feat: allow Resource transformation in TracerProviderBuilder

opentelemetry-sdk/src/resource/mod.rs

@@ -78,6 +78,11 @@ impl Resource {
         }
     }
 
+    /// Returns a [ResourceBuilder] initialized from this resource.
+    pub fn into_builder(self) -> ResourceBuilder {
+        ResourceBuilder { resource: self }
+    }
+
     /// Creates an empty resource.
     /// This is the basic constructor that initializes a resource with no attributes and no schema URL.
     pub(crate) fn empty() -> Self {
@@ -230,6 +235,12 @@ impl Resource {
     }
 }
 
+impl From<Resource> for ResourceBuilder {
+    fn from(resource: Resource) -> Self {
+        resource.into_builder()
+    }
+}
+
 /// An iterator over the entries of a `Resource`.
 #[derive(Debug)]
 pub struct Iter<'a>(hash_map::Iter<'a, Key, Value>);
@@ -549,4 +560,51 @@ mod tests {
             },
         )
     }
+
+    #[test]
+    fn into_builder() {
+        // Create a resource with some attributes and schema URL
+        let original_resource = Resource::from_schema_url(
+            [
+                KeyValue::new("service.name", "test-service"),
+                KeyValue::new("service.version", "1.0.0"),
+                KeyValue::new("environment", "test"),
+            ],
+            "http://example.com/schema",
+        );
+
+        // Get a builder from the resource
+        let builder: ResourceBuilder = original_resource.clone().into();
+        let rebuilt_resource = builder.build();
+
+        // The rebuilt resource should be identical to the original
+        assert_eq!(original_resource, rebuilt_resource);
+        assert_eq!(
+            original_resource.schema_url(),
+            rebuilt_resource.schema_url()
+        );
+        assert_eq!(original_resource.len(), rebuilt_resource.len());
+
+        // Verify we can modify the builder and get a different resource
+        let modified_resource = original_resource
+            .clone()
+            .into_builder()
+            .with_attribute(KeyValue::new("new_key", "new_value"))
+            .build();
+
+        // The modified resource should have the original attributes plus the new one
+        assert_eq!(modified_resource.len(), original_resource.len() + 1);
+        assert_eq!(
+            modified_resource.get(&Key::new("new_key")),
+            Some(Value::from("new_value"))
+        );
+        assert_eq!(
+            modified_resource.get(&Key::new("service.name")),
+            Some(Value::from("test-service"))
+        );
+        assert_eq!(
+            modified_resource.schema_url(),
+            original_resource.schema_url()
+        );
+    }
 }

opentelemetry-sdk/src/trace/provider.rs

@@ -422,6 +422,25 @@ impl TracerProviderBuilder {
         TracerProviderBuilder { resource, ..self }
     }
 
