RUBY-899 Cluster returns empty list if there are no servers

lib/mongo/cluster.rb

@@ -181,7 +181,7 @@ def scan!
     #
     # @since 2.0.0
     def servers
-      topology.servers(@servers)
+      topology.servers(@servers.compact).compact
     end
 
     # Create a cluster for the provided client, for use when we don't want the

lib/mongo/cluster/topology/unknown.rb

@@ -106,6 +106,7 @@ def replica_set_name; nil; end
         #
         # @since 2.0.0
         def servers(servers)
+          []
         end
 
         # An unknown topology is not sharded.

lib/mongo/error.rb

@@ -71,6 +71,7 @@ class Error < StandardError
 require 'mongo/error/invalid_file'
 require 'mongo/error/invalid_nonce'
 require 'mongo/error/invalid_replacement_document'
+require 'mongo/error/invalid_server_preference'
 require 'mongo/error/invalid_signature'
 require 'mongo/error/invalid_update_document'
 require 'mongo/error/invalid_uri'
@@ -79,6 +80,7 @@ class Error < StandardError
 require 'mongo/error/max_message_size'
 require 'mongo/error/multi_index_drop'
 require 'mongo/error/need_primary_server'
+require 'mongo/error/no_server_available'
 require 'mongo/error/socket_error'
 require 'mongo/error/socket_timeout_error'
 require 'mongo/error/unsupported_features'

lib/mongo/error/invalid_server_preference.rb

@@ -0,0 +1,36 @@
+# Copyright (C) 2014-2015 MongoDB, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+module Mongo
+  class Error
+
+    # Raised when an invalid server preference is provided.
+    #
+    # @since 2.0.0
+    class InvalidServerPreference < Error
+
+      # Instantiate the new exception.
+      #
+      # @example Instantiate the exception.
+      #   Mongo::ServerSelector::InvalidServerPreference.new
+      #
+      # @param [ String ] name The preference name.
+      #
+      # @since 2.0.0
+      def initialize(name)
+        super("This server preference #{name} cannot be combined with tags.")
+      end
+    end
+  end
+end

lib/mongo/error/no_server_available.rb

@@ -0,0 +1,37 @@
+# Copyright (C) 2014-2015 MongoDB, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+module Mongo
+  class Error
+
+    # Raised if there are no servers available matching the preference.
+    #
+    # @since 2.0.0
+    class NoServerAvailable < Error
+
+      # Instantiate the new exception.
+      #
+      # @example Instantiate the exception.
+      #   Mongo::Error::NoServerAvailable.new(server_selector)
+      #
+      # @param [ Hash ] server_selector The server preference that could not be
+      #   satisfied.
+      #
+      # @since 2.0.0
+      def initialize(server_selector)
+        super("No server is available matching preference: #{server_selector.inspect}")
+      end
+    end
+  end
+end

lib/mongo/server_selector.rb

@@ -58,24 +58,5 @@ def get(preference = {}, options = {})
         options
       )
     end
-
-    # Exception raised if there are no servers available matching the preference.
-    #
-    # @since 2.0.0
-    class NoServerAvailable < Error
-
-      # Instantiate the new exception.
-      #
-      # @example Instantiate the exception.
-      #   Mongo::ServerSelector::NoServerAvailable.new(server_selector)
-      #
-      # @param [ Hash ] server_selector The server preference that could not be
-      #   satisfied.
-      #
-      # @since 2.0.0
-      def initialize(server_selector)
-        super("No server is available matching preference: #{server_selector.inspect}")
-      end
-    end
   end
 end

lib/mongo/server_selector/selectable.rb

@@ -67,7 +67,7 @@ def ==(other)
       # @since 2.0.0
       def initialize(tag_sets = [], options = {})
         if !tag_sets.all? { |set| set.empty? } && !tags_allowed?
-          raise ServerSelector::InvalidServerPreference.new(name)
+          raise Error::InvalidServerPreference.new(name)
         end
         @tag_sets = tag_sets
         @options = options
@@ -96,7 +96,7 @@ def select_server(cluster)
           return servers.first if servers && !servers.compact.empty?
           cluster.scan!
         end
-        raise NoServerAvailable.new(self)
+        raise Error::NoServerAvailable.new(self)
       end
 
       # Get the timeout for server selection.
@@ -187,23 +187,5 @@ def match_tag_sets(candidates)
         matches || []
       end
     end
-
-    # Raised when an invalid server preference is provided.
-    #
-    # @since 2.0.0
-    class InvalidServerPreference < Error
-
-      # Instantiate the new exception.
-      #
-      # @example Instantiate the exception.
-      #   Mongo::ServerSelector::InvalidServerPreference.new
-      #
-      # @param [ String ] name The preference name.
-      #
-      # @since 2.0.0
-      def initialize(name)
-        super("This server preference #{name} cannot be combined with tags.")
-      end
-    end
   end
 end

