Gemfile

gem 'nokogiri, '~> 1.10'
gem 'httparty'
gem 'wasabi'

soap_evelope.rb

class SoapEnvelopeBuilder
  SCHEMA_TYPES = {
    'xmlns:xsd' => 'http://www.w3.org/2001/XMLSchema',
    'xmlns:xsi' => 'http://www.w3.org/2001/XMLSchema-instance'
  }

  SOAP_NAMESPACE = {
    1 => { 'soap11' => 'http://schemas.xmlsoap.org/soap/envelope/' },
    2 => { 'soap12' => 'http://www.w3.org/2003/05/soap-envelope' }
  }

  attr_accessor :soap_version, :wsdl

  def initialize(wsdl:, soap_version: 2)
    @wsdl = wsdl
    @soap_version = soap_version
  end

  def build(operation, message:)
    input = wsdl.operations[operation][:input]

    xml = Nokogiri::XML::Builder.new(encoding: 'UTF-8') do |doc|
      doc.Envelope(SCHEMA_TYPES) {
        doc.parent.namespace = doc.parent.add_namespace_definition(soap_namespace, soap_namespace_uri)
        doc[soap_namespace].Body {
          doc.send(input, 'xmlns' => wsdl.namespace) {
            parameters(operation, message, doc)
          }
        }
      }
    end

    xml.to_xml(save_with: Nokogiri::XML::Node::SaveOptions::AS_XML).strip
  end

  private

  def parameters(operation, message, xml_doc)
    if wsdl.operations[operation][:parameters].blank?
      xml_doc.parent << message
    else
      wsdl.operations[operation][:parameters].each do |key, value|
        xml_doc.send(value[:name]) {
          xml_doc.parent << (message.class == Hash ? message[key] : message)
        }
      end
    end
  end

  def soap_namespace
    @soap_namespace ||= SOAP_NAMESPACE[soap_version].keys.first
  end

  def soap_namespace_uri
    @soap_namespace_uri ||= SOAP_NAMESPACE[soap_version][soap_namespace]
  end
end