Refactored - Hid the EM calls

Author: davebryson

README.textile

@@ -2,7 +2,6 @@ h2. rinterface: Ruby to Erlang client
 
 rinterface is a pure Ruby client that can send RPC calls to an Erlang node. It's very much a work in progress.
 
-
 h3. Requirements
 
  * Erlang 12B-5
@@ -12,114 +11,71 @@ h3. Requirements
 
 h3. Try it out
 
-1. Open a terminal, Cd into the test directory and run:
+ 1. Open a terminal, Cd into the test directory and run:
    'make'
    'make run'
-   this will start the erlang node named 'math'
+   
+This will start the erlang node named 'math'
 
-2. Open another terminal, and run: 'ruby sample.rb'
+ 2. Open another terminal, and run: 'ruby sample.rb'
 
 h3. How to use?
 
-See 'sample.rb' for an example:
-
+In your Ruby code, make a call to the Erlang node like this:
 <pre>
 <code>
-EM.run do
-  # Connect to epmd to get the port of 'math'. 'math' is the -sname of the erlang node
-  epmd = EpmdConnection.lookup_node("math")
-  epmd.callback do |port|
-    puts "got the port #{port}"
-    
-    # make the rpc call to 'math' on port for mod 'math_server' on fun 'add' with args
-    node = Node.rpc_call("math",port.to_i,"math_server","add",[10,20])
-    node.callback{ |result|
-      puts "Sum is: #{result}"
-      EM.stop
-    }
-    
-    node.errback{ |err|
-      puts "Error: #{err}"
-      EM.stop
-    }
-  end
-  
-  epmd.errback do |err|
-    puts "Error: #{err}"
-    EM.stop
-  end
-end
-</code>
-</pre>
+ # Erlang::Node(nodename,module,function,args) => [:ok,Response] | [:badprc,Reason]
 
+ r = Erlang::Node.rpc("math","math_server","add",[10,20])
 
-h3. So you wanna call Erlang from your Rails app...
-
-Here's a quick and simple example. Make sure you put the rinterface lib into RAILS_ROOT/lib and start the math_server in 'test'
-
-First we'll wrap rinterface in a class to call from Rails:
+ if r[0] == :badrpc
+   puts "Got and Error. Reason #{r[1]}"
+ else
+   puts "Success: #{r[1]}"
+ end
+</code>
+</pre>
 
-models/math_service.rb
+Where:
+ * 'math' is the node name (the -sname of the Erlang node)
+ * 'math_server' is the name of the module
+ * 'add' is the funtion to call
+ *  args is an array of arguments to pass to the function
 
+The result will always be an Array of the form:
 <pre>
 <code>
-require 'lib/rinterface'
-
-class MathService
-  include Erlang
-  attr_accessor :result
+ [:ok,Response] where Response is the result from the Erlang
+ 
+  or
 
-  def self.sum(args)
-    s = self.new
-    s.call_erlang(args)
-    s.result
-  end
-  
-  def initialize
-    @result = 0
-  end
-  
-  def call_erlang(args)
-    EM.run do
-      # Connect to epmd to get the port of 'math'. 
-      # 'math' is the -sname of the erlang node
-      epmd = EpmdConnection.lookup_node("math")
-      epmd.callback do |port|
-     
-        # make the rpc call to 'math' on port for mod 'math_server' on 
-        # fun 'add' with args
-        node = Node.rpc_call("math",port.to_i,"math_server","add",args)
-        node.callback{ |result|
-          @result = result
-          EM.stop
-        }
-    
-        node.errback{ |err|
-          EM.stop
-        }
-      end
-  
-      epmd.errback do |err|
-        EM.stop
-      end
-    end
-  end
-  
-end
+ [:badrpc,Reason] where Reason is the 'why' it failed
 </code>
 </pre>
 
-Now here's the controller:
+h3. So you wanna call Erlang from your Rails app...
 
