CloudWatch Log Events With Metadata

cloudwatch-log-events-with-metadata.ts

type JSONValue =
  | string
  | number
  | boolean
  | { [x: string]: JSONValue }
  | Array<JSONValue>;

/**
 * A CloudWatch Logs type.
 */
type InputLogEvent = {
  timestamp: number;
  message: string;
};

type LogEvent = {
  /**
   * In case we want to store other types of events in the future, like e.g. "completedStage".
   */
  type: 'logEntry';
  /**
   * The time when the log event occurred, expressed as milliseconds since the Unix epoch.
   */
  timestamp: number;
  /**
   * The actual log event body. Can be arbitrary JSON.
   */
  payload: JSONValue;
  /**
   * The stage or component of the pipeline that produced this log entry.
   */
  stage: string;
};

const isValidJson = (s: string) => {
  try {
    JSON.parse(s);
    return true;
  } catch {
    return false;
  }
};

const createLogEvent = (
  { timestamp, message }: InputLogEvent,
  stage: string,
): LogEvent => {
  const payload = isValidJson(message) ? JSON.parse(message) : message;
  return { type: 'logEntry', timestamp, payload, stage };
};

describe('json log statements', () => {
  it('can represent log events correctly', () => {
    const testCases: string[] = [
      '{"foo": "bar", "msg": "I am a valid JSON string."}',
      '"I am not a valid JSON string but I use "reserved [JSON characters}.',
      'I am a plain string.',
    ];
    testCases.forEach((testCase) => {
      const event = createLogEvent(
        { timestamp: Date.now(), message: testCase },
        'train-001',
      );
      // The event must be stringifiable and parseable.
      const stringified = JSON.stringify(event);
      const parsed = JSON.parse(stringified);
      console.log(
        '---------------------------------------------------------------',
      );
      console.log(stringified);
      console.log(parsed);
    });
  });
});