feat(socket-mode): support undici v8 as a peer dependency

.changeset/socket-mode-undici-v8.md

@@ -0,0 +1,7 @@
+---
+"@slack/socket-mode": minor
+---
+
+Support `undici@^8` as a peer dependency in addition to `undici@^7`. `undici@^8` requires Node.js >=22.19; `undici@^7` continues to support Node.js >=20.
+
+The default dispatcher now pins the WebSocket connection to HTTP/1.1, since `undici@^8` offers HTTP/2 by default. To do the same with a custom `ProxyAgent` dispatcher, pass `requestTls: { allowH2: false }`.

.github/workflows/ci-build.yml

@@ -23,6 +23,12 @@ jobs:
           - "22.x"
           - "24.x"
           - "26.x"
+        undici:
+          - "undici@^7"
+          - "undici@^8"
+        exclude:
+          - node-version: "20.x"
+            undici: "undici@^8"
     runs-on: ${{ matrix.os }}
     permissions:
       contents: read
@@ -45,6 +51,8 @@ jobs:
           npm --version
       - name: Install dependencies
         run: npm ci --verbose
+      - name: Install undici
+        run: npm install ${{ matrix.undici }} --workspace=packages/socket-mode --no-save
       - name: Build packages
         run: npm run build
       - name: Lint

packages/socket-mode/package.json

@@ -57,7 +57,7 @@
     "eventemitter3": "^5"
   },
   "peerDependencies": {
-    "undici": "^7.0.0"
+    "undici": "^7.0.0 || ^8.0.0"
   },
   "devDependencies": {
     "@types/proxyquire": "^1.3.31",

packages/socket-mode/src/SlackWebSocket.ts

@@ -229,7 +229,8 @@ export class SlackWebSocket {
    * leaving no other way to close a stalled peer.
    */
   private buildDefaultDispatcher(): Dispatcher {
-    const baseConnect = buildConnector({});
+    // undici v8 defaults allowH2 to true; pin HTTP/1.1 so the WebSocket keeps a dedicated socket.
+    const baseConnect = buildConnector({ allowH2: false });
     return new Agent({
       connect: (opts, callback) => {
         baseConnect(opts, (err, socket) => {