feat: new overridable routing headers implementation

gapic-common/gapic-common.gemspec

@@ -53,4 +53,5 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "rake", ">= 12.0"
   spec.add_development_dependency "redcarpet", "~> 3.0"
   spec.add_development_dependency "yard", "~> 0.9"
+  spec.add_development_dependency "debug"
 end

gapic-common/lib/gapic/grpc.rb

@@ -16,3 +16,4 @@
 require "gapic/grpc/errors"
 require "gapic/grpc/service_stub"
 require "gapic/grpc/status_details"
+require "gapic/routing_headers"

gapic-common/lib/gapic/rest.rb

@@ -29,4 +29,6 @@
 require "gapic/rest/paged_enumerable"
 require "gapic/rest/server_stream"
 require "gapic/rest/threaded_enumerator"
+require "gapic/routing_headers"
 require "json"
+

gapic-common/lib/gapic/routing_headers.rb

@@ -0,0 +1,15 @@
+# Copyright 2023 Google LLC
+#
+# 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
+#
+#     https://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.
+
+require "gapic/routing_headers/headers_extractor"

gapic-common/lib/gapic/routing_headers/header_binding.rb

@@ -0,0 +1,41 @@
+# Copyright 2023 Google LLC
+#
+# 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
+#
+#     https://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 Gapic
+  module RoutingHeaders
+    class HeadersExtractor
+      ##
+      # @private
+      class HeaderBinding
+        attr_reader :field
+        attr_reader :header_name
+        attr_reader :regex
+
+        def initialize field, header_name=nil, regex=nil
+          @field = field
+          @header_name = header_name
+          @regex = regex
+        end
+
+        ##
+        # @private
+        # Creates a new HeaderBinding.
+        #
+        def self.create field:, header_name: nil, regex: nil
+          HeaderBinding.new field, header_name, regex
+        end
+      end
+    end
+  end
+end

gapic-common/lib/gapic/routing_headers/headers_extractor.rb

@@ -0,0 +1,80 @@
+# Copyright 2023 Google LLC
+#
+# 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
+#
+#     https://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.
+
+require "gapic/routing_headers/header_binding"
+
+module Gapic
+  module RoutingHeaders
+    class HeadersExtractor
+      attr_accessor :bindings
+
+      def initialize bindings = nil
+        @bindings = bindings || []
+      end
+
+      def with_bindings(field:, header_name: nil, regex: nil)
+        binding = HeaderBinding.create(field: field, header_name: header_name, regex: regex)
+        HeadersExtractor.new @bindings + [binding]
+      end
+
+      def extract_headers request
+        header_params = {}
+
+        unless request
+          err_msg = "Incorrect header extraction request: request is nil."
+          raise ::Gapic::Common::Error, err_msg
+        end
+
+        @bindings.each do |header_binding|
+          field_value = get_field_val request, header_binding.field
+          next unless field_value
+
+          if header_binding.regex && !field_value.is_a?(::String)
+            err_msg = "Header binding configuration is incorrect: regex" \
+                      "is given with a non-string field #{field}.\n" \
+                      "When the regex is present the field in the regex must be a ::String."
+            raise ::Gapic::Common::Error, err_msg
+          end
+
+          header_name = header_binding.header_name || header_binding.field
+
+          header_value = if header_binding.regex
+            match = header_binding.regex.match field_value
+            match[1] if match
+          else
+            field_value.to_s
+          end
+
+          header_params[header_name] = header_value if header_value && !header_value.empty?
+        end
+
+        header_params
+      end
+
+      private
+
+      def get_field_val request, field
+        field_path = field.split "."
+
+        curr_submessage = request
+        field_path.each do |curr_field|
+          return nil unless curr_submessage.respond_to? curr_field
+          curr_submessage = curr_submessage.send curr_field
+        end
+
+        return curr_submessage.to_s if curr_submessage
+      end
+    end
+  end
+end