File upload with Lambda function

Applicable when

• A file is transferred as a body of API call
• A compressed file is to be unpacked and put to S3

Non-applicable when

• A file is transferred directly to S3 bucket from UI

Implementation

The file content is received base64-encoded in the Lambda. To store it correctly in the S3 bucket, the Buffer object has to be created with the proper encoding and then sent to S3.

The implementation differs if the request contains binary or multipart form-data.

Binary sample

export async function handler(event: APIGatewayProxyEvent): Promise<APIGatewayProxyResult> {
  const bucketName = process.env.BUCKET;

  if (!bucketName) {
    throw new Error('Bucket name is missing!');
  }

  if (event.isBase64Encoded) {
    // binary
    event.body = Buffer.from(event.body as string, 'base64');
  }

  const s3 = new S3();
  const imageKey = uuid();
  const params: PutObjectRequest = {
    Bucket: bucketName,
    Key: imageKey,
    ContentType: 'image',
    Body: event.body
  };

  await s3.putObject(params).promise();

  return {
    statusCode: 200,
    body: 'success'
  };
}

Multipart form-data sample

const multipart = require('aws-lambda-multipart-parser');

export async function handler(event: APIGatewayProxyEvent): Promise<APIGatewayProxyResult> {
  const bucketName = process.env.BUCKET;

  if (!bucketName) {
    throw new Error('Bucket name is missing!');
  }

  if (event.isBase64Encoded) {
    // form-data
    event.body = Buffer.from(event.body as string, 'base64').toString('binary');
  }

  const form = multipart.parse(event, true);

  const s3 = new S3();
  const imageKey = uuid();
  const params: PutObjectRequest = {
    Bucket: bucketName,
    Key: imageKey,
    ContentType: 'image',
    Body: form.image.content
  };

  await s3.putObject(params).promise();

  return {
    statusCode: 200,
    body: 'success'
  };
}