1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
use crate::PreSampledTracer;
use opentelemetry::{trace as otel, trace::TraceContextExt, Context as OtelContext, Key, KeyValue};
use std::any::TypeId;
use std::fmt;
use std::marker;
use std::time::{Instant, SystemTime};
use tracing_core::span::{self, Attributes, Id, Record};
use tracing_core::{field, Event, Subscriber};
#[cfg(feature = "tracing-log")]
use tracing_log::NormalizeEvent;
use tracing_subscriber::layer::Context;
use tracing_subscriber::registry::LookupSpan;
use tracing_subscriber::Layer;

const SPAN_NAME_FIELD: &str = "otel.name";
const SPAN_KIND_FIELD: &str = "otel.kind";
const SPAN_STATUS_CODE_FIELD: &str = "otel.status_code";
const SPAN_STATUS_MESSAGE_FIELD: &str = "otel.status_message";

/// An [OpenTelemetry] propagation layer for use in a project that uses
/// [tracing].
///
/// [OpenTelemetry]: https://opentelemetry.io
/// [tracing]: https://github.com/tokio-rs/tracing
pub struct OpenTelemetryLayer<S, T> {
    tracer: T,
    tracked_inactivity: bool,
    get_context: WithContext,
    _registry: marker::PhantomData<S>,
}

impl<S> Default for OpenTelemetryLayer<S, otel::NoopTracer>
where
    S: Subscriber + for<'span> LookupSpan<'span>,
{
    fn default() -> Self {
        OpenTelemetryLayer::new(otel::NoopTracer::new())
    }
}

/// Construct a layer to track spans via [OpenTelemetry].
///
/// [OpenTelemetry]: https://opentelemetry.io
///
/// # Examples
///
/// ```rust,no_run
/// use tracing_subscriber::layer::SubscriberExt;
/// use tracing_subscriber::Registry;
///
/// // Use the tracing subscriber `Registry`, or any other subscriber
/// // that impls `LookupSpan`
/// let subscriber = Registry::default().with(tracing_opentelemetry::layer());
/// # drop(subscriber);
/// ```
pub fn layer<S>() -> OpenTelemetryLayer<S, otel::NoopTracer>
where
    S: Subscriber + for<'span> LookupSpan<'span>,
{
    OpenTelemetryLayer::default()
}

// this function "remembers" the types of the subscriber so that we
// can downcast to something aware of them without knowing those
// types at the callsite.
//
// See https://github.com/tokio-rs/tracing/blob/4dad420ee1d4607bad79270c1520673fa6266a3d/tracing-error/src/layer.rs
pub(crate) struct WithContext(
    fn(
        &tracing::Dispatch,
        &span::Id,
        f: &mut dyn FnMut(&mut otel::SpanBuilder, &dyn PreSampledTracer),
    ),
);

impl WithContext {
    // This function allows a function to be called in the context of the
    // "remembered" subscriber.
    pub(crate) fn with_context<'a>(
        &self,
        dispatch: &'a tracing::Dispatch,
        id: &span::Id,
        mut f: impl FnMut(&mut otel::SpanBuilder, &dyn PreSampledTracer),
    ) {
        (self.0)(dispatch, id, &mut f)
    }
}

fn str_to_span_kind(s: &str) -> Option<otel::SpanKind> {
    match s {
        s if s.eq_ignore_ascii_case("server") => Some(otel::SpanKind::Server),
        s if s.eq_ignore_ascii_case("client") => Some(otel::SpanKind::Client),
        s if s.eq_ignore_ascii_case("producer") => Some(otel::SpanKind::Producer),
        s if s.eq_ignore_ascii_case("consumer") => Some(otel::SpanKind::Consumer),
        s if s.eq_ignore_ascii_case("internal") => Some(otel::SpanKind::Internal),
        _ => None,
    }
}

