Start flushing out clean failover strategies

.gitignore

@@ -10,3 +10,4 @@ tmp/
 .replica
 mongo.key
 TODO
+.DS_Store

lib/moped/failover.rb

@@ -0,0 +1,32 @@
+# encoding: utf-8
+require "moped/failover/ignore"
+
+module Moped
+
+  # Provides behaviour around failover scenarios for different types of
+  # exceptions that get raised on connection and execution of operations.
+  #
+  # @since 2.0.0
+  module Failover
+    extend self
+
+    # Hash lookup for the failover classes based off the exception type.
+    #
+    # @since 2.0.0
+    STRATEGIES = {}.freeze
+
+    # Get the appropriate failover handler given the provided exception.
+    #
+    # @example Get the failover handler for an IOError.
+    #   Moped::Failover.get(IOError)
+    #
+    # @param [ Exception ] exception The raised exception.
+    #
+    # @return [ Object ] The failover handler.
+    #
+    # @since 2.0.0
+    def get(exception)
+      STRATEGIES.fetch(exception, Ignore).new(exception)
+    end
+  end
+end

lib/moped/failover/ignore.rb

@@ -0,0 +1,44 @@
+# encoding: utf-8
+module Moped
+  module Failover
+
+    # Ignore is for the case when we get exceptions we do not know about, or
+    # exceptions we deem are proper user errors and should be re-raised.
+    #
+    # @since 2.0.0
+    class Ignore
+
+      # @!attribute exception
+      #   @return [ Exception ] The raised exception.
+      attr_reader :exception
+
+      # Instantiate the new Ignore handler.
+      #
+      # @example Instantiate the new ignore handler.
+      #   Moped::Failover::Ignore.new(exception)
+      #
+      # @param [ Exception ] exception The raised exception.
+      #
+      # @since 2.0.0
+      def initialize(exception)
+        @exception = exception
+      end
+
+      # Executes the failover strategy. In the case of ignore, we just re-raise
+      # the exception that was thrown previously.
+      #
+      # @example Execute the ignore strategy.
+      #   ignore.execute(node)
+      #
+      # @param [ Node ] node The node the exception got raised on.
+      # @param [ Proc ] block The optional block.
+      #
+      # @raise [ Exception ] The exception that was previously thrown.
+      #
+      # @since 2.0.0
+      def execute(node, &block)
+        raise(exception)
+      end
+    end
+  end
+end

lib/moped/node.rb

@@ -1,3 +1,7 @@
+# encoding: utf-8
+require "moped/failover"
+require "moped/read"
+
 module Moped
 
   # Represents a client to a node in a server cluster.
@@ -132,13 +136,22 @@ def down?
     # @return [ nil ] nil.
     #
     # @since 1.0.0
-    def ensure_connected
+    def ensure_connected(&block)
       # Don't run the reconnection login if we're already inside an
       # +ensure_connected+ block.
       return yield if Threaded.executing?(:connection)
       Threaded.begin(:connection)
       retry_on_failure = true
 
+      # @todo: Durran: Let's get failover scenarios to look like this:
+      #
+      # begin
+        # connect unless connected?
+        # yield
+      # rescue Exception => e
+        # Failover.get(e).execute(self, &block)
+      # end
+
       begin
         connect unless connected?
         yield

lib/moped/read_preference.rb

@@ -23,7 +23,7 @@ module ReadPreference
       primary_preferred: PrimaryPreferred,
       secondary: Secondary,
       secondary_preferred: SecondaryPreferred
-    }
+    }.freeze
 
     # Get a read preference for the provided name. Valid names are:
     #   - :nearest

lib/moped/session.rb

@@ -1,5 +1,4 @@
 # encoding: utf-8
-require "moped/read"
 require "moped/read_preference"
 
 module Moped

lib/moped/write.rb

@@ -4,16 +4,14 @@ module Moped
   class Write
 
     # The operation can be a Protocol::Insert, Protocol::Update,
-    # Protocol::Delete, Protocol::Command.
+    # Protocol::Delete
     def initialize(operation)
       @operation = operation
     end
 
     def execute(node)
-      reply = node.process(operation)
-      # @todo: Durran check the reply for failover situations and handle them
-      # here.
-      reply
+      node.process(operation)
+      # Check our write concern and then do the right thing.
     end
   end
 end

spec/moped/failover/ignore_spec.rb

@@ -0,0 +1,40 @@
+require "spec_helper"
+
+describe Moped::Failover::Ignore do
+
+  describe "#initialize" do
+
+    let(:exception) do
+      RuntimeError.new
+    end
+
+    let(:ignore) do
+      described_class.new(exception)
+    end
+
+    it "sets the exception" do
+      expect(ignore.exception).to eq(exception)
+    end
+  end
+
+  describe "#execute" do
+
+    let(:exception) do
+      RuntimeError.new
+    end
+
+    let(:node) do
+      Moped::Node.new("127.0.0.1:27017")
+    end
+
+    let(:ignore) do
+      described_class.new(exception)
+    end
+
+    it "raises the exception" do
+      expect {
+        ignore.execute(node)
+      }.to raise_error(exception)
+    end
+  end
+end

spec/moped/failover_spec.rb

@@ -0,0 +1,18 @@
+require "spec_helper"
+
+describe Moped::Failover do
+
+  describe ".get" do
+
+    context "when providing an unregistered exception" do
+
+      let(:failover) do
+        described_class.get(RuntimeError)
+      end
+
+      it "returns ignore" do
+        expect(failover).to be_a(Moped::Failover::Ignore)
+      end
+    end
+  end
+end