;
import io.opentracing.v_030.Tracer;
import io.opentracing.v_030.shim.TracerShim;


public class CustomTracerShim extends TracerShim {
    public CustomTracerShim(io.opentracing.Tracer tracer) {
        super(tracer);
    }

    @Override
    public ActiveSpanShim createActiveSpanShim(Scope scope) {
        return CustomActiveSpanShim(scope);
    }

    static final class CustomActiveSpanShim extends ActiveSpanShim {
        public CustomActiveSpanShim(Scope scope) {
            super(scope);
        }

        @Override
        public Continuation capture() {
            ...
        }
    }
}

The returned ActiveSpanShim instance must react properly to ActiveSpan.capture() and return a ActiveSpan.Continuation object than can later be reactivated. Observe the default implementation of ActiveSpanShim.capture() throws UnsupportedOperationException.

Contributing

See Contributing for matters such as license headers.