+    /// Transforms the current [Resource] in this builder using a function.
+    ///
+    /// The transformed [Resource] represents the entity producing telemetry and
+    /// is associated with all [Tracer]s the [SdkTracerProvider] will create.
+    ///
+    /// By default, if this option is not used, the default [Resource] will be used.
+    ///
+    /// *Note*: Calls to this method are not additive, the returned resource will
+    /// completely replace the existing [Resource].
+    ///
+    /// [Tracer]: opentelemetry::trace::Tracer
+    pub fn transform_resource<F>(self, f: F) -> Self
+    where
+        F: FnOnce(Option<&Resource>) -> Resource,
+    {
+        let resource = Some(f(self.resource.as_ref()));
+        TracerProviderBuilder { resource, ..self }
+    }
+
     /// Create a new provider from this configuration.
     pub fn build(self) -> SdkTracerProvider {
         let mut config = self.config;
@@ -882,4 +901,138 @@ mod tests {
         // Verify that shutdown was only called once, even after drop
         assert_eq!(shutdown_count.load(Ordering::SeqCst), 1);
     }
+
+    #[test]
+    fn transform_resource_with_none() {
+        // Test transform_resource when no resource is set initially
+        let provider = super::SdkTracerProvider::builder()
+            .transform_resource(|existing| {
+                assert!(existing.is_none());
+                Resource::new(vec![KeyValue::new("transformed", "value")])
+            })
+            .build();
+
+        assert_eq!(
+            provider.config().resource.get(&Key::new("transformed")),
+            Some(Value::from("value"))
+        );
+    }
+
+    #[test]
+    fn transform_resource_with_existing() {
+        // Test transform_resource when a resource already exists
+        let provider = super::SdkTracerProvider::builder()
+            .with_resource(Resource::new(vec![KeyValue::new("original", "value1")]))
+            .transform_resource(|existing| {
+                assert!(existing.is_some());
+                let existing_resource = existing.unwrap();
+                assert_eq!(
+                    existing_resource.get(&Key::new("original")),
+                    Some(Value::from("value1"))
+                );
+
+                // Create a new resource that merges with the existing one
+                existing_resource
+                    .merge(&Resource::new(vec![KeyValue::new("transformed", "value2")]))
+            })
+            .build();
+
+        // Both original and transformed attributes should be present
+        assert_eq!(
+            provider.config().resource.get(&Key::new("original")),
+            Some(Value::from("value1"))
+        );
+        assert_eq!(
+            provider.config().resource.get(&Key::new("transformed")),
+            Some(Value::from("value2"))
+        );
+    }
+
+    #[test]
+    fn transform_resource_replace_existing() {
+        // Test transform_resource that completely replaces the existing resource
+        let provider = super::SdkTracerProvider::builder()
+            .with_resource(Resource::new(vec![KeyValue::new("original", "value1")]))
+            .transform_resource(|_existing| {
+                // Ignore existing and create a completely new resource
+                Resource::new(vec![KeyValue::new("replaced", "new_value")])
+            })
+            .build();
+
+        // Only the new resource should be present
+        assert_eq!(provider.config().resource.get(&Key::new("original")), None);
+        assert_eq!(
+            provider.config().resource.get(&Key::new("replaced")),
+            Some(Value::from("new_value"))
+        );
+    }
+
+    #[test]
+    fn transform_resource_multiple_calls() {
+        // Test multiple calls to transform_resource
+        let provider = super::SdkTracerProvider::builder()
+            .with_resource(Resource::new(vec![KeyValue::new("initial", "value")]))
+            .transform_resource(|existing| {
+                existing.unwrap().merge(&Resource::new(vec![KeyValue::new(
+                    "first_transform",
+                    "value1",
+                )]))
+            })
+            .transform_resource(|existing| {
+                existing.unwrap().merge(&Resource::new(vec![KeyValue::new(
+                    "second_transform",
+                    "value2",
+                )]))
+            })
+            .build();
+
+        // All attributes should be present
+        assert_eq!(
+            provider.config().resource.get(&Key::new("initial")),
+            Some(Value::from("value"))
+        );
+        assert_eq!(
+            provider.config().resource.get(&Key::new("first_transform")),
+            Some(Value::from("value1"))
+        );
+        assert_eq!(
+            provider
+                .config()
+                .resource
+                .get(&Key::new("second_transform")),
+            Some(Value::from("value2"))
+        );
+    }
+
+    #[test]
+    fn transform_resource_with_schema_url() {
+        // Test transform_resource preserving schema URL
+        let provider = super::SdkTracerProvider::builder()
+            .with_resource(
+                Resource::builder_empty()
+                    .with_schema_url(
+                        vec![KeyValue::new("original", "value")],
+                        "http://example.com/schema",
+                    )
+                    .build(),
+            )
+            .transform_resource(|existing| {
+                let existing_resource = existing.unwrap();
+                existing_resource.merge(&Resource::new(vec![KeyValue::new("added", "new_value")]))
+            })
+            .build();
+
+        assert_eq!(
+            provider.config().resource.get(&Key::new("original")),
+            Some(Value::from("value"))
+        );
+        assert_eq!(
+            provider.config().resource.get(&Key::new("added")),
+            Some(Value::from("new_value"))
+        );
+        assert_eq!(
+            provider.config().resource.schema_url(),
+            Some("http://example.com/schema")
+        );
+    }
 }