Beginning of automatic API version detection

When we make a request to a chef server, we capture the minimum and
maximum support API versions and allow them to be queried.
We then provide some infrastructure for making decisions on which class
should be used, in a middleware-ish mechanism.

Signed-off-by: Thom May <thom@chef.io>

4 files changed, 137 insertions, 0 deletions

diff --git a/lib/chef/http/api_versions.rb b/lib/chef/http/api_versions.rb
new file mode 100644
index 0000000000..e164da262d
--- /dev/null
+++ b/lib/chef/http/api_versions.rb
@@ -0,0 +1,50 @@
+#--
+# Copyright:: Copyright 2017, Chef Software Inc.
+# License:: Apache License, Version 2.0
+#
+# 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.
+#
+
+require "chef/server_api_versions"
+
+class Chef
+  class HTTP
+    # An HTTP middleware to retrieve and store the Chef Server's minimum
+    # and maximum supported API versions.
+    class APIVersions
+
+      def initialize(options = {})
+      end
+
+      def handle_request(method, url, headers = {}, data = false)
+        [method, url, headers, data]
+      end
+
+      def handle_response(http_response, rest_request, return_value)
+        if http_response.key?("x-ops-server-api-version")
+          ServerAPIVersions.instance.set_versions(http_response["x-ops-server-api-version"])
+        end
+        [http_response, rest_request, return_value]
+      end
+
+      def stream_response_handler(response)
+        nil
+      end
+
+      def handle_stream_complete(http_response, rest_request, return_value)
+        [http_response, rest_request, return_value]
+      end
+
+    end
+  end
+end
diff --git a/lib/chef/mixin/versioned_api.rb b/lib/chef/mixin/versioned_api.rb
new file mode 100644
index 0000000000..b8ec61c5f0
--- /dev/null
+++ b/lib/chef/mixin/versioned_api.rb
@@ -0,0 +1,49 @@
+#--
+# Copyright:: Copyright 2017, Chef Software Inc.
+# License:: Apache License, Version 2.0
+#
+# 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.
+#
+
+class Chef
+  module Mixin
+    module VersionedAPI
+
+      def self.included(base)
+        # When this file is mixed in, make sure we also add the class methods
+        base.send :extend, ClassMethods
+      end
+
+      module ClassMethods
+        def versioned_interfaces
+          @versioned_interfaces ||= []
+        end
+
+        def add_api_version(klass)
+          versioned_interfaces << klass
+        end
+      end
+
+      def select_api_version
+        self.class.versioned_interfaces.select do |klass|
+          version = klass.send(:supported_api_version)
+          # min and max versions will be nil if we've not made a request to the server yet,
+          # in which case we'll just start with the highest version and see what happens
+          ServerAPIVersions.instance.min_server_version.nil? || (version >= ServerAPIVersions.instance.min_server_version && version <= ServerAPIVersions.instance.max_server_version)
+        end
+          .sort { |a, b| a.send(:supported_api_version) <=> b.send(:supported_api_version) }
+          .last
+      end
+    end
+  end
+end
diff --git a/lib/chef/server_api.rb b/lib/chef/server_api.rb
index d233d25232..2bdc5d9fe8 100644
--- a/lib/chef/server_api.rb
+++ b/lib/chef/server_api.rb
@@ -24,6 +24,7 @@ require "chef/http/json_input"
 require "chef/http/json_output"
 require "chef/http/remote_request_id"
 require "chef/http/validate_content_length"
+require "chef/http/api_versions"
 
 class Chef
   class ServerAPI < Chef::HTTP
@@ -42,6 +43,7 @@ class Chef
     use Chef::HTTP::Decompressor
     use Chef::HTTP::Authenticator
     use Chef::HTTP::RemoteRequestID
+    use Chef::HTTP::APIVersions
 
     # ValidateContentLength should come after Decompressor
     # because the order of middlewares is reversed when handling
diff --git a/lib/chef/server_api_versions.rb b/lib/chef/server_api_versions.rb
new file mode 100644
index 0000000000..91591875a4
--- /dev/null
+++ b/lib/chef/server_api_versions.rb
@@ -0,0 +1,36 @@
+#--
+# Copyright:: Copyright 2017, Chef Software Inc.
+# License:: Apache License, Version 2.0
+#
+# 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.
+#
+
+require "singleton"
+
+class Chef
+  class ServerAPIVersions
+    include Singleton
+
+    def set_versions(versions)
+      @versions ||= versions
+    end
+
+    def min_server_version
+      !@versions.nil? ? @versions["min_version"] : nil
+    end
+
+    def max_server_version
+      !@versions.nil? ? @versions["max_version"] : nil
+    end
+  end
+end