Support Last-Event-Id as a method of resuming channel events after a disconnect

1 files changed, 34 insertions, 0 deletions

diff --git a/src/channel/header.rs b/src/channel/header.rs
new file mode 100644
index 0000000..eda8214
--- /dev/null
+++ b/src/channel/header.rs
@@ -0,0 +1,34 @@
+use axum::http::{HeaderName, HeaderValue};
+
+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));
+    }
+}