/**
* Simple logger that outputs to stderr (required for MCP servers)
* but with proper log level prefixes for clarity.
*
* MCP servers must keep stdout clean for JSON-RPC communication,
* so all logs go to stderr regardless of level.
*
* Security: All log output is automatically redacted to remove sensitive
* information like cookies, tokens, passwords, and API keys.
*/
import { redactForLogging } from './security.js';
export type LogLevel = 'debug' | 'info' | 'warn' | 'error';
const LOG_LEVEL_PRIORITY: Record<LogLevel, number> = {
debug: 0,
info: 1,
warn: 2,
error: 3,
};
// Default to 'info' level, can be changed via environment variable
const currentLevel: LogLevel = (process.env.LOG_LEVEL as LogLevel) || 'info';
function shouldLog(level: LogLevel): boolean {
return LOG_LEVEL_PRIORITY[level] >= LOG_LEVEL_PRIORITY[currentLevel];
}
function formatArg(arg: unknown): string {
if (arg instanceof Error) {
// Error objects don't serialize well with JSON.stringify
const errorStr = `${arg.name}: ${arg.message}${arg.stack ? `\n${arg.stack}` : ''}`;
return redactForLogging(errorStr);
}
if (typeof arg === 'object' && arg !== null) {
try {
const jsonStr = JSON.stringify(arg, null, 2);
return redactForLogging(jsonStr);
} catch {
return redactForLogging(String(arg));
}
}
return redactForLogging(String(arg));
}
function formatMessage(level: LogLevel, message: string, ...args: unknown[]): string {
const timestamp = new Date().toISOString();
const prefix = `[${timestamp}] [${level.toUpperCase()}]`;
// Redact the main message as well
const safeMessage = redactForLogging(message);
if (args.length > 0) {
return `${prefix} ${safeMessage} ${args.map(formatArg).join(' ')}`;
}
return `${prefix} ${safeMessage}`;
}
export const logger = {
debug(message: string, ...args: unknown[]): void {
if (shouldLog('debug')) {
console.error(formatMessage('debug', message, ...args));
}
},
info(message: string, ...args: unknown[]): void {
if (shouldLog('info')) {
console.error(formatMessage('info', message, ...args));
}
},
warn(message: string, ...args: unknown[]): void {
if (shouldLog('warn')) {
console.error(formatMessage('warn', message, ...args));
}
},
error(message: string, ...args: unknown[]): void {
if (shouldLog('error')) {
console.error(formatMessage('error', message, ...args));
}
},
};
