Tracing

The telemetry.TracerInvoker creates OpenTelemetry spans for every handler invocation.

Setup

import (
    "go.opentelemetry.io/otel"
    "github.com/isaquesb/go-event-bus/telemetry"
)

tracer := otel.Tracer("my-service")
tracerInvoker := telemetry.NewTracerInvoker(tracer)

Place it as the first invoker in the chain for complete visibility:

chain := invoker.NewChain(
    tracerInvoker,
    invoker.NewMetrics(metrics),
    // ... other invokers
)

Span Attributes

Each span includes:

Attribute	Value
`event.name`	Event’s `Name()` return value
`handler.name`	Handler identifier
Span kind	`Consumer`
Operation name	`event.handle`

On error, the span records the error and sets status to Error.

Trace Propagation

Traces are propagated across transport boundaries via the envelope:

Producer side: json.Registry.Encode() extracts TraceID and SpanID from the current span context and embeds them in the envelope
Consumer side: json.Registry.Decode() restores the remote span context from the envelope

This enables end-to-end trace correlation:

Producer Service                  Consumer Service
    │                                 │
    ├─ emit span                      │
    │  └─ encode (embed trace)        │
    │     └─ transport ──────────────→│
    │                                 ├─ decode (restore trace)
    │                                 │  └─ event.handle span (linked)
    │                                 │     └─ handler execution

NATS/JetStream Transport Spans

The NATS and JetStream buses also create producer spans:

Transport	Operation	Kind	Attributes
NatsBus	`eventbus.emit`	Producer	messaging.system, messaging.destination, event.name
NatsBus	`eventbus.emit_sync`	Producer	messaging.system, messaging.destination, event.name
JetStreamBus	`eventbus.emit`	Producer	messaging.system, messaging.destination, event.name