RUBY-1896 Raise an actionable error message when retryWrites fails due to using an unsupported storage engine (#1481)

* initial actionable error message and tests

* integration test for mmapv1 retryable write

* remove unsupported error check from legacy retry writes, as it is not subject to current spec

* implemented feedback

Author: HanaPearlman

lib/mongo/error/operation_failure.rb

@@ -252,6 +252,18 @@ def wtimeout?
       def max_time_ms_expired?
         code == 50 # MaxTimeMSExpired
       end
+
+      # Whether the error is caused by an attempted retryable write
+      # on a storage engine that does not support retryable writes.
+      #
+      # @return [ true | false ] Whether the error is caused by an attempted
+      # retryable write on a storage engine that does not support retryable writes.
+      #
+      # @since 2.11.0
+      def unsupported_retryable_write?
+        # code 20 is IllegalOperation
+        code == 20 && message.start_with?("Transaction numbers")
+      end
     end
   end
 end

lib/mongo/retryable.rb

@@ -215,9 +215,12 @@ def write_with_retry(session, write_concern, ending_transaction = false, &block)
         end
         retry_write(e, session, txn_num, &block)
       rescue Error::OperationFailure => e
-        if (session.in_transaction? && !ending_transaction) || !e.write_retryable?
+        if e.unsupported_retryable_write?
+          raise_unsupported_error(e)
+        elsif (session.in_transaction? && !ending_transaction) || !e.write_retryable?
           raise
         end
+
         retry_write(e, session, txn_num, &block)
       end
     end
@@ -403,5 +406,15 @@ def log_retry(e, options = nil)
       end
       Logger.logger.warn "#{message} due to: #{e.class.name} #{e.message}"
     end
+
+    # Retry writes on MMAPv1 should raise an actionable error; append actionable
+    # information to the error message and preserve the backtrace.
+    def raise_unsupported_error(e)
+      new_error = Error::OperationFailure.new("#{e.class}: #{e} "\
+        "This MongoDB deployment does not support retryable writes. Please add "\
+        "retryWrites=false to your connection string or use the retry_writes: false Ruby client option")
+      new_error.set_backtrace(e.backtrace)
+      raise new_error
+    end
   end
 end

spec/integration/retryable_writes_errors_spec.rb

@@ -0,0 +1,34 @@
+require 'spec_helper'
+
+describe 'Retryable writes errors tests' do
+  describe 'when the storage engine does not support retryable writes but the server does' do
+    require_mmapv1
+    min_server_fcv '3.6'
+    require_topology :replica_set, :sharded
+
+    before do
+      collection.delete_many
+    end
+
+    let(:collection) do
+      client[authorized_collection.name]
+    end
+
+    let(:client) do
+      authorized_client.with(retry_writes: true)
+    end
+
+    after do
+      client.close(true)
+    end
+
+    context 'when a retryable write is attempted' do
+      it 'raises an actionable error message' do
+        expect {
+          collection.insert_one(a:1)
+        }.to raise_error(Mongo::Error::OperationFailure, /This MongoDB deployment does not support retryable writes. Please add retryWrites=false to your connection string or use the retry_writes: false Ruby client option/)
+        expect(collection.find.count).to eq(0)
+      end
+    end
+  end
+end

spec/mongo/retryable_spec.rb

@@ -591,5 +591,18 @@ class RetryableHost
       end
     end
 
+    context 'when an error due to using an unsupported storage engine occurs' do
+      before do
+        expect(operation).to receive(:execute).and_raise(
+          Mongo::Error::OperationFailure.new('Transaction numbers are only allowed on...',
+            nil, :code=>20)).ordered
+      end
+
+      it 'raises an exception with the correct error message' do
+        expect {
+          retryable.write
+        }.to raise_error(Mongo::Error::OperationFailure, /This MongoDB deployment does not support retryable writes. Please add retryWrites=false to your connection string or use the retry_writes: false Ruby client option/)
+      end
+    end
   end
 end