feat(core): add some DSC fields to transaction envelope headers

CHANGELOG.md

@@ -9,6 +9,8 @@
 - feat(types): add all the missing supported envelope headers ([#867](https://github.com/getsentry/sentry-rust/pull/867)) by @lcian
 - feat(types): add setters for envelope headers ([#868](https://github.com/getsentry/sentry-rust/pull/868)) by @lcian
   - It's now possible to set all of the [envelope headers](https://develop.sentry.dev/sdk/data-model/envelopes/#headers) supported by the protocol when constructing envelopes.
+- feat(core): add some DSC fields to transaction envelope headers ([#869](https://github.com/getsentry/sentry-rust/pull/869)) by @lcian
+  - The SDK now sends additional envelope headers with transactions. This should solve some extrapolation issues for span metrics.
 
 ### Behavioral changes
 

sentry-core/src/performance.rs

@@ -594,26 +594,33 @@ fn transaction_sample_rate(
 ) -> f32 {
     match (traces_sampler, traces_sample_rate) {
         (Some(traces_sampler), _) => traces_sampler(ctx),
-        (None, traces_sample_rate) => ctx
-            .sampled
-            .map(|sampled| if sampled { 1.0 } else { 0.0 })
-            .unwrap_or(traces_sample_rate),
+        (None, traces_sample_rate) => ctx.sampled.map(f32::from).unwrap_or(traces_sample_rate),
     }
 }
 
 /// Determine whether the new transaction should be sampled.
 #[cfg(feature = "client")]
 impl Client {
-    fn is_transaction_sampled(&self, ctx: &TransactionContext) -> bool {
+    fn determine_sampling_decision(&self, ctx: &TransactionContext) -> (bool, f32) {
         let client_options = self.options();
-        self.sample_should_send(transaction_sample_rate(
+        let sample_rate = transaction_sample_rate(
             client_options.traces_sampler.as_deref(),
             ctx,
             client_options.traces_sample_rate,
-        ))
+        );
+        let sampled = self.sample_should_send(sample_rate);
+        (sampled, sample_rate)
     }
 }
 
+/// Some metadata associated with a transaction.
+#[cfg(feature = "client")]
+#[derive(Clone, Debug)]
+struct TransactionMetadata {
+    /// The sample rate used when making the sampling decision for the associated transaction.
+    sample_rate: f32,
+}
+
 /// A running Performance Monitoring Transaction.
 ///
 /// The transaction needs to be explicitly finished via [`Transaction::finish`],
@@ -622,6 +629,8 @@ impl Client {
 #[derive(Clone, Debug)]
 pub struct Transaction {
     pub(crate) inner: TransactionArc,
+    #[cfg(feature = "client")]
+    metadata: TransactionMetadata,
 }
 
 /// Iterable for a transaction's [data attributes](protocol::TraceContext::data).
@@ -660,15 +669,21 @@ impl<'a> TransactionData<'a> {
 impl Transaction {
     #[cfg(feature = "client")]
     fn new(client: Option<Arc<Client>>, ctx: TransactionContext) -> Self {
-        let (sampled, transaction) = match client.as_ref() {
+        let ((sampled, sample_rate), transaction) = match client.as_ref() {
             Some(client) => (
-                client.is_transaction_sampled(&ctx),
+                client.determine_sampling_decision(&ctx),
                 Some(protocol::Transaction {
                     name: Some(ctx.name),
                     ..Default::default()
                 }),
             ),
-            None => (ctx.sampled.unwrap_or(false), None),
+            None => (
+                (
+                    ctx.sampled.unwrap_or(false),
+                    ctx.sampled.map_or(0.0, f32::from),
+                ),
+                None,
+            ),
         };
 
         let context = protocol::TraceContext {
@@ -686,6 +701,7 @@ impl Transaction {
                 context,
                 transaction,
             })),
+            metadata: TransactionMetadata { sample_rate },
         }
     }
 
@@ -820,9 +836,19 @@ impl Transaction {
                     transaction.sdk = Some(std::borrow::Cow::Owned(client.sdk_info.clone()));
                     transaction.server_name.clone_from(&opts.server_name);
 
+                    let mut dsc = protocol::DynamicSamplingContext::new()
+                        .with_trace_id(inner.context.trace_id)
+                        .with_sample_rate(self.metadata.sample_rate)
+                        .with_sampled(inner.sampled);
+                    if let Some(public_key) = client.dsn().map(|dsn| dsn.public_key()) {
+                        dsc = dsc.with_public_key(public_key.to_owned());
+                    }
+
                     drop(inner);
 
-                    let mut envelope = protocol::Envelope::new();
+                    let mut envelope = protocol::Envelope::new().with_headers(
+                        protocol::EnvelopeHeaders::new().with_trace(dsc)
+                    );
                     envelope.add_item(transaction);
 
                     client.send_envelope(envelope)

sentry/tests/test_basic.rs

@@ -3,8 +3,10 @@
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::Arc;
 
-use sentry::protocol::{Attachment, Context, EnvelopeItem};
-use sentry::types::Uuid;
+use sentry::protocol::{
+    Attachment, Context, DynamicSamplingContext, EnvelopeHeaders, EnvelopeItem,
+};
+use sentry::types::{Dsn, Uuid};
 
 #[test]
 fn test_basic_capture_message() {
@@ -578,3 +580,39 @@ fn test_basic_capture_log_macro_message_formatted_with_attributes() {
         _ => panic!("expected item container"),
     }
 }
+
+#[test]
+fn test_transaction_envelope_dsc_headers() {
+    let mut trace_id: Option<sentry::protocol::TraceId> = None;
+    let dsn: Option<Dsn> = "http://[email protected]/42".parse().ok();
+    let envelopes = sentry::test::with_captured_envelopes_options(
+        || {
+            let transaction_ctx = sentry::TransactionContext::new("name transaction", "op");
+            trace_id = Some(transaction_ctx.trace_id());
+            let transaction = sentry::start_transaction(transaction_ctx);
+            sentry::configure_scope(|scope| scope.set_span(Some(transaction.clone().into())));
+            transaction.finish();
+        },
+        sentry::ClientOptions {
+            dsn: dsn.clone(),
+            traces_sample_rate: 1.0,
+            ..Default::default()
+        },
+    );
+
+    assert!(trace_id.is_some());
+    let trace_id = trace_id.unwrap();
+    assert_eq!(envelopes.len(), 1);
+    let envelope = envelopes.into_iter().next().unwrap();
+    assert!(envelope.uuid().is_some());
+    let uuid = envelope.uuid().copied().unwrap();
+
+    let expected = EnvelopeHeaders::new().with_event_id(uuid).with_trace(
+        DynamicSamplingContext::new()
+            .with_trace_id(trace_id)
+            .with_public_key(dsn.unwrap().public_key().to_owned())
+            .with_sample_rate(1.0)
+            .with_sampled(true),
+    );
+    assert_eq!(envelope.headers(), &expected);
+}