transport.js

import SonicBoom from 'sonic-boom'
import { once } from 'node:events'
import build from 'pino-abstract-transport'
import logfmt from 'logfmt'
import { snakeCase } from 'case-anything'
import { treeToKeyValue } from './tree-to-key-value.js'
import dateFormat from 'dateformat'

/**
 *
 * @type {Record<number, string>}
 */
export const baseLevelToLabel = {
  10: 'trace',
  20: 'debug',
  30: 'info',
  40: 'warn',
  50: 'error',
  60: 'fatal'
}

/**
 * Escapes multi-line strings in an object, recursively and in place.
 *
 * @param {Record<unknown, unknown>} object
 * @returns {Record<string, unknown>}
 */
function deeplyEscapeMultilineStringsInObject (obj) {
  for (const field in obj) {
    if (typeof obj[field] === 'string') {
      obj[field] = obj[field].replace(/\n/g, '\\n')
    } else if (typeof obj[field] === 'object') {
      deeplyEscapeMultilineStringsInObject(obj[field])
    }
  }
}

/**
 *
 * @param {LogFmtTransportOptions} opts
 * @returns {Promise<Transform & build.OnUnknown>}
 */
export default async function (opts = {}) {
  const {
    includeLevelLabel,
    levelLabelKey = 'level_label',
    formatTime,
    timeKey = 'time',
    convertToSnakeCase,
    flattenNestedObjects,
    flattenNestedSeparator,
    customLevels = baseLevelToLabel,
    timeFormat = 'isoDateTime',
    escapeMultilineStrings
  } = opts

  // SonicBoom is necessary to avoid loops with the main thread.
  // It is the same of pino.destination().
  const destination = new SonicBoom({
    dest: opts.destination || 1,
    sync: opts.sync ?? false
  })
  await once(destination, 'ready')

  return build(async function (source) {
    for await (let obj of source) {
      if (includeLevelLabel === true) {
        obj[levelLabelKey] = customLevels[obj.level] ?? 'unknown'
      }

      if (formatTime === true) {
        obj[timeKey] = dateFormat(obj[timeKey], timeFormat)
      }

      // treeToKeyValue transforms the field name to snake case
      // if flattenNestedObjects is enabled.
      if (convertToSnakeCase === true && flattenNestedObjects !== true) {
        for (const field in obj) {
          const snakeCaseName = snakeCase(field)

          if (snakeCaseName !== field) {
            obj[snakeCase(field)] = obj[field]
            delete obj[field]
          }
        }
      }

      if (escapeMultilineStrings === true) {
        deeplyEscapeMultilineStringsInObject(obj)
      }

      if (flattenNestedObjects === true) {
        obj = treeToKeyValue(obj, flattenNestedSeparator, convertToSnakeCase)
      }

      const toDrain = !destination.write(logfmt.stringify(obj) + '\n')
      // This block will handle backpressure
      if (toDrain) {
        await once(destination, 'drain')
      }
    }
  }, {
    async close () {
      destination.end()
      await once(destination, 'close')
    }
  })
}