export function decomposeAwsKmsKeyArn()

in modules/kms-keyring/src/region_from_kms_key_arn.ts [29:65]

• 15 lines of code
• 7 McCabe index (conditional complexity)

export function decomposeAwsKmsKeyArn(kmsKeyArn: string): {
  partition: string
  region: string
  account: string
} {
  /* Precondition: A KMS key arn must be a string. */
  needs(typeof kmsKeyArn === 'string', 'KMS key arn must be a string.')

  /* See: https://docs.aws.amazon.com/general/latest/gr/aws-arns-and-namespaces.html#arn-syntax-kms
   * arn:aws:kms:us-east-1:123456789012:key/12345678-1234-1234-1234-123456789012
   * arn:aws:kms:us-east-1:123456789012:alias/example-alias
   */
  const [arnLiteral, partition, service, region = '', account = ''] =
    kmsKeyArn.split(':')

  /* Postcondition: The ARN must be well formed.
   * The arn and kms section have defined values,
   * but the aws section does not.
   * It is also possible to have a key or alias.
   * In this case the partition, service, region
   * will be empty.
   * In this case the arnLiteral should look like an alias.
   */
  needs(
    (arnLiteral === 'arn' && partition && service === 'kms' && region) ||
      /* Partition may or may not have a value.
       * If the resourceType delimiter is /,
       * it will not have a value.
       * However if the delimiter is : it will
       * because of the split(':')
       */
      (!service && !region && arnLiteral.match(aliasOrKeyResourceType)),
    'Malformed arn.'
  )

  return { partition, region, account }
}