refactor(server): share event stream encoding (#36484)

packages/server/src/event-feed.ts

@@ -0,0 +1,90 @@
+export * as EventFeed from "./event-feed"
+
+import { EventV2 } from "@opencode-ai/core/event"
+import { isOpenCodeEvent, OpenCodeEvent } from "@opencode-ai/protocol/groups/event"
+import { Cause, Context, Effect, Layer, Queue, Schema, Scope, Stream } from "effect"
+
+export const SubscriberCapacity = 4_096
+
+export class SubscriberOverflowError extends Schema.TaggedErrorClass<SubscriberOverflowError>()(
+  "EventFeed.SubscriberOverflow",
+  { capacity: Schema.Int },
+) {}
+
+export class EncodingError extends Schema.TaggedErrorClass<EncodingError>()("EventFeed.EncodingError", {
+  eventID: EventV2.ID,
+  eventType: Schema.String,
+  cause: Schema.Defect(),
+}) {}
+
+export type Error = SubscriberOverflowError | EncodingError
+
+export interface Interface {
+  readonly subscribe: Effect.Effect<Stream.Stream<string, Error>, never, Scope.Scope>
+}
+
+export class Service extends Context.Service<Service, Interface>()("@opencode/server/EventFeed") {}
+
+const encode = Schema.encodeUnknownSync(OpenCodeEvent)
+
+export function frame(event: OpenCodeEvent) {
+  return `data: ${JSON.stringify(encode(event))}\n\n`
+}
+
+export const make = Effect.fn("EventFeed.make")(function* (
+  observe: (subscriber: EventV2.Subscriber) => Effect.Effect<EventV2.Unsubscribe>,
+  options?: { readonly capacity?: number; readonly encode?: (event: OpenCodeEvent) => string },
+) {
+  const capacity = options?.capacity ?? SubscriberCapacity
+  const render = options?.encode ?? frame
+  const subscribers = new Set<Queue.Queue<string, Error>>()
+
+  const fail = (error: Error) =>
+    Effect.sync(() => {
+      const current = Array.from(subscribers)
+      subscribers.clear()
+      for (const subscriber of current) Queue.failCauseUnsafe(subscriber, Cause.fail(error))
+    })
+
+  const publish = Effect.fnUntraced(function* (event: EventV2.Payload) {
+    if (!isOpenCodeEvent(event)) return
+    if (subscribers.size === 0) return
+    const encoded = yield* Effect.try({
+      try: () => render(event),
+      catch: (cause) => new EncodingError({ eventID: event.id, eventType: event.type, cause }),
+    }).pipe(
+      Effect.catch((error) =>
+        Effect.logError("Failed to encode public event", {
+          eventID: error.eventID,
+          eventType: error.eventType,
+          cause: error.cause,
+        }).pipe(Effect.andThen(fail(error)), Effect.as(undefined)),
+      ),
+    )
+    if (encoded === undefined) return
+    for (const subscriber of subscribers) {
+      if (Queue.offerUnsafe(subscriber, encoded)) continue
+      subscribers.delete(subscriber)
+      Queue.failCauseUnsafe(subscriber, Cause.fail(new SubscriberOverflowError({ capacity })))
+    }
+  })
+
+  const unsubscribe = yield* observe(publish)
+  yield* Effect.addFinalizer(() => unsubscribe)
+
+  return Service.of({
+    subscribe: Effect.acquireRelease(
+      Queue.dropping<string, Error>(capacity).pipe(Effect.tap((queue) => Effect.sync(() => subscribers.add(queue)))),
+      (queue) =>
+        Effect.sync(() => subscribers.delete(queue)).pipe(Effect.andThen(Queue.shutdown(queue)), Effect.asVoid),
+    ).pipe(Effect.map(Stream.fromQueue)),
+  })
+})
+
+export const layer = Layer.effect(
+  Service,
+  Effect.gen(function* () {
+    const events = yield* EventV2.Service
+    return yield* make(events.listen)
+  }),
+)

packages/server/src/handlers.ts

@@ -26,6 +26,7 @@ import { CredentialHandler } from "./handlers/credential"
 import { ProjectHandler } from "./handlers/project"
 import { ProjectCopyHandler } from "./handlers/project-copy"
 import { VcsHandler } from "./handlers/vcs"
+import { EventFeed } from "./event-feed"
 
 export const handlers = Layer.mergeAll(
   HealthHandler,
@@ -48,7 +49,7 @@ export const handlers = Layer.mergeAll(
   FileSystemHandler,
   CommandHandler,
   SkillHandler,
-  EventHandler,
+  EventHandler.pipe(Layer.provide(EventFeed.layer)),
   PtyHandler,
   ShellHandler,
   QuestionHandler,

packages/server/src/handlers/event.ts

@@ -1,44 +1,23 @@
 import { EventV2 } from "@opencode-ai/core/event"
-import { isOpenCodeEvent, OpenCodeEvent } from "@opencode-ai/protocol/groups/event"
-import { Effect, Schema, Stream } from "effect"
-import { Sse } from "effect/unstable/encoding"
+import { Effect, Stream } from "effect"
 import { HttpServerResponse } from "effect/unstable/http"
 import { HttpApiBuilder } from "effect/unstable/httpapi"
 import { Api } from "../api"
-
-// Session execution emits dense event bursts; allow healthy SSE clients enough
-// time to absorb one without weakening the bounded slow-subscriber failure.
-const subscriberCapacity = 4_096
-
-function eventData(data: unknown): Sse.Event {
-  return {
-    _tag: "Event",
-    event: "message",
-    id: undefined,
-    data: JSON.stringify(Schema.encodeUnknownSync(OpenCodeEvent)(data)),
-  }
-}
+import { EventFeed } from "../event-feed"
 
 export const EventHandler = HttpApiBuilder.group(Api, "server.event", (handlers) =>
   Effect.gen(function* () {
-    const events = yield* EventV2.Service
+    const feed = yield* EventFeed.Service
     return handlers.handleRaw("event.subscribe", () =>
       Effect.gen(function* () {
         const connected = {
           id: EventV2.ID.create(),
           type: "server.connected",
           data: {},
-        }
+        } as const
         const output = Stream.unwrap(
-          Effect.gen(function* () {
-            // Acquiring the bounded stream installs its listener before readiness is observable.
-            const live = yield* EventV2.liveBounded(events, {
-              capacity: subscriberCapacity,
-              accept: isOpenCodeEvent,
-            })
-            return Stream.make(connected).pipe(Stream.concat(live))
-          }),
-        ).pipe(Stream.map(eventData), Stream.pipeThroughChannel(Sse.encode()))
+          feed.subscribe.pipe(Effect.map((live) => Stream.make(EventFeed.frame(connected)).pipe(Stream.concat(live)))),
+        )
         const heartbeat = Stream.tick("15 seconds").pipe(Stream.map(() => ": heartbeat\n\n"))
         return HttpServerResponse.stream(
           output.pipe(Stream.merge(heartbeat, { haltStrategy: "left" }), Stream.encodeText),