From fadc75c731368d39edc718246b6dedff40e097e3 Mon Sep 17 00:00:00 2001
From: "Gabriel A. Giovanini" <mail@gabrielgio.me>
Date: Sat, 4 May 2024 23:28:05 +0200
Subject: feat: Close worker on error

If a worker error the application, as a whole, is terminadated.
---
 pkg/worker/http.go   | 20 ++++++++++++++++----
 pkg/worker/worker.go | 46 +++++++++++++++++++++++++++++-----------------
 2 files changed, 45 insertions(+), 21 deletions(-)

diff --git a/pkg/worker/http.go b/pkg/worker/http.go
index 1d56f86..973775e 100644
--- a/pkg/worker/http.go
+++ b/pkg/worker/http.go
@@ -16,11 +16,23 @@ func NewServerTask(server *http.Server) *ServerTask {
 }
 
 func (self *ServerTask) Start(ctx context.Context) error {
+	done := make(chan error)
+
 	go func() {
-		// nolint: errcheck
-		self.server.ListenAndServe()
+		done <- self.server.ListenAndServe()
 	}()
 
-	<-ctx.Done()
-	return self.server.Shutdown(ctx)
+	select {
+	// if ListenAndServe error for something other than context.Canceled
+	//(e.g.: address already in use) it trigger done to return sonner with
+	// the return error
+	case err := <-done:
+		return err
+
+	// in case of context canceled it will manually trigger the server to
+	// shutdown, and return its error, which is most cases, but not limited, is
+	// context.Canceled.
+	case <-ctx.Done():
+		return self.server.Shutdown(ctx)
+	}
 }
diff --git a/pkg/worker/worker.go b/pkg/worker/worker.go
index 6b5c21c..fc97c97 100644
--- a/pkg/worker/worker.go
+++ b/pkg/worker/worker.go
@@ -10,31 +10,42 @@ import (
 )
 
 type (
+
+	// Task defines a long running core component of the application.
 	Task interface {
+		// Start defines when the component will be started.
+		// The task MUST watch for the context and return when the context is
+		// canceled.
+		//
+		// Start MUST only error on unhandled catastrophic errors, since
+		// returning an error will cause the application to halt.
+		//
+		// Context canceled error is ignored and not reported as error as they
+		// will be trigger by OS signals or some other component erring. But in
+		// any case the task SHOULD handle and return context cancellation
+		// error.
 		Start(context.Context) error
 	}
 
-	Work struct {
+	// TaskPool manages the life-cycle of a pool of tasks.
+	TaskPool struct {
+		tasks []*work
+	}
+
+	// work is wrapper around task to add metadata to it.
+	work struct {
 		Name string
 		Task Task
 		wait time.Duration
 	}
-
-	TaskPool struct {
-		tasks []*Work
-	}
-)
-
-const (
-	format = "2006.01.02 15:04:05"
 )
 
 func NewTaskPool() *TaskPool {
 	return &TaskPool{}
 }
 
-func (w *Work) run(ctx context.Context) error {
-	// first time fire from the get go
+func (w *work) run(ctx context.Context) error {
+	// first time fire the task from the get go
 	timer := time.NewTimer(time.Nanosecond)
 
 	for {
@@ -42,7 +53,7 @@ func (w *Work) run(ctx context.Context) error {
 		case <-ctx.Done():
 			return ctx.Err()
 		case <-timer.C:
-			if err := w.Task.Start(ctx); err != nil && !errors.Is(err, context.Canceled) {
+			if err := w.Task.Start(ctx); err != nil {
 				return err
 			}
 		}
@@ -51,7 +62,7 @@ func (w *Work) run(ctx context.Context) error {
 }
 
 func (self *TaskPool) AddTask(name string, wait time.Duration, task Task) {
-	self.tasks = append(self.tasks, &Work{
+	self.tasks = append(self.tasks, &work{
 		Name: name,
 		Task: task,
 		wait: wait,
@@ -60,27 +71,28 @@ func (self *TaskPool) AddTask(name string, wait time.Duration, task Task) {
 
 func (self *TaskPool) Start(ctx context.Context) error {
 	var g errgroup.Group
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
 
 	for _, w := range self.tasks {
-		g.Go(func(w *Work) func() error {
+		g.Go(func(w *work) func() error {
 			return func() error {
-				slog.Info("Process starting", "time", time.Now().Format(format), "name", w.Name)
+				slog.Info("Process starting", "name", w.Name)
 				now := time.Now()
 				if err := w.run(ctx); err != nil && !errors.Is(context.Canceled, err) {
 					since := time.Since(now)
 					slog.Error(
 						"Process erred",
-						"time", time.Now().Format(format),
 						"name", w.Name,
 						"error", err,
 						"duration", since,
 					)
+					cancel()
 					return err
 				} else {
 					since := time.Since(now)
 					slog.Info(
 						"Process ended",
-						"time", time.Now().Format(format),
 						"name", w.Name,
 						"duration", since,
 					)
-- 
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