3 files changed, 68 insertions, 37 deletions

diff --git a/src/events.rs b/src/events.rs
index 38d53fc..9b5901e 100644
--- a/src/events.rs
+++ b/src/events.rs
@@ -1,6 +1,5 @@
 use axum::{
     extract::State,
-    http::{HeaderName, HeaderValue},
     response::{
         sse::{self, Sse},
         IntoResponse,
@@ -8,7 +7,7 @@ use axum::{
     routing::get,
     Router,
 };
-use axum_extra::{extract::Query, typed_header::TypedHeader};
+use axum_extra::extract::Query;
 use chrono::{format::SecondsFormat, DateTime};
 use futures::{
     future,
@@ -19,6 +18,7 @@ use crate::{
     app::App,
     channel::repo::broadcast,
     error::{BoxedError, InternalError},
+    header::LastEventId,
     repo::{channel, login::Login},
 };
 
@@ -35,11 +35,10 @@ struct EventsQuery {
 async fn on_events(
     State(app): State<App>,
     _: Login, // requires auth, but doesn't actually care who you are
-    last_event_id: Option<TypedHeader<LastEventId>>,
+    last_event_id: Option<LastEventId>,
     Query(query): Query<EventsQuery>,
 ) -> Result<impl IntoResponse, InternalError> {
     let resume_at = last_event_id
-        .map(|TypedHeader(header)| header)
         .map(|LastEventId(header)| header)
         .map(|header| DateTime::parse_from_rfc3339(&header))
         .transpose()?
@@ -53,10 +52,7 @@ async fn on_events(
                     .channels()
                     .events(&channel, resume_at.as_ref())
                     .await?
-                    .map_ok(move |message| ChannelEvent {
-                        channel: channel.clone(),
-                        message,
-                    });
+                    .map_ok(ChannelEvent::wrap(channel));
 
                 Ok::<_, BoxedError>(events)
             }
@@ -89,35 +85,11 @@ struct ChannelEvent<M> {
     message: M,
 }
 
-pub struct LastEventId(pub String);
-
-static LAST_EVENT_ID: HeaderName = HeaderName::from_static("last-event-id");
-
-impl headers::Header for LastEventId {
-    fn name() -> &'static HeaderName {
-        &LAST_EVENT_ID
-    }
-
-    fn decode<'i, I>(values: &mut I) -> Result<Self, headers::Error>
-    where
-        I: Iterator<Item = &'i HeaderValue>,
-    {
-        let value = values.next().ok_or_else(headers::Error::invalid)?;
-        if let Ok(value) = value.to_str() {
-            Ok(Self(value.into()))
-        } else {
-            Err(headers::Error::invalid())
+impl<M> ChannelEvent<M> {
+    fn wrap(channel: channel::Id) -> impl Fn(M) -> Self {
+        move |message| Self {
+            channel: channel.clone(),
+            message,
         }
     }
-
-    fn encode<E>(&self, values: &mut E)
-    where
-        E: Extend<HeaderValue>,
-    {
-        let Self(value) = self;
-        // Must panic or suppress; the trait provides no other options.
-        let value = HeaderValue::from_str(value).expect("LastEventId is a valid header value");
-
-        values.extend(std::iter::once(value));
-    }
 }
diff --git a/src/header.rs b/src/header.rs
new file mode 100644
index 0000000..904e29d
--- /dev/null
+++ b/src/header.rs
@@ -0,0 +1,58 @@
+use axum::{
+    extract::FromRequestParts,
+    http::{request::Parts, HeaderName, HeaderValue},
+};
+use axum_extra::typed_header::TypedHeader;
+
+/// A typed header. When used as a bare extractor, reads from the
+/// `Last-Event-Id` HTTP header.
+pub struct LastEventId(pub String);
+
+static LAST_EVENT_ID: HeaderName = HeaderName::from_static("last-event-id");
+
+impl headers::Header for LastEventId {
+    fn name() -> &'static HeaderName {
+        &LAST_EVENT_ID
+    }
+
+    fn decode<'i, I>(values: &mut I) -> Result<Self, headers::Error>
+    where
+        I: Iterator<Item = &'i HeaderValue>,
+    {
+        let value = values.next().ok_or_else(headers::Error::invalid)?;
+        if let Ok(value) = value.to_str() {
+            Ok(Self(value.into()))
+        } else {
+            Err(headers::Error::invalid())
+        }
+    }
+
+    fn encode<E>(&self, values: &mut E)
+    where
+        E: Extend<HeaderValue>,
+    {
+        let Self(value) = self;
+        // Must panic or suppress; the trait provides no other options.
+        let value = HeaderValue::from_str(value).expect("LastEventId is a valid header value");
+
+        values.extend(std::iter::once(value));
+    }
+}
+
+#[async_trait::async_trait]
+impl<S> FromRequestParts<S> for LastEventId
+where
+    S: Send + Sync,
+{
+    type Rejection = <TypedHeader<Self> as FromRequestParts<S>>::Rejection;
+
+    async fn from_request_parts(parts: &mut Parts, state: &S) -> Result<Self, Self::Rejection> {
+        // This is purely for ergonomics: it allows `RequestedAt` to be extracted
+        // without having to wrap it in `Extension<>`. Callers _can_ still do that,
+        // but they aren't forced to.
+        let TypedHeader(requested_at) =
+            TypedHeader::<Self>::from_request_parts(parts, state).await?;
+
+        Ok(requested_at)
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index f71ef95..8b6a78f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -4,6 +4,7 @@ pub mod cli;
 mod clock;
 mod error;
 mod events;
+mod header;
 mod id;
 mod index;
 mod login;