1681638 - browser.runtime.connectNative().postMessage fails to handle JavaScript object with nested array

Status: UNCONFIRMED

(GeckoView :: Extensions, defect, P3)

Description

[ugling88]

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36

Steps to reproduce:

I am using GeckoView's connection-based messaging feature following the official documentation here: https://firefox-source-docs.mozilla.org/mobile/android/geckoview/consumer/web-extensions.html.

On the JavaScript side, when using the port.postMessage function, it fails to post JavaScript object with a nested array.
Steps:

1. Create a nativePort using let aport = browser.runtime.connectNative("browser");
2. Send a simple empty array object: aport.postMessage([]), Android side receives the correct message.
3. Send a simple empty object with a nested array: aport.postMessage([[]]), Android side does not receive any message

Actual results:

On JavaScript running inside GeckoView.

1. Send a simple empty array object: aport.postMessage([]), Android side receives the correct message.
2. Send a simple empty object with a nested array: aport.postMessage([[]]), Android side does not receive any message.

GeckoView logs in the console:

1. [Warning] Error dispatching GeckoView:WebExtension:PortMessage Messaging.jsm:76:24
2. [Error] Invalid event data property data

Expected results:

JavaScript objects [] and [[]] shoule be correctly serialized & encoded, Android side onPortMessage callback should receive the correct message object.

Comment 1

[[:owlish] 🦉 PST]

According to the documentation, a message should be either a JS object or a primitive type. JS array is neither of those, so it's not supposed to work. Some type validation with clear error messages might be nice though - adding those is relevant.

Comment 2

[Rob Wu [:robwu]]

In the WebExtensions API definition level, an array is a valid type for the message. In general, any JSON-serializable value is valid, including nested arrays. The WebExtension API itself supports structured cloning (up to the sender of "GeckoView:WebExtension:PortMessage"), but since structured cloning outside of Gecko doesn't make sense, we only claim support for JSON-serializable values.

At the GeckoView layer, somehow the documentation states that it can only be a primitive or an object: https://searchfox.org/mozilla-central/rev/be684f13a4ce71e7ca5e0b354a0f56a665842922/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/WebExtension.java#393-401

This requirement is also propagated further down to A-C: https://searchfox.org/mozilla-central/rev/be684f13a4ce71e7ca5e0b354a0f56a665842922/mobile/android/android-components/components/concept/engine/src/main/java/mozilla/components/concept/engine/webextension/WebExtension.kt#257-258

I'm curious why support for org.json.JSONArray is not documented.

The error message in the report is:

[Error] Invalid event data property data

... that comes either from UnboxBundle in EventDispatcher.cpp or BoxObject in GeckoBundleUtils.cpp.