feat(otlp): add build() on base exporter builders to auto-select from env (#3394)

Co-authored-by: Lalit Kumar Bhasin <lalit_fin@yahoo.com>

Author: scottgerring

opentelemetry-otlp/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## vNext
 
+- Add `build()` directly on `SpanExporterBuilder`, `MetricExporterBuilder`, and `LogExporterBuilder`
+  (before selecting a transport), which auto-selects the transport based on the
+  `OTEL_EXPORTER_OTLP_PROTOCOL` environment variable or enabled features.
+  [#3394](https://github.com/open-telemetry/opentelemetry-rust/pull/3394)
 - **Breaking** Removed `ExportConfig`, `HasExportConfig`, `with_export_config()`, `HasTonicConfig`, `HasHttpConfig`, `TonicConfig`, and `HttpConfig` from public API.
   Use the public `WithExportConfig`, `WithTonicConfig`, and `WithHttpConfig` trait methods instead, which remain unchanged.
 - The gRPC/tonic OTLP exporter's build method now returns an error for all signals (traces, metrics, logs) when

opentelemetry-otlp/examples/basic-otlp/src/main.rs

@@ -26,7 +26,6 @@ fn get_resource() -> Resource {
 
 fn init_traces() -> SdkTracerProvider {
     let exporter = SpanExporter::builder()
-        .with_tonic()
         .build()
         .expect("Failed to create span exporter");
     SdkTracerProvider::builder()
@@ -37,7 +36,6 @@ fn init_traces() -> SdkTracerProvider {
 
 fn init_metrics() -> SdkMeterProvider {
     let exporter = MetricExporter::builder()
-        .with_tonic()
         .build()
         .expect("Failed to create metric exporter");
 
@@ -49,7 +47,6 @@ fn init_metrics() -> SdkMeterProvider {
 
 fn init_logs() -> SdkLoggerProvider {
     let exporter = LogExporter::builder()
-        .with_tonic()
         .build()
         .expect("Failed to create log exporter");
 

opentelemetry-otlp/src/logs.rs

@@ -61,6 +61,28 @@ impl LogExporterBuilder<NoExporterBuilderSet> {
             endpoint: self.endpoint,
         }
     }
+
+    /// Build the [LogExporter] with the default transport selected by environment
+    /// variable or feature flags.
+    ///
+    /// The transport is chosen based on:
+    /// 1. The `OTEL_EXPORTER_OTLP_PROTOCOL` environment variable (if set and the
+    ///    corresponding feature is enabled)
+    /// 2. Enabled features, with priority: `http-json` > `http-proto` > `grpc-tonic`
+    ///
+    /// Use [`with_tonic`](Self::with_tonic) or [`with_http`](Self::with_http) to
+    /// explicitly select a transport and access transport-specific configuration.
+    #[cfg(any(feature = "grpc-tonic", feature = "http-proto", feature = "http-json"))]
+    pub fn build(self) -> Result<LogExporter, ExporterBuildError> {
+        match crate::Protocol::default() {
+            #[cfg(feature = "grpc-tonic")]
+            crate::Protocol::Grpc => self.with_tonic().build(),
+            #[cfg(feature = "http-proto")]
+            crate::Protocol::HttpBinary => self.with_http().build(),
+            #[cfg(feature = "http-json")]
+            crate::Protocol::HttpJson => self.with_http().build(),
+        }
+    }
 }
 
 #[cfg(feature = "grpc-tonic")]
@@ -172,3 +194,15 @@ impl opentelemetry_sdk::logs::LogExporter for LogExporter {
         }
     }
 }
+
+#[cfg(test)]
+#[cfg(any(feature = "grpc-tonic", feature = "http-proto", feature = "http-json"))]
+mod tests {
+    use crate::LogExporter;
+
+    #[test]
+    fn build_with_default_transport() {
+        let result = LogExporter::builder().build();
+        assert!(result.is_ok(), "build() should succeed: {:?}", result.err());
+    }
+}