fn str_to_status_code(s: &str) -> Option<otel::StatusCode> {
    match s {
        s if s.eq_ignore_ascii_case("unset") => Some(otel::StatusCode::Unset),
        s if s.eq_ignore_ascii_case("ok") => Some(otel::StatusCode::Ok),
        s if s.eq_ignore_ascii_case("error") => Some(otel::StatusCode::Error),
        _ => None,
    }
}

struct SpanEventVisitor<'a>(&'a mut otel::Event);

impl<'a> field::Visit for SpanEventVisitor<'a> {
    /// Record events on the underlying OpenTelemetry [`Span`] from `bool` values.
    ///
    /// [`Span`]: opentelemetry::trace::Span
    fn record_bool(&mut self, field: &field::Field, value: bool) {
        match field.name() {
            "message" => self.0.name = value.to_string().into(),
            // Skip fields that are actually log metadata that have already been handled
            #[cfg(feature = "tracing-log")]
            name if name.starts_with("log.") => (),
            name => {
                self.0.attributes.push(KeyValue::new(name, value));
            }
        }
    }

    /// Record events on the underlying OpenTelemetry [`Span`] from `i64` values.
    ///
    /// [`Span`]: opentelemetry::trace::Span
    fn record_i64(&mut self, field: &field::Field, value: i64) {
        match field.name() {
            "message" => self.0.name = value.to_string().into(),
            // Skip fields that are actually log metadata that have already been handled
            #[cfg(feature = "tracing-log")]
            name if name.starts_with("log.") => (),
            name => {
                self.0.attributes.push(KeyValue::new(name, value));
            }
        }
    }

    /// Record events on the underlying OpenTelemetry [`Span`] from `&str` values.
    ///
    /// [`Span`]: opentelemetry::trace::Span
    fn record_str(&mut self, field: &field::Field, value: &str) {
        match field.name() {
            "message" => self.0.name = value.to_string().into(),
            // Skip fields that are actually log metadata that have already been handled
            #[cfg(feature = "tracing-log")]
            name if name.starts_with("log.") => (),
            name => {
                self.0
                    .attributes
                    .push(KeyValue::new(name, value.to_string()));
            }
        }
    }

    /// Record events on the underlying OpenTelemetry [`Span`] from values that
    /// implement Debug.
    ///
    /// [`Span`]: opentelemetry::trace::Span
    fn record_debug(&mut self, field: &field::Field, value: &dyn fmt::Debug) {
        match field.name() {
            "message" => self.0.name = format!("{:?}", value).into(),
            // Skip fields that are actually log metadata that have already been handled
            #[cfg(feature = "tracing-log")]
            name if name.starts_with("log.") => (),
            name => {
                self.0
                    .attributes
                    .push(KeyValue::new(name, format!("{:?}", value)));
            }
        }
    }
}

struct SpanAttributeVisitor<'a>(&'a mut otel::SpanBuilder);

impl<'a> SpanAttributeVisitor<'a> {
    fn record(&mut self, attribute: KeyValue) {
        debug_assert!(self.0.attributes.is_some());
        if let Some(v) = self.0.attributes.as_mut() {
            v.push(attribute);
        }
    }
}

impl<'a> field::Visit for SpanAttributeVisitor<'a> {
    /// Set attributes on the underlying OpenTelemetry [`Span`] from `bool` values.
    ///
    /// [`Span`]: opentelemetry::trace::Span
    fn record_bool(&mut self, field: &field::Field, value: bool) {
        self.record(KeyValue::new(field.name(), value));
    }

    /// Set attributes on the underlying OpenTelemetry [`Span`] from `i64` values.
    ///
    /// [`Span`]: opentelemetry::trace::Span
    fn record_i64(&mut self, field: &field::Field, value: i64) {
        self.record(KeyValue::new(field.name(), value));
    }

