使用Sinatra創建Soap Web Service

簡單對象訪問協議（SOAP）是一種輕量的、簡單的、基於 XML 的協議，它被設計成在 WEB 上交換結構化的和固化的信息。 SOAP 可以和現存的許多因特網協議和格式結合使用，包括超文本傳輸協議（ HTTP），簡單郵件傳輸協議（SMTP），多用途網際郵件擴充協議（MIME）。它還支持從消息系統到遠程過程調用（RPC）等大量的應用程序。

本文中得示例是Soap與Http結合的Web service。其實現了一個簡單的Echo和Reverse Echo的服務，既請求原文返回和請求倒序返回。就純技術層面來說，本質上就是post 一個製造xml格式的請求，獲得一個xml格式的response的Http Request。

首先，使用xsd明確request和response的xml結構

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="http://www.xianlinbox.net/echo" xmlns="http://www.xianlinbox.com/echo" xmlns:xs="http://www.w3.org/2001/XMLSchema" attributeFormDefault="qualified" elementFormDefault="qualified">
  <xs:complexType name="EchoMessageType">
    <xs:sequence>
      <xs:element name="Message" type="xs:string" minOccurs="1" />
    </xs:sequence>
  </xs:complexType>
  <xs:element name="EchoRequest" type="EchoMessageType"/>
  <xs:element name="EchoResponse" type="EchoMessageType"/>
  <xs:element name="ReverseEchoRequest" type="EchoMessageType"/>
  <xs:element name="ReverseEchoResponse" type="EchoMessageType"/>
</xs:schema>

然後，創建http服務

require 'bundler'
Bundler.setup
require 'sinatra/base'
	# XML 解析需用到nokogiri
require 'nokogiri'
require 'builder'

class EchoService < Sinatra::Base

  set :root, File.dirname(__FILE__)


  # 添加http basic authentication
  use Rack::Auth::Basic, "Restricted Area" do |username, password|
    username == 'admin' and password == 'admin'
  end

  # 創建Soap消息異常對象
  module SoapFault
    class MustUnderstandError < StandardError
      def fault_code
        "MustUnderstand"
      end
    end

    class ClientError < StandardError
      def fault_code
        "Client"
      end
    end
  end
	# SOAP要求SOAP messages使用Content-Type:text/xml，Sinatra默認的是application/xml,因此需配置。 
  configure do
     mime_type :xml, "text/xml"
  end

	#xsd讀取request和response的schema， xslt用於從soap message中獲取消息體，
  def initialize(*args)
    @xsd = Nokogiri::XML::Schema(File.read("#{File.dirname(__FILE__)}/public/echo_service.xsd"))
    @xslt = Nokogiri::XSLT(File.read("#{File.dirname(__FILE__)}/lib/soap_body.xslt"))
    super
  end

  # SOAP endpoint
  post '/echo_service' do
    begin
      soap_message = Nokogiri::XML(request.body.read)
      # 通過消息頭來判斷是否是當前服務可處理的消息。
      raise(SoapFault::MustUnderstandError, "SOAP Must Understand Error", "MustUnderstand") if soap_message.root.at_xpath('//soap:Header/*[@soap:mustUnderstand="1" and not(@soap:actor)]', 'soap' => 'http://schemas.xmlsoap.org/soap/envelope/')
      # 獲取消息體
      soap_body = @xslt.transform(soap_message)
      # 通過schema驗證request的結構是否合法。
      errors = @xsd.validate(soap_body).map { |e| e.message }.join(", ")
      # 如果request格式不正確，拋錯。
      raise(SoapFault::ClientError, errors) unless errors == ""
      # 從request中獲取該request請求的操作，通過動態分發的方式發送到對應的處理方法。
      self.send(soap_operation_to_method(soap_body), soap_body)
    rescue StandardError => e
      fault_code = e.respond_to?(:fault_code) ? e.fault_code : "Server"
      halt(500, builder(:fault, :locals => {:fault_string => e.message, :fault_code => fault_code}))
    end
  end

  private

  # 解析消息體獲取request請求的操作。
  def soap_operation_to_method(soap_body)
    method = soap_body.root.name.sub(/Request$/, '').gsub(/([A-Z]+)([A-Z][a-z])/, '\1_\2').gsub(/([a-z\d])([A-Z])/, '\1_\2').downcase.to_sym
  end

  # Echo服務的具體處理函數
  def echo(soap_body)
    message = soap_body.root.at_xpath('//echo:Message/text()', 'echo' => 'http://www.without-brains.net/echo').to_s
    builder(:echo_response, :locals => {:message => message})
  end

  # ReverseEcho服務的具體處理函數
  def reverse_echo(soap_body)
    message = soap_body.root.at_xpath('//echo:Message/text()', 'echo' => 'http://www.without-brains.net/echo').to_s.reverse!
    builder(:reverse_echo_response, :locals => {:message => message})
  end
end

通過使用builder可以更方便的構建response的內容，
Fault Builder

xml.SOAP(:Envelope, "xmlns:SOAP" => "http://schemas.xmlsoap.org/soap/envelope/") do
  xml.SOAP :Body do
    xml.SOAP :Fault do
      xml.faultcode "SOAP:#{fault_code}"
      xml.faultstring fault_string
    end
  end
end

EchoResponse Builder

xml.SOAP(:Envelope, "xmlns:SOAP" => "http://schemas.xmlsoap.org/soap/envelope/", "xmlns:echo" => "http://www.without-brains.net/echo") do
  xml.SOAP :Body do
    xml.echo :EchoResponse do
      xml.echo(:Message, message)
    end
  end
end

ReverseEchoRespose Builder

xml.SOAP(:Envelope, "xmlns:SOAP" => "http://schemas.xmlsoap.org/soap/envelope/", "xmlns:echo" => "http://www.without-brains.net/echo") do
  xml.SOAP :Body do
    xml.echo :ReverseEchoResponse do
      xml.echo(:Message, message)
    end
  end
end

That's all！