Hermod

This gem makes it easier to talk to HMRC through the Government Gateway by providing a DSL you can use to create Ruby classes to build the XML required in a form that meets HMRC's specification.

It ensures that nodes appear in the correct order with the correct formatting and allows you to preprocess values and apply validations at submission time.

Installation

Add this line to your application's Gemfile:

gem 'hermod'

And then execute:

$ bundle

Or install it yourself as:

$ gem install hermod

Usage

This gem allows you to describe classes that represent a section of XML that will be sent to HMRC. This description includes type, validation, and format information as well as any runtime mutations that should be applied to inputs you provide.

Supported Types

The following types of XML node are supported:

• Strings
• Integers
• Dates
• Yes/No
• Yes only
• Monetary values
• Parent XML

Global Options

There are some options that can be passed to all or some of the different node types.

XML Name

By default the name used for the XML node is generated by converting the node name from snake_case to TitleCase. For example, the date_of_birth node in the example above would become DateOfBirth. By providing an xml_name you can override this, thus changing it to BirthDate

Building an XmlSection

Example = Hermod::XmlSection.build do |builder|
  builder.string_node :ni_number, xml_name: "NINumber"
end

Using that XmlSection

Example.new do |example|
  example.ni_number "AB123456C"
end

The Resulting XML

<Example>
  <NINumber>AB123456C</NINumber>
</Example>

Attributes

Any node can have attributes which are defined by passing a Hash of symbol, string pairs. The symbol is used to refer to the attribute when setting the value of the node and the string is the form that will be sent to HMRC.

Building an XmlSection

Example = Hermod::XmlSection.build do |builder|
  builder.string_node :tax_code, attributes: {week_1_month_1: "WeekOneMonthOne"}
end

Using that XmlSection

Example.new do |example|
  example.tax_code "1000L", week_1_month_1: true
end

The Resulting XML

<Example>
  <TaxCode WeekOneMonthOne="yes">1000L</TaxCode>
</Example>

Optional

Not all nodes allow this but for those that do (String, Date and Monetary nodes) if a node is marked as optional then any blank values (like nil or an empty string) will be ignored.

Building an XmlSection

Example = Hermod::XmlSection.build do |builder|
  builder.string_node :middle_name, optional: true
end

Using that XmlSection

Example.new do |example|
  example.middle_name nil
end

No XML will be produced

String Nodes

String nodes handle a wide variety of cases and can take regular expressions and lists of values to restrict the provided values. If they are marked as optional then the node will be excluded if the value given is blank (nil or the empty string).

Regular Expressions

The matches option allows you to provide a regular expression that is used to validate the input. If you try to pass a value that doesn't match the expression a Hermod::InvalidInputError will be raised.

Building an XmlSection

Example = Hermod::XmlSection.build do |builder|
  builder.string_node :ni_number, matches: /\A[A-Z]{2}[0-9]{6}[A-D ]\z/
end

Using that XmlSection

Example.new do |example|
  example.ni_number "I can't remember it"
end

A Hermod::InvalidInputError will be raised

Allowable Values

The allowable_values lets you specify a list of string that are allowed for this node. Passing a value not in this list will raise a Hermod::InvalidInputError.

Building an XmlSection

Example = Hermod::XmlSection.build do |builder|
  builder.string_node :mood, allowable_values: %w(Happy Sad Hangry)
end

Using that XmlSection

Example.new do |example|
  example.gender "Wrathful"
end

A Hermod::InvalidInputError will be raised

Input Mutator

The input_mutator option allows you to provide a lambda that is provided with two arguments, the value assigned to the node and the Hash of attributes (if any). This can be used to change either or both of these and the lambda must return both the value and the attributes as an array ([value, attributes]) after they've been modified.

