Add the rollback util

lib/utils/rollback.js

@@ -0,0 +1,47 @@
+
+module.exports = rollback
+rollback.register = register
+
+var stack = []
+  , log = require("./log")
+  , inRollback = false
+
+function rollback (cb) {
+  inRollback = true
+  if (stack.length === 0) return log("completed", "rollback", cb)
+  var r = stack.pop()
+    , fn = r.shift()
+  r.push(function (er) {
+    if (er) return log.er(cb, "error during rollback")(er)
+    rollback(cb)
+  })
+  fn.rollback.apply(null, r)
+}
+
+function register () {
+  if (inRollback) return undefined
+  var caller = arguments.callee.caller
+    , args = Array.prototype.slice.call(caller.arguments)
+    , cb = args.pop()
+  if (!caller.rollback) return undefined
+  if (typeof cb !== "function") return log(
+    "Trying to register a rollback from a non-cb function."
+    , "warning")
+  log(caller.name || "(anonymous) ", "rollback register")
+  stack.push([caller].concat(args))
+}
+
+if (module !== process.mainModule) return undefined
+
+function foo (a, b, c, cb) { rollback.register() }
+foo.rollback = function () {
+  log([].slice.call(arguments), "rolling back foo")
+  var cb = Array.prototype.pop.call(arguments)
+  cb()
+}
+
+foo(1,2,3,function () { log("foo") })
+rollback(function (er) {
+  if (er) throw er
+  log("rolled back")
+})