spec/mongo/cluster_spec.rb

@@ -149,5 +149,65 @@
         end
       end
     end
+
+    context 'when the cluster has no servers' do
+
+      let(:cluster) do
+        described_class.new(ADDRESSES)
+      end
+
+      let(:servers) do
+        [nil]
+      end
+
+      before do
+        cluster.instance_variable_set(:@servers, servers)
+        cluster.instance_variable_set(:@topology, topology)
+      end
+
+      context 'when topology is Single' do
+
+        let(:topology) do
+          Mongo::Cluster::Topology::Single.new({})
+        end
+
+        it 'returns an empty array' do
+          expect(cluster.servers).to eq([])
+        end
+      end
+
+      context 'when topology is ReplicaSet' do
+
+        let(:topology) do
+          Mongo::Cluster::Topology::ReplicaSet.new({})
+        end
+
+        it 'returns an empty array' do
+          expect(cluster.servers).to eq([])
+        end
+      end
+
+      context 'when topology is Sharded' do
+
+        let(:topology) do
+          Mongo::Cluster::Topology::Sharded.new({})
+        end
+
+        it 'returns an empty array' do
+          expect(cluster.servers).to eq([])
+        end
+      end
+
+      context 'when topology is Unknown' do
+
+        let(:topology) do
+          Mongo::Cluster::Topology::Unknown.new({})
+        end
+
+        it 'returns an empty array' do
+          expect(cluster.servers).to eq([])
+        end
+      end
+    end
   end
 end

spec/mongo/database_spec.rb

@@ -176,7 +176,7 @@
       it 'uses that read preference', unless: sharded? do
         expect do
           database.command({ ping: 1 }, { read: read })
-        end.to raise_error(Mongo::ServerSelector::NoServerAvailable)
+        end.to raise_error(Mongo::Error::NoServerAvailable)
       end
     end
   end

spec/mongo/server_selection_spec.rb

@@ -61,7 +61,7 @@
         allow(cluster).to receive(:scan!).and_return(true)
       end
 
-      context 'Valid read preference and matching server available', unless: spec.raises_exception? do
+      context 'Valid read preference and matching server available', if: spec.server_available? do
 
         it 'Finds all suitable servers in the latency window', if: spec.replica_set? do
           expect(server_selector.send(:select, cluster.servers)).to eq(in_latency_window)   
@@ -72,21 +72,12 @@
         end
       end
 
-      context 'Invalid read preference', if: spec.invalid_server_preference? do
+      context 'No matching server available', if: !spec.server_available? do
 
         it 'Raises exception' do
           expect do
             server_selector.select_server(cluster)
-          end.to raise_exception(Mongo::ServerSelector::InvalidServerPreference) 
-        end
-      end
-
-      context 'No matching server available', unless: spec.server_available? do
-
-        it 'Raises exception' do
-          expect do
-            server_selector.select_server(cluster)
-          end.to raise_exception(Mongo::ServerSelector::NoServerAvailable) 
+          end.to raise_exception(Mongo::Error::NoServerAvailable)
         end
       end
     end

spec/mongo/server_selector_spec.rb

@@ -94,8 +94,59 @@
       it 'raises a NoServerAvailable error' do
         expect do
           read_pref.select_server(cluster)
-        end.to raise_exception(Mongo::ServerSelector::NoServerAvailable)
+        end.to raise_exception(Mongo::Error::NoServerAvailable)
       end
     end
   end
+
+  shared_context 'a ServerSelector' do
+
+    context 'when cluster#servers is empty' do
+
+      let(:servers) { [] }
+
+      let(:cluster) do
+        double('cluster').tap do |c|
+          allow(c).to receive(:servers).and_return(servers)
+          allow(c).to receive(:single?).and_return(single)
+          allow(c).to receive(:sharded?).and_return(sharded)
+          allow(c).to receive(:scan!).and_return(true)
+        end
+      end
+
+      let(:read_pref) do
+        described_class.get({ mode: :primary }, server_selection_timeout: 1)
+      end
+
+      it 'raises a NoServerAvailable error' do
+        expect do
+          read_pref.select_server(cluster)
+        end.to raise_exception(Mongo::Error::NoServerAvailable)
+      end
+    end
+  end
+
+  context 'when the cluster has a Single topology' do
+
+    let(:single) { true }
+    let(:sharded) { false }
+
+    it_behaves_like 'a ServerSelector'
+  end
+
+  context 'when the cluster has a ReplicaSet topology' do
+
+    let(:single) { false }
+    let(:sharded) { false }
+
+    it_behaves_like 'a ServerSelector'
+  end
+
+  context 'when the cluster has a Sharded topology' do
+
+    let(:single) { false }
+    let(:sharded) { true }
+
+    it_behaves_like 'a ServerSelector'
+  end
 end

spec/support/server_selection.rb

@@ -92,18 +92,6 @@ def replica_set?
           type == Mongo::Cluster::Topology::ReplicaSet
         end
 
-        # Does this spec raise an exception.
-        #
-        # @example Determine if the spec raises an exception.
-        #   spec.raises_exception?
-        #
-        # @return [true, false] If the spec raises an exception.
-        #
-        # @since 2.0.0
-        def raises_exception?
-          !server_available? || invalid_server_preference?
-        end
-
         # Does this spec expect a server to be found.
         #
         # @example Will a server be found with this spec.
@@ -116,18 +104,6 @@ def server_available?
           !in_latency_window.empty?
         end
 
-        # Is the read preference defined in the spec invalid.
-        #
-        # @example Determine if the spec's read preference is invalid.
-        #   spec.invalid_server_preference?
-        #
-        # @return [true, false] If the spec's read preference is invalid.
-        #
-        # @since 2.0.0
-        def invalid_server_preference?
-          read_preference['mode'] == 'Primary' && read_preference['tag_sets']
-        end
-
         # The subset of suitable servers that falls within the allowable latency
         #   window.
         # We have to correct for our server selection algorithm that adds the primary