    /// Set attributes on the underlying OpenTelemetry [`Span`] from `&str` values.
    ///
    /// [`Span`]: opentelemetry::trace::Span
    fn record_str(&mut self, field: &field::Field, value: &str) {
        match field.name() {
            SPAN_NAME_FIELD => self.0.name = value.to_string().into(),
            SPAN_KIND_FIELD => self.0.span_kind = str_to_span_kind(value),
            SPAN_STATUS_CODE_FIELD => self.0.status_code = str_to_status_code(value),
            SPAN_STATUS_MESSAGE_FIELD => self.0.status_message = Some(value.to_owned().into()),
            _ => self.record(KeyValue::new(field.name(), value.to_string())),
        }
    }

    /// Set attributes on the underlying OpenTelemetry [`Span`] from values that
    /// implement Debug.
    ///
    /// [`Span`]: opentelemetry::trace::Span
    fn record_debug(&mut self, field: &field::Field, value: &dyn fmt::Debug) {
        match field.name() {
            SPAN_NAME_FIELD => self.0.name = format!("{:?}", value).into(),
            SPAN_KIND_FIELD => self.0.span_kind = str_to_span_kind(&format!("{:?}", value)),
            SPAN_STATUS_CODE_FIELD => {
                self.0.status_code = str_to_status_code(&format!("{:?}", value))
            }
            SPAN_STATUS_MESSAGE_FIELD => {
                self.0.status_message = Some(format!("{:?}", value).into())
            }
            _ => self.record(Key::new(field.name()).string(format!("{:?}", value))),
        }
    }
}

impl<S, T> OpenTelemetryLayer<S, T>
where
    S: Subscriber + for<'span> LookupSpan<'span>,
    T: otel::Tracer + PreSampledTracer + 'static,
{
    /// Set the [`Tracer`] that this layer will use to produce and track
    /// OpenTelemetry [`Span`]s.
    ///
    /// [`Tracer`]: opentelemetry::trace::Tracer
    /// [`Span`]: opentelemetry::trace::Span
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tracing_opentelemetry::OpenTelemetryLayer;
    /// use tracing_subscriber::layer::SubscriberExt;
    /// use tracing_subscriber::Registry;
    ///
    /// // Create a jaeger exporter pipeline for a `trace_demo` service.
    /// let tracer = opentelemetry_jaeger::new_pipeline()
    ///     .with_service_name("trace_demo")
    ///     .install_simple()
    ///     .expect("Error initializing Jaeger exporter");
    ///
    /// // Create a layer with the configured tracer
    /// let otel_layer = OpenTelemetryLayer::new(tracer);
    ///
    /// // Use the tracing subscriber `Registry`, or any other subscriber
    /// // that impls `LookupSpan`
    /// let subscriber = Registry::default().with(otel_layer);
    /// # drop(subscriber);
    /// ```
    pub fn new(tracer: T) -> Self {
        OpenTelemetryLayer {
            tracer,
            tracked_inactivity: true,
            get_context: WithContext(Self::get_context),
            _registry: marker::PhantomData,
        }
    }

    /// Set the [`Tracer`] that this layer will use to produce and track
    /// OpenTelemetry [`Span`]s.
    ///
    /// [`Tracer`]: opentelemetry::trace::Tracer
    /// [`Span`]: opentelemetry::trace::Span
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tracing_subscriber::layer::SubscriberExt;
    /// use tracing_subscriber::Registry;
    ///
    /// // Create a jaeger exporter pipeline for a `trace_demo` service.
    /// let tracer = opentelemetry_jaeger::new_pipeline()
    ///     .with_service_name("trace_demo")
    ///     .install_simple()
    ///     .expect("Error initializing Jaeger exporter");
    ///
    /// // Create a layer with the configured tracer
    /// let otel_layer = tracing_opentelemetry::layer().with_tracer(tracer);
    ///
    /// // Use the tracing subscriber `Registry`, or any other subscriber
    /// // that impls `LookupSpan`
    /// let subscriber = Registry::default().with(otel_layer);
    /// # drop(subscriber);
    /// ```
    pub fn with_tracer<Tracer>(self, tracer: Tracer) -> OpenTelemetryLayer<S, Tracer>
    where
        Tracer: otel::Tracer + PreSampledTracer + 'static,
    {
        OpenTelemetryLayer {
            tracer,
            tracked_inactivity: self.tracked_inactivity,
            get_context: WithContext(OpenTelemetryLayer::<S, Tracer>::get_context),
            _registry: self._registry,
        }
    }

