cmd/cue: handle signals and perform a graceful shutdown for mod registry

The registry did not handle signals. The default behavior of a Go
program for receiving `SIGINT` and `SIGTERM` signals is to exit and
return `128 + <signal number>`, regardless of whether it exits
successfully or not.

Handle signals and perform a graceful shutdown for the registry. Return
zero when it exits successfully.

Fixes #3224

Change-Id: I90a534d47f43b2d9f93db7f460df8892a695f134
Signed-off-by: haoqixu <hq.xu0o0@gmail.com>
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1196370
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>

cmd/cue/cmd/modregistry.go

@@ -16,18 +16,21 @@ package cmd
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"net"
 	"net/http"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
 
 	"cuelabs.dev/go/oci/ociregistry"
 	"cuelabs.dev/go/oci/ociregistry/ocimem"
 	"cuelabs.dev/go/oci/ociregistry/ociserver"
 	"github.com/spf13/cobra"
 )
 
-// TODO: add testing for this command.
-
 func newModRegistryCmd(c *Command) *cobra.Command {
 	cmd := &cobra.Command{
 		// This command is hidden, for now at least,
@@ -63,7 +66,28 @@ func runModRegistry(cmd *Command, args []string) error {
 	r := ocimem.NewWithConfig(&ocimem.Config{
 		ImmutableTags: true,
 	})
-	return http.Serve(l, ociserver.New(ociTagLoggerRegistry{r}, nil))
+
+	srv := http.Server{
+		Handler: ociserver.New(ociTagLoggerRegistry{r}, nil),
+	}
+	var serveErr error
+	go func() {
+		if err := srv.Serve(l); !errors.Is(err, http.ErrServerClosed) {
+			serveErr = err
+		}
+	}()
+
+	sigint := make(chan os.Signal, 1)
+	signal.Notify(sigint, os.Interrupt, syscall.SIGTERM)
+	<-sigint
+
+	ctx, cancal := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancal()
+	if err := srv.Shutdown(ctx); err != nil {
+		fmt.Printf("HTTP server Shutdown: %v\n", err)
+		return err
+	}
+	return serveErr
 }
 
 type ociTagLoggerRegistry struct {

cmd/cue/cmd/testdata/script/mod_registry.txtar

@@ -0,0 +1,19 @@
+# TODO: use a random unused port
+env CUE_REGISTRY=localhost:41331
+exec cue mod registry ${CUE_REGISTRY} &
+exec cue mod publish v0.0.1
+cmpenv stdout expect-stdout
+
+-- expect-stdout --
+published mod.example/blah@v0.0.1 to ${CUE_REGISTRY}/mod.example/blah:v0.0.1
+-- blah.cue --
+package blah
+blah: 42
+-- cue.mod/module.cue --
+module: "mod.example/blah@v0"
+language: {
+	version: "v0.9.0"
+}
+source: {
+	kind: "self"
+}