feat(logging): JSON形式の構造化ログでログを出力できるように (MisskeyIO#346)

packages/backend/src/boot/master.ts

@@ -28,7 +28,7 @@ const bootLogger = logger.createSubLogger('boot', 'magenta', false);
 const themeColor = chalk.hex('#86b300');
 
 function greet() {
-	if (!envOption.quiet) {
+	if (!envOption.quiet && !envOption.logJson) {
 		//#region Misskey logo
 		const v = `v${meta.version}`;
 		console.log(themeColor('  _____ _         _           '));
@@ -46,7 +46,7 @@ function greet() {
 	}
 
 	bootLogger.info('Welcome to Misskey!');
-	bootLogger.info(`Misskey v${meta.version}`, null, true);
+	bootLogger.info(`Misskey v${meta.version}`, { version: meta.version, hostname: os.hostname(), pid: process.pid }, true);
 }
 
 /**

packages/backend/src/env.ts

@@ -9,6 +9,7 @@ const envOption = {
 	noDaemons: false,
 	disableClustering: false,
 	verbose: false,
+	logJson: false,
 	withLogTime: false,
 	quiet: false,
 };

packages/backend/src/logger.ts

@@ -41,7 +41,7 @@ export default class Logger {
 
 	@bindThis
 	private log(level: Level, message: string, data?: Record<string, any> | null, important = false, subContexts: Context[] = [], store = true): void {
-		if (envOption.quiet) return;
+		if (envOption.quiet && !envOption.logJson) return;
 		if (!this.store) store = false;
 		if (level === 'debug') store = false;
 
@@ -50,6 +50,19 @@ export default class Logger {
 			return;
 		}
 
+		if (envOption.logJson) {
+			console.log(JSON.stringify({
+				time: new Date().toISOString(),
+				level: level,
+				message: message,
+				data: data,
+				important: important,
+				context: [this.context].concat(subContexts).join('.'),
+				cluster: cluster.isPrimary ? 'primary' : `worker-${cluster.worker!.id}`,
+			}));
+			return;
+		}
+
 		const time = dateFormat(new Date(), 'HH:mm:ss');
 		const worker = cluster.isPrimary ? '*' : cluster.worker!.id;
 		const l =