denoland/deno · warning

Failed to inject with ${propagator.constructor.name}.

Error message

Failed to inject with ${propagator.constructor.name}.

What it means

Deno's vendored OpenTelemetry SDK (ext/telemetry/telemetry.ts) wraps CompositePropagator.inject: each registered propagator runs inside try/catch, and a throw is reduced to this warning carrying the propagator's constructor name and the error, then the loop continues with the remaining propagators. Trace/context headers may be partially or fully missing from outgoing carriers afterwards.

Source

Thrown at ext/telemetry/telemetry.ts:1829

        ArrayPrototypeReduce(
          ArrayPrototypeMap(
            this.#propagators,
            (p) => p.fields(),
          ),
          (x, y) => ArrayPrototypeConcat(x, y),
          [],
        ),
      ),
    );
  }

  inject(context: Context, carrier: unknown, setter: TextMapSetter): void {
    for (const propagator of new SafeArrayIterator(this.#propagators)) {
      try {
        propagator.inject(context, carrier, setter);
      } catch (err) {
        // deno-lint-ignore no-console
        console.warn(
          `Failed to inject with ${propagator.constructor.name}.`,
          err,
        );
      }
    }
  }

  extract(context: Context, carrier: unknown, getter: TextMapGetter): Context {
    return ArrayPrototypeReduce(this.#propagators, (ctx, propagator) => {
      try {
        return propagator.extract(ctx, carrier, getter);
      } catch (err) {
        // deno-lint-ignore no-console
        console.warn(
          `Failed to extract with ${propagator.constructor.name}.`,
          err,
        );
      }

View on GitHub (pinned to a961cdec3b)

Solutions

1. Inspect the err logged right after the message; invalid trace/span ids are the most common cause
2. Build contexts only through the otel API (trace.setSpan, valid SpanContext objects) instead of assembling ids manually
3. Upgrade Deno, since fixes to the vendored propagators land in runtime releases
4. If a custom propagator is registered, unit-test its inject() against your exact carrier and setter types before registration

Example fix

// before: hand-built context with a bad trace id -> propagator.inject throws, warning logged
const ctx = trace.setSpan(ROOT_CONTEXT, { spanContext: { traceId: "xyz", spanId: "1", ... } });
propagator.inject(ctx, outgoingHeaders, defaultSetter);

// after: use the API to build valid contexts
const span = tracer.startSpan("out");
propagator.inject(trace.setSpan(ROOT_CONTEXT, span), outgoingHeaders, defaultSetter);
span.end();

// verify the active context is injectable before propagating
const span = trace.getSpan(activeContext);
const sc = span?.spanContext();
const safeContext = sc && /^[\da-f]{32}$/.test(sc.traceId) && /^[\da-f]{16}$/.test(sc.spanId)
  ? activeContext
  : ROOT_CONTEXT;
propagator.inject(safeContext, carrier, setter);

function hasValidTrace(ctx: Context): boolean {
  const sc = trace.getSpan(ctx)?.spanContext();
  return !!sc && /^[\da-f]{32}$/.test(sc.traceId) && /^[\da-f]{16}$/.test(sc.spanId) && sc.traceFlags !== undefined;
}

// never let a broken propagator take down the request path
try {
  propagator.inject(context, carrier, setter);
} catch (err) {
  diag.warn?.("trace inject failed; continuing without propagation", err);
}

When it happens

Trigger: Calling the inject path (directly or via automatic outbound instrumentation) while the active Context holds an invalid SpanContext (malformed traceId/spanId, usually from hand-built contexts or custom samplers), or a registered custom propagator throwing against the supplied carrier/setter. W3CTraceContextPropagator and B3 variants are the usual constructor names in the message.

Common situations: Hand-crafted trace ids that are the wrong length or contain non-hex characters; custom propagators registered via propagation.setGlobalPropagator that assume a header-map carrier but receive something else; context lost/reset mid-request leaving inconsistent state; SDK version drift after Deno upgrades.

Related errors

• Failed to extract with ${propagator.constructor.name}.
• TracerProvider can not be constructed
• startActiveSpan requires a function argument
• vsock is not supported on this platform
• invalid vsock addr

AI-assisted analysis of denoland/deno@a961cdec3b (2026-08-20). Data as JSON: /api/errors/5c88ccede0e946b3. Report an issue: GitHub.