ryanflorence · November 5, 2022 15:27 · Nov 5, 2022
diff --git a/event-stream.ts b/event-stream.ts
@@ -0,0 +1,35 @@
+type InitFunction = (send: SendFunction) => CleanupFunction;
+type SendFunction = (event: string, data: string) => void;
+type CleanupFunction = () => void;
+
+export function eventStream(request: Request, init: InitFunction) {
+  let stream = new ReadableStream({
+    start(controller) {
+      let encoder = new TextEncoder();
+      let send = (event: string, data: string) => {
+        controller.enqueue(encoder.encode(`event: ${event}\n`));
+        controller.enqueue(encoder.encode(`data: ${data}\n\n`));
+      };
+      let cleanup = init(send);
+
+      let closed = false;
+      let close = () => {
+        if (closed) return;
+        cleanup();
+        closed = true;
+        request.signal.removeEventListener("abort", close);
+        controller.close();
+      };
+
+      request.signal.addEventListener("abort", close);
+      if (request.signal.aborted) {
+        close();
+        return;
+      }
+    },
+  });
+
+  return new Response(stream, {
+    headers: { "Content-Type": "text/event-stream" },
+  });
+}