Add cleanstack util (#35)

utils/cleanstack.go

@@ -0,0 +1,58 @@
+package utils
+
+import (
+	"github.com/hashicorp/go-multierror"
+)
+
+type CleanJob func() error
+
+// NewCleanStack returns a new stack.
+// It's used to push jobs into it that need to be executed in order, like unmounting disks or removing dirs, and it
+// will run those jobs in the order they were pushed into it to maintain order
+// So you can create a dir, push its removal into the stack, mount something into that dir and push its unmounting into
+// the stack and when cleanup is triggered it will first unmount and then remove the dir
+// Usually its setup inside a function with a defer immediately so it auto cleans if you return from anywhere in the function
+// That way you don't need to track on each return what needs to be cleaned and whatnot
+// cleanup := utils.NewCleanStack()
+// defer func() { err = cleanup.Cleanup(err) }()
+func NewCleanStack() *CleanStack {
+	return &CleanStack{}
+}
+
+// CleanStack is a basic LIFO stack that resizes as needed.
+type CleanStack struct {
+	jobs    []CleanJob
+	current int
+}
+
+// Push adds a node to the stack
+func (clean *CleanStack) Push(job CleanJob) {
+	clean.jobs = append(clean.jobs[:clean.current], job)
+	clean.current++
+}
+
+// Pop removes and returns a node from the stack in last to first order.
+func (clean *CleanStack) Pop() CleanJob {
+	if clean.current == 0 {
+		return nil
+	}
+	clean.current--
+	return clean.jobs[clean.current]
+}
+
+// Cleanup runs the whole cleanup stack. In case of error it runs all jobs
+// and returns the first error occurrence.
+func (clean *CleanStack) Cleanup(err error) error {
+	var errs error
+	if err != nil {
+		errs = multierror.Append(errs, err)
+	}
+	for clean.current > 0 {
+		job := clean.Pop()
+		err = job()
+		if err != nil {
+			errs = multierror.Append(errs, err)
+		}
+	}
+	return errs
+}