A real example

This is a real session against two real WhatsApp Web releases. The feature it finds is passkey sign-in, which had not been announced when this code shipped.

Step 1: compare the two releases

cellar diff whatsapp-1030882912 whatsapp-1044822804 --filter protocol --no-hunks

whatsapp-1030882912 -> whatsapp-1044822804  (filter `protocol`)
  considered 4711 of 172040 modules (old) / 5269 of 187892 (new)
  added 913 | removed 355 | modified 1515 | unchanged 2841
  suppressed as noise: 41 | diffs skipped for size: 0

The newer release has 187,892 modules. Most belong to Facebook and Instagram, which share the bundle. The protocol filter leaves 5,269 that actually talk to WhatsApp’s servers. Scanning the added names, a cluster of them mentions passkeys.

Step 2: narrow it down

cellar module search --name 'Passkey' --bundle whatsapp-1044822804

193 module(s) matched of 193 considered

Too many, because most are Facebook’s business login screens. Add the filter:

cellar module search --name 'Passkey' --filter protocol --bundle whatsapp-1044822804

12 module(s) matched of 12 considered

WASmaxInMdGetPasskeyRequestOptionsResponseError
WASmaxInMdGetPasskeyRequestOptionsResponseSuccess
WASmaxInMdPasskeyPrologueRequestNotificationRequest
WASmaxInMdPasskeyRequestOptionsMixin
WASmaxInMdSetPasskeyPrologueResponseSuccess
WASmaxMdGetPasskeyRequestOptionsRPC
WASmaxMdPasskeyPrologueRequestNotificationRPC
WASmaxMdSetPasskeyPrologueRPC
WASmaxOutMdGetPasskeyRequestOptionsRequest
WASmaxOutMdPasskeyPrologueRequestNotificationResponseAck
…

Twelve modules describing a request, a success response, an error response and a notification. That is a complete feature, not a stray reference.

Step 3: read the code

cellar module show WASmaxOutMdGetPasskeyRequestOptionsRequest

__d("WASmaxOutMdGetPasskeyRequestOptionsRequest", [
	"WASmaxJsx",
	"WASmaxOutMdBaseIQGetRequestMixin",
	"WAWap"
], (function(t, n, r, o, a, i, l) {
	function e() {
		var e = o("WASmaxOutMdBaseIQGetRequestMixin").mergeBaseIQGetRequestMixin(o("WASmaxJsx").smax("iq", {
			to: o("WAWap").S_WHATSAPP_NET,
			xmlns: "md"
		}, o("WASmaxJsx").smax("passkey_request_options", null)));
		return e;
	}
	l.makeGetPasskeyRequestOptionsRequest = e;
}), 98);

That is the exact message the client sends:

<iq to="s.whatsapp.net" type="get" xmlns="md">
  <passkey_request_options/>
</iq>

WhatsApp ships this on one very long line. cellar reformats while unpacking, which is why it is readable here. The original bytes are still fingerprinted, so comparisons between versions stay exact.

Step 4: find out what it belongs to

The code is scrambled, so nothing mentions this module by name and searching for usages finds nothing. cellar recorded the connections while unpacking:

cellar graph WASmaxMdGetPasskeyRequestOptionsRPC --direction dependents --depth 2

nodes, 3 edges  (bundle whatsapp-1044822804, direction dependents)

DEPTH  STATE    DEPS  USED  MODULE
    ok          7     1  WASmaxMdGetPasskeyRequestOptionsRPC
    ok         12     4  WAWebShortcakeLinkingApi
    ok          6     2  WAWebShortcakeLinkingIq
    ok          4     2  WAWebShortcakeLinkingRequestOptionsCache

The passkey request is used by the device linking code. So this is not a login screen. It is passkeys replacing the QR code when you link a new device.

What that took

Four commands and about a minute, with no browser and no debugger. We went from “something changed in this release” to the exact message format and the feature it belongs to. Ask your AI assistant to do the same thing and it will run these commands itself, then read the modules it finds.

Get started

Commands

A real example

Step 1: compare the two releases

Step 2: narrow it down

Step 3: read the code

Step 4: find out what it belongs to

What that took

​Step 1: compare the two releases

​Step 2: narrow it down

​Step 3: read the code

​Step 4: find out what it belongs to

​What that took

Step 1: compare the two releases

Step 2: narrow it down

Step 3: read the code

Step 4: find out what it belongs to

What that took