De minimis "send me a notification" implementation.

When a user clicks "send a test notification," Pilcrow delivers a push message (with a fixed payload) to all active subscriptions. The included client then displays this as a notification, using browser APIs to do so. This lets us verify that push notification works, end to end - and it appears to.

The API endpoint for sending a test notification is not documented. I didn't feel it prudent to extensively document an endpoint that is intended to be temporary and whose side effects are very much subject to change. However, for posterity, the endpoint is

    POST /api/push/ping

    {}

and the push message payload is

    ping

Subscriptions with permanent delivery failures are nuked when we encounter them. Subscriptions with temporary failures cause the `ping` endpoint to return an internal server error, and are not retried. We'll likely want retry logic - including retry logic to handle server restarts - for any more serious use, but for a smoke test, giving up immediately is fine.

To make the push implementation testable, `App` is now generic over it. Tests use a dummy implementation that stores sent messages in memory. This has some significant limitations, documented in the test suite, but it beats sending real notifications to nowhere in tests.

6 files changed, 211 insertions, 10 deletions

diff --git a/src/push/app.rs b/src/push/app.rs
index 358a8cc..56b9a02 100644
--- a/src/push/app.rs
+++ b/src/push/app.rs
@@ -1,17 +1,23 @@
+use futures::future::join_all;
+use itertools::Itertools as _;
 use p256::ecdsa::VerifyingKey;
 use sqlx::SqlitePool;
-use web_push::SubscriptionInfo;
+use web_push::{
+    ContentEncoding, PartialVapidSignatureBuilder, SubscriptionInfo, WebPushClient, WebPushError,
+    WebPushMessage, WebPushMessageBuilder,
+};
 
 use super::repo::Provider as _;
-use crate::{token::extract::Identity, vapid, vapid::repo::Provider as _};
+use crate::{login::Login, token::extract::Identity, vapid, vapid::repo::Provider as _};
 
-pub struct Push {
+pub struct Push<P> {
     db: SqlitePool,
+    webpush: P,
 }
 
-impl Push {
-    pub const fn new(db: SqlitePool) -> Self {
-        Self { db }
+impl<P> Push<P> {
+    pub const fn new(db: SqlitePool, webpush: P) -> Self {
+        Self { db, webpush }
     }
 
     pub async fn subscribe(
@@ -60,6 +66,76 @@ impl Push {
     }
 }
 
+impl<P> Push<P>
+where
+    P: WebPushClient,
+{
+    fn prepare_ping(
+        signer: &PartialVapidSignatureBuilder,
+        subscription: &SubscriptionInfo,
+    ) -> Result<WebPushMessage, WebPushError> {
+        let signature = signer.clone().add_sub_info(subscription).build()?;
+
+        let payload = "ping".as_bytes();
+
+        let mut message = WebPushMessageBuilder::new(subscription);
+        message.set_payload(ContentEncoding::Aes128Gcm, payload);
+        message.set_vapid_signature(signature);
+        let message = message.build()?;
+
+        Ok(message)
+    }
+
+    pub async fn ping(&self, recipient: &Login) -> Result<(), PushError> {
+        let mut tx = self.db.begin().await?;
+
+        let signer = tx.vapid().signer().await?;
+        let subscriptions = tx.push().by_login(recipient).await?;
+
+        let pings: Vec<_> = subscriptions
+            .into_iter()
+            .map(|sub| Self::prepare_ping(&signer, &sub).map(|message| (sub, message)))
+            .try_collect()?;
+
+        let deliveries = pings
+            .into_iter()
+            .map(async |(sub, message)| (sub, self.webpush.send(message).await));
+
+        let failures: Vec<_> = join_all(deliveries)
+            .await
+            .into_iter()
+            .filter_map(|(sub, result)| result.err().map(|err| (sub, err)))
+            .collect();
+
+        if !failures.is_empty() {
+            for (sub, err) in &failures {
+                match err {
+                    // I _think_ this is the complete set of permanent failures. See
+                    // <https://docs.rs/web-push/latest/web_push/enum.WebPushError.html> for a complete
+                    // list.
+                    WebPushError::Unauthorized(_)
+                    | WebPushError::InvalidUri
+                    | WebPushError::EndpointNotValid(_)
+                    | WebPushError::EndpointNotFound(_)
+                    | WebPushError::InvalidCryptoKeys
+                    | WebPushError::MissingCryptoKeys => {
+                        tx.push().unsubscribe(sub).await?;
+                    }
+                    _ => (),
+                }
+            }
+
+            return Err(PushError::Delivery(
+                failures.into_iter().map(|(_, err)| err).collect(),
+            ));
+        }
+
+        tx.commit().await?;
+
+        Ok(())
+    }
+}
+
 #[derive(Debug, thiserror::Error)]
 pub enum SubscribeError {
     #[error(transparent)]
@@ -74,3 +150,29 @@ pub enum SubscribeError {
     // client, which already knows the endpoint anyways and doesn't need us to tell them.
     Duplicate,
 }
+
+#[derive(Debug, thiserror::Error)]
+pub enum PushError {
+    #[error(transparent)]
+    Database(#[from] sqlx::Error),
+    #[error(transparent)]
+    Ecdsa(#[from] p256::ecdsa::Error),
+    #[error(transparent)]
+    Pkcs8(#[from] p256::pkcs8::Error),
+    #[error(transparent)]
+    WebPush(#[from] WebPushError),
+    #[error("push message delivery failures: {0:?}")]
+    Delivery(Vec<WebPushError>),
+}
+
+impl From<vapid::repo::Error> for PushError {
+    fn from(error: vapid::repo::Error) -> Self {
+        use vapid::repo::Error;
+        match error {
+            Error::Database(error) => error.into(),
+            Error::Ecdsa(error) => error.into(),
+            Error::Pkcs8(error) => error.into(),
+            Error::WebPush(error) => error.into(),
+        }
+    }
+}
diff --git a/src/push/handlers/mod.rs b/src/push/handlers/mod.rs
index 86eeea0..bb58774 100644
--- a/src/push/handlers/mod.rs
+++ b/src/push/handlers/mod.rs
@@ -1,3 +1,5 @@
+mod ping;
 mod subscribe;
 
