feat(tvix/tracing): gRPC trace context propagation

This introduces optional helper function in tvix/tracing for trace
propagation and uses these helper in the `tvix-store`.

The GRPCBlobService, GRPCDirectoryService and GRPCPathInfoService now
accept a generic client, meaning the client can be generated with either
`::new` or `::with_interceptor`.

This was tested and validated by starting a `tvix-store daemon` and
`tvix-store import`.

Change-Id: I4b194483bf09266820104b4b56e4a135dca2b77a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11863
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

tvix/store/src/pathinfoservice/from_addr.rs

@@ -105,9 +105,12 @@ pub async fn from_addr(
             // - In the case of unix sockets, there must be a path, but may not be a host.
             // - In the case of non-unix sockets, there must be a host, but no path.
             // Constructing the channel is handled by tvix_castore::channel::from_url.
-            let client =
-                PathInfoServiceClient::new(tvix_castore::tonic::channel_from_url(&url).await?);
-            Box::new(GRPCPathInfoService::from_client(client))
+            Box::new(GRPCPathInfoService::from_client(
+                PathInfoServiceClient::with_interceptor(
+                    tvix_castore::tonic::channel_from_url(&url).await?,
+                    tvix_tracing::propagate::tonic::send_trace,
+                ),
+            ))
         }
         #[cfg(feature = "cloud")]
         "bigtable" => {

tvix/store/src/pathinfoservice/grpc.rs

@@ -6,31 +6,43 @@ use crate::{
 use async_stream::try_stream;
 use futures::stream::BoxStream;
 use nix_compat::nixbase32;
-use tonic::{async_trait, transport::Channel, Code};
+use tonic::{async_trait, Code};
 use tracing::{instrument, Span};
 use tracing_indicatif::span_ext::IndicatifSpanExt;
 use tvix_castore::{proto as castorepb, Error};
 
 /// Connects to a (remote) tvix-store PathInfoService over gRPC.
 #[derive(Clone)]
-pub struct GRPCPathInfoService {
+pub struct GRPCPathInfoService<T>
+where
+    T: Clone,
+{
     /// The internal reference to a gRPC client.
     /// Cloning it is cheap, and it internally handles concurrent requests.
-    grpc_client: proto::path_info_service_client::PathInfoServiceClient<Channel>,
+    grpc_client: proto::path_info_service_client::PathInfoServiceClient<T>,
 }
 
-impl GRPCPathInfoService {
+impl<T> GRPCPathInfoService<T>
+where
+    T: tonic::client::GrpcService<tonic::body::BoxBody> + Clone,
+{
     /// construct a [GRPCPathInfoService] from a [proto::path_info_service_client::PathInfoServiceClient].
     /// panics if called outside the context of a tokio runtime.
     pub fn from_client(
-        grpc_client: proto::path_info_service_client::PathInfoServiceClient<Channel>,
+        grpc_client: proto::path_info_service_client::PathInfoServiceClient<T>,
     ) -> Self {
         Self { grpc_client }
     }
 }
 
 #[async_trait]
-impl PathInfoService for GRPCPathInfoService {
+impl<T> PathInfoService for GRPCPathInfoService<T>
+where
+    T: tonic::client::GrpcService<tonic::body::BoxBody> + Send + Sync + Clone + 'static,
+    T::ResponseBody: tonic::codegen::Body<Data = tonic::codegen::Bytes> + Send + 'static,
+    <T::ResponseBody as tonic::codegen::Body>::Error: Into<tonic::codegen::StdError> + Send,
+    T::Future: Send,
+{
     #[instrument(level = "trace", skip_all, fields(path_info.digest = nixbase32::encode(&digest)))]
     async fn get(&self, digest: [u8; 20]) -> Result<Option<PathInfo>, Error> {
         let path_info = self
@@ -107,7 +119,13 @@ impl PathInfoService for GRPCPathInfoService {
 }
 
 #[async_trait]
-impl NarCalculationService for GRPCPathInfoService {
+impl<T> NarCalculationService for GRPCPathInfoService<T>
+where
+    T: tonic::client::GrpcService<tonic::body::BoxBody> + Send + Sync + Clone + 'static,
+    T::ResponseBody: tonic::codegen::Body<Data = tonic::codegen::Bytes> + Send + 'static,
+    <T::ResponseBody as tonic::codegen::Body>::Error: Into<tonic::codegen::StdError> + Send,
+    T::Future: Send,
+{
     #[instrument(level = "trace", skip_all, fields(root_node = ?root_node, indicatif.pb_show=1))]
     async fn calculate_nar(
         &self,

tvix/store/src/pathinfoservice/tests/utils.rs

@@ -16,8 +16,11 @@ use crate::{
 /// Constructs and returns a gRPC PathInfoService.
 /// We also return memory-based {Blob,Directory}Service,
 /// as the consumer of this function accepts a 3-tuple.
-pub async fn make_grpc_path_info_service_client(
-) -> (impl BlobService, impl DirectoryService, GRPCPathInfoService) {
+pub async fn make_grpc_path_info_service_client() -> (
+    impl BlobService,
+    impl DirectoryService,
+    GRPCPathInfoService<tonic::transport::Channel>,
+) {
     let (left, right) = tokio::io::duplex(64);
 
     let blob_service = blob_service();