1 files changed, 58 insertions, 0 deletions
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)
+    }
+}