From f96c80e8ce0d70033f0c0c2321fa02fdfc4426d0 Mon Sep 17 00:00:00 2001
From: Jason Bedard <jason+github@jbedard.ca>
Date: Sat, 1 Nov 2025 15:30:02 -0700
Subject: [PATCH] feat: support watch protocol v1

---
 .../watch/src/aspect_watch_protocol.mts       | 70 +++++++++++++++++--
 1 file changed, 64 insertions(+), 6 deletions(-)

diff --git a/js/private/watch/src/aspect_watch_protocol.mts b/js/private/watch/src/aspect_watch_protocol.mts
index 61c3001ba..83ea5ba2c 100644
--- a/js/private/watch/src/aspect_watch_protocol.mts
+++ b/js/private/watch/src/aspect_watch_protocol.mts
@@ -11,6 +11,8 @@ export enum MessageType {
     CYCLE_COMPLETED = 'CYCLE_COMPLETED',
     NEGOTIATE = 'NEGOTIATE',
     NEGOTIATE_RESPONSE = 'NEGOTIATE_RESPONSE',
+    SUBSCRIBE = 'SUBSCRIBE',
+    SUBSCRIBE_RESPONSE = 'SUBSCRIBE_RESPONSE',
     EXIT = 'EXIT',
 }
 
@@ -18,6 +20,27 @@ export interface Message {
     readonly kind: MessageType
 }
 
+export interface NegotiateMessage extends Message {
+    readonly kind: MessageType.NEGOTIATE
+    readonly versions: number[]
+}
+
+export interface NegotiateResponseMessage extends Message {
+    readonly kind: MessageType.NEGOTIATE_RESPONSE
+    readonly version: number
+}
+
+export type WatchType = 'sources' | 'runfiles'
+
+export interface SubscribeMessage extends Message {
+    readonly kind: MessageType.SUBSCRIBE
+    readonly watch_type: WatchType
+}
+
+export interface SubscribeResponseMessage extends Message {
+    readonly kind: MessageType.SUBSCRIBE_RESPONSE
+}
+
 export interface SourceInfo {
     readonly is_symlink?: boolean
     readonly is_source?: boolean
@@ -40,12 +63,29 @@ export interface CycleSourcesMessage extends CycleMessage {
     readonly sources: CycleMessageSources
 }
 
+export interface ExitMessage extends Message {
+    readonly kind: MessageType.EXIT
+}
+
 // Environment constants
 const { JS_BINARY__LOG_DEBUG } = process.env
 
+function selectVersion(versions: number[]): number {
+    if (versions.includes(1)) {
+        return 1
+    }
+    if (versions.includes(0)) {
+        return 0
+    }
+
+    throw new Error(`No supported protocol versions: ${versions.join(', ')}`)
+}
+
 export class AspectWatchProtocol {
     private readonly socketFile: string
     private readonly connection: net.Socket
+
+    private _version: number = -1
     private _error: (err: Error) => void
     private _cycle: (msg: CycleMessage) => Promise<void>
 
@@ -74,9 +114,18 @@ export class AspectWatchProtocol {
             }
         })
 
-        await this._receive(MessageType.NEGOTIATE)
-        // TODO: throw if unsupported version
-        await this._send(MessageType.NEGOTIATE_RESPONSE, { version: 0 })
+        const { versions } = await this._receive<NegotiateMessage>(
+            MessageType.NEGOTIATE
+        )
+
+        const version = selectVersion(versions)
+
+        await this._send<NegotiateResponseMessage>(
+            MessageType.NEGOTIATE_RESPONSE,
+            { version }
+        )
+
+        this._version = version
 
         return this
     }
@@ -87,7 +136,7 @@ export class AspectWatchProtocol {
     async disconnect() {
         if (this.connection.writable) {
             try {
-                await this._send(MessageType.EXIT)
+                await this._send<ExitMessage>(MessageType.EXIT, {})
             } catch (e) {
                 if (JS_BINARY__LOG_DEBUG) {
                     console.log(
@@ -124,6 +173,15 @@ export class AspectWatchProtocol {
      * build has completed before proceeding.
      */
     async awaitFirstCycle() {
+        if (this._version > 0) {
+            await this._send<SubscribeMessage>(MessageType.SUBSCRIBE, {
+                watch_type: 'runfiles',
+            })
+            await this._receive<SubscribeResponseMessage>(
+                MessageType.SUBSCRIBE_RESPONSE
+            )
+        }
+
         await this.cycle(true)
     }
 
@@ -163,7 +221,7 @@ export class AspectWatchProtocol {
     }
 
     async _receive<M extends Message>(
-        type: MessageType | null = null
+        type: M['kind'] | null = null
     ): Promise<M> {
         return await new Promise((resolve, reject) => {
             const dataBufs: Buffer[] = []
@@ -217,7 +275,7 @@ export class AspectWatchProtocol {
         })
     }
 
-    async _send(type: MessageType, data: Omit<Message, 'kind'> = {}) {
+    async _send<M extends Message>(type: M['kind'], data: Omit<M, 'kind'>) {
         await new Promise<void>((resolve, reject) => {
             try {
                 this.connection.write(