Refactor to Use Hash#fetch

Additionally, supports switching the endpoints.json file to another
path.

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

@@ -113,6 +113,7 @@ module Aws
   autoload :ParamConverter, 'aws-sdk-core/param_converter'
   autoload :ParamValidator, 'aws-sdk-core/param_validator'
   autoload :RefreshingCredentials, 'aws-sdk-core/refreshing_credentials'
+  autoload :RegionsAndEndpoints, 'aws-sdk-core/regions_and_endpoints'
   autoload :Service, 'aws-sdk-core/service'
   autoload :SharedCredentials, 'aws-sdk-core/shared_credentials'
   autoload :Structure, 'aws-sdk-core/structure'

aws-sdk-core/lib/aws-sdk-core/endpoint_provider.rb

@@ -2,71 +2,17 @@ module Aws
   # @api private
   class EndpointProvider
 
-    PATH = File.join(File.dirname(__FILE__), '..', '..', 'endpoints.json')
-    RULES = Json.load_file(PATH)
+    RULES = RegionsAndEndpoints.new
 
     class << self
 
       def resolve(region, service)
-        "https://" + endpoint_for(region, service)
+        RULES.resolve(region, service)
       end
 
       def signing_region(region, service)
-        partition = get_partition(region)
-        [
-          "services", service, "endpoints", region, "credentialScope", "region"
-        ].inject(partition) do |acc, key|
-          if acc && acc[key]
-            acc[key]
-          else
-            region
-          end
-        end
+        RULES.signing_region(region, service)
       end
-
-      private
-      def endpoint_for(region, service)
-        partition = get_partition(region)
-        endpoint = default_endpoint(partition, service, region)
-        if service_cfg = partition["services"][service]
-          if service_cfg["isRegionalized"] == false
-            if partition_endpoint = service_cfg["partitionEndpoint"]
-              region = partition_endpoint
-            end
-          end
-          if service_defaults = service_cfg["defaults"]
-            if host = service_defaults["hostname"]
-              endpoint = host
-            end
-          end
-          if endpoint_cfg = service_cfg["endpoints"][region]
-            if host = endpoint_cfg["hostname"]
-              endpoint = host
-            end
-          end
-        end
-        endpoint
-      end
-
-      def default_endpoint(partition, service, region)
-        hostname_template = partition["defaults"]["hostname"]
-        hostname_template.sub(
-          '{region}', region
-        ).sub(
-          '{service}', service
-        ).sub(
-          '{dnsSuffix}', partition["dnsSuffix"]
-        )
-      end
-
-      def get_partition(region)
-        partition = RULES["partitions"].find do |p|
-          region.match(p["regionRegex"])
-        end
-        partition ||= RULES["partitions"].find { |p| p["partition"] == "aws" }
-        partition
-      end
-
     end
   end
 end

aws-sdk-core/lib/aws-sdk-core/regions_and_endpoints.rb

@@ -0,0 +1,73 @@
+module Aws
+  # @api private
+  class RegionsAndEndpoints
+
+    attr_reader :rules
+
+    PATH = File.join(File.dirname(__FILE__), '..', '..', 'endpoints.json')
+
+    def initialize(file = PATH)
+      @rules = Json.load_file(file)
+    end
+
+    def set_endpoints_file(file)
+      @rules = Json.load_file(file)
+    end
+
+    def resolve(region, service)
+      "https://" + endpoint_for(region, service)
+    end
+
+    def signing_region(region, service)
+      partition = get_partition(region)
+      config_region = partition.fetch("services", {}).
+        fetch(service, {}).
+        fetch("endpoints", {}).
+        fetch(region, {}).
+        fetch("credentialScope", {})["region"]
+      config_region ||= region
+      config_region
+    end
+
+    private
+    def endpoint_for(region, service)
+      partition = get_partition(region)
+      endpoint = default_endpoint(partition, service, region)
+      service_cfg = partition.fetch("services", {}).fetch(service, {})
+
+      # Check for service-level default endpoint.
+      endpoint = service_cfg.fetch("defaults", {}).fetch("hostname", endpoint)
+
+      # Check for global endpoint.
+      if service_cfg["isRegionalized"] == false
+        region = service_cfg.fetch("partitionEndpoint", region)
+      end
+
+      # Check for service/region level endpoint.
+      endpoint = service_cfg.fetch("endpoints", {}).
+        fetch(region, {}).fetch("hostname", endpoint)
+
+      endpoint
+    end
+
+    def default_endpoint(partition, service, region)
+      hostname_template = partition["defaults"]["hostname"]
+      hostname_template.sub(
+        '{region}', region
+      ).sub(
+        '{service}', service
+      ).sub(
+        '{dnsSuffix}', partition["dnsSuffix"]
+      )
+    end
+
+    def get_partition(region)
+      partition = @rules["partitions"].find do |p|
+        region.match(p["regionRegex"])
+      end
+      partition ||= @rules["partitions"].find { |p| p["partition"] == "aws" }
+      partition
+    end
+
+  end
+end