adapter-node - support writable sockets

Current the socket is created based on the umask (commonly `0022`),
resulting in read only sockets.

This change adds the env variable `SOCKET_PATH_IS_WRITABLE`, which configures
`writableAll`, supporting writable sockets.

Author: DamianZaremba

.changeset/blue-glasses-hug.md

@@ -0,0 +1,5 @@
+---
+"@sveltejs/adapter-node": minor
+---
+
+feat: ability to create writable sockets

documentation/docs/25-build-and-deploy/40-adapter-node.md

@@ -60,7 +60,7 @@ If you use Node.js v20.6+, you can use the [`--env-file`](https://nodejs.org/en/
 node +++--env-file=.env+++ build
 ```
 
-### `PORT`, `HOST` and `SOCKET_PATH`
+### `PORT`, `HOST`, `SOCKET_PATH` and `SOCKET_PATH_IS_WRITABLE`
 
 By default, the server will accept connections on `0.0.0.0` using port 3000. These can be customised with the `PORT` and `HOST` environment variables:
 
@@ -74,6 +74,13 @@ Alternatively, the server can be configured to accept connections on a specified
 SOCKET_PATH=/tmp/socket node build
 ```
 
+By default, node will create a socket based on the `umask` (commonly `0022`, resulting in `0755`). When `SOCKET_PATH_IS_WRITABLE` is set to `1`, the socket will be created with `0777`.
+
+```
+SOCKET_PATH_IS_WRITABLE=1 SOCKET_PATH=/tmp/socket node build
+```
+
+
 ### `ORIGIN`, `PROTOCOL_HEADER`, `HOST_HEADER`, and `PORT_HEADER`
 
 HTTP doesn't give SvelteKit a reliable way to know the URL that is currently being requested. The simplest way to tell SvelteKit where the app is being served is to set the `ORIGIN` environment variable:

packages/adapter-node/src/env.js

@@ -3,6 +3,7 @@ import process from 'node:process';
 
 const expected = new Set([
 	'SOCKET_PATH',
+	'SOCKET_PATH_IS_WRITABLE',
 	'HOST',
 	'PORT',
 	'ORIGIN',

packages/adapter-node/src/index.js

@@ -4,6 +4,7 @@ import { env } from 'ENV';
 import polka from 'polka';
 
 export const path = env('SOCKET_PATH', false);
+const writableAll = parseInt(env('SOCKET_PATH_IS_WRITABLE', 0)) === 1;
 export const host = env('HOST', '0.0.0.0');
 export const port = env('PORT', !path && '3000');
 
@@ -38,7 +39,7 @@ if (socket_activation) {
 		console.log(`Listening on file descriptor ${SD_LISTEN_FDS_START}`);
 	});
 } else {
-	server.listen({ path, host, port }, () => {
+	server.listen({ path, host, port, writableAll }, () => {
 		console.log(`Listening on ${path || `http://${host}:${port}`}`);
 	});
 }