Cause clause error in otel_telemetry.erl

[AndrewDryga]

Here is an issue we saw in our production logs:

Handler :opentelemetry_cowboy_handlers has failed and has been detached. Class=:error
Reason={:case_clause, []}
Stacktrace=[
  {:otel_telemetry, :peek_from_tracer_stack, 1,
   [file: ~c"src/otel_telemetry.erl", line: 99]},
  {:otel_telemetry, :set_current_telemetry_span, 2,
   [file: ~c"src/otel_telemetry.erl", line: 49]},
  {:opentelemetry_cowboy, :handle_event, 4,
   [
     file: ~c"/app/deps/opentelemetry_cowboy/src/opentelemetry_cowboy.erl",
     line: 53
   ]},
  {:telemetry, :"-execute/3-fun-0-", 4,
   [file: ~c"/app/deps/telemetry/src/telemetry.erl", line: 160]},
  {:lists, :foreach_1, 2, [file: ~c"lists.erl", line: 1686]},
  {:cowboy_metrics_h, :terminate, 3,
   [file: ~c"/app/deps/cowboy/src/cowboy_metrics_h.erl", line: 302]},
  {:cowboy_stream, :terminate, 3,
   [file: ~c"/app/deps/cowboy/src/cowboy_stream.erl", line: 138]},
  {:cowboy_http, :stream_call_terminate, 4,
   [file: ~c"/app/deps/cowboy/src/cowboy_http.erl", line: 1391]}
]

It only happened twice in the last week so there must be some rare edge case we need to handle.

Deps used:

❯ mix deps | grep opentelemetry
* opentelemetry 1.4.0 (Hex package) (rebar3)
  locked at 1.4.0 (opentelemetry) 50b32ce1
* opentelemetry_api 1.3.0 (Hex package) (mix)
  locked at 1.3.0 (opentelemetry_api) b9e5ff77
* opentelemetry_cowboy 0.3.0 (Hex package) (rebar3)
  locked at 0.3.0 (opentelemetry_cowboy) 4f44537b
* opentelemetry_ecto 1.2.0 (Hex package) (mix)
  locked at 1.2.0 (opentelemetry_ecto) 70dfa2e7
* opentelemetry_exporter 1.7.0 (Hex package) (rebar3)
  locked at 1.7.0 (opentelemetry_exporter) d0f25f64
* opentelemetry_finch 0.2.0 (Hex package) (mix)
  locked at 0.2.0 (opentelemetry_finch) 7364f708
* opentelemetry_liveview 1.0.0-rc.4 (Hex package) (mix)
  locked at 1.0.0-rc.4 (opentelemetry_liveview) e06ab69d
* opentelemetry_logger_metadata 0.1.0 (Hex package) (mix)
  locked at 0.1.0 (opentelemetry_logger_metadata) 772976d3
* opentelemetry_phoenix 1.2.0 (Hex package) (mix)
  locked at 1.2.0 (opentelemetry_phoenix) acab991d
* opentelemetry_process_propagator 0.3.0 (Hex package) (mix)
  locked at 0.3.0 (opentelemetry_process_propagator) 7243cb6d
* opentelemetry_semantic_conventions 0.2.0 (Hex package) (mix)
  locked at 0.2.0 (opentelemetry_semantic_conventions) d61fa1f5
* opentelemetry_telemetry 1.0.0 (Hex package) (mix)
  locked at 1.0.0 (opentelemetry_telemetry) 3401d13a

Versions:

elixir -v
Erlang/OTP 26 [erts-14.2.2] [source] [64-bit] [smp:10:10] [ds:10:10:10] [async-threads:1] [jit]

Elixir 1.16.2 (compiled with Erlang/OTP 26)