-controllers/math_controller.rb
+Here's a quick and simple example. Make sure you put the rinterface lib into RAILS_ROOT/lib and start the math_server in 'test'
+
+In the controller:
 
+controllers/math_controller.rb
 <pre>
 <code>
+require 'lib/rinterface'
+
 class MathController < ApplicationController
   def index
     a = params[:a]
     b = params[:b]
-    @result = MathService.sum([a.to_i,b.to_i])
+    r = Erlang::Node.rpc("math","math_server","add",[a.to_i,b.to_i])
+    
+    if r[0] == :badrpc
+      @result = "Error"
+    else
+      @result = r[1]
+    end
+    
   end
 end
 </code>

lib/erlang/node.rb

@@ -5,7 +5,68 @@
 # - makes the RPC call
 #
 module Erlang
-  class Node < EM::Connection
+  class Node
+    attr_reader :result
+    
+    def initialize
+      @result = nil
+    end
+    
+    def self.rpc(node,mod,fun,args)
+      n = self.new
+      setup = proc{ n.do_connect(node,mod,fun,args) }
+      
+      if EM.reactor_running?
+        setup.call
+      else
+        EM.run(&setup)
+      end
+      n.result
+    end
+    
+    def do_connect(node,mod,fun,args)
+      epmd = EpmdConnection.lookup_node(node)
+      epmd.callback do |port|
+        conn = NodeConnection.rpc_call(node,port,mod,fun,args) do |c|
+          c.destnode = node
+          c.mod = mod
+          c.fun = fun
+          c.args = args
+          c.port = port
+          c.myname = build_nodename
+          c.cookie = get_cookie
+        end
+        conn.callback do |r|
+          # Check for bad rpc response
+          # this is where I miss the patten matching in Erlang
+          if r.is_a?(Array)
+            if !r.empty? && r[0] == :badrpc
+              @result = [:badrpc,r[1]]
+            else
+              @result = [:ok,r]
+            end
+          else
+            @result = [:ok,r]
+          end
+          EM.stop
+        end
+        conn.errback do |err|
+          # never called??
+          @result = [:badrpc,err]
+          EM.stop
+        end
+      end
+      epmd.errback do |err|
+        # return bad RPC no port found (0)
+        @result = [:badrpc,"no port found for service"]
+        EM.stop
+      end
+    end
+    
+  end
+  
+  
+  class NodeConnection < EM::Connection
     include EM::Deferrable
 
     attr_accessor :host,:myname,:destnode,:port,:cookie,:mod,:fun,:args
@@ -27,6 +88,7 @@ def self.rpc_call(node,port,mod,fun,args)
       end
     end
 
+    
     # Get the Cookie from the home directory
     def self.get_cookie
       # ... I did it all for the cookie, come on the cookie ...
@@ -67,11 +129,13 @@ def handle_any_response
         decoder.read_any 
         # read the message
         result = decoder.read_any
-        puts "Raw Response: #{result.inspect}"
+        #puts "Raw Response: #{result.inspect}"
+        set_deferred_success result[1]
       else
+        # This seems to never happen...always 'p'
         result = decoder.read_any
+        set_deferred_failure result
       end
-      set_deferred_success result[1]
     end
 
     def send_name
@@ -140,6 +204,7 @@ def make_challenge(her_challenge)
       encoder.out.string
     end
 
+    # Handshake complete...send the RPC
     def receive_challenge_ack(packet_size,decoder)
       @responder = :handle_any_response
       call_remote

sample.rb

@@ -1,31 +1,19 @@
 require 'lib/rinterface'
 
 
-# Example of connecting to an Erlang node and making an RPC call
-include Erlang
+# Try different responses...
 
-EM.run do
-  # Connect to epmd to get the port of 'math'. 'math' is the -sname of the erlang node
-  epmd = EpmdConnection.lookup_node("math")
-  epmd.callback do |port|
-    puts "got the port #{port}"
-    
-    # make the rpc call to 'math' on port for mod 'math_server' on fun 'add' with args
-    node = Node.rpc_call("math",port.to_i,"math_server","add",[10,20])
-    node.callback{ |result|
-      puts "Sum is: #{result}"
-      EM.stop
-    }
-    
-    node.errback{ |err|
-      puts "Error: #{err}"
-      EM.stop
-    }
-  end
-  
-  epmd.errback do |err|
-    puts "Error: #{err}"
-    EM.stop
-  end
-end
+# Bad rpc. Try to call the wrong service
+r = Erlang::Node.rpc("math","matx_server","add",[10,20])
+puts "Got: #{r.inspect}"
+
+puts "--------"
+# No Port for Service. Can't find a port for 'ath'
+r = Erlang::Node.rpc("ath","matx_server","add",[10,20])
+puts "Got: #{r.inspect}"
+
+puts "--------"
+# Good call
+r = Erlang::Node.rpc("math","math_server","add",[10,20])
+puts "Got: #{r.inspect}"