From ce8f889a6b35c32dbc3fab5d089a620eea933493 Mon Sep 17 00:00:00 2001
From: Frederik Braun <fb@frederik-braun.com>
Date: Tue, 29 Oct 2024 19:35:45 +0000
Subject: [PATCH] Bug 1915257 - refactor webchannel to use actor's principal
 r=nalexander,nika

Differential Revision: https://phabricator.services.mozilla.com/D227161
---
 toolkit/actors/WebChannelChild.sys.mjs  |  6 -----
 toolkit/actors/WebChannelParent.sys.mjs | 33 ++++++++++---------------
 2 files changed, 13 insertions(+), 26 deletions(-)

diff --git a/toolkit/actors/WebChannelChild.sys.mjs b/toolkit/actors/WebChannelChild.sys.mjs
index d84659bcde72..b7a37238aa89 100644
--- a/toolkit/actors/WebChannelChild.sys.mjs
+++ b/toolkit/actors/WebChannelChild.sys.mjs
@@ -21,11 +21,6 @@ export class WebChannelChild extends JSWindowActorChild {
   }
 
   _onMessageToChrome(e) {
-    // If target is window then we want the document principal, otherwise fallback to target itself.
-    let principal = e.target.nodePrincipal
-      ? e.target.nodePrincipal
-      : e.target.document.nodePrincipal;
-
     if (e.detail) {
       if (typeof e.detail != "string") {
         console.error("WebChannelMessageToChrome must only send strings");
@@ -39,7 +34,6 @@ export class WebChannelChild extends JSWindowActorChild {
       this.sendAsyncMessage("WebChannelMessageToChrome", {
         contentData: e.detail,
         eventTarget,
-        principal,
       });
     } else {
       console.error("WebChannel message failed. No message detail.");
diff --git a/toolkit/actors/WebChannelParent.sys.mjs b/toolkit/actors/WebChannelParent.sys.mjs
index 98b3ad093a31..c5d78235cc40 100644
--- a/toolkit/actors/WebChannelParent.sys.mjs
+++ b/toolkit/actors/WebChannelParent.sys.mjs
@@ -5,7 +5,9 @@
 
 import { WebChannelBroker } from "resource://gre/modules/WebChannel.sys.mjs";
 
-const ERRNO_MISSING_PRINCIPAL = 1;
+// Note: ERRNO 1 deprecated and unused.
+// We used to err for cases where the child did not send a principal,
+// but now we infer it from the actor.
 const ERRNO_NO_SUCH_CHANNEL = 2;
 
 export class WebChannelParent extends JSWindowActorParent {
@@ -15,7 +17,7 @@ export class WebChannelParent extends JSWindowActorParent {
       browsingContext: this.browsingContext,
       browser: this.browsingContext.top.embedderElement,
       eventTarget: msg.data.eventTarget,
-      principal: msg.data.principal,
+      principal: this.manager.documentPrincipal,
     };
     // data must be a string except for a few legacy origins allowed by browser-content.js.
     if (typeof data == "string") {
@@ -28,28 +30,19 @@ export class WebChannelParent extends JSWindowActorParent {
     }
 
     if (data && data.id) {
-      if (!msg.data.principal) {
+      let validChannelFound = WebChannelBroker.tryToDeliver(
+        data,
+        sendingContext
+      );
+
+      // if no valid origins send an event that there is no such valid channel
+      if (!validChannelFound) {
         this._sendErrorEventToContent(
           data.id,
           sendingContext,
-          ERRNO_MISSING_PRINCIPAL,
-          "Message principal missing"
+          ERRNO_NO_SUCH_CHANNEL,
+          "No Such Channel"
         );
-      } else {
-        let validChannelFound = WebChannelBroker.tryToDeliver(
-          data,
-          sendingContext
-        );
-
-        // if no valid origins send an event that there is no such valid channel
-        if (!validChannelFound) {
-          this._sendErrorEventToContent(
-            data.id,
-            sendingContext,
-            ERRNO_NO_SUCH_CHANNEL,
-            "No Such Channel"
-          );
-        }
       }
     } else {
       console.error("WebChannel channel id missing");