+pub use ping::handler as ping;
 pub use subscribe::handler as subscribe;
diff --git a/src/push/handlers/ping/mod.rs b/src/push/handlers/ping/mod.rs
new file mode 100644
index 0000000..db828fa
--- /dev/null
+++ b/src/push/handlers/ping/mod.rs
@@ -0,0 +1,23 @@
+use axum::{Json, extract::State, http::StatusCode};
+use web_push::WebPushClient;
+
+use crate::{error::Internal, push::app::Push, token::extract::Identity};
+
+#[cfg(test)]
+mod test;
+
+#[derive(serde::Deserialize)]
+pub struct Request {}
+
+pub async fn handler<P>(
+    State(push): State<Push<P>>,
+    identity: Identity,
+    Json(_): Json<Request>,
+) -> Result<StatusCode, Internal>
+where
+    P: WebPushClient,
+{
+    push.ping(&identity.login).await?;
+
+    Ok(StatusCode::ACCEPTED)
+}
diff --git a/src/push/handlers/ping/test.rs b/src/push/handlers/ping/test.rs
new file mode 100644
index 0000000..5725131
--- /dev/null
+++ b/src/push/handlers/ping/test.rs
@@ -0,0 +1,40 @@
+use axum::{
+    extract::{Json, State},
+    http::StatusCode,
+};
+
+use crate::test::fixtures;
+
+#[tokio::test]
+async fn ping_without_subscriptions() {
+    let app = fixtures::scratch_app().await;
+
+    let recipient = fixtures::identity::create(&app, &fixtures::now()).await;
+
+    app.vapid()
+        .refresh_key(&fixtures::now())
+        .await
+        .expect("refreshing the VAPID key always succeeds");
+
+    let response = super::handler(State(app.push()), recipient, Json(super::Request {}))
+        .await
+        .expect("sending a ping with no subscriptions always succeeds");
+
+    assert_eq!(StatusCode::ACCEPTED, response);
+
+    assert!(app.webpush().sent().is_empty());
+}
+
+// More complete testing requires that we figure out how to generate working p256 ECDH keys for
+// testing _with_, as `web_push` will actually parse and use those keys even if push messages are
+// ultimately never serialized or sent over HTTP.
+//
+// Tests that are missing:
+//
+// * Verify that subscribing and sending a ping causes a ping to be delivered to that subscription.
+// * Verify that two subscriptions both get pings.
+// * Verify that other users' subscriptions are not pinged.
+// * Verify that a ping that causes a permanent error causes the subscription to be deleted.
+// * Verify that a ping that causes a non-permanent error does not cause the subscription to be
+//   deleted.
+// * Verify that a failure on one subscription doesn't affect delivery on other subscriptions.
diff --git a/src/push/handlers/subscribe/mod.rs b/src/push/handlers/subscribe/mod.rs
index d142df6..a1a5899 100644
--- a/src/push/handlers/subscribe/mod.rs
+++ b/src/push/handlers/subscribe/mod.rs
@@ -36,8 +36,8 @@ pub struct Keys {
     auth: String,
 }
 
-pub async fn handler(
-    State(push): State<Push>,
+pub async fn handler<P>(
+    State(push): State<Push<P>>,
     identity: Identity,
     Json(request): Json<Request>,
 ) -> Result<StatusCode, Error> {
@@ -58,8 +58,7 @@ impl From<Subscription> for SubscriptionInfo {
             endpoint,
             keys: Keys { p256dh, auth },
         } = request;
-        let info = SubscriptionInfo::new(endpoint, p256dh, auth);
-        info
+        SubscriptionInfo::new(endpoint, p256dh, auth)
     }
 }
 
diff --git a/src/push/repo.rs b/src/push/repo.rs
index 6c18c6e..4183489 100644
--- a/src/push/repo.rs
+++ b/src/push/repo.rs
@@ -37,6 +37,24 @@ impl Push<'_> {
         Ok(())
     }
 
+    pub async fn by_login(&mut self, login: &Login) -> Result<Vec<SubscriptionInfo>, sqlx::Error> {
+        sqlx::query!(
+            r#"
+                select
+                    subscription.endpoint,
+                    subscription.p256dh,
+                    subscription.auth
+                from push_subscription as subscription
+                join token on subscription.token = token.id
+                where token.login = $1
+            "#,
+            login.id,
+        )
+        .map(|row| SubscriptionInfo::new(row.endpoint, row.p256dh, row.auth))
+        .fetch_all(&mut *self.0)
+        .await
+    }
+
     pub async fn by_endpoint(
         &mut self,
         subscriber: &Login,
@@ -65,6 +83,23 @@ impl Push<'_> {
         Ok(info)
     }
 
+    pub async fn unsubscribe(
+        &mut self,
+        subscription: &SubscriptionInfo,
+    ) -> Result<(), sqlx::Error> {
+        sqlx::query!(
+            r#"
+                delete from push_subscription
+                where endpoint = $1
+            "#,
+            subscription.endpoint,
+        )
+        .execute(&mut *self.0)
+        .await?;
+
+        Ok(())
+    }
+
     pub async fn unsubscribe_token(&mut self, token: &Token) -> Result<(), sqlx::Error> {
         sqlx::query!(
             r#"