backend-rotation-for-riak-client.diff

diff --git a/riak-client/lib/riak/client.rb b/riak-client/lib/riak/client.rb
index 127c2c8..be94f75 100644
--- a/riak-client/lib/riak/client.rb
+++ b/riak-client/lib/riak/client.rb
@@ -35,6 +35,9 @@ module Riak
     # @return [Fixnum] The port of the Riak HTTP endpoint
     attr_reader :port
 
+    # @return [Array] of Riak HTTP endpoint hashes each consisting of :host and :port
+    attr_accessor :backends
+
     # @return [String] The internal client ID used by Riak to route responses
     attr_reader :client_id
 
@@ -60,6 +63,24 @@ module Riak
       self.prefix    = options[:prefix]    || "/riak/"
       self.mapred    = options[:mapred]    || "/mapred"
       raise ArgumentError, t("missing_host_and_port") unless @host && @port
+
+      self.backends = [{:host => self.host, :port => self.port}]
+    end
+
+    # Add a backend to the pool
+    # @param [String] the host (IP or hostname) of the riak node to be added
+    # @param [Fixnum] the port of the riak node to be added
+    def add_backend(host, port)
+      self.backends << {:host => host, :port => port}
+    end
+
+    # Switches through the backends by settinh the next one and appending the current to the end of the pool
+    # @return [Hash] the new backend (may be the same, if self.backends only contains one element)
+    def next_backend
+      self.backends << self.backends.shift
+      self.host = self.backends[0][:host]
+      self.port = self.backends[0][:port]
+      self.backends[0]
     end
 
     # Set the client ID for this client. Must be a string or Fixnum value 0 =< value < MAX_CLIENT_ID.
diff --git a/riak-client/lib/riak/client/http_backend.rb b/riak-client/lib/riak/client/http_backend.rb
index 072c4f7..ff63f3f 100644
--- a/riak-client/lib/riak/client/http_backend.rb
+++ b/riak-client/lib/riak/client/http_backend.rb
@@ -68,7 +68,9 @@ module Riak
       def get(expect, *resource, &block)
         headers = default_headers.merge(resource.extract_options!)
         verify_path!(resource)
-        perform(:get, path(*resource), headers, expect, &block)
+        retry_and_switch_backend_if_needed do
+          perform(:get, path(*resource), headers, expect, &block)
+        end
       end
 
       # Performs a PUT request to the specified resource on the Riak server.
@@ -89,7 +91,9 @@ module Riak
       def put(expect, *resource, &block)
         headers = default_headers.merge(resource.extract_options!)
         uri, data = verify_path_and_body!(resource)
-        perform(:put, path(*uri), headers, expect, data, &block)
+        retry_and_switch_backend_if_needed do
+          perform(:put, path(*uri), headers, expect, data, &block)
+        end
       end
 
       # Performs a POST request to the specified resource on the Riak server.
@@ -110,7 +114,9 @@ module Riak
       def post(expect, *resource, &block)
         headers = default_headers.merge(resource.extract_options!)
         uri, data = verify_path_and_body!(resource)
-        perform(:post, path(*uri), headers, expect, data, &block)
+        retry_and_switch_backend_if_needed do
+          perform(:post, path(*uri), headers, expect, data, &block)
+        end
       end
 
       # Performs a DELETE request to the specified resource on the Riak server.
@@ -130,7 +136,9 @@ module Riak
       def delete(expect, *resource, &block)
         headers = default_headers.merge(resource.extract_options!)
         verify_path!(resource)
-        perform(:delete, path(*resource), headers, expect, &block)
+        retry_and_switch_backend_if_needed do
+          perform(:delete, path(*resource), headers, expect, &block)
+        end
       end
 
       # @return [URI] The calculated root URI for the Riak HTTP endpoint
@@ -170,7 +178,7 @@ module Riak
         resource = Array(resource).flatten
         raise ArgumentError, t("resource_path_short") unless resource.length > 1 || resource.include?(@client.mapred)
       end
-      
+
       # Checks the expected response codes against the actual response code. Use internally when
       # implementing {#perform}.
       # @param [String, Fixnum, Array<String,Fixnum>] expected the expected response code(s)
@@ -189,7 +197,7 @@ module Riak
       def return_body?(method, code, has_block)
         method != :head && !valid_response?([204,205,304], code) && !has_block
       end
-      
+
       # Executes requests according to the underlying HTTP client library semantics.
       # @abstract Subclasses must implement this internal method to perform HTTP requests
       #           according to the API of their HTTP libraries.
@@ -204,6 +212,23 @@ module Riak
       def perform(method, uri, headers, expect, body=nil)
         raise NotImplementedError
       end
+
+      private
+
+      # Meant to be used internally for the get, put, post and delete methods
+      # to keep them DRY and catch errors from the (actual) HTTP backend
+      # implementation, switch the backend and retry again. FailedRequest
+      # Exceptions are raised again
+      def retry_and_switch_backend_if_needed
+        begin
+          yield
+        rescue Exception => e
+          raise e if e.class == FailedRequest
+          warn t("backend_not_working", :uri => root_uri.to_s, :exception => e.to_s)
+          client.next_backend
+          retry
+        end
+      end
     end
   end
 end
diff --git a/riak-client/lib/riak/locale/en.yml b/riak-client/lib/riak/locale/en.yml
index 9a217fb..4c95291 100644
--- a/riak-client/lib/riak/locale/en.yml
+++ b/riak-client/lib/riak/locale/en.yml
@@ -35,3 +35,4 @@ en:
     too_few_arguments: "too few arguments: %{params}"
     walk_spec_invalid_unless_link: "WalkSpec is only valid for a function when the type is :link"
     wrong_argument_count_walk_spec: "wrong number of arguments (one Hash or bucket,tag,keep required)"
+    backend_not_working: "backend %{uri} is not working properly: %{exception}"