feat: init declarative functions go

README.md

@@ -216,6 +216,28 @@ These functions are registered with the handler via `funcframework.RegisterCloud
 
 To learn more about CloudEvents, see the [Go SDK for CloudEvents](https://github.com/cloudevents/sdk-go).
 
+### Declarative Functions
+
+The Functions Framework also provides a way to declaratively define functions:
+
+```golang
+package function
+
+import (
+	"net/http"
+
+	funcframework "github.com/GoogleCloudPlatform/functions-framework-go/funcframework"
+)
+
+func init() {
+	funcframework.HTTPFunction("foo", func(w http.ResponseWriter, r *http.Request) {
+		w.Write([]byte("Hello, World!"))
+	})
+}
+```
+
+Upon starting, the framework will register your function with the function name in the URL path.
+
 [ff_go_unit_img]: https://github.com/GoogleCloudPlatform/functions-framework-go/workflows/Go%20Unit%20CI/badge.svg
 [ff_go_unit_link]: https://github.com/GoogleCloudPlatform/functions-framework-go/actions?query=workflow%3A"Go+Unit+CI"
 [ff_go_lint_img]: https://github.com/GoogleCloudPlatform/functions-framework-go/workflows/Go%20Lint%20CI/badge.svg

funcframework/registry.go

@@ -0,0 +1,47 @@
+package funcframework
+
+import (
+	"context"
+	"net/http"
+
+	cloudevents "github.com/cloudevents/sdk-go/v2"
+)
+
+// A declaratively registered function
+type RegisteredFunction struct {
+	Name         string
+	CloudEventFn func(context.Context, cloudevents.Event) error
+	HTTPFn       func(http.ResponseWriter, *http.Request)
+}
+
+var (
+	function_registry = map[string]RegisteredFunction{}
+)
+
+// Registers a HTTP function with a given name
+func HTTPFunction(name string, fn func(http.ResponseWriter, *http.Request)) error {
+	function_registry[name] = RegisteredFunction{
+		Name:         name,
+		CloudEventFn: nil,
+		HTTPFn:       fn,
+	}
+	RegisterHTTPFunctionContext(context.Background(), name, fn)
+	return nil
+}
+
+// Registers a CloudEvent function with a given name
+func CloudEventFunction(name string, fn func(context.Context, cloudevents.Event) error) error {
+	function_registry[name] = RegisteredFunction{
+		Name:         name,
+		CloudEventFn: fn,
+		HTTPFn:       nil,
+	}
+	RegisterCloudEventFunctionContext(context.Background(), name, fn)
+	return nil
+}
+
+// Gets a registered function by name
+func GetRegisteredFunction(name string) (RegisteredFunction, bool) {
+	fn, ok := function_registry[name]
+	return fn, ok
+}

testdata/declarative/declarative_function.go

@@ -0,0 +1,28 @@
+// Copyright 2021 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
+//
+//      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.
+
+// Package function contains test functions to validate the framework.
+package function
+
+import (
+	"net/http"
+
+	funcframework "github.com/GoogleCloudPlatform/functions-framework-go/funcframework"
+)
+
+func init() {
+	funcframework.HTTPFunction("foo", func(w http.ResponseWriter, r *http.Request) {
+		w.Write([]byte("Hello, World!"))
+	})
+}