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 #70.

utils.go

@@ -2,6 +2,7 @@ package zfs
 
 import (
 	"bytes"
+	"context"
 	"errors"
 	"fmt"
 	"io"
@@ -10,18 +11,57 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"sync/atomic"
+	"syscall"
+	"time"
 
 	"github.com/google/uuid"
 )
 
+// Runner specifies the parameters used when executing ZFS commands.
+type Runner struct {
+	// Timeout specifies how long to wait before sending a SIGTERM signal to the running process.
+	Timeout time.Duration
+
+	// Grace specifies the time waited after signaling the running process with SIGTERM before it is forcefully
+	// killed with SIGKILL.
+	Grace time.Duration
+}
+
+var defaultRunner atomic.Value
+
+func init() {
+	defaultRunner.Store(&Runner{})
+}
+
+func Default() *Runner {
+	return defaultRunner.Load().(*Runner) //nolint: forcetypeassert // Impossible for it to be anything else.
+}
+
+func SetRunner(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