Add --socket-fd CLI option (#7940)

docs/FAQ.md

@@ -41,6 +41,7 @@
 - [How do I disable the proxy?](#how-do-i-disable-the-proxy)
 - [How do I disable file download?](#how-do-i-disable-file-download)
 - [Why do web views not work?](#why-do-web-views-not-work)
+- [Can I run code-server with systemd socket activation?](#can-i-run-code-server-with-systemd-socket-activation)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
 <!-- prettier-ignore-end -->
@@ -560,3 +561,41 @@ To fix this, you must either:
   create and trust a certificate manually).
 - Disable security if your browser allows it. For example, in Chromium see
   `chrome://flags/#unsafely-treat-insecure-origin-as-secure`
+
+## Can I run code-server with systemd socket activation?
+
+Yes. Pass the inherited socket to code-server with `--socket-fd`. systemd
+passes the first listening socket as file descriptor `3`.
+
+Create a socket unit, `~/.config/systemd/user/code-server.socket`:
+
+```ini
+[Socket]
+ListenStream=8080
+
+[Install]
+WantedBy=sockets.target
+```
+
+And a matching service unit, `~/.config/systemd/user/code-server.service`:
+
+```ini
+[Service]
+ExecStart=/usr/bin/code-server --socket-fd 3
+```
+
+Then enable and start the socket:
+
+```bash
+systemctl --user enable --now code-server.socket
+```
+
+code-server will start on the first connection and listen on the socket
+systemd created. `--socket-fd` takes precedence over `--socket` and
+`--bind-addr`/`--port`/`--host`, and `--socket-mode` is ignored because
+systemd owns the socket's permissions.
+
+Socket activation only changes how code-server binds; your usual
+authentication still applies (it keeps prompting for the configured password
+unless you set `--auth none`), so keep authentication enabled when exposing the
+server.

src/node/app.ts

@@ -13,7 +13,8 @@ import { EditorSessionManager, makeEditorSessionManagerServer } from "./vscodeSo
 import { handleUpgrade } from "./wsRouter"
 
 type SocketOptions = { socket: string; "socket-mode"?: string }
-type ListenOptions = DefaultedArgs | SocketOptions
+type FdOptions = { "socket-fd": number }
+type ListenOptions = DefaultedArgs | SocketOptions | FdOptions
 
 export interface App extends Disposable {
   /** Handles regular HTTP requests. */
@@ -30,8 +31,12 @@ const isSocketOpts = (opts: ListenOptions): opts is SocketOptions => {
   return !!(opts as SocketOptions).socket || !(opts as DefaultedArgs).host
 }
 
+export const isFdOpts = (opts: ListenOptions): opts is FdOptions => {
+  return typeof (opts as FdOptions)["socket-fd"] === "number"
+}
+
 export const listen = async (server: http.Server, opts: ListenOptions) => {
-  if (isSocketOpts(opts)) {
+  if (!isFdOpts(opts) && isSocketOpts(opts)) {
     try {
       await fs.unlink(opts.socket)
     } catch (error: any) {
@@ -46,7 +51,9 @@ export const listen = async (server: http.Server, opts: ListenOptions) => {
       server.on("error", (err) => util.logError(logger, "http server error", err))
       resolve()
     }
-    if (isSocketOpts(opts)) {
+    if (isFdOpts(opts)) {
+      server.listen({ fd: opts["socket-fd"] }, onListen)
+    } else if (isSocketOpts(opts)) {
       server.listen(opts.socket, onListen)
     } else {
       // [] is the correct format when using :: but Node errors with them.
@@ -56,7 +63,7 @@ export const listen = async (server: http.Server, opts: ListenOptions) => {
 
   // NOTE@jsjoeio: we need to chmod after the server is finished
   // listening. Otherwise, the socket may not have been created yet.
-  if (isSocketOpts(opts)) {
+  if (!isFdOpts(opts) && isSocketOpts(opts)) {
     if (opts["socket-mode"]) {
       await fs.chmod(opts.socket, opts["socket-mode"])
     }

src/node/cli.ts

@@ -83,6 +83,7 @@ export interface UserProvidedArgs extends UserProvidedCodeArgs {
   open?: boolean
   "bind-addr"?: string
   socket?: string
+  "socket-fd"?: number
   "socket-mode"?: string
   "trusted-origins"?: string[]
   version?: boolean
@@ -236,6 +237,10 @@ export const options: Options<Required<UserProvidedArgs>> = {
   port: { type: "number", description: "" },
 
   socket: { type: "string", path: true, description: "Path to a socket (bind-addr will be ignored)." },
+  "socket-fd": {
+    type: "number",
+    description: "File descriptor of a pre-bound, listening socket to use (for systemd socket activation).",
+  },
   "socket-mode": { type: "string", description: "File mode of the socket." },
   "trusted-origins": {
     type: "string[]",

test/unit/node/app.test.ts

@@ -3,7 +3,7 @@ import { promises } from "fs"
 import * as http from "http"
 import * as https from "https"
 import * as path from "path"
-import { createApp, ensureAddress, handleArgsSocketCatchError, listen } from "../../../src/node/app"
+import { createApp, ensureAddress, handleArgsSocketCatchError, isFdOpts, listen } from "../../../src/node/app"
 import { OptionalString, setDefaults } from "../../../src/node/cli"
 import { generateCertificate } from "../../../src/node/util"
 import { clean, mockLogger, getAvailablePort, tmpdir } from "../../utils/helpers"
@@ -261,3 +261,47 @@ describe("listen", () => {
     }
   })
 })
+
+describe("listen (socket-fd)", () => {
+  // Wrap a bound-but-not-yet-listening TCP socket so we get a real file
+  // descriptor that listen({ fd }) can adopt, mirroring the systemd socket
+  // activation case where the process inherits an fd and calls listen(2) on it.
+  // Using a live net.Server's fd instead fails with EEXIST because the socket
+  // is already listening in-process.
+  // eslint-disable-next-line @typescript-eslint/no-var-requires
+  const { TCP, constants: TCPConstants } = (process as any).binding("tcp_wrap")
+
+  let inherited: any
+  let httpServer: http.Server
+  let unlinkSpy: jest.SpyInstance
+
+  beforeEach(async () => {
+    mockLogger()
+    unlinkSpy = jest.spyOn(promises, "unlink")
+    inherited = new TCP(TCPConstants.SERVER)
+    inherited.bind("127.0.0.1", 0)
+    httpServer = http.createServer()
+  })
+
+  afterEach(() => {
+    httpServer.close()
+    try {
+      inherited.close()
+    } catch {
+      // The fd is adopted by httpServer.close() above; ignore double-close.
+    }
+    jest.clearAllMocks()
+  })
+
+  it("isFdOpts detects a numeric socket-fd", () => {
+    expect(isFdOpts({ "socket-fd": 3 })).toBe(true)
+    expect(isFdOpts({ socket: "/tmp/x.sock" } as any)).toBe(false)
+  })
+
+  it("listens on an inherited fd without unlinking", async () => {
+    const fd = inherited.fd as number
+    await listen(httpServer, { "socket-fd": fd })
+    expect(httpServer.address()).not.toBeNull()
+    expect(unlinkSpy).not.toHaveBeenCalled()
+  })
+})