flipper-server refactor

Summary:
This changes moves most of the functionality found in flipper-server to flipper-server-core.

flipper-server will mostly be a package that wraps around flipper-server-core. Staying in flipper-server:
- Command line args
- Orchestration to start the necessary servers

Reviewed By: aigoncharov

Differential Revision: D36807087

fbshipit-source-id: f29002c7cc5d08b8c5184fdaaa02ba22562a9f45

desktop/flipper-server-core/src/server/utilities.tsx

@@ -0,0 +1,73 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import os from 'os';
+import xdgBasedir from 'xdg-basedir';
+import net from 'net';
+import fs from 'fs-extra';
+
+/**
+ * Checks if a socket is in used for given path.
+ * If the path doesn't exist then is not in use. If it does,
+ * create a socket client and attempt to connect to it.
+ * If the connection is established, then there's a process
+ * already listening. Otherwise, it kind of indicates the
+ * contrary.
+ * @param path Path used instead of port number.
+ * @returns True or false dependning on whether the socket is in
+ * use or not.
+ */
+export async function checkSocketInUse(path: string): Promise<boolean> {
+  if (!(await fs.pathExists(path))) {
+    return false;
+  }
+  return new Promise((resolve, _reject) => {
+    const client = net
+      .createConnection(path, () => {
+        resolve(true);
+        client.destroy();
+      })
+      .on('error', (e) => {
+        if (e.message.includes('ECONNREFUSED')) {
+          resolve(false);
+        } else {
+          console.warn(
+            `[conn] Socket ${path} is in use, but we don't know why.`,
+            e,
+          );
+          resolve(false);
+        }
+        client.destroy();
+      });
+  });
+}
+
+/**
+ * Creates a socket path. Used to open the socket at location.
+ * Format: flipper-server-${userInfo}.sock
+ * @returns The created socket path.
+ */
+export async function makeSocketPath(): Promise<string> {
+  const runtimeDir = xdgBasedir.runtime || '/tmp';
+  await fs.mkdirp(runtimeDir);
+  const filename = `flipper-server-${os.userInfo().uid}.sock`;
+  const path = `${runtimeDir}/${filename}`;
+
+  // Depending on the OS this is between 104 and 108:
+  // https://unix.stackexchange.com/a/367012/10198
+  if (path.length >= 104) {
+    console.warn(
+      'Ignoring XDG_RUNTIME_DIR as it would exceed the total limit for domain socket paths. See man 7 unix.',
+    );
+    // Even with the INT32_MAX userid, we should have plenty of room.
+    return `/tmp/${filename}`;
+  }
+
+  return path;
+}