feat: init declarative functions go

[grant]

Declarative functions interface for the Go Functions Framework.

Example usage

main.go

Sample main package used for local development only.

package main

import (
	"os"

	"github.com/GoogleCloudPlatform/functions-framework-go/funcframework"
)

func main() {
	port := "8080"
	if envPort := os.Getenv("PORT"); envPort != "" {
		port = envPort
	}
	if err := funcframework.Start(port); err != nil {
		log.Fatalf("Failed to start functions framework: %v", err)
	}
}

function.go

Sample declarative function, registered in init.

package function

import (
	"net/http"
	"os"

	"github.com/GoogleCloudPlatform/functions-framework-go/funcframework"
)

func HelloWorld(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("Hello, World!"))
}

func init() {
	// Register your function named "hello"
	funcframework.HTTP("hello", HelloWorld)
}

Features

• Exposes new functions HTTP and CloudEvent that allows you to declaratively register a function with a given name.
• Creates a function registry (similar to python and Node). I expect the registry to be more useful as we add more features to declarative functions.
• Adds sample declarative functions for conformance tests.
• Adds sample runnable functions in testdata.
• Adds basic docs in the README.md.

Example tests

• go run testdata/declarative/http/main.go
  • 2021/10/28 15:38:50 Listening to function "http" at http://localhost:8080/ Serving function...
• go run testdata/declarative/cloudevent/main.go
  • 2021/10/28 15:40:54 Listening to function "cloudevent" at http://localhost:8080/ Serving function...

Example conformance functions

FUNCTION_TARGET=declarativeHTTP go run testdata/conformance/cmd/declarative/main.go
FUNCTION_TARGET=declarativeCE go run testdata/conformance/cmd/declarative/main.go

I'm not an expert in Go, so feel free to suggest any changes!

[grant]

I've made some significant changes and added a handful of example functions.

[anniefu]

Registration should be done in the function package conformance/function/function.go, or a new one if you prefer. The GCP buildpacks ignore the main.go, so this would not work in production.

[grant]

I think the conformance main.gos are just for testing – we're mirroring the existing testing main.gos here.

https://github.com/GoogleCloudPlatform/functions-framework-go/blob/master/testdata/conformance/cmd/http/main.go

I think we're going to need multiple conformance/function/function.go packages to be able to test multiple different declarative functions if going that route.

[grant]

TODO: Look at modifying test handlers in funcframework/framework_test.go

	for _, tc := range tests {
		h := http.NewServeMux()
		if err := registerEventFunction("/", tc.fn, h); err != nil {
			t.Fatalf("registerEventFunction(): %v", err)
		}

		srv := httptest.NewServer(h)
		defer srv.Close()

->

	for _, tc := range tests {
		handler = http.NewServeMux()
		if err := RegisterEventFunctionContext(context.Background(), "/", tc.fn); err != nil {
			t.Fatalf("registerEventFunction(): %v", err)
		}

		srv := httptest.NewServer(handler)
		defer srv.Close()

[anniefu]

Nice!! It's pretty much there. Mostly just nits and a couple of implementation details.

[KaylaNguyen]

Looks great!

[anniefu]

Could you modify the PR description too so that the function registration happens in outside of main.go?

[grant]

Could you modify the PR description too so that the function registration happens in outside of main.go?

Done!