command/state: helpers for UX with lock/unlock state

command/state/state.go

@@ -0,0 +1,83 @@
+// Package state exposes common helpers for working with state from the CLI.
+//
+// This is a separate package so that backends can use this for consistent
+// messaging without creating a circular reference to the command package.
+package message
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/hashicorp/terraform/helper/slowmessage"
+	"github.com/hashicorp/terraform/state"
+	"github.com/mitchellh/cli"
+	"github.com/mitchellh/colorstring"
+)
+
+const (
+	LockThreshold = 250 * time.Millisecond
+	LockMessage   = "Acquiring state lock. This may take a few moments..."
+	UnlockMessage = "Releasing state lock. This may take a few moments..."
+
+	UnlockErrorMessage = `
+[reset][bold][red]Error releasing the state lock![reset][red]
+
+Error message: %s
+
+Terraform acquires a lock when accessing your state to prevent others
+running Terraform to potentially modify the state at the same time. An
+error occurred while releasing this lock. This could mean that the lock
+did or did not release properly. If the lock didn't release properly,
+Terraform may not be able to run future commands since it'll appear as if
+the lock is held.
+
+In this scenario, please call the "force-unlock" command to unlock the
+state manually. This is a very dangerous operation since if it is done
+erroneously it could result in two people modifying state at the same time.
+Only call this command if you're certain that the unlock above failed and
+that no one else is holding a lock.
+`
+)
+
+// Lock locks the given state and outputs to the user if locking
+// is taking longer than the threshold.
+func Lock(s state.State, info string, ui cli.Ui, color *colorstring.Colorize) error {
+	sl, ok := s.(state.Locker)
+	if !ok {
+		return nil
+	}
+
+	return slowmessage.Do(LockThreshold, func() error {
+		return sl.Lock(info)
+	}, func() {
+		if ui != nil {
+			ui.Output(color.Color(LockMessage))
+		}
+	})
+}
+
+// Unlock unlocks the given state and outputs to the user if the
+// unlock fails what can be done.
+func Unlock(s state.State, ui cli.Ui, color *colorstring.Colorize) error {
+	sl, ok := s.(state.Locker)
+	if !ok {
+		return nil
+	}
+
+	err := slowmessage.Do(LockThreshold, sl.Unlock, func() {
+		if ui != nil {
+			ui.Output(color.Color(UnlockMessage))
+		}
+	})
+
+	if err != nil {
+		ui.Output(color.Color(fmt.Sprintf(
+			"\n"+strings.TrimSpace(UnlockErrorMessage)+"\n", err)))
+
+		err = fmt.Errorf(
+			"Error releasing the state lock. Please see the longer error message above.")
+	}
+
+	return err
+}