Add placeholder webhook handler

Register the handler with the underlying baseserver.

Author: Andrew Farries

components/usage/pkg/server/server.go

@@ -109,6 +109,9 @@ func Start(cfg Config) error {
 		return fmt.Errorf("failed to register gRPC services: %w", err)
 	}
 
+	h := stripe.NewWebhookHandler()
+	registerHttpHandlers(srv, h)
+
 	err = controller.RegisterMetrics(srv.MetricsRegistry())
 	if err != nil {
 		return fmt.Errorf("failed to register controller metrics: %w", err)
@@ -131,3 +134,7 @@ func registerGRPCServices(srv *baseserver.Server, conn *gorm.DB, stripeClient *s
 	}
 	return nil
 }
+
+func registerHttpHandlers(srv *baseserver.Server, h *stripe.WebhookHandler) {
+	srv.HTTPMux().HandleFunc("/webhook", h.Handle)
+}

components/usage/pkg/stripe/webhook.go

@@ -0,0 +1,47 @@
+// Copyright (c) 2022 Gitpod GmbH. All rights reserved.
+// Licensed under the GNU Affero General Public License (AGPL).
+// See License-AGPL.txt in the project root for license information.
+
+package stripe
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/gitpod-io/gitpod/common-go/log"
+	"github.com/stripe/stripe-go/v72"
+)
+
+type WebhookHandler struct {
+	stripeWebhookSecret string
+}
+
+func NewWebhookHandler(secret string) *WebhookHandler {
+	return &WebhookHandler{stripeWebhookSecret: secret}
+}
+
+func (h *WebhookHandler) Handle(w http.ResponseWriter, req *http.Request) {
+	const maxBodyBytes = int64(65536)
+
+	req.Body = http.MaxBytesReader(w, req.Body, maxBodyBytes)
+	payload, err := ioutil.ReadAll(req.Body)
+	if err != nil {
+		log.WithError(err).Error("Stripe webhook error when reading request body")
+		w.WriteHeader(http.StatusServiceUnavailable)
+		return
+	}
+
+	event := stripe.Event{}
+	if err := json.Unmarshal(payload, &event); err != nil {
+		log.WithError(err).Error("Stripe webhook error while parsing event payload")
+		w.WriteHeader(http.StatusBadRequest)
+		return
+	}
+
+	// TODO: verify webhook signature.
+	// Conditional on there being a secret configured.
+
+	fmt.Fprintf(w, "event type: %s", event.Type)
+}