    /// Sets whether or not spans metadata should include the _busy time_
    /// (total time for which it was entered), and _idle time_ (total time
    /// the span existed but was not entered).
    pub fn with_tracked_inactivity(self, tracked_inactivity: bool) -> Self {
        Self {
            tracked_inactivity,
            ..self
        }
    }

    /// Retrieve the parent OpenTelemetry [`Context`] from the current tracing
    /// [`span`] through the [`Registry`]. This [`Context`] links spans to their
    /// parent for proper hierarchical visualization.
    ///
    /// [`Context`]: opentelemetry::Context
    /// [`span`]: tracing::Span
    /// [`Registry`]: tracing_subscriber::Registry
    fn parent_context(&self, attrs: &Attributes<'_>, ctx: &Context<'_, S>) -> OtelContext {
        // If a span is specified, it _should_ exist in the underlying `Registry`.
        if let Some(parent) = attrs.parent() {
            let span = ctx.span(parent).expect("Span not found, this is a bug");
            let mut extensions = span.extensions_mut();
            extensions
                .get_mut::<otel::SpanBuilder>()
                .map(|builder| self.tracer.sampled_context(builder))
                .unwrap_or_default()
        // Else if the span is inferred from context, look up any available current span.
        } else if attrs.is_contextual() {
            ctx.lookup_current()
                .and_then(|span| {
                    let mut extensions = span.extensions_mut();
                    extensions
                        .get_mut::<otel::SpanBuilder>()
                        .map(|builder| self.tracer.sampled_context(builder))
                })
                .unwrap_or_else(OtelContext::current)
        // Explicit root spans should have no parent context.
        } else {
            OtelContext::new()
        }
    }

    fn get_context(
        dispatch: &tracing::Dispatch,
        id: &span::Id,
        f: &mut dyn FnMut(&mut otel::SpanBuilder, &dyn PreSampledTracer),
    ) {
        let subscriber = dispatch
            .downcast_ref::<S>()
            .expect("subscriber should downcast to expected type; this is a bug!");
        let span = subscriber
            .span(id)
            .expect("registry should have a span for the current ID");
        let layer = dispatch
            .downcast_ref::<OpenTelemetryLayer<S, T>>()
            .expect("layer should downcast to expected type; this is a bug!");

        let mut extensions = span.extensions_mut();
        if let Some(builder) = extensions.get_mut::<otel::SpanBuilder>() {
            f(builder, &layer.tracer);
        }
    }
}

impl<S, T> Layer<S> for OpenTelemetryLayer<S, T>
where
    S: Subscriber + for<'span> LookupSpan<'span>,
    T: otel::Tracer + PreSampledTracer + 'static,
{
    /// Creates an [OpenTelemetry `Span`] for the corresponding [tracing `Span`].
    ///
    /// [OpenTelemetry `Span`]: opentelemetry::trace::Span
    /// [tracing `Span`]: tracing::Span
    fn new_span(&self, attrs: &Attributes<'_>, id: &span::Id, ctx: Context<'_, S>) {
        let span = ctx.span(id).expect("Span not found, this is a bug");
        let mut extensions = span.extensions_mut();

        if self.tracked_inactivity && extensions.get_mut::<Timings>().is_none() {
            extensions.insert(Timings::new());
        }

        let mut builder = self
            .tracer
            .span_builder(attrs.metadata().name())
            .with_start_time(SystemTime::now())
            .with_parent_context(self.parent_context(attrs, &ctx))
            // Eagerly assign span id so children have stable parent id
            .with_span_id(self.tracer.new_span_id());