Building an XmlSection

Example = Hermod::XmlSection.build do |builder|
  builder.string_node :ni_number, xml_name: "NINO", optional: true, matches: /\A[A-Z]{2}[0-9]{6}[A-D ]\z/,
    input_mutator: (lambda { |value, attrs| [value.delete(' ').upcase, attrs] })
end

Using that XmlSection

Example.new do |example|
  example.ni_number "AB 12 34 56 C"
end

The Resulting XML

<Example>
  <NiNumber>AB123456C</NiNumber>
</Example>

Integer Nodes

Integer nodes let you provide a whole number that won't be formatted as a monetary value.

Range

You can specify a range option as a hash with a min and max value. If you provide a value outwith the range (inclusive) then a Hermod::InvalidInputError exception will be raised.

Building an XmlSection

Example = Hermod::XmlSection.build do |builder|
  builder.integer_node :day_of_the_week, range: {min: 1, max: 7}
end

Using that XmlSection

Example.new do |example|
  example.day_of_the_week 8
end

A Hermod::InvalidInputError will be raised

Date Nodes

Date nodes let you send through a date to HMRC. It will be converted to the given date format which you can specify as a format string in the formats option passed to the Hermod::XmlSection.build call. Anything that responds to strftime can be passed to the node. Anything else will cause an Hermod::InvalidInputError exception to be raised.

Building an XmlSection

Example = Hermod::XmlSection.build(formats: {date: "%Y-%m-%d"}) do |builder|
  builder.date_node :date_of_birth
end

Using that XmlSection

Example.new do |example|
  example.date_of_birth Date.new(1988, 8, 13)
end

The Resulting XML

<Example>
  <DateOfBirth>1988-08-13</DateOfBirth>
</Example>

DateTime Nodes

Datetime nodes let you send through a date and a time to HMRC. It will be converted to the given datetime format which you can specify as a format string in the formats option passed to the Hermod::XmlSection.build call. Anything that responds to strftime can be passed to the node. Anything else will cause an Hermod::InvalidInputError exception to be raised.

Building an XmlSection

Example = Hermod::XmlSection.build(formats: {datetime: "%Y-%m-%d %H:%M:%S"}) do |builder|
  builder.datetime_node :published
end

Using that XmlSection

Example.new do |example|
  example.published DateTime.new(2014, 9, 3, 10, 42, 50)
end

The Resulting XML

<Example>
  <Published>2014-09-03 10:42:50</Published>
</Example>

Yes Nodes

Yes nodes allow you to send a boolean value to HMRC provided that value is true. Nothing will be sent if the value is false. This pattern is commonly used by HMRC for optional boolean nodes. They're known as "yes nodes" because HMRC use "yes" and "no" in place of true and false in their XML.

Building an XmlSection

Example = Hermod::XmlSection.build do |builder|
  builder.yes_node :verily
  builder.yes_node :nae
end

Using that XmlSection

Example.new do |example|
  example.verily true
  example.nae false
end

The Resulting XML

<Example>
  <Verily>yes</Verily>
</Example>

Yes/No Nodes

This works in a similar fashion to the yes nodes described above but if a false value is provided a "no" will be sent instead of the node being excluded.

Building an XmlSection

Example = Hermod::XmlSection.build do |builder|
  builder.yes_no_node :verily
  builder.yes_no_node :nae
end

Using that XmlSection

Example.new do |example|
  example.verily true
  example.nae false
end

The Resulting XML

<Example>
  <Verily>yes</Verily>
  <Nae>no</Nae>
</Example>

Monetary Nodes

Monetary nodes let you send through monetary values to HMRC. They will be converted to the given monetary format which you can specify as a format string in the formats option passed to the Hermod::XmlSection.build call. Values passed to monetary nodes should be BigDecimal objects.

Negative

By default negative numbers are allowed. If you need to prevent them you can set the negative option to false.

Building an XmlSection

Example = Hermod::XmlSection.build(formats: {money: "%.2f"}) do |builder|
  builder.monetary_node :taxable_pay, negative: false
end

Using that XmlSection

Example.new do |example|
  example.taxable_pay BigDecimal("-300")
end

A Hermod::InvalidInputError will be raised

Whole Units

Sometimes HMRC require that you send through a value as a whole unit. If this is the case you can set the whole_units option to true and if an invalid value is passed