feat(spans): Reintroduce OTLP endpoint (#4223)

Restore the OTLP endpoint that was removed in
#3973.

This PR moves the parsing of the trace data to the processor to ensure
fast response times.

I also renamed the endpoint from `/spans/` to `/otlp/v1/traces/` to be
consistent with
https://opentelemetry.io/docs/languages/sdk-configuration/otlp-exporter/#otel_exporter_otlp_endpoint.

CHANGELOG.md

@@ -78,6 +78,7 @@
 - Feature flags of graduated features are now hard-coded in Relay so they can be removed from Sentry. ([#4076](https://github.com/getsentry/relay/pull/4076), [#4080](https://github.com/getsentry/relay/pull/4080))
 - Add parallelization in Redis commands. ([#4118](https://github.com/getsentry/relay/pull/4118))
 - Extract user ip for spans. ([#4144](https://github.com/getsentry/relay/pull/4144))
+- Add support for an experimental OTLP `/v1/traces/` endpoint. The endpoint is disabled by default. ([#4223](https://github.com/getsentry/relay/pull/4223))
 
 ## 24.9.0
 

Cargo.toml

@@ -131,6 +131,7 @@ pin-project-lite = "0.2.12"
 pretty-hex = "0.4.1"
 priority-queue = "2.0.3"
 proc-macro2 = "1.0.8"
+prost = "0.13.3"
 psl = "2.1.33"
 quote = "1.0.2"
 r2d2 = "0.8.10"

relay-dynamic-config/src/feature.rs

@@ -56,7 +56,7 @@ pub enum Feature {
     /// Serialized as `organizations:standalone-span-ingestion`.
     #[serde(rename = "organizations:standalone-span-ingestion")]
     StandaloneSpanIngestion,
-    /// Enable standalone span ingestion via the `/spans/` OTel endpoint.
+    /// Enable standalone span ingestion via the `/traces/` OTel endpoint.
     ///
     /// Serialized as `projects:relay-otel-endpoint`.
     #[serde(rename = "projects:relay-otel-endpoint")]

relay-server/Cargo.toml

@@ -58,6 +58,7 @@ once_cell = { workspace = true }
 papaya = { workspace = true }
 pin-project-lite = { workspace = true }
 priority-queue = { workspace = true }
+prost = { workspace = true }
 rand = { workspace = true }
 rayon = { workspace = true }
 regex = { workspace = true }

relay-server/src/endpoints/mod.rs

@@ -19,6 +19,7 @@ mod public_keys;
 mod security_report;
 mod statics;
 mod store;
+mod traces;
 mod unreal;
 
 use axum::extract::DefaultBodyLimit;
@@ -74,6 +75,7 @@ pub fn routes(config: &Config) -> Router<ServiceState>{
         .route("/api/:project_id/minidump/", minidump::route(config))
         .route("/api/:project_id/events/:event_id/attachments/", post(attachments::handle))
         .route("/api/:project_id/unreal/:sentry_key/", unreal::route(config))
+        .route("/api/:project_id/otlp/v1/traces/", traces::route(config))
         // NOTE: If you add a new (non-experimental) route here, please also list it in
         // https://github.com/getsentry/sentry-docs/blob/master/docs/product/relay/operating-guidelines.mdx
         .route_layer(middlewares::cors());

relay-server/src/endpoints/traces.rs

@@ -0,0 +1,43 @@
+use axum::extract::{DefaultBodyLimit, Request};
+use axum::http::StatusCode;
+use axum::response::IntoResponse;
+use axum::routing::{post, MethodRouter};
+use axum::RequestExt;
+use bytes::Bytes;
+use relay_config::Config;
+use relay_dynamic_config::Feature;
+
+use crate::endpoints::common;
+use crate::envelope::{ContentType, Envelope, Item, ItemType};
+use crate::extractors::{RawContentType, RequestMeta};
+use crate::service::ServiceState;
+
+async fn handle(
+    state: ServiceState,
+    content_type: RawContentType,
+    meta: RequestMeta,
+    request: Request,
+) -> axum::response::Result<impl IntoResponse> {
+    let content_type @ (ContentType::Json | ContentType::Protobuf) =
+        ContentType::from(content_type.as_ref())
+    else {
+        return Ok(StatusCode::UNSUPPORTED_MEDIA_TYPE);
+    };
+    let payload: Bytes = request.extract().await?;
+    let mut envelope = Envelope::from_request(None, meta);
+    envelope.require_feature(Feature::OtelEndpoint);
+
+    envelope.add_item({
+        let mut item = Item::new(ItemType::OtelTracesData);
+        item.set_payload(content_type, payload);
+        item
+    });
+
+    common::handle_envelope(&state, envelope).await?;
+
+    Ok(StatusCode::ACCEPTED)
+}
+
+pub fn route(config: &Config) -> MethodRouter<ServiceState> {
+    post(handle).route_layer(DefaultBodyLimit::max(config.max_envelope_size()))
+}