feat: implement isAlive check

- Implemented isAlive check for start and status commands
- Added separated option for commands
- Created helper function to obtain socket

bin/eslint_d.js

@@ -1,8 +1,8 @@
 #!/usr/bin/env node
 
-import { loadConfig } from '../lib/config.js';
+import { loadConfig, removeConfig } from '../lib/config.js';
 import { createResolver } from '../lib/resolver.js';
-import { forwardToDaemon } from '../lib/forwarder.js';
+import { forwardToDaemon, isAlive } from '../lib/forwarder.js';
 import { launchDaemon, stopDaemon } from '../lib/launcher.js';
 import { filesHash } from '../lib/hash.js';
 
@@ -31,11 +31,17 @@ const command = process.argv[2];
   ]);
   switch (command) {
     case 'start':
-      if (config) {
+      if (await isAlive(config)) {
         console.log('eslint_d: Already running');
-      } else {
-        await launchDaemon(resolver, hash);
+        return;
+      }
+
+      if (config) {
+        await removeConfig(resolver);
       }
+
+      await launchDaemon(resolver, hash);
+
       return;
     case 'stop':
       if (config) {

lib/commands.js

@@ -0,0 +1,3 @@
+export const PING_COMMAND = 'ESLINT_D_PING';
+export const SHUTDOWN_COMMAND = 'ESLINT_D_SHUTDOWN';
+export const LINT_COMMAND = 'ESLINT_D_LINT';

lib/forwarder.js

@@ -1,15 +1,45 @@
 import net from 'node:net';
 import supportsColor from 'supports-color';
 import { removeConfig } from '../lib/config.js';
+import { LINT_COMMAND, PING_COMMAND } from './commands.js';
 
 /**
- * @import { Config} from '../lib/config.js'
- * @import { Resolver} from '../lib/resolver.js'
+ * @import { Config } from './config.js'
+ * @import { Resolver } from './resolver.js'
  */
 
 const EXIT_TOKEN_REGEXP = new RegExp(/EXIT([0-9]{3})/);
 const EXIT_TOKEN_LENGTH = 7;
 
+/**
+ * @param {Config | null} config
+ * @returns {Promise<boolean>}
+ */
+export function isAlive(config) {
+  return forwardCommandToDaemon(config, PING_COMMAND)
+    .then(() => true)
+    .catch(() => false);
+}
+
+/**
+ * @param {Config | null} config
+ * @param {string} command
+ * @returns {Promise<void>}
+ */
+export async function forwardCommandToDaemon(config, command) {
+  if (!config) {
+    return Promise.reject(new Error('config not found'));
+  }
+
+  const socket = await connectToDaemon(config);
+  socket.write(JSON.stringify([config.token, command]));
+  socket.end();
+
+  return new Promise((resolve, reject) => {
+    socket.on('end', () => resolve()).on('error', (err) => reject(err));
+  });
+}
+
 /**
  * @param {Resolver} resolver
  * @param {Config} config
@@ -38,9 +68,24 @@ export async function forwardToDaemon(resolver, config) {
     );
   }
 
-  const socket = net.connect(config.port, '127.0.0.1');
+  let socket;
+  try {
+    socket = await connectToDaemon(config);
+  } catch (/** @type {any} */ err) {
+    if (err['code'] === 'ECONNREFUSED') {
+      console.error(`eslint_d: ${err} - removing config`);
+      await removeConfig(resolver);
+    } else {
+      console.error(`eslint_d: ${err}`);
+    }
+    // eslint-disable-next-line require-atomic-updates
+    process.exitCode = 1;
+    return;
+  }
+
   const args = [
     config.token,
+    LINT_COMMAND,
     stdout ? stdout.level : 0,
     process.cwd(),
     eslint_args
@@ -90,13 +135,8 @@ export async function forwardToDaemon(resolver, config) {
         process.exitCode = 1;
       }
     })
-    .on('error', async (err) => {
-      if (err['code'] === 'ECONNREFUSED') {
-        console.error(`eslint_d: ${err} - removing config`);
-        await removeConfig(resolver);
-      } else {
-        console.error(`eslint_d: ${err}`);
-      }
+    .on('error', (err) => {
+      console.error(`eslint_d: ${err}`);
       process.exitCode = 1;
     });
 
@@ -113,6 +153,22 @@ export async function forwardToDaemon(resolver, config) {
   }
 }
 
+/**
+ * @param {Config} config
+ * @returns {Promise<net.Socket>}
+ */
+function connectToDaemon(config) {
+  return new Promise((resolve, reject) => {
+    const socket = net.connect(config.port, '127.0.0.1');
+    socket
+      .on('connect', () => resolve(socket))
+      .on('connectionAttemptFailed', (err) => {
+        reject(err);
+        socket.end();
+      });
+  });
+}
+
 function readStdin() {
   return new Promise((resolve, reject) => {
     let content = '';