OTLP HTTP Metrics Exporter (#1020)

* initial changes

* changes

* changes

* changes

* changes

* changes

* changes

* changes

* changes

* fix formatting issues

* changes

* changes

* changes

* fix CI and lint

* more lint

* removed commented code

* fix

* fix format

* review comments

Author: lalitb

examples/basic-otlp-http/Cargo.toml

@@ -5,6 +5,7 @@ edition = "2021"
 publish = false
 
 [dependencies]
+once_cell = "1.17"
 opentelemetry_api = { path = "../../opentelemetry-api" }
 opentelemetry_sdk = { path = "../../opentelemetry-sdk", features = ["rt-tokio", "metrics"] }
 opentelemetry-otlp = { path = "../../opentelemetry-otlp", features = ["http-proto", "reqwest-client"] }

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

@@ -1,10 +1,13 @@
+use once_cell::sync::Lazy;
 use opentelemetry_api::global;
 use opentelemetry_api::trace::TraceError;
 use opentelemetry_api::{
+    metrics,
     trace::{TraceContextExt, Tracer},
-    Key,
+    Context, Key, KeyValue,
 };
 use opentelemetry_otlp::WithExportConfig;
+use opentelemetry_sdk::metrics as sdkmetrics;
 use opentelemetry_sdk::trace as sdktrace;
 use std::error::Error;
 
@@ -19,14 +22,44 @@ fn init_tracer() -> Result<sdktrace::Tracer, TraceError> {
         .install_batch(opentelemetry_sdk::runtime::Tokio)
 }
 
+fn init_metrics() -> metrics::Result<sdkmetrics::MeterProvider> {
+    let export_config = opentelemetry_otlp::ExportConfig {
+        endpoint: "http://localhost:4318/v1/metrics".to_string(),
+        ..opentelemetry_otlp::ExportConfig::default()
+    };
+    opentelemetry_otlp::new_pipeline()
+        .metrics(opentelemetry_sdk::runtime::Tokio)
+        .with_exporter(
+            opentelemetry_otlp::new_exporter()
+                .http()
+                .with_export_config(export_config),
+        )
+        .build()
+}
+
 const LEMONS_KEY: Key = Key::from_static_str("ex.com/lemons");
 const ANOTHER_KEY: Key = Key::from_static_str("ex.com/another");
 
+static COMMON_ATTRIBUTES: Lazy<[KeyValue; 4]> = Lazy::new(|| {
+    [
+        LEMONS_KEY.i64(10),
+        KeyValue::new("A", "1"),
+        KeyValue::new("B", "2"),
+        KeyValue::new("C", "3"),
+    ]
+});
+
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
     let _ = init_tracer()?;
+    let meter_provider = init_metrics()?;
 
     let tracer = global::tracer("ex.com/basic");
+    let meter = global::meter("ex.com/basic");
+
+    let histogram = meter.f64_histogram("ex.com.two").init();
+    let cx = Context::new();
+    histogram.record(&cx, 5.5, COMMON_ATTRIBUTES.as_ref());
 
     tracer.in_span("operation", |cx| {
         let span = cx.span();
@@ -44,6 +77,7 @@ async fn main() -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
         });
     });
 
+    meter_provider.shutdown()?;
     global::shutdown_tracer_provider();
 
     Ok(())

opentelemetry-http/src/lib.rs

@@ -1,11 +1,10 @@
+use async_trait::async_trait;
 use std::fmt::Debug;
 
 #[doc(no_inline)]
 pub use bytes::Bytes;
 #[doc(no_inline)]
 pub use http::{Request, Response};
-
-use async_trait::async_trait;
 use opentelemetry_api::{
     propagation::{Extractor, Injector},
     trace::TraceError,

opentelemetry-otlp/CHANGELOG.md

@@ -1,4 +1,10 @@
 # Changelog
+
+## Main
+
+### Added
+- Add OTLP HTTP Metrics Exporter [#1020](https://github.com/open-telemetry/opentelemetry-rust/pull/1020).
+
 ## v0.12.0
 
 ### Added

opentelemetry-otlp/Cargo.toml

@@ -80,7 +80,7 @@ openssl = ["grpcio/openssl"]
 openssl-vendored = ["grpcio/openssl-vendored"]
 
 # http binary
-http-proto = ["prost", "opentelemetry-http", "opentelemetry-proto/gen-tonic", "http", "trace"]
+http-proto = ["prost", "opentelemetry-http", "opentelemetry-proto/gen-tonic", "http", "trace", "metrics"]
 reqwest-blocking-client = ["reqwest/blocking", "opentelemetry-http/reqwest"]
 reqwest-client = ["reqwest", "opentelemetry-http/reqwest"]
 reqwest-rustls = ["reqwest", "reqwest/rustls-tls-native-roots"]

opentelemetry-otlp/src/lib.rs

@@ -251,8 +251,7 @@ impl OtlpExporterPipeline {
     /// Use HTTP as transport layer, return a `HttpExporterBuilder` to config the http transport
     /// and build the exporter.
     ///
-    /// This exporter can only be used in `tracing` pipeline. Support for `metrics` pipeline will be
-    /// added in the future.
+    /// This exporter can be used in both `tracing` and `metrics` pipeline.
     #[cfg(feature = "http-proto")]
     pub fn http(self) -> HttpExporterBuilder {
         HttpExporterBuilder::default()