fix: graceful shutdown with asynchronous processes - fixes #1022

pkg/modules/webhook/middleware.go

@@ -173,10 +173,13 @@ func webhookMiddleware(w *Webhook) api.Middleware {
 						}
 					}
 
+					w.asyncCount.Add(1)
+
 					// As a webhook URL has been given, we handle the request in a
 					// goroutine and return immediately.
 					go func() {
 						defer cancel()
+						defer w.asyncCount.Add(-1)
 
 						// Call the next middleware in the chain.
 						err := next(c)

pkg/modules/webhook/webhook.go

@@ -1,6 +1,7 @@
 package webhook
 
 import (
+	"sync/atomic"
 	"time"
 
 	"github.com/dlclark/regexp2"
@@ -25,6 +26,7 @@ type Webhook struct {
 	retryMinWait   time.Duration
 	retryMaxWait   time.Duration
 	clientTimeout  time.Duration
+	asyncCount     atomic.Int64
 	disable        bool
 }
 
@@ -62,6 +64,7 @@ func (w *Webhook) Provision(ctx *gotenberg.Context) error {
 	w.retryMaxWait = flags.MustDuration("webhook-retry-max-wait")
 	w.clientTimeout = flags.MustDuration("webhook-client-timeout")
 	w.disable = flags.MustBool("webhook-disable")
+	w.asyncCount.Store(0)
 
 	return nil
 }
@@ -77,9 +80,15 @@ func (w *Webhook) Middlewares() ([]api.Middleware, error) {
 	}, nil
 }
 
+// AsyncCount returns the number of asynchronous requests.
+func (w *Webhook) AsyncCount() int64 {
+	return w.asyncCount.Load()
+}
+
 // Interface guards.
 var (
-	_ gotenberg.Module       = (*Webhook)(nil)
-	_ gotenberg.Provisioner  = (*Webhook)(nil)
-	_ api.MiddlewareProvider = (*Webhook)(nil)
+	_ gotenberg.Module        = (*Webhook)(nil)
+	_ gotenberg.Provisioner   = (*Webhook)(nil)
+	_ api.MiddlewareProvider  = (*Webhook)(nil)
+	_ api.AsynchronousCounter = (*Webhook)(nil)
 )