Support timeout for commands

Commands can now be stopped after the specified timeout. The default
behaviour of no timeouts is kept the same. Users wanting to opt into
this feature must set a new DefaultRunner with properly set values.

Related to mistifyio#70.

utils.go

@@ -2,6 +2,7 @@ package zfs
 
 import (
 	"bytes"
+	"context"
 	"errors"
 	"fmt"
 	"io"
@@ -10,18 +11,52 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"sync/atomic"
+	"syscall"
+	"time"
 
 	"github.com/google/uuid"
 )
 
+type Runner struct {
+	Timeout time.Duration
+	Grace   time.Duration
+}
+
+var defaultRunner atomic.Value
+
+func init() {
+	defaultRunner.Store(&Runner{})
+}
+
+func Default() *Runner {
+	return defaultRunner.Load().(*Runner)
+}
+
+func SetDefault(runner *Runner) {
+	defaultRunner.Store(runner)
+}
+
 type command struct {
 	Command string
 	Stdin   io.Reader
 	Stdout  io.Writer
 }
 
 func (c *command) Run(arg ...string) ([][]string, error) {
-	cmd := exec.Command(c.Command, arg...)
+	var cmd *exec.Cmd
+	if Default().Timeout == 0 {
+		cmd = exec.Command(c.Command, arg...)
+	} else {
+		ctx, cancel := context.WithTimeout(context.Background(), Default().Timeout)
+		defer cancel()
+
+		cmd = exec.CommandContext(ctx, c.Command, arg...)
+		cmd.Cancel = func() error {
+			return cmd.Process.Signal(syscall.SIGTERM)
+		}
+		cmd.WaitDelay = Default().Grace
+	}
 
 	var stdout, stderr bytes.Buffer