Savon/Ruby question: Variable context in block when initializing Client WSDL

Question

I am creating a class to wrap around a Savon SOAP connection, as follows:

class SOAPConnection

  attr_reader :url, :namespace

  def initialize(url, namespace)
    @url = url
    @namespace = namespace

    @client = Savon::Client.new do
      wsdl.endpoint = @url
      wsdl.namespace = @namespace
    end
  end

end

This code does not work. The wsdl document that gets initialized has a nil endpoint and a nil namespace.

To make the code work, I have to use the following:

class SOAPConnection

  attr_reader :url, :namespace

  def initialize(url, namespace)
    @url = url
    @namespace = namespace

    @client = Savon::Client.new do
      wsdl.endpoint = url          # <=== use local variable
      wsdl.namespace = namespace   # <=== use local variable
    end
  end

end

Note that when setting up the wsdl.endpoint and wsdl.namespace I am using the local url and namespace variables, not the @url and @namespace instance variables.

So it seems that when passing in the block to initialize the wsdl document, the context of local variables is preserved while the context of instance variables is not. Is this a fundamental behaviour of Ruby?

Answer 1

Luckily this is not "a fundamental behaviour of Ruby", but related to how Savon evaluates the block passed to Savon::Client.new.

If you don't pass any arguments to the block, Savon uses instance_eval with delegation to evaluate the block which unfortunately doesn't work with instance variables, but can access local variables and also methods from your class.

As an alternative, you can pass between 1 and 3 arguments to the block and receive the objects available to you in the following order:

[wsdl, http, wsse]

In your case, you would only need the first object, so your code would look like:

@client = Savon::Client.new do |wsdl|    # <= one argument
  wsdl.endpoint = @url
  wsdl.namespace = @namespace
end

Please take a look at the documentation for Savon for more information.