Fix crash in res.send()

[gramakri]

In commit c6fa259, "var" usage
was replaced with const. The code previously worked because "var"
has function scoping unlike const which has block scoping.

TypeError: Cannot read property 'attributes' of null

[gramakri]

The backtrace we got is

2020-12-01T17:39:21.517Z box:ldap TypeError: Cannot read property 'attributes' of null
    at /home/yellowtent/box/node_modules/ldapjs/lib/messages/search_response.js:100:12
    at Array.forEach (<anonymous>)
    at SearchResponse.send (/home/yellowtent/box/node_modules/ldapjs/lib/messages/search_response.js:99:29)
    at /home/yellowtent/box/src/ldap.js:113:17
    at Array.forEach (<anonymous>)
    at finalSend (/home/yellowtent/box/src/ldap.js:112:17)
    at /home/yellowtent/box/src/ldap.js:370:17
    at /home/yellowtent/box/node_modules/async/dist/async.js:473:16
    at replenish (/home/yellowtent/box/node_modules/async/dist/async.js:1006:25)
    at iterateeCallback (/home/yellowtent/box/node_modules/async/dist/async.js:995:17) %s failure to write message %j 172.18.0.7:57498 { messageID: 1075,
  protocolOp: 'LDAPResult',
  status: 0,
  matchedDN: '',
  errorMessage: '',
  referrals: [],
  controls: [] }

[UziTech]

I wonder if there are more cases of variable shadowing gone wrong. We should add a rule to the linter to prevent this.

[jsumners]

This is what I was afraid of in #674.

[jsumners]

I really want to ask for test coverage here to prevent a regression, but I'm unclear how feasible that would be.

[UziTech]

I did a search with eslint and only found this shadowing to be a problem. I would prefer to move to eslint and use eslint-config-standard instead of using standard so we can add the no-shadow rule.

During that search I also found that the callback on getEntryChangeNotificationControl is never used. I'm not sure if that is a problem.

node-ldapjs/lib/persistent_search.js

Lines 80 to 96 in da358a8

	function getEntryChangeNotificationControl (req, obj, callback) {
	// if we want to return a ECNC
	if (req.persistentSearch.value.returnECs) {
	const attrs = obj.attributes
	const value = {}
	value.changeType = getOperationType(attrs.changetype)
	// if it's a modDN request, fill in the previous DN
	if (value.changeType === 8 && attrs.previousDN) {
	value.previousDN = attrs.previousDN
	}
	value.changeNumber = attrs.changenumber
	return new EntryChangeNotificationControl({ value: value })
	} else {
	return false
	}
	}

[jsumners]

I would prefer to move to eslint and use eslint-config-standard instead of using standard so we can add the no-shadow rule.

🤔 the point of using standard though is that we shouldn't have to keep playing the "update rules" game. We can discuss in a separate issue.

During that search I also found that the callback on getEntryChangeNotificationControl is never used. I'm not sure if that is a problem.

I don't know if it is, but I'd just leave it. One day someone will work up the constitution to clean this whole mess up and these things will get resolved.

[jsumners]

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