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//! Send email off the request path via the [`crate::jobs`] queue.
//!
//! Render the message in the request, push it on the queue, and let a
//! worker talk to SMTP, SES or Mailgun. SMTP is slow and flaky, so
//! this keeps handler latency steady and gets retry with backoff from
//! the queue.
//!
//! ## Quick start
//!
//! ```ignore
//! use rustango::email_jobs::{EmailJobConfig, register_email_job, dispatch_email};
//! use rustango::jobs::JobQueue;
//! use rustango::email::BoxedMailer;
//! use std::sync::Arc;
//!
//! // Once at startup — register the worker handler with the queue.
//! let mailer: BoxedMailer = Arc::new(SmtpMailer::new(...));
//! register_email_job(&queue, EmailJobConfig::new(mailer.clone())).await;
//! queue.start().await;
//!
//! // From a handler:
//! let email = renderer.render("welcome", &ctx)?
//! .from("noreply@example.com")
//! .to("alice@example.com");
//! dispatch_email(&queue, &email).await?;
//! ```
//!
//! ## Behavior
//!
//! - The whole [`Email`] goes into the job payload, so the worker
//! rebuilds it before sending.
//! - A send failure becomes [`crate::jobs::JobError::Retryable`], so
//! the queue backs off and retries. A job that runs out of attempts
//! goes to the dead-letter callback.
//! - The worker reads the [`crate::email::Mailer`] from a static
//! registry keyed by job name. Registering again replaces it, which
//! is handy in tests.
//!
//! [`Email`]: crate::email::Email
use std::sync::{OnceLock, RwLock};
use serde::{Deserialize, Serialize};
use crate::email::{BoxedMailer, Email};
use crate::jobs::{Job, JobError, JobQueue};
/// Mailers by [`Job::NAME`]. The worker looks one up here so the
/// mailer stays out of the job payload, which would need
/// `Mailer: Serialize`.
fn mailer_registry() -> &'static RwLock<std::collections::HashMap<&'static str, BoxedMailer>> {
static REG: OnceLock<RwLock<std::collections::HashMap<&'static str, BoxedMailer>>> =
OnceLock::new();
REG.get_or_init(|| RwLock::new(std::collections::HashMap::new()))
}
/// Config registered together with the job.
#[derive(Clone)]
pub struct EmailJobConfig {
/// The mailer the worker sends with.
pub mailer: BoxedMailer,
}
impl EmailJobConfig {
#[must_use]
pub fn new(mailer: BoxedMailer) -> Self {
Self { mailer }
}
}
/// The job payload: a copy of the [`Email`].
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct EmailJob {
pub email: Email,
}
#[async_trait::async_trait]
impl Job for EmailJob {
const NAME: &'static str = "rustango.send_email";
/// 5 attempts at the queue's `1s · 2^attempt` backoff, about a
/// minute in all.
const MAX_ATTEMPTS: u32 = 5;
async fn run(&self) -> Result<(), JobError> {
let mailer = mailer_registry()
.read()
.unwrap_or_else(|e| e.into_inner())
.get(Self::NAME)
.cloned()
.ok_or_else(|| {
JobError::Queue(
"EmailJob: no mailer registered (call register_email_job at startup)".into(),
)
})?;
mailer
.send(&self.email)
.await
.map_err(|e| JobError::Retryable(format!("mailer: {e}")))
}
}
/// Register the email job and its mailer on `queue`, once at startup.
/// Calling it again replaces the mailer.
pub async fn register_email_job<Q: JobQueue>(queue: &Q, cfg: EmailJobConfig) {
mailer_registry()
.write()
.unwrap_or_else(|e| e.into_inner())
.insert(EmailJob::NAME, cfg.mailer);
queue.register::<EmailJob>().await;
}
/// Queue an email and return at once; a worker delivers it.
///
/// # Errors
/// [`JobError::Queue`] when the enqueue fails, for example the
/// database is down or the payload will not serialize.
pub async fn dispatch_email<Q: JobQueue>(queue: &Q, email: &Email) -> Result<(), JobError> {
queue
.dispatch(&EmailJob {
email: email.clone(),
})
.await
}
/// Clear the mailer registry between tests.
