Exemvi

Exemvi is a library to work with EMV QR Code Specification for Payment Systems.

Exemvi only supports validating and parsing Merchant-Presented Mode (MPM) QR Code. Support for generating MPM QR Code is planned for future versions.

At this moment, support for Consumer-Presented Mode (CPM) is not planned.

The specifications of EMV QR Code can be found at https://www.emvco.com/emv-technologies/qrcodes/

Installation

Add exemvi to your list of dependencies in mix.exs:

def deps do
  [
    {:exemvi, "~> 0.1.0"}
  ]
end

Basic Usage

  1. Validating the whole QR Code:

    qr_code = "qr_code_string"
    result = Exemvi.QR.MP.validate_qr(qr_code)

    The result is either:

    • {:ok, qr_code} where qr_code is the QR Code orginally supplied to the function
    • {:error, reasons} where reasons is a list of validation error reasons as atoms
  2. Parsing QR Code into data objects:

    qr_code = "qr_code_string"
    result = Exemvi.QR.MP.parse_to_objects(qr_code)

    The result is either:

    • {:ok, objects} where objects is a list of Exemvi.MP.Object structs
    • {:error, reasons} where reasons is a list of parsing error reasons as atoms
  3. Validating parsed data objects:

    objects = [%Exemvi.QR.MP.Object{id: "00", value: "01"}, ...]
    result = Exemvi.QR.MP.validate_objects(qr_code)

    The result is either:

    • {:ok, objects} where objects is the objects originally supplied to the function
    • {:error, reasons} where reasons is a list of validation error reasons as atoms
  4. All three functions above can be piped:

    result = qr_code
             |> Exemvi.QR.MP.validate_qr()
             |> Exemvi.QR.MP.parse_to_objects()
             |> Exemvi.QR.MP.validate_objects()

Example

Let's try parsing the official sample.

official_sample = "00020101021229300012D156000000000510A93FO3230Q31280012D15600000001030812345678520441115802CN5914BEST TRANSPORT6007BEIJING64200002ZH0104最佳运输0202北京540523.7253031565502016233030412340603***0708A60086670902ME91320016A0112233449988770708123456786304A13A"

{:ok, objects} <- Exemvi.QR.MP.parse_to_objects(official_sample)

The resulting objects looks like below:

[
  %Exemvi.QR.MP.Object{id: "00", objects: nil, value: "01"},
  %Exemvi.QR.MP.Object{id: "01", objects: nil, value: "12"},
  %Exemvi.QR.MP.Object{
    id: "29",
    objects: [
      %Exemvi.QR.MP.Object{id: "00", objects: nil, value: "D15600000000"},
      %Exemvi.QR.MP.Object{id: "05", objects: nil, value: "A93FO3230Q"}
    ],
    value: nil
  },
  %Exemvi.QR.MP.Object{
    id: "31",
    objects: [
      %Exemvi.QR.MP.Object{id: "00", objects: nil, value: "D15600000001"},
      %Exemvi.QR.MP.Object{id: "03", objects: nil, value: "12345678"}
    ],
    value: nil
  },
  #... Other objects are removed for brevity
]

Let's try validating an obviously invalid QR Code.

wrong_qr_code = "0002XX"
{:error, reasons} = Exemvi.QR.MP.validate_qr(wrong_qr_code)

The resulting error reason is [:invalid_qr]. Note that the error is a list containing error atoms.

Data Object Names

When represented as atoms, data object names in this library are formatted in snake case (lower case with underscores). For example :payload_format_indicator.

Error Values

The data object naming convention is relevant when figuring out error reason atoms.

Below are the possible types of failures when validating data objects:

  • Invalid data object value

    The error atom is the snake case object name prefixed with invalid_. For example :invalid_additional_consumer_data_request

  • Missing mandatory data object

    The error atom is the snake case object name prefixed with missing_. For example :missing_country_code

  • Orphaned data object

    The error atom is the snake case object name prefixed with orphaned_. For example :orphaned_value_of_convenience_fee_fixed