Regression fix for serializing structures for EC2.

Fixes #881.

CHANGELOG.md

@@ -1,6 +1,16 @@
 Unreleased Changes
 ------------------
 
+* Issue - Aws::EC2 - Resolved a regression with serializing `Aws::Structure` types in
+  `Aws::EC2::Client` requests. The `Aws::Query::EC2ParamBuilder` class is responsible
+  for testing protocol specific implementations but it tests with input that is loaded
+  from a JSON document into a vanilla Ruby hash which does not trigger this behavior.
+
+  The other protocol builder classes have full unit test suites, while the EC2 param
+  builder did not. A test case has been added to cover this regression.
+
+  See [related GitHub issue #881](https://github.com/aws/aws-sdk-ruby/issues/881).
+
 * Feature - KMS Client-Side-Encryption - Added support to `Aws::S3::Encryption::Client` for using AWS Key Management Service (KMS) to manage master encryption keys.
 
   ```ruby

aws-sdk-core/lib/aws-sdk-core/query/ec2_param_builder.rb

@@ -20,7 +20,7 @@ def apply(ref, params)
 
       def structure(ref, values, prefix)
         shape = ref.shape
-        values.each do |name, value|
+        values.each_pair do |name, value|
           unless value.nil?
             member_ref = shape.member(name)
             format(member_ref, value, prefix + query_name(member_ref))

aws-sdk-core/spec/aws/query/ec2_param_builder_spec.rb

@@ -0,0 +1,34 @@
+require 'spec_helper'
+
+module Aws
+  module Query
+    describe EC2ParamBuilder do
+
+      let(:shapes) { ApiHelper.sample_shapes }
+
+      let(:rules) {
+        shape_map = Api::ShapeMap.new(shapes)
+        shape_map.shape_ref('shape' => 'StructureShape')
+      }
+
+      def query(params = {})
+        param_list = ParamList.new
+        EC2ParamBuilder.new(param_list).apply(rules, params)
+        param_list.map { |param| [param.name, param.value ] }.sort
+      end
+
+      it 'can serialize structures' do
+        params = Structure.new(*rules.shape.member_names).new
+        params.boolean = true
+        params.integer = 123
+        params.string = 'abc'
+        expect(query(params)).to eq([
+          ['Boolean', 'true'],
+          ['Integer', '123'],
+          ['String', 'abc'],
+        ])
+      end
+
+    end
+  end
+end