opentelemetry-otlp/src/metric.rs

@@ -58,6 +58,28 @@ impl MetricExporterBuilder<NoExporterBuilderSet> {
     pub fn new() -> Self {
         MetricExporterBuilder::default()
     }
+
+    /// Build the [MetricExporter] with the default transport selected by environment
+    /// variable or feature flags.
+    ///
+    /// The transport is chosen based on:
+    /// 1. The `OTEL_EXPORTER_OTLP_PROTOCOL` environment variable (if set and the
+    ///    corresponding feature is enabled)
+    /// 2. Enabled features, with priority: `http-json` > `http-proto` > `grpc-tonic`
+    ///
+    /// Use [`with_tonic`](Self::with_tonic) or [`with_http`](Self::with_http) to
+    /// explicitly select a transport and access transport-specific configuration.
+    #[cfg(any(feature = "grpc-tonic", feature = "http-proto", feature = "http-json"))]
+    pub fn build(self) -> Result<MetricExporter, ExporterBuildError> {
+        match crate::Protocol::default() {
+            #[cfg(feature = "grpc-tonic")]
+            crate::Protocol::Grpc => self.with_tonic().build(),
+            #[cfg(feature = "http-proto")]
+            crate::Protocol::HttpBinary => self.with_http().build(),
+            #[cfg(feature = "http-json")]
+            crate::Protocol::HttpJson => self.with_http().build(),
+        }
+    }
 }
 
 impl<C> MetricExporterBuilder<C> {
@@ -250,6 +272,20 @@ impl MetricExporter {
     }
 }
 
+#[cfg(test)]
+#[cfg(any(feature = "grpc-tonic", feature = "http-proto", feature = "http-json"))]
+mod build_tests {
+    use crate::MetricExporter;
+
+    #[test]
+    fn build_with_default_transport() {
+        // Verify that `MetricExporter::builder().build()` succeeds
+        // when at least one transport feature is enabled.
+        let result = MetricExporter::builder().build();
+        assert!(result.is_ok(), "build() should succeed: {:?}", result.err());
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

opentelemetry-otlp/src/span.rs

@@ -63,6 +63,28 @@ impl SpanExporterBuilder<NoExporterBuilderSet> {
             client: HttpExporterBuilderSet(HttpExporterBuilder::default()),
         }
     }
+
+    /// Build the [SpanExporter] with the default transport selected by environment
+    /// variable or feature flags.
+    ///
+    /// The transport is chosen based on:
+    /// 1. The `OTEL_EXPORTER_OTLP_PROTOCOL` environment variable (if set and the
+    ///    corresponding feature is enabled)
+    /// 2. Enabled features, with priority: `http-json` > `http-proto` > `grpc-tonic`
+    ///
+    /// Use [`with_tonic`](Self::with_tonic) or [`with_http`](Self::with_http) to
+    /// explicitly select a transport and access transport-specific configuration.
+    #[cfg(any(feature = "grpc-tonic", feature = "http-proto", feature = "http-json"))]
+    pub fn build(self) -> Result<SpanExporter, ExporterBuildError> {
+        match crate::Protocol::default() {
+            #[cfg(feature = "grpc-tonic")]
+            crate::Protocol::Grpc => self.with_tonic().build(),
+            #[cfg(feature = "http-proto")]
+            crate::Protocol::HttpBinary => self.with_http().build(),
+            #[cfg(feature = "http-json")]
+            crate::Protocol::HttpJson => self.with_http().build(),
+        }
+    }
 }
 
 #[cfg(feature = "grpc-tonic")]
@@ -166,3 +188,15 @@ impl opentelemetry_sdk::trace::SpanExporter for SpanExporter {
         }
     }
 }
+
+#[cfg(test)]
+#[cfg(any(feature = "grpc-tonic", feature = "http-proto", feature = "http-json"))]
+mod tests {
+    use crate::SpanExporter;
+
+    #[test]
+    fn build_with_default_transport() {
+        let result = SpanExporter::builder().build();
+        assert!(result.is_ok(), "build() should succeed: {:?}", result.err());
+    }
+}