#[cfg(test)]
pub fn reset_mailer_registry() {
if let Ok(mut g) = mailer_registry().write() {
g.clear();
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::email::{InMemoryMailer, NullMailer};
use crate::jobs::InMemoryJobQueue;
use std::sync::Arc as StdArc;
use std::time::Duration;
use tokio::sync::Mutex;
/// These tests share the global mailer registry, so they must run
/// one at a time.
fn lock() -> &'static Mutex<()> {
static M: std::sync::OnceLock<Mutex<()>> = std::sync::OnceLock::new();
M.get_or_init(|| Mutex::new(()))
}
fn email() -> Email {
Email::new()
.from("noreply@x.com")
.to("alice@x.com")
.subject("Hi")
.body("hello")
}
#[tokio::test]
async fn dispatch_then_worker_sends() {
let _g = lock().lock().await;
reset_mailer_registry();
let mailer = StdArc::new(InMemoryMailer::new());
let q = InMemoryJobQueue::with_workers(1);
register_email_job(&q, EmailJobConfig::new(mailer.clone())).await;
q.start().await;
dispatch_email(&q, &email()).await.unwrap();
for _ in 0..50 {
if mailer.count() > 0 {
break;
}
tokio::time::sleep(Duration::from_millis(50)).await;
}
assert_eq!(mailer.count(), 1);
let sent = mailer.sent();
assert_eq!(sent[0].subject, "Hi");
assert_eq!(sent[0].to, vec!["alice@x.com"]);
q.shutdown().await;
}
#[tokio::test]
async fn no_mailer_registered_returns_queue_error() {
let _g = lock().lock().await;
reset_mailer_registry();
// Register the job so dispatch works, but no mailer.
let q = InMemoryJobQueue::with_workers(1);
q.register::<EmailJob>().await;
// Count dead letters to see the worker reject the job.
let dl_count = StdArc::new(std::sync::atomic::AtomicUsize::new(0));
let dl = dl_count.clone();
q.on_dead_letter(move |_dl| {
let dl = dl.clone();
async move {
dl.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
}
})
.await;
q.start().await;
dispatch_email(&q, &email()).await.unwrap();
// JobError::Queue is not retried, so it dead-letters at once.
for _ in 0..40 {
if dl_count.load(std::sync::atomic::Ordering::SeqCst) > 0 {
break;
}
tokio::time::sleep(Duration::from_millis(50)).await;
}
assert_eq!(dl_count.load(std::sync::atomic::Ordering::SeqCst), 1);
q.shutdown().await;
}
#[tokio::test]
async fn re_register_swaps_the_mailer() {
let _g = lock().lock().await;
reset_mailer_registry();
let m1 = StdArc::new(InMemoryMailer::new());
let m2 = StdArc::new(InMemoryMailer::new());
let q = InMemoryJobQueue::with_workers(1);
register_email_job(&q, EmailJobConfig::new(m1.clone())).await;
register_email_job(&q, EmailJobConfig::new(m2.clone())).await;
q.start().await;
dispatch_email(&q, &email()).await.unwrap();
for _ in 0..50 {
if m2.count() > 0 {
break;
}
tokio::time::sleep(Duration::from_millis(50)).await;
}
assert_eq!(m1.count(), 0, "old mailer should not receive");
assert_eq!(m2.count(), 1, "new mailer should receive");
q.shutdown().await;
}
#[tokio::test]
async fn null_mailer_succeeds_silently() {
let _g = lock().lock().await;
reset_mailer_registry();
let mailer: BoxedMailer = StdArc::new(NullMailer);
let q = InMemoryJobQueue::with_workers(1);
register_email_job(&q, EmailJobConfig::new(mailer)).await;
q.start().await;
// Nothing to observe: it must not panic or dead-letter.
dispatch_email(&q, &email()).await.unwrap();
tokio::time::sleep(Duration::from_millis(100)).await;
// Back to 0 once the job is done.
assert_eq!(q.pending_count().await, 0);
q.shutdown().await;
}
}