From fb6b4dc9a95f4268775e674323a2b84c7b4ae7f0 Mon Sep 17 00:00:00 2001
From: Alex Auvolat <alex@adnab.me>
Date: Fri, 18 Feb 2022 20:10:46 +0100
Subject: Correct implementation of distributed tracing

---
 src/client.rs | 39 ++++++++++++++++++++++++++-------------
 src/server.rs | 47 ++++++++++++++++++++++++++---------------------
 2 files changed, 52 insertions(+), 34 deletions(-)

(limited to 'src')

diff --git a/src/client.rs b/src/client.rs
index 7ef772d..e08b30b 100644
--- a/src/client.rs
+++ b/src/client.rs
@@ -11,6 +11,14 @@ use tokio::select;
 use tokio::sync::{mpsc, oneshot, watch};
 use tokio_util::compat::*;
 
+#[cfg(feature = "telemetry")]
+use opentelemetry::{
+	trace::{FutureExt, Span, SpanKind, TraceContextExt, Tracer},
+	Context,
+};
+#[cfg(feature = "telemetry")]
+use opentelemetry_contrib::trace::propagator::binary::*;
+
 use futures::io::AsyncReadExt;
 
 use async_trait::async_trait;
@@ -127,18 +135,14 @@ impl ClientConn {
 
 		cfg_if::cfg_if! {
 			if #[cfg(feature = "telemetry")] {
-				use opentelemetry::{trace::{TraceId, TraceContextExt}, Context};
-				let trace_id_int = Context::current()
-					.span()
-					.span_context()
-					.trace_id();
-				let trace_id = if trace_id_int == TraceId::INVALID {
-					None
-				} else {
-					Some(trace_id_int.to_bytes().to_vec())
-				};
+				let tracer = opentelemetry::global::tracer("netapp");
+				let span = tracer.span_builder(format!("RPC >> {}", path))
+					.with_kind(SpanKind::Server)
+					.start(&tracer);
+				let propagator = BinaryPropagator::new();
+				let telemetry_id = Some(propagator.to_bytes(span.span_context()).to_vec());
 			} else {
-				let trace_id: Option<Vec<u8>> = None;
+				let telemetry_id: Option<Vec<u8>> = None;
 			}
 		};
 
@@ -148,7 +152,7 @@ impl ClientConn {
 		bytes.extend_from_slice(&[prio, path.as_bytes().len() as u8]);
 		bytes.extend_from_slice(path.as_bytes());
 
-		if let Some(by) = trace_id {
+		if let Some(by) = telemetry_id {
 			bytes.push(by.len() as u8);
 			bytes.extend(by);
 		} else {
@@ -172,7 +176,16 @@ impl ClientConn {
 		trace!("request: query_send {}, {} bytes", id, bytes.len());
 		query_send.send((id, prio, bytes))?;
 
-		let resp = resp_recv.await?;
+		cfg_if::cfg_if! {
+			if #[cfg(feature = "telemetry")] {
+				let resp = resp_recv
+					.with_context(Context::current_with_span(span))
+					.await?;
+			} else {
+				let resp = resp_recv.await?;
+			}
+		}
+
 		if resp.is_empty() {
 			return Err(Error::Message(
 				"Response is 0 bytes, either a collision or a protocol error".into(),
diff --git a/src/server.rs b/src/server.rs
index 937d65a..8b60e17 100644
--- a/src/server.rs
+++ b/src/server.rs
@@ -5,6 +5,13 @@ use arc_swap::ArcSwapOption;
 use bytes::Bytes;
 use log::{debug, trace};
 
+#[cfg(feature = "telemetry")]
+use opentelemetry::{
+	trace::{FutureExt, Span, SpanKind, TraceContextExt, TraceId, Tracer},
+	Context, KeyValue,
+};
+#[cfg(feature = "telemetry")]
+use opentelemetry_contrib::trace::propagator::binary::*;
 #[cfg(feature = "telemetry")]
 use rand::{thread_rng, Rng};
 
@@ -122,9 +129,9 @@ impl ServerConn {
 		let path = &bytes[2..2 + path_length];
 		let path = String::from_utf8(path.to_vec())?;
 
-		let trace_id_len = bytes[2 + path_length] as usize;
+		let telemetry_id_len = bytes[2 + path_length] as usize;
 
-		let data = &bytes[3 + path_length + trace_id_len..];
+		let data = &bytes[3 + path_length + telemetry_id_len..];
 
 		let handler_opt = {
 			let endpoints = self.netapp.endpoints.read().unwrap();
@@ -134,28 +141,26 @@ impl ServerConn {
 		if let Some(handler) = handler_opt {
 			cfg_if::cfg_if! {
 				if #[cfg(feature = "telemetry")] {
-					use opentelemetry::{
-						KeyValue,
-						trace::{FutureExt, TraceContextExt, Tracer},
-						Context, trace::TraceId
-					};
-					let trace_id = if trace_id_len == 16 {
-						let mut by = [0u8; 16];
-						by.copy_from_slice(&bytes[3+path_length..19+path_length]);
-						TraceId::from_bytes(by)
+					let tracer = opentelemetry::global::tracer("netapp");
+
+					let mut span = if telemetry_id_len > 0 {
+						let by = bytes[3+path_length..3+path_length+telemetry_id_len].to_vec();
+						let propagator = BinaryPropagator::new();
+						let context = propagator.from_bytes(by);
+						let context = Context::new().with_remote_span_context(context);
+						tracer.span_builder(format!(">> RPC {}", path))
+							.with_kind(SpanKind::Server)
+							.start_with_context(&tracer, &context)
 					} else {
 						let mut rng = thread_rng();
-						TraceId::from_bytes(rng.gen())
+						let trace_id = TraceId::from_bytes(rng.gen());
+						tracer
+							.span_builder(format!(">> RPC {}", path))
+							.with_kind(SpanKind::Server)
+							.with_trace_id(trace_id)
+							.start(&tracer)
 					};
-
-					let tracer = opentelemetry::global::tracer("garage");
-					let span = tracer
-						.span_builder(format!("RPC handler {}", path))
-						.with_trace_id(trace_id)
-						.with_attributes(vec![
-							KeyValue::new("path", path),
-						])
-						.start(&tracer);
+					span.set_attribute(KeyValue::new("path", path.to_string()));
 
 					handler.handle(data, self.peer_id)
 						.with_context(Context::current_with_span(span))
-- 
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