fix: use bundled devtools frontend URL for remote debugging (#51413)

* fix: use bundled devtools frontend URL for remote debugging (#51236)

fix: add ShouldUseBundledFrontendResources delegate for remote debugging

Co-authored-by: John Kleinschmidt <jkleinsc@electronjs.org>

Co-authored-by: Om Ghante <mr.omghante1@gmail.com>

* chore: e patches all (trivial only)

---------

Co-authored-by: trop[bot] <37223003+trop[bot]@users.noreply.github.com>
Co-authored-by: Om Ghante <mr.omghante1@gmail.com>
Co-authored-by: Charles Kerr <charles@charleskerr.com>

patches/chromium/.patches

@@ -173,3 +173,4 @@ patch_osr_control_screen_info.patch
 cherry-pick-cve-2026-6920.patch
 fix_make_macos_text_replacement_work_on_contenteditable.patch
 fix-dcheck-failure-when-starting-heap-profiler-for-renderer.patch
+fix_use_bundled_devtools_frontend_url_for_remote_debugging.patch

patches/chromium/fix_use_bundled_devtools_frontend_url_for_remote_debugging.patch

@@ -0,0 +1,74 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Om Ghante <omghante@users.noreply.github.com>
+Date: Tue, 21 Apr 2026 23:30:00 +0530
+Subject: fix: add ShouldUseBundledFrontendResources delegate for remote
+ debugging
+
+Adds a new `ShouldUseBundledFrontendResources()` virtual method to
+`DevToolsManagerDelegate` that embedders can override to control whether
+the bundled DevTools frontend URL is used in the `/json` response,
+regardless of `CHROMIUM_GIT_REVISION`.
+
+This is needed because embedders like Electron ship bundled frontend
+resources, but the remote frontend on the CDN may not be available for
+their custom Chromium revisions or may expire before their extended
+release cycles end.
+
+Without this, `GetFrontendURLInternal()` generates a
+`devtoolsFrontendUrl` pointing to
+`chrome-devtools-frontend.appspot.com`, which returns 404 for
+embedder-specific Chromium builds, causing Chrome's `chrome://inspect`
+page to show an empty DevTools window.
+
+The default implementation returns `false` to preserve existing
+behavior for Chrome and other embedders.
+
+Fixes: https://github.com/electron/electron/issues/51035
+
+diff --git a/content/browser/devtools/devtools_http_handler.cc b/content/browser/devtools/devtools_http_handler.cc
+index 79bf965d5dd4a9466a518f29f55d4769d9cbb060..869db7f6d090627ed8f0c301c8a11f33b2a9c944 100644
+--- a/content/browser/devtools/devtools_http_handler.cc
++++ b/content/browser/devtools/devtools_http_handler.cc
+@@ -538,7 +538,8 @@ std::string DevToolsHttpHandler::GetFrontendURLInternal(
+     const std::string& host) {
+   std::string frontend_url;
+   const std::string git_revision = CHROMIUM_GIT_REVISION;
+-  if (git_revision == kMissingGitRevision &&
++  if ((git_revision == kMissingGitRevision ||
++       delegate_->ShouldUseBundledFrontendResources()) &&
+       delegate_->HasBundledFrontendResources()) {
+     frontend_url = "/devtools/inspector.html";
+   } else {
+diff --git a/content/public/browser/devtools_manager_delegate.cc b/content/public/browser/devtools_manager_delegate.cc
+index 02e70247e20fda68510d0e1eb4e7114a1b29d153..8c191135fb73e4141041b93ac1bd8348fbdbbe2b 100644
+--- a/content/public/browser/devtools_manager_delegate.cc
++++ b/content/public/browser/devtools_manager_delegate.cc
+@@ -106,6 +106,10 @@ bool DevToolsManagerDelegate::HasBundledFrontendResources() {
+   return false;
+ }
+ 
++bool DevToolsManagerDelegate::ShouldUseBundledFrontendResources() {
++  return false;
++}
++
+ bool DevToolsManagerDelegate::IsBrowserTargetDiscoverable() {
+   return false;
+ }
+diff --git a/content/public/browser/devtools_manager_delegate.h b/content/public/browser/devtools_manager_delegate.h
+index e6e5ba7be2551ff1482dd18cf7f7492aa0f5b609..778426dc9ced79d663c0f75d1436a9aa6d118318 100644
+--- a/content/public/browser/devtools_manager_delegate.h
++++ b/content/public/browser/devtools_manager_delegate.h
+@@ -148,6 +148,13 @@ class CONTENT_EXPORT DevToolsManagerDelegate {
+   // Returns whether frontend resources are bundled within the binary.
+   virtual bool HasBundledFrontendResources();
+ 
++  // Returns whether the bundled frontend resources should be preferred over
++  // the remote frontend served from the CDN. Embedders that ship bundled
++  // frontend resources and whose Chromium revisions may not be available on
++  // the CDN (or may expire before their release cycle ends) should override
++  // this to return true.
++  virtual bool ShouldUseBundledFrontendResources();
++
+   // Makes browser target easily discoverable for remote debugging.
+   // This should only return true when remote debugging endpoint is not
+   // accessible by the web (for example in Chrome for Android where it is

