深入学习 Winston

[nonocast]

目录

• 基本逻辑
• 使用方式
• 其他

基本逻辑

• 通过winston.createLogger创建logger
• winston自身就扮演了一个defaultLogger

const winston = require('winston');
winston.add(new winston.transports.Console());
winston.info('hello')

• winston.loggers是一个Container, Container就是一个logger的map，如果你自己创建多个logger也是一样的
• 核心的logger对象本身一个Node Stream, pipe到对应的Transport, 需要了解一下Node Stream的基本flow
• createLogger是一个factory method. 创建对应的logger
• logger.log直接走到logger然后call this.push, 接着通过_transform来应用logger上的format，将format后的内容pipe到logger对应的transports, transports再应用一次transports上的format，最后根据transport自身属性实现输出
• logger.info则是通过createLogger中根据level挂上去的方法

使用方式

javascript本身的弱类型带来的灵活和不确定性相辅相成。最简单的方式直接看quick start

标准调用方法:

logger.info(msg);
logger.info(msg, meta);

具体来说：

winston.info('hello'); // {"message":"hello","level":"info"}
winston.info('hello', { foo: 'bar' }); // {"foo":"bar","level":"info","message":"hello"}

winston.info({ foo: 'bar' }); // {"message":{"foo":"bar"},"level":"info"}
winston.info({ message: 'hello' }); // {"message":"hello","level":"info"}
winston.info('hello', { message: 'world' }); // {"message":"hello world","level":"info"}

winston.info(); // {"level":"info","message":""}
winston.info('hello', 'world'); //x {"level":"info","message":"hello"}
winston.info(null); // {"message":null,"level":"info"}
winston.info(''); // {"message":"","level":"info"}
winston.info({}); // {"message":{},"level":"info"}

winston.info({ message: 'hello', foo: 'bar' }, { tag: 'user-service' }); // {"tag":"user-service","level":"info","message":{"message":"hello","foo":"bar"}}
winston.info({ message: 'hello', foo: 'bar' }, { message: 'world', tag: 'user-service' }); // {"message":"[object Object] world","tag":"user-service","level":"info"}

无参数逻辑:

// When provided nothing assume the empty string
if (args.length === 0) {
  self.log(level, '');
  return self;
}

一个参数逻辑：

// Optimize the hot-path which is the single object.
if (args.length === 1) {
  const [msg] = args;
  const info = msg && msg.message && msg || { message: msg };
  info.level = info[LEVEL] = level;
  self._addDefaultMeta(info);
  self.write(info);
  return (this || logger);
}

二个及以上参数逻辑：

// Otherwise build argument list which could potentially conform to either:
// 1. v3 API: log(obj)
// 2. v1/v2 API: log(level, msg, ... [string interpolate], [{metadata}], [callback])
return self.log(level, ...args);

所以一般来说，禁用splat, 然后常规记录信息的方式：

logger.info(message, meta);

如果是error，

logger.error(error);
logger.error(message, error);

但问题是logger.error(error)有bug，所以需要一个format进行修复，将Error提前转换为plain object。

winston.info(new Error('user not found')); // {"level":"info"}

所以需要通过format fix掉这个bug

const winston = require('winston');
const { serializeError } = require('serialize-error');

let fixerror = winston.format((info, opts) => {
  if (info instanceof Error) {
    // logger.error(new Error('message'));
    let error = serializeError(info);
    error[Symbol.for('level')] = info.level;
    return error;
  } else if (info.message instanceof Error) {
    // logger.error(new Error());
    let error = serializeError(info.message);
    if(!error.message) error.message = info.message.constructor.name;
    error[Symbol.for('level')] = info.level;
    return error;
  } else {
    return info;
  }
});

let logger = winston.createLogger({
  transports: [new winston.transports.Console()],
  format: winston.format.combine(fixerror(), winston.format.json()),
});

logger.info('hello');
logger.info(new Error());
logger.info(new Error('user not found'));

输出:

{"name":"Error","message":"Error","stack":"Error\n    at Object../src/index.js (/Users/nonocast/Develop/hello/hello-winston/test1/dist/bundle.js:126:13)\n    at __webpack_require__ (/Users/nonocast/Develop/hello/hello-winston/test1/dist/bundle.js:20:30)\n    at /Users/nonocast/Develop/hello/hello-winston/test1/dist/bundle.js:84:18\n    at Object.<anonymous> (/Users/nonocast/Develop/hello/hello-winston/test1/dist/bundle.js:87:10)\n    at Module._compile (internal/modules/cjs/loader.js:1137:30)\n    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1157:10)\n    at Module.load (internal/modules/cjs/loader.js:985:32)\n    at Function.Module._load (internal/modules/cjs/loader.js:878:14)\n    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:71:12)\n    at internal/main/run_main_module.js:17:47"}
{"level":"info","name":"Error","message":"user not found","stack":"Error: user not found\n    at Object../src/index.js (/Users/nonocast/Develop/hello/hello-winston/test1/dist/bundle.js:127:13)\n    at __webpack_require__ (/Users/nonocast/Develop/hello/hello-winston/test1/dist/bundle.js:20:30)\n    at /Users/nonocast/Develop/hello/hello-winston/test1/dist/bundle.js:84:18\n    at Object.<anonymous> (/Users/nonocast/Develop/hello/hello-winston/test1/dist/bundle.js:87:10)\n    at Module._compile (internal/modules/cjs/loader.js:1137:30)\n    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1157:10)\n    at Module.load (internal/modules/cjs/loader.js:985:32)\n    at Function.Module._load (internal/modules/cjs/loader.js:878:14)\n    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:71:12)\n    at internal/main/run_main_module.js:17:47"}

Error有没有message都会发生不一样的情况，所以说，fixerror也只是权宜，还是在log之前就将Error转换为string或者plain object再继续，否则很麻烦。

create-logger.js中，

const info = msg && msg.message && msg || { message: msg };

也就是说传入没有message的Error，winston就会将其置为info.message，而如果是有message则会将Error误认为是info object。winston通过format.error来处理error问题，

const logger = winston.createLogger({
  format: winston.format.combine(
    winston.format.errors({ stack: true }),
    winston.format.json()
  ),
  transports: [
    new winston.transports.Console(),
  ]
});

logger.info(new Error());
logger.info(new Error('user not found'));

此时message会采用error的message, 然后加上stack，完美。

logger.info(new Error());
logger.info(new Error('user not found'));
logger.info('error:', new Error('null refenerce'));

如果有显示message，则最终message会是error: null reference。

其他

• child

const winston = require('winston');

winston.add(new winston.transports.Console());

let logger = winston.child({
  source: 'user-service'
});

logger.info('hi');

output

{"source":"user-service","message":"hi","level":"info"}

如果每个unit需要对自己的日志打上tag，则通过child就可以很方便实现：

const winston = require('winston');
const logger = winston.createLogger({
  transports: [new winston.transports.Console()],
});

const userServiceLogger = logger.child({ tag: 'service:user' });
userServiceLogger.info('create user1');

const deviceServiceLogger = logger.child({ tag: 'service:device' });
deviceServiceLogger.info('del device1');

output:

{"tag":"service:user","message":"create user1","level":"info"}
{"tag":"service:device","message":"del device1","level":"info"}

如果日志根据情况不同需要写入不同的transport，形式或者文件，那么应该采用多个logger，通过container save&load。而如果是打不同tag，则通过meta实现即可。

参考

• [3.0.0] Error object is not parsed or printed · Issue #1338 · winstonjs/winston