        // Record new trace id if there is no active parent span
        if !builder.parent_context.has_active_span() {
            builder.trace_id = Some(self.tracer.new_trace_id());
        }

        let builder_attrs = builder
            .attributes
            .get_or_insert(Vec::with_capacity(attrs.fields().len() + 3));

        let meta = attrs.metadata();

        if let Some(filename) = meta.file() {
            builder_attrs.push(KeyValue::new("code.filepath", filename));
        }

        if let Some(module) = meta.module_path() {
            builder_attrs.push(KeyValue::new("code.namespace", module));
        }

        if let Some(line) = meta.line() {
            builder_attrs.push(KeyValue::new("code.lineno", line as i64));
        }

        attrs.record(&mut SpanAttributeVisitor(&mut builder));
        extensions.insert(builder);
    }

    fn on_enter(&self, id: &span::Id, ctx: Context<'_, S>) {
        if !self.tracked_inactivity {
            return;
        }

        let span = ctx.span(id).expect("Span not found, this is a bug");
        let mut extensions = span.extensions_mut();

        if let Some(timings) = extensions.get_mut::<Timings>() {
            let now = Instant::now();
            timings.idle += (now - timings.last).as_nanos() as i64;
            timings.last = now;
        }
    }

    fn on_exit(&self, id: &span::Id, ctx: Context<'_, S>) {
        if !self.tracked_inactivity {
            return;
        }

        let span = ctx.span(id).expect("Span not found, this is a bug");
        let mut extensions = span.extensions_mut();

        if let Some(timings) = extensions.get_mut::<Timings>() {
            let now = Instant::now();
            timings.busy += (now - timings.last).as_nanos() as i64;
            timings.last = now;
        }
    }

    /// Record OpenTelemetry [`attributes`] for the given values.
    ///
    /// [`attributes`]: opentelemetry::trace::SpanBuilder::attributes
    fn on_record(&self, id: &Id, values: &Record<'_>, ctx: Context<'_, S>) {
        let span = ctx.span(id).expect("Span not found, this is a bug");
        let mut extensions = span.extensions_mut();
        if let Some(builder) = extensions.get_mut::<otel::SpanBuilder>() {
            values.record(&mut SpanAttributeVisitor(builder));
        }
    }

    fn on_follows_from(&self, id: &Id, follows: &Id, ctx: Context<S>) {
        let span = ctx.span(id).expect("Span not found, this is a bug");
        let mut extensions = span.extensions_mut();
        let builder = extensions
            .get_mut::<otel::SpanBuilder>()
            .expect("Missing SpanBuilder span extensions");

        let follows_span = ctx
            .span(follows)
            .expect("Span to follow not found, this is a bug");
        let mut follows_extensions = follows_span.extensions_mut();
        let follows_builder = follows_extensions
            .get_mut::<otel::SpanBuilder>()
            .expect("Missing SpanBuilder span extensions");

        let follows_context = self
            .tracer
            .sampled_context(follows_builder)
            .span()
            .span_context()
            .clone();
        let follows_link = otel::Link::new(follows_context, Vec::new());
        if let Some(ref mut links) = builder.links {
            links.push(follows_link);
        } else {
            builder.links = Some(vec![follows_link]);
        }
    }

    /// Records OpenTelemetry [`Event`] data on event.
    ///
    /// Note: an [`ERROR`]-level event will also set the OpenTelemetry span status code to
    /// [`Error`], signaling that an error has occurred.
    ///
    /// [`Event`]: opentelemetry::trace::Event
    /// [`ERROR`]: tracing::Level::ERROR
    /// [`Error`]: opentelemetry::trace::StatusCode::Error
    fn on_event(&self, event: &Event<'_>, ctx: Context<'_, S>) {
        // Ignore events that are not in the context of a span
        if let Some(span) = ctx.lookup_current() {
            // Performing read operations before getting a write lock to avoid a deadlock
            // See https://github.com/tokio-rs/tracing/issues/763
            #[cfg(feature = "tracing-log")]
            let normalized_meta = event.normalized_metadata();
            #[cfg(feature = "tracing-log")]
            let meta = normalized_meta.as_ref().unwrap_or_else(|| event.metadata());
            #[cfg(not(feature = "tracing-log"))]
            let meta = event.metadata();
            let mut otel_event = otel::Event::new(
                String::new(),
                SystemTime::now(),
                vec![
                    Key::new("level").string(meta.level().to_string()),
                    Key::new("target").string(meta.target().to_string()),
                ],
                0,
            );
            event.record(&mut SpanEventVisitor(&mut otel_event));

