feat: Use builder pattern for constructing Metric Streams

examples/metrics-advanced/src/main.rs

@@ -9,9 +9,11 @@ fn init_meter_provider() -> opentelemetry_sdk::metrics::SdkMeterProvider {
     let my_view_rename_and_unit = |i: &Instrument| {
         if i.name == "my_histogram" {
             Some(
-                Stream::new()
-                    .name("my_histogram_renamed")
-                    .unit("milliseconds"),
+                Stream::builder()
+                    .with_name("my_histogram_renamed")
+                    .with_unit("milliseconds")
+                    .build()
+                    .unwrap(),
             )
         } else {
             None
@@ -21,7 +23,11 @@ fn init_meter_provider() -> opentelemetry_sdk::metrics::SdkMeterProvider {
     // for example 2
     let my_view_change_cardinality = |i: &Instrument| {
         if i.name == "my_second_histogram" {
-            Some(Stream::new().cardinality_limit(2))
+            // Note: If Stream is invalid, build() will return an error. By
+            // calling `.ok()`, any such error is ignored and treated as if the
+            // view does not match the instrument. If this is not the desired
+            // behavior, consider handling the error explicitly.
+            Stream::builder().with_cardinality_limit(2).build().ok()
         } else {
             None
         }

opentelemetry-sdk/CHANGELOG.md

@@ -42,14 +42,17 @@ also modified to suppress telemetry before invoking exporters.
   behind feature flag "experimental_metrics_custom_reader".
   [#2928](https://github.com/open-telemetry/opentelemetry-rust/pull/2928)
 
-- TODO: Placeholder for View related changelog. Polish this after all
-  - The `Stream` struct now has its public fields hidden.
+- TODO: Placeholder for View related changelog. Polish this after all changs done
   - Core view functionality is now available by default—users can change the
     name, unit, description, and cardinality limit of a metric via views without
     enabling the `spec_unstable_metrics_views` feature flag. Advanced view
     features, such as custom aggregation or attribute filtering, still require
     the `spec_unstable_metrics_views` feature.
-  - TODO: Add Stream::builder() pattern change, validation when done.
+- Introduced a builder pattern for `Stream` creation to use with "Views".
+  - Added `StreamBuilder` struct with methods to configure stream properties
+  - Added `Stream::builder()` method that returns a new `StreamBuilder`
+  - `StreamBuilder::build()` returns `Result<Stream, Box<dyn Error>>` enabling
+    proper validation
 
 - *Breaking* `Aggregation` enum moved behind feature flag
   "spec_unstable_metrics_views". This was only required when using Views.

opentelemetry-sdk/benches/metric.rs

@@ -223,7 +223,10 @@ fn counters(c: &mut Criterion) {
         Some(
             new_view(
                 Instrument::new().name("*"),
-                Stream::new().allowed_attribute_keys([Key::new("K")]),
+                Stream::builder()
+                    .with_allowed_attribute_keys([Key::new("K")])
+                    .build()
+                    .unwrap(),
             )
             .unwrap(),
         ),
@@ -273,10 +276,13 @@ fn bench_histogram(bound_count: usize) -> (SharedReader, Histogram<u64>) {
     let view = Some(
         new_view(
             Instrument::new().name("histogram_*"),
-            Stream::new().aggregation(Aggregation::ExplicitBucketHistogram {
-                boundaries: bounds.iter().map(|&x| x as f64).collect(),
-                record_min_max: true,
-            }),
+            Stream::builder()
+                .with_aggregation(Aggregation::ExplicitBucketHistogram {
+                    boundaries: bounds.iter().map(|&x| x as f64).collect(),
+                    record_min_max: true,
+                })
+                .build()
+                .unwrap(),
         )
         .unwrap(),
     );

opentelemetry-sdk/src/metrics/instrument.rs

@@ -1,4 +1,4 @@
-use std::{borrow::Cow, collections::HashSet, sync::Arc};
+use std::{borrow::Cow, collections::HashSet, error::Error, sync::Arc};
 
 use opentelemetry::{
     metrics::{AsyncInstrument, SyncInstrument},
@@ -73,10 +73,13 @@
 /// Instruments can be used as criteria for views.
 ///
 /// ```
-/// use opentelemetry_sdk::metrics::{new_view, Aggregation, Instrument, Stream};
+/// use opentelemetry_sdk::metrics::{new_view, Aggregation, Instrument, Stream, StreamBuilder};
 ///
 /// let criteria = Instrument::new().name("counter_*");
-/// let mask = Stream::new().aggregation(Aggregation::Sum);
+/// let mask = Stream::builder()
+///     .with_aggregation(Aggregation::Sum)
+///     .build()
+///     .unwrap();
 ///
 /// let view = new_view(criteria, mask);
 /// # drop(view);
@@ -169,71 +172,60 @@
     }
 }
 
