OpenTelemetryBunyanStream.ts

/*
 * Copyright The OpenTelemetry Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import { logs, SeverityNumber, Logger } from '@opentelemetry/api-logs';
import type { LoggerOptions } from '@opentelemetry/api-logs';
import type { LogLevelString } from 'bunyan';
import { VERSION } from './version';

const DEFAULT_INSTRUMENTATION_SCOPE_NAME = 'io.opentelemetry.contrib.bunyan';
const DEFAULT_INSTRUMENTATION_SCOPE_VERSION = VERSION;

// This block is a copy (modulo code style and TypeScript types) of the Bunyan
// code that defines log level value and names. These values won't ever change
// in bunyan@1. This file is part of *instrumenting* Bunyan, so we want to
// avoid a dependency on the library.
const TRACE = 10;
const DEBUG = 20;
const INFO = 30;
const WARN = 40;
const ERROR = 50;
const FATAL = 60;
const levelFromName: Record<LogLevelString, number> = {
  trace: TRACE,
  debug: DEBUG,
  info: INFO,
  warn: WARN,
  error: ERROR,
  fatal: FATAL,
};
const nameFromLevel: { [level: number]: string } = {};
Object.keys(levelFromName).forEach(function (name) {
  nameFromLevel[levelFromName[name as LogLevelString]] = name;
});

const OTEL_SEV_NUM_FROM_BUNYAN_LEVEL: { [level: number]: SeverityNumber } = {
  [TRACE]: SeverityNumber.TRACE,
  [DEBUG]: SeverityNumber.DEBUG,
  [INFO]: SeverityNumber.INFO,
  [WARN]: SeverityNumber.WARN,
  [ERROR]: SeverityNumber.ERROR,
  [FATAL]: SeverityNumber.FATAL,
};

const EXTRA_SEV_NUMS = [
  SeverityNumber.TRACE2,
  SeverityNumber.TRACE3,
  SeverityNumber.TRACE4,
  SeverityNumber.DEBUG2,
  SeverityNumber.DEBUG3,
  SeverityNumber.DEBUG4,
  SeverityNumber.INFO2,
  SeverityNumber.INFO3,
  SeverityNumber.INFO4,
  SeverityNumber.WARN2,
  SeverityNumber.WARN3,
  SeverityNumber.WARN4,
  SeverityNumber.ERROR2,
  SeverityNumber.ERROR3,
  SeverityNumber.ERROR4,
  SeverityNumber.FATAL2,
  SeverityNumber.FATAL3,
  SeverityNumber.FATAL4,
];

function severityNumberFromBunyanLevel(lvl: number) {
  // Fast common case: one of the known levels
  const sev = OTEL_SEV_NUM_FROM_BUNYAN_LEVEL[lvl];
  if (sev !== undefined) {
    return sev;
  }

  // Otherwise, scale the Bunyan level range -- 10 (TRACE) to 70 (FATAL+10)
  // -- onto the extra OTel severity numbers (TRACE2, TRACE3, ..., FATAL4).
  // Values below bunyan.TRACE map to SeverityNumber.TRACE2, which is a bit
  // weird.
  return EXTRA_SEV_NUMS[
    Math.min(
      EXTRA_SEV_NUMS.length - 1,
      Math.max(0, Math.floor(((lvl - 10) / (70 - 10)) * EXTRA_SEV_NUMS.length))
    )
  ];
}

/**
 * A Bunyan stream for sending log records to the OpenTelemetry Logs Bridge API.
 */
export class OpenTelemetryBunyanStream {
  private _otelLogger: Logger;

  constructor(name?: string, version?: string, options?: LoggerOptions) {
    this._otelLogger = logs.getLogger(
      name || DEFAULT_INSTRUMENTATION_SCOPE_NAME,
      version || DEFAULT_INSTRUMENTATION_SCOPE_VERSION,
      options
    );
  }

  /**
   * Convert from https://github.com/trentm/node-bunyan#log-record-fields
   * to https://opentelemetry.io/docs/specs/otel/logs/data-model/
   *
   * Dev Notes:
   * - We drop the Bunyan 'v' field. It is meant to indicate the format
   *   of the Bunyan log record. FWIW, it has always been `0`.
   * - Some Bunyan fields would naturally map to Resource attributes:
   *      hostname -> host.name
   *      name -> service.name
   *      pid -> process.pid
   *   However, AFAIK there isn't a way to influence the LoggerProvider's
   *   `resource` from here.
   * - Strip the `trace_id` et al fields that may have been added by the
   *   the _emit wrapper.
   */
  write(rec: Record<string, any>) {
    // eslint-disable-next-line @typescript-eslint/no-unused-vars
    const { time, level, msg, v, trace_id, span_id, trace_flags, ...fields } =
      rec;
    let timestamp = undefined;
    if (typeof time.getTime === 'function') {
      timestamp = time.getTime(); // ms
    } else {
      fields.time = time; // Expose non-Date "time" field on attributes.
    }
    const otelRec = {
      timestamp,
      observedTimestamp: timestamp,
      severityNumber: severityNumberFromBunyanLevel(level),
      severityText: nameFromLevel[level],
      body: msg,
      attributes: fields,
    };
    this._otelLogger.emit(otelRec);
  }
}