Do not lose context when using spawn blocking.

src/routes/newsletters.rs

@@ -1,6 +1,7 @@
 use crate::domain::SubscriberEmail;
 use crate::email_client::EmailClient;
 use crate::routes::error_chain_fmt;
+use crate::telemetry::spawn_blocking_with_tracing;
 use actix_web::http::{HeaderMap, HeaderValue, StatusCode};
 use actix_web::{web, HttpResponse, ResponseError};
 use anyhow::Context;
@@ -114,23 +115,36 @@ async fn validate_credentials(
         .map_err(PublishError::UnexpectedError)?
         .ok_or_else(|| PublishError::AuthError(anyhow::anyhow!("Unknown username.")))?;
 
-    let expected_password_hash = PasswordHash::new(&expected_password_hash)
-        .context("Failed to parse hash in PHC string format.")
-        .map_err(PublishError::UnexpectedError)?;
-
-    tracing::info_span!("Verify password hash")
-        .in_scope(|| {
-            Argon2::default()
-                .verify_password(credentials.password.as_bytes(), &expected_password_hash)
-        })
-        .context("Invalid password.")
-        .map_err(PublishError::AuthError)?;
+    spawn_blocking_with_tracing(move || {
+        verify_password_hash(expected_password_hash, credentials.password)
+    })
+    .await
+    .context("Failed to spawn blocking task.")
+    .map_err(PublishError::UnexpectedError)??;
 
     Ok(user_id)
 }
 
 #[tracing::instrument(
-    name = "Publish a newsletter issue", 
+    name = "Validate credentials",
+    skip(expected_password_hash, password_candidate)
+)]
+fn verify_password_hash(
+    expected_password_hash: String,
+    password_candidate: String,
+) -> Result<(), PublishError> {
+    let expected_password_hash = PasswordHash::new(&expected_password_hash)
+        .context("Failed to parse hash in PHC string format.")
+        .map_err(PublishError::UnexpectedError)?;
+
+    Argon2::default()
+        .verify_password(password_candidate.as_bytes(), &expected_password_hash)
+        .context("Invalid password.")
+        .map_err(PublishError::AuthError)
+}
+
+#[tracing::instrument(
+name = "Publish a newsletter issue", 
     skip(body, pool, email_client, request),
     fields(username=tracing::field::Empty, user_id=tracing::field::Empty)
 )]

src/telemetry.rs

@@ -1,3 +1,4 @@
+use actix_web::rt::task::JoinHandle;
 use tracing::subscriber::set_global_default;
 use tracing::Subscriber;
 use tracing_bunyan_formatter::{BunyanFormattingLayer, JsonStorageLayer};
@@ -32,3 +33,12 @@ pub fn init_subscriber(subscriber: impl Subscriber + Sync + Send) {
     LogTracer::init().expect("Failed to set logger");
     set_global_default(subscriber).expect("Failed to set subscriber");
 }
+
+pub fn spawn_blocking_with_tracing<F, R>(f: F) -> JoinHandle<R>
+where
+    F: FnOnce() -> R + Send + 'static,
+    R: Send + 'static,
+{
+    let current_span = tracing::Span::current();
+    actix_web::rt::task::spawn_blocking(move || current_span.in_scope(f))
+}