-/// Describes the stream of data an instrument produces.
+/// A builder for creating Stream objects.
 ///
 /// # Example
 ///
-/// Streams can be used as masks in views.
-///
 /// ```
-/// use opentelemetry_sdk::metrics::{new_view, Aggregation, Instrument, Stream};
-///
-/// let criteria = Instrument::new().name("counter_*");
-/// let mask = Stream::new().aggregation(Aggregation::Sum);
+/// use opentelemetry_sdk::metrics::{Aggregation, Stream};
+/// use opentelemetry::Key;
 ///
-/// let view = new_view(criteria, mask);
-/// # drop(view);
+/// let stream = Stream::builder()
+///     .with_name("my_stream")
+///     .with_aggregation(Aggregation::Sum)
+///     .with_cardinality_limit(100)
+///     .build()
+///     .unwrap();
 /// ```
 #[derive(Default, Debug)]
 #[non_exhaustive]
-#[allow(unreachable_pub)]
-pub struct Stream {
-    /// The human-readable identifier of the stream.
-    pub(crate) name: Option<Cow<'static, str>>,
-    /// Describes the purpose of the data.
-    pub(crate) description: Option<Cow<'static, str>>,
-    /// the unit of measurement recorded.
-    pub(crate) unit: Option<Cow<'static, str>>,
-    /// Aggregation the stream uses for an instrument.
-    pub(crate) aggregation: Option<Aggregation>,
-    /// An allow-list of attribute keys that will be preserved for the stream.
-    ///
-    /// Any attribute recorded for the stream with a key not in this set will be
-    /// dropped. If the set is empty, all attributes will be dropped, if `None` all
-    /// attributes will be kept.
-    pub(crate) allowed_attribute_keys: Option<Arc<HashSet<Key>>>,
-
-    /// Cardinality limit for the stream.
-    pub(crate) cardinality_limit: Option<usize>,
+pub struct StreamBuilder {
+    name: Option<Cow<'static, str>>,
+    description: Option<Cow<'static, str>>,
+    unit: Option<Cow<'static, str>>,
+    aggregation: Option<Aggregation>,
+    allowed_attribute_keys: Option<Arc<HashSet<Key>>>,
+    cardinality_limit: Option<usize>,
 }
 
-impl Stream {
-    /// Create a new stream with empty values.
-    pub fn new() -> Self {
-        Stream::default()
+impl StreamBuilder {
+    /// Create a new stream builder with default values.
+    pub(crate) fn new() -> Self {
+        StreamBuilder::default()
     }
 
-    /// Set the stream name.
-    pub fn name(mut self, name: impl Into<Cow<'static, str>>) -> Self {
+    /// Set the stream name. If this is not set, name provide while creating the instrument will be used.
+    pub fn with_name(mut self, name: impl Into<Cow<'static, str>>) -> Self {
         self.name = Some(name.into());
         self
     }
 
-    /// Set the stream description.
-    pub fn description(mut self, description: impl Into<Cow<'static, str>>) -> Self {
+    /// Set the stream description. If this is not set, description provided while creating the instrument will be used.
+    pub fn with_description(mut self, description: impl Into<Cow<'static, str>>) -> Self {
         self.description = Some(description.into());
         self
     }
 
-    /// Set the stream unit.
-    pub fn unit(mut self, unit: impl Into<Cow<'static, str>>) -> Self {
+    /// Set the stream unit. If this is not set, unit provided while creating the instrument will be used.
+    pub fn with_unit(mut self, unit: impl Into<Cow<'static, str>>) -> Self {
         self.unit = Some(unit.into());
         self
     }
 
     #[cfg(feature = "spec_unstable_metrics_views")]
-    /// Set the stream aggregation.
-    pub fn aggregation(mut self, aggregation: Aggregation) -> Self {
+    /// Set the stream aggregation. This is used to customize the aggregation.
+    /// If not set, the default aggregation based on the instrument kind will be used.
+    pub fn with_aggregation(mut self, aggregation: Aggregation) -> Self {
         self.aggregation = Some(aggregation);
         self
     }
@@ -242,18 +234,130 @@
     /// Set the stream allowed attribute keys.
     ///
     /// Any attribute recorded for the stream with a key not in this set will be
-    /// dropped. If this set is empty all attributes will be dropped.
-    pub fn allowed_attribute_keys(mut self, attribute_keys: impl IntoIterator<Item = Key>) -> Self {
+    /// dropped. If the set is empty, all attributes will be dropped, if `None` all
+    /// attributes will be kept.
+    pub fn with_allowed_attribute_keys(
+        mut self,
+        attribute_keys: impl IntoIterator<Item = Key>,
+    ) -> Self {
         self.allowed_attribute_keys = Some(Arc::new(attribute_keys.into_iter().collect()));
-
         self
     }
 
