[micro-s3-example] Get Signed URL

s3-get.js

const getS3 = async (req, res) => {
  const s3key = `${req.url.substr(1)}` // we need to remove the first backslash from the url

  const params = {
    Bucket: config.bucket_name,
    Key: s3key,
    Expires: 60 * 60 * 24 // 1 day
  }
  
  try {
    // key exists?
    await s3.headObject({
      Bucket: params.Bucket,
      Key: params.Key
    }).promise()

    // if it does, generate a signed url
    const url = await s3.getSignedUrl('getObject', params)
    return url
  } catch (err) {
    if (err.statusCode === 404) {
      throw createError(404, 'Not Found')
    } else throw err
  }
}