            let mut extensions = span.extensions_mut();
            if let Some(builder) = extensions.get_mut::<otel::SpanBuilder>() {
                if builder.status_code.is_none() && *meta.level() == tracing_core::Level::ERROR {
                    builder.status_code = Some(otel::StatusCode::Error);
                }

                if let Some(ref mut events) = builder.events {
                    events.push(otel_event);
                } else {
                    builder.events = Some(vec![otel_event]);
                }
            }
        };
    }

    /// Exports an OpenTelemetry [`Span`] on close.
    ///
    /// [`Span`]: opentelemetry::trace::Span
    fn on_close(&self, id: span::Id, ctx: Context<'_, S>) {
        let span = ctx.span(&id).expect("Span not found, this is a bug");
        let mut extensions = span.extensions_mut();
        if let Some(mut builder) = extensions.remove::<otel::SpanBuilder>() {
            if self.tracked_inactivity {
                // Append busy/idle timings when enabled.
                if let Some(timings) = extensions.get_mut::<Timings>() {
                    let busy_ns = KeyValue::new("busy_ns", timings.busy);
                    let idle_ns = KeyValue::new("idle_ns", timings.idle);

                    if let Some(ref mut attributes) = builder.attributes {
                        attributes.push(busy_ns);
                        attributes.push(idle_ns);
                    } else {
                        builder.attributes = Some(vec![busy_ns, idle_ns]);
                    }
                }
            }

            // Assign end time, build and start span, drop span to export
            builder.with_end_time(SystemTime::now()).start(&self.tracer);
        }
    }

    // SAFETY: this is safe because the `WithContext` function pointer is valid
    // for the lifetime of `&self`.
    unsafe fn downcast_raw(&self, id: TypeId) -> Option<*const ()> {
        match id {
            id if id == TypeId::of::<Self>() => Some(self as *const _ as *const ()),
            id if id == TypeId::of::<WithContext>() => {
                Some(&self.get_context as *const _ as *const ())
            }
            _ => None,
        }
    }
}

struct Timings {
    idle: i64,
    busy: i64,
    last: Instant,
}

impl Timings {
    fn new() -> Self {
        Self {
            idle: 0,
            busy: 0,
            last: Instant::now(),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use opentelemetry::trace::{SpanKind, TraceFlags};
    use std::borrow::Cow;
    use std::sync::{Arc, Mutex};
    use std::time::SystemTime;
    use tracing_subscriber::prelude::*;

    #[derive(Debug, Clone)]
    struct TestTracer(Arc<Mutex<Option<otel::SpanBuilder>>>);
    impl otel::Tracer for TestTracer {
        type Span = otel::NoopSpan;
        fn invalid(&self) -> Self::Span {
            otel::NoopSpan::new()
        }
        fn start_with_context<T>(&self, _name: T, _context: OtelContext) -> Self::Span
        where
            T: Into<Cow<'static, str>>,
        {
            self.invalid()
        }
        fn span_builder<T>(&self, name: T) -> otel::SpanBuilder
        where
            T: Into<Cow<'static, str>>,
        {
            otel::SpanBuilder::from_name(name)
        }
        fn build(&self, builder: otel::SpanBuilder) -> Self::Span {
            *self.0.lock().unwrap() = Some(builder);
            self.invalid()
        }
    }

    impl PreSampledTracer for TestTracer {
        fn sampled_context(&self, _builder: &mut otel::SpanBuilder) -> OtelContext {
            OtelContext::new()
        }
        fn new_trace_id(&self) -> otel::TraceId {
            otel::TraceId::invalid()
        }
        fn new_span_id(&self) -> otel::SpanId {
            otel::SpanId::invalid()
        }
    }