-    /// Set the stream cardinality limit.
-    pub fn cardinality_limit(mut self, limit: usize) -> Self {
+    /// Set the stream cardinality limit. If this is not set, the default limit of 2000 will be used.
+    pub fn with_cardinality_limit(mut self, limit: usize) -> Self {
         self.cardinality_limit = Some(limit);
         self
     }
+
+    /// Build a new Stream instance using the configuration in this builder.
+    ///
+    /// # Returns
+    ///
+    /// A Result containing the new Stream instance or an error if the build failed.
+    pub fn build(self) -> Result<Stream, Box<dyn Error>> {
+        // TODO: Add same validation as already done while
+        // creating instruments. It is better to move validation logic
+        // to a common helper and call it from both places.
+        // The current implementations does a basic validation
+        // only to close the overall API design.
+
+        // if name is provided, it must not be empty
+        if let Some(name) = &self.name {
+            if name.is_empty() {
+                return Err("Stream name must not be empty".into());
+            }
+        }
+
+        // if cardinality limit is provided, it must be greater than 0
+        if let Some(limit) = self.cardinality_limit {
+            if limit == 0 {
+                return Err("Cardinality limit must be greater than 0".into());
+            }
+        }
+
+        // If the aggregation is set to ExplicitBucketHistogram, validate the bucket boundaries.
+        if let Some(Aggregation::ExplicitBucketHistogram { boundaries, .. }) = &self.aggregation {
+            validate_bucket_boundaries(boundaries)?;
+        }
+
+        Ok(Stream {
+            name: self.name,
+            description: self.description,
+            unit: self.unit,
+            aggregation: self.aggregation,
+            allowed_attribute_keys: self.allowed_attribute_keys,
+            cardinality_limit: self.cardinality_limit,
+        })
+    }
+}
+
+fn validate_bucket_boundaries(boundaries: &[f64]) -> Result<(), String> {
+    // Validate boundaries do not contain f64::NAN, f64::INFINITY, or f64::NEG_INFINITY
+    for boundary in boundaries {
+        if boundary.is_nan() || boundary.is_infinite() {
+            return Err(
+                "Bucket boundaries must not contain NaN, Infinity, or -Infinity".to_string(),
+            );
+        }
+    }
+
+    // validate that buckets are sorted and non-duplicate
+    for i in 1..boundaries.len() {
+        if boundaries[i] <= boundaries[i - 1] {
+            return Err("Bucket boundaries must be sorted and non-duplicate".to_string());
+        }
+    }
+
+    Ok(())
+}
+
+/// Describes the stream of data an instrument produces.
+///
+/// # Example
+///
+/// Streams can be used as masks in views.
+///
+/// ```
+/// use opentelemetry_sdk::metrics::{new_view, Aggregation, Instrument, Stream};
+///
+/// let criteria = Instrument::new().name("counter_*");
+/// let mask = Stream::builder()
+///     .with_aggregation(Aggregation::Sum)
+///     .build()
+///     .unwrap();
+///
+/// let view = new_view(criteria, mask);
+/// # drop(view);
+/// ```
+#[derive(Default, Debug)]
+#[non_exhaustive]
+#[allow(unreachable_pub)]
+pub struct Stream {
+    /// The human-readable identifier of the stream.
+    pub(crate) name: Option<Cow<'static, str>>,
+    /// Describes the purpose of the data.
+    pub(crate) description: Option<Cow<'static, str>>,
+    /// the unit of measurement recorded.
+    pub(crate) unit: Option<Cow<'static, str>>,
+    /// Aggregation the stream uses for an instrument.
+    pub(crate) aggregation: Option<Aggregation>,
+    /// An allow-list of attribute keys that will be preserved for the stream.
+    ///
+    /// Any attribute recorded for the stream with a key not in this set will be
+    /// dropped. If the set is empty, all attributes will be dropped, if `None` all
+    /// attributes will be kept.
+    pub(crate) allowed_attribute_keys: Option<Arc<HashSet<Key>>>,
+
+    /// Cardinality limit for the stream.
+    pub(crate) cardinality_limit: Option<usize>,
+}
+
+impl Stream {
+    /// Create a new stream builder with default values.
+    pub fn builder() -> StreamBuilder {
+        StreamBuilder::new()
+    }
 }
 
 /// The identifying properties of an instrument.