shell/browser/ui/devtools_manager_delegate.cc

@@ -138,6 +138,10 @@ bool DevToolsManagerDelegate::HasBundledFrontendResources() {
   return true;
 }
 
+bool DevToolsManagerDelegate::ShouldUseBundledFrontendResources() {
+  return true;
+}
+
 content::BrowserContext* DevToolsManagerDelegate::GetDefaultBrowserContext() {
   return ElectronBrowserContext::GetDefaultBrowserContext();
 }

shell/browser/ui/devtools_manager_delegate.h

@@ -37,6 +37,7 @@ class DevToolsManagerDelegate : public content::DevToolsManagerDelegate {
       bool new_window) override;
   std::string GetDiscoveryPageHTML() override;
   bool HasBundledFrontendResources() override;
+  bool ShouldUseBundledFrontendResources() override;
   content::BrowserContext* GetDefaultBrowserContext() override;
 };
 

spec/chromium-spec.ts

@@ -556,6 +556,67 @@ describe('command line switches', () => {
         }
       });
     });
+
+    it('should use bundled devtools frontend URL in /json response', async () => {
+      // Regression test for https://github.com/electron/electron/issues/51035
+      // Verifies that devtoolsFrontendUrl points to the local bundled path
+      // (/devtools/inspector.html) rather than the remote CDN URL
+      // (https://chrome-devtools-frontend.appspot.com), which would 404 for
+      // Electron's custom Chromium builds.
+      const electronPath = process.execPath;
+      let stderr = '';
+      appProcess = ChildProcess.spawn(electronPath, ['--remote-debugging-port=0']);
+
+      const port = await new Promise<string>((resolve, reject) => {
+        appProcess!.stderr.on('data', (data: Buffer) => {
+          stderr += data.toString();
+          const m = /DevTools listening on ws:\/\/127\.0\.0\.1:(\d+)\//.exec(stderr);
+          if (m) {
+            appProcess!.stderr.removeAllListeners('data');
+            resolve(m[1]);
+          }
+        });
+        appProcess!.on('exit', () =>
+          reject(new Error(`Process exited before DevTools port was found. stderr: ${stderr}`))
+        );
+      });
+
+      const jsonTargets = await new Promise<any[]>((resolve, reject) => {
+        http
+          .get(`http://127.0.0.1:${port}/json`, (res) => {
+            let body = '';
+            res.on('data', (chunk: Buffer) => {
+              body += chunk.toString();
+            });
+            res.on('end', () => {
+              try {
+                resolve(JSON.parse(body));
+              } catch {
+                reject(new Error(`Failed to parse /json response: ${body}`));
+              }
+            });
+            res.on('error', reject);
+          })
+          .on('error', reject);
+      });
+
+      expect(jsonTargets).to.be.an('array');
+      expect(jsonTargets.length).to.be.greaterThan(0);
+
+      // Every target's devtoolsFrontendUrl must use the bundled path,
+      // not the remote CDN (chrome-devtools-frontend.appspot.com).
+      for (const target of jsonTargets) {
+        expect(target).to.have.property('devtoolsFrontendUrl');
+        expect(target.devtoolsFrontendUrl).to.match(
+          /^\/devtools\//,
+          `devtoolsFrontendUrl should start with /devtools/ (bundled), got: ${target.devtoolsFrontendUrl}`
+        );
+        expect(target.devtoolsFrontendUrl).to.not.include(
+          'chrome-devtools-frontend.appspot.com',
+          'devtoolsFrontendUrl should not point to the remote CDN'
+        );
+      }
+    });
   });
 
   describe('--trace-startup switch', () => {