    #[derive(Debug, Clone)]
    struct TestSpan(otel::SpanContext);
    impl otel::Span for TestSpan {
        fn add_event_with_timestamp(&mut self, _: String, _: SystemTime, _: Vec<KeyValue>) {}
        fn span_context(&self) -> &otel::SpanContext {
            &self.0
        }
        fn is_recording(&self) -> bool {
            false
        }
        fn set_attribute(&mut self, _attribute: KeyValue) {}
        fn set_status(&mut self, _code: otel::StatusCode, _message: String) {}
        fn update_name(&mut self, _new_name: String) {}
        fn end_with_timestamp(&mut self, _timestamp: SystemTime) {}
    }

    #[test]
    fn dynamic_span_names() {
        let dynamic_name = "GET http://example.com".to_string();
        let tracer = TestTracer(Arc::new(Mutex::new(None)));
        let subscriber = tracing_subscriber::registry().with(layer().with_tracer(tracer.clone()));

        tracing::subscriber::with_default(subscriber, || {
            tracing::debug_span!("static_name", otel.name = dynamic_name.as_str());
        });

        let recorded_name = tracer.0.lock().unwrap().as_ref().map(|b| b.name.clone());
        assert_eq!(recorded_name, Some(dynamic_name.into()))
    }

    #[test]
    fn span_kind() {
        let tracer = TestTracer(Arc::new(Mutex::new(None)));
        let subscriber = tracing_subscriber::registry().with(layer().with_tracer(tracer.clone()));

        tracing::subscriber::with_default(subscriber, || {
            tracing::debug_span!("request", otel.kind = %SpanKind::Server);
        });

        let recorded_kind = tracer.0.lock().unwrap().as_ref().unwrap().span_kind.clone();
        assert_eq!(recorded_kind, Some(otel::SpanKind::Server))
    }

    #[test]
    fn span_status_code() {
        let tracer = TestTracer(Arc::new(Mutex::new(None)));
        let subscriber = tracing_subscriber::registry().with(layer().with_tracer(tracer.clone()));

        tracing::subscriber::with_default(subscriber, || {
            tracing::debug_span!("request", otel.status_code = ?otel::StatusCode::Ok);
        });
        let recorded_status_code = tracer.0.lock().unwrap().as_ref().unwrap().status_code;
        assert_eq!(recorded_status_code, Some(otel::StatusCode::Ok))
    }

    #[test]
    fn span_status_message() {
        let tracer = TestTracer(Arc::new(Mutex::new(None)));
        let subscriber = tracing_subscriber::registry().with(layer().with_tracer(tracer.clone()));

        let message = "message";

        tracing::subscriber::with_default(subscriber, || {
            tracing::debug_span!("request", otel.status_message = message);
        });

        let recorded_status_message = tracer
            .0
            .lock()
            .unwrap()
            .as_ref()
            .unwrap()
            .status_message
            .clone();

        assert_eq!(recorded_status_message, Some(message.into()))
    }

    #[test]
    fn trace_id_from_existing_context() {
        let tracer = TestTracer(Arc::new(Mutex::new(None)));
        let subscriber = tracing_subscriber::registry().with(layer().with_tracer(tracer.clone()));
        let trace_id = otel::TraceId::from_u128(42);
        let existing_cx = OtelContext::current_with_span(TestSpan(otel::SpanContext::new(
            trace_id,
            otel::SpanId::from_u64(1),
            TraceFlags::default(),
            false,
            Default::default(),
        )));
        let _g = existing_cx.attach();

        tracing::subscriber::with_default(subscriber, || {
            tracing::debug_span!("request", otel.kind = %SpanKind::Server);
        });

        let recorded_trace_id = tracer
            .0
            .lock()
            .unwrap()
            .as_ref()
            .unwrap()
            .parent_context
            .span()
            .span_context()
            .trace_id();
        assert_eq!(recorded_trace_id, trace_id)
    }
}