feat!: support sending OTEL trace data to stdout, for debugging

packages/opentelemetry-tracing-utils/CHANGELOG.md

@@ -9,6 +9,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased] - ReleaseDate
 
+## [0.8.0] - 2025-11-24
+
+### Changed
+- **BREAKING**: Support sending OTEL trace data to stdout, for debugging. This is a breaking change, as the type of `LoggingSetupBuilder` has changed.
+- Fix some new clippy warnings.
+
 ## [0.7.1] - 2025-11-21
 
 ## [0.7.0] - 2025-11-21
@@ -42,7 +48,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - make_tower_http_otel_trace_layer function, to create a tower layer that will propagate OTEL traces and also log requests.
 
 <!-- next-url -->
-[Unreleased]: https://github.com/sg60/sg-rust-utils/compare/opentelemetry-tracing-utils-v0.7.1...HEAD
+[Unreleased]: https://github.com/sg60/sg-rust-utils/compare/opentelemetry-tracing-utils-v0.8.0...HEAD
+[0.8.0]: https://github.com/sg60/sg-rust-utils/compare/opentelemetry-tracing-utils-v0.7.1...opentelemetry-tracing-utils-v0.8.0
 [0.7.1]: https://github.com/sg60/sg-rust-utils/compare/opentelemetry-tracing-utils-v0.7.0...opentelemetry-tracing-utils-v0.7.1
 [0.7.0]: https://github.com/sg60/sg-rust-utils/compare/opentelemetry-tracing-utils-v0.7.0...opentelemetry-tracing-utils-v0.7.0
 [0.7.0]: https://github.com/sg60/sg-rust-utils/compare/opentelemetry-tracing-utils-v0.6.0...opentelemetry-tracing-utils-v0.7.0

packages/opentelemetry-tracing-utils/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "opentelemetry-tracing-utils"
-version = "0.7.1"
+version = "0.8.0"
 edition.workspace = true
 license = "MIT OR Apache-2.0"
 authors.workspace = true

packages/opentelemetry-tracing-utils/src/lib.rs

@@ -41,10 +41,20 @@ pub const NO_OTLP: &str = "NO_OTLP";
 
 #[derive(Debug)]
 pub struct LoggingSetupBuilder {
-    pub otlp_output_enabled: bool,
+    pub otel_traces_exporter: OtelTracesExporterOption,
     pub pretty_logs: bool,
     pub use_test_writer: bool,
 }
+#[derive(Debug)]
+pub enum OtelTracesExporterOption {
+    /// Send traces to an OTLP endpoint
+    Otlp,
+    /// Write OTLP traces to stdout. Useful for debugging otel stuff.
+    Stdout,
+    /// Don't send OTEL traces anywhere
+    None,
+}
+
 impl Default for LoggingSetupBuilder {
     fn default() -> Self {
         let no_otlp = match std::env::var(NO_OTLP).as_deref() {
@@ -53,42 +63,37 @@ impl Default for LoggingSetupBuilder {
             Err(_) => false,
         };
 
-        let otel_traces_exporter = match std::env::var(OTEL_TRACES_EXPORTER).as_deref() {
-            Ok("otlp") => OtelTracesExporterOption::Otlp,
-            Ok("none") => OtelTracesExporterOption::None,
-            _ => OtelTracesExporterOption::Otlp,
+        let otel_traces_exporter = match no_otlp {
+            true => OtelTracesExporterOption::None,
+            false => match std::env::var(OTEL_TRACES_EXPORTER).as_deref() {
+                Ok("otlp") => OtelTracesExporterOption::Otlp,
+                Ok("none") => OtelTracesExporterOption::None,
+                Ok("stdout") => OtelTracesExporterOption::Stdout,
+                _ => OtelTracesExporterOption::Otlp,
+            },
         };
 
-        let otlp_enabled = no_otlp == false
-            && match otel_traces_exporter {
-                OtelTracesExporterOption::Otlp => true,
-                OtelTracesExporterOption::None => false,
-            };
-
         // either use the otlp state or PRETTY_LOGS env var to decide log format
         let pretty_logs = std::env::var("PRETTY_LOGS")
             .map(|e| &e == "1")
-            .unwrap_or_else(|_| !otlp_enabled);
+            // if PRETTY_LOGS is not set, and the otel traces exporter is set to none, then use
+            // pretty logs (since this is probably a dev environment)
+            .unwrap_or_else(|_| matches!(otel_traces_exporter, OtelTracesExporterOption::None));
 
         Self {
-            otlp_output_enabled: otlp_enabled,
+            otel_traces_exporter,
             pretty_logs,
             use_test_writer: false,
         }
     }
 }
 
-enum OtelTracesExporterOption {
-    Otlp,
-    None,
-}
-
 impl LoggingSetupBuilder {
     pub fn new() -> Self {
         Self::default()
     }
     pub fn build(&self) -> Result<LoggingSetupBuildResult> {
-        let otlp_enabled = self.otlp_output_enabled;
+        let otlp_enabled = &self.otel_traces_exporter;
 
         // First create 1 or more propagators
         let baggage_propagator = BaggagePropagator::new();
@@ -103,7 +108,11 @@ impl LoggingSetupBuilder {
         global::set_text_map_propagator(composite_propagator);
 
         // An exporter to be used when there is no OTLP endpoint
-        let basic_no_otlp_tracer_provider = SdkTracerProvider::builder().build();
+        let otel_tracer_provider_no_output = SdkTracerProvider::builder().build();
+        // An exporter that sends otel traces to stdout. Useful for debugging otel stuff.
+        let otel_tracer_provider_stdout = SdkTracerProvider::builder()
+            .with_simple_exporter(opentelemetry_stdout::SpanExporter::default())
+            .build();
 
         // Install a new OpenTelemetry trace pipeline
         // OTLP over GRPC tracer exporter
@@ -116,9 +125,10 @@ impl LoggingSetupBuilder {
             .build();
 
         let tracer_provider = match otlp_enabled {
-            true => otlp_tracer,
+            OtelTracesExporterOption::Otlp => otlp_tracer,
+            OtelTracesExporterOption::Stdout => otel_tracer_provider_stdout,
             // BUG: the non-otlp tracer isn't correctly setting context/linking ids
-            false => basic_no_otlp_tracer_provider,
+            OtelTracesExporterOption::None => otel_tracer_provider_no_output,
         };
         let tracer = tracer_provider.tracer(env!("CARGO_PKG_NAME"));
 

packages/opentelemetry-tracing-utils/src/trace_output_fmt.rs

@@ -22,11 +22,9 @@ impl<'a> io::Write for WriteAdaptor<'a> {
         let s =
             std::str::from_utf8(buf).map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
 
-        self.fmt_write
-            .write_str(s)
-            .map_err(|e| io::Error::new(io::ErrorKind::Other, e))?;
+        self.fmt_write.write_str(s).map_err(io::Error::other)?;
 
-        Ok(s.as_bytes().len())
+        Ok(s.len())
     }
 
     fn flush(&mut self) -> io::Result<()> {