feat: graceful shutdown when CI job is cancelled (#196)

By listening on SIGINT and SIGTERM signals we can stop executing as soon
as reasonably possible. This helps to avoid uncessary work and stop the
job earlier.

Right now we have no manual checks for cancelled contexts, and rely on
the http client to check for it while making requests.

cmd/rp/cmd/root.go

@@ -1,9 +1,12 @@
 package cmd
 
 import (
+	"context"
 	"log/slog"
 	"os"
+	"os/signal"
 	"runtime/debug"
+	"syscall"
 	"time"
 
 	"github.com/lmittmann/tint"
@@ -13,10 +16,12 @@ import (
 var logger *slog.Logger
 
 var rootCmd = &cobra.Command{
-	Use:     "rp",
-	Short:   "",
-	Long:    ``,
-	Version: version(),
+	Use:           "rp",
+	Short:         "",
+	Long:          ``,
+	Version:       version(),
+	SilenceUsage:  true, // Makes it harder to find the actual error
+	SilenceErrors: true, // We log manually with slog
 }
 
 func version() string {
@@ -41,8 +46,33 @@ func version() string {
 }
 
 func Execute() {
-	err := rootCmd.Execute()
+	// Behaviour when cancelling jobs:
+	//
+	//   GitHub Actions: https://docs.github.com/en/actions/managing-workflow-runs-and-deployments/managing-workflow-runs/canceling-a-workflow#steps-github-takes-to-cancel-a-workflow-run
+	// 	   1. SIGINT
+	//     2. Wait 7500ms
+	//     3. SIGTERM
+	//     4. Wait 2500ms
+	//     5. SIGKILL
+	//
+	//   GitLab CI/CD: https://gitlab.com/gitlab-org/gitlab-runner/-/merge_requests/4446
+	//     1. SIGTERM
+	//     2. Wait ???
+	//     3. SIGKILL
+	//
+	// We therefore need to listen on SIGINT and SIGTERM
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	go func() {
+		// Make sure to stop listening on signals after receiving the first signal to hand control of the signal back
+		// to the runtime. The Go runtime implements a "force shutdown" if the signal is received again.
+		<-ctx.Done()
+		logger.InfoContext(ctx, "Received shutdown signal, stopping...")
+		stop()
+	}()
+
+	err := rootCmd.ExecuteContext(ctx)
 	if err != nil {
+		logger.ErrorContext(ctx, err.Error())
 		os.Exit(1)
 	}
 }