AWS Lambda S3 Notification to SNS with S3 MetaData

s3_sns_lambda.js

'use strict';

// ENV vars
const AWS_REGION_STRING = process.env.AWS_REGION || 'us-east-1';
const AWS_ACCOUNT_ID = process.env.AWS_ACCOUNT_ID;
const SNS_TOPIC_NAME = process.env.SNS_TOPIC_NAME;
const SNS_TOPIC_ARN = `arn:aws:sns:${AWS_REGION_STRING}:${AWS_ACCOUNT_ID}:${SNS_TOPIC_NAME}`;

const AWS = require('aws-sdk');
AWS.config.update({
  region: AWS_REGION_STRING
});

const s3 = new AWS.S3();
const sns = new AWS.SNS();

const S3_PATH_MAP = {
  0: 'environment',
  3: 'customer',
  4: 'source',
  5: 'file'
};

exports.handler = (event, context, callback) => {
  return main(event).then(function(result){
    callback(null, result);
  }).catch(function(error){
    callback(error);
  });
};

const main = async (event) => {
  let record = event.Records[0];
  let pathAttributes = getS3PathAttributes(record);
  let s3MetaData = await fetchS3MetaData(record);
  let metaData = {
    ...pathAttributes,
    ...s3MetaData
  };
  let messageAttributes = getMessageAttributes(metaData);
  let sendSnsResponse = await sendSns(record, messageAttributes);
  return sendSnsResponse.MessageId;
}

const getS3PathAttributes = function (record) {
  let attributes = {};
  try {
    let pathSegments = record.s3.object.key.split('/');
    Object.entries(S3_PATH_MAP).forEach(
      ([position, attr]) => {
        let value = pathSegments[position];
        if (value) {
          attributes[attr] = value;
        }
      }
    );
    return attributes;
  } catch (error) {
    console.log('error', error);
    return attributes;
  }
}

const fetchS3MetaData = async (record) => {
  try {
    let params = {
      Bucket: record.s3.bucket.name,
      Key: record.s3.object.key
    }

    let response = await s3.headObject(params).promise();
    return response.Metadata;
  } catch (error) {
    console.log('error', error);
    return {};
  }
}

const getMessageAttributes = function(metaData) {
  let messageAttributes = {};
  Object.entries(metaData).forEach(
    ([key, value]) => {
      messageAttributes[key] = {
        DataType: 'String',
        StringValue: value
      }
    }
  );
  return messageAttributes;
}

const sendSns = async (record, messageAttributes) => {
  let params = {
    TopicArn: SNS_TOPIC_ARN,
    Message: JSON.stringify(record),
    MessageStructure: 'string',
    MessageAttributes: messageAttributes
  }
  return await sns.publish(params).promise();
}