【node】koa-logger

koa-logger source code analysis

Taking the GET request "/" as an example, koa-logger will print the following log:

 <-- GET /
GET / - 790ms
  --> GET / 200 803ms 185b

Divided into request and response logs

 // koa-logger 主函数
function dev (opts) {
  // print函数，默认参数为空时是调用console.log，如果有transporter选项，则调用transporter函数代替
  const print = (function () {
    let transporter
    if (typeof opts === 'function') {
      transporter = opts
    } else if (opts && opts.transporter) {
      transporter = opts.transporter
    }

    return function printFunc (...args) {
      // 注意：这里做了格式说明符替换
      const str = util.format(...args)
      if (transporter) {
        transporter(str, args)
      } else {
        console.log(...args)
      }
    }
  }())

  return async function logger (ctx, next) {
    // request
    const start = ctx[Symbol.for('request-received.startTime')] ? ctx[Symbol.for('request-received.startTime')].getTime() : Date.now()
    // 打印请求日志
    print('  ' + chalk.gray('<--') +
      ' ' + chalk.bold('%s') +
      ' ' + chalk.gray('%s'),
    ctx.method,
    ctx.originalUrl)

    try {
      await next()
    } catch (err) {
      // log uncaught downstream errors
      log(print, ctx, start, null, err)
      throw err
    }

    // calculate the length of a streaming response
    // by intercepting the stream with a counter.
    // only necessary if a content-length header is currently not set.
    // 通过使用计数器拦截流来计算响应流的长度。只有在当前没有设置Content-Length的响应报头时才需要。
    const length = ctx.response.length
    const body = ctx.body
    let counter
    if (length == null && body && body.readable) {
      ctx.body = body
        .pipe(counter = Counter())
        .on('error', ctx.onerror)
    }

    // log when the response is finished or closed,
    // whichever happens first.
    // 记录响应完成或关闭的时间，以先发生的时间为准。一般都是触发finish事件
    const res = ctx.res

    const onfinish = done.bind(null, 'finish')
    const onclose = done.bind(null, 'close')

    // 重点：判断一个流请求是否结束
    res.once('finish', onfinish)
    res.once('close', onclose)

    function done (event) {
      res.removeListener('finish', onfinish)
      res.removeListener('close', onclose)
      // 打印 请求方式 路径 状态码 响应时间 报文长度
      log(print, ctx, start, counter ? counter.length : length, null, event)
    }
  }
}

There is also a logger helper function:

 /**
 * Log helper. 封装的输出打点数据的辅助函数
 */

function log (print, ctx, start, len, err, event) {
  // 从err获取响应的状态码
  // 以下字段比如err.isBoom、err.output.statusCode、err.status等都是根据业务来的
  // 一般业务都有统一的处理响应的中间件
  // 注意500、404的处理区分
  const status = err
    ? (err.isBoom ? err.output.statusCode : err.status || 500)
    : (ctx.status || 404)

  // set the color of the status code;
  // 根据不同状态码区间，1xx、2xx、3xx、4xx、5xx，映射选择不用颜色输出加以区分
  const s = status / 100 | 0
  // eslint-disable-next-line
  const color = colorCodes.hasOwnProperty(s) ? colorCodes[s] : colorCodes[0]

  // get the human readable response length
  let length
  // 204、205、304特殊处理
  if (~[204, 205, 304].indexOf(status)) {
    length = ''
  } else if (len == null) {
    length = '-'
  } else {
    // 借助bytes库，计算响应内容大小、输出类似2b、2kb
    length = bytes(len).toLowerCase()
  }

  const upstream = err ? chalk.red('xxx')
    : event === 'close' ? chalk.yellow('-x-')
      : chalk.gray('-->')

  print('  ' + upstream +
    ' ' + chalk.bold('%s') +
    ' ' + chalk.gray('%s') +
    ' ' + chalk[color]('%s') +
    ' ' + chalk.gray('%s') +
    ' ' + chalk.gray('%s'),
  ctx.method,
  ctx.originalUrl,
  status,
  time(start),
  length)
}

/**
 * Show the response time in a human readable format.
 * In milliseconds if less than 10 seconds,
 * in seconds otherwise.
 */

function time (start) {
  const delta = Date.now() - start
  return humanize(delta < 10000
    ? delta + 'ms'
    : Math.round(delta / 1000) + 's')
}

Summarize

The code of this package is very simple, less than 200 lines of code, and the function is also very simple. It